Buoyant Plastics at Sea:

Concentrations and Impacts

Júlia Wiener Reisser

B.Sc. Oceanography (Hons)

M.Sc. Biological Oceanography

This thesis is presented for the degree of Doctor of Philosophy of

The University of Western Australia

November 2015

School of Civil, Environmental, and Mining Engineering

The UWA Oceans Institute

The University of Western Australia

iii

Thesis Declaration

This thesis is presented as a series of three scientific papers, which is in agreement with

the Postgraduate and Research Scholarship Regulation 1.3.1.33 of the University of

Western Australia.

Chapter 2: Reisser J, Shaw J, Wilcox C, Hardesty BD, Proietti M, Thums M,

Pattiaratchi C (2013) Marine Plastic Pollution in Waters around Australia:

Characteristics, Concentrations, and Pathways. PLOS ONE 8(11):e80466

Chapter 3: Reisser J, Shaw J, Hallegraeff G, Proietti M, Barnes D, Thums M, Wilcox

C, Hardesty B, Pattiaratchi C (2014) Millimeter-sized Marine Plastics: A New Pelagic

Habitat for Microorganisms and Invertebrates. PLOS ONE 9(6): e100289

Chapter 4: Reisser J, Slat B, Noble K, du Plessis K, Epp M, Proietti M, de Sonneville

J, Becker T, Pattiaratchi C (2015) The Vertical Distribution of Buoyant Plastics at Sea:

an Observational Study in the North Atlantic Gyre. Biogeosciences 12: 1249-1256

Some parts of the other chapters (chapters 1 and 5) have also been previously published

in journals, magazines, and reports produced by J. Reisser during her PhD candidature.

Main supervisor C. Pattiaratchi provided guidance for the entire thesis and scientific

publications. The contributions of other collaborators to PhD chapters are mostly

associated with research directions, assistance with data processing, and editorial input

in manuscript drafts. The exceptions are the substantial contributions of G. Hallegraeff

towards the identifications of the ‘epiplastic’ organisms described in chapter 3, and B.

Slat towards designing the innovative sampling protocol presented in chapter 4. Besides

the three scientific papers that compose the data chapters of this thesis, J. Reisser co-

produced eleven additional scientific publications and five media articles during her

PhD candidature. The full references to these manuscripts are provided in ‘Appendix 1

Outputs produced during this candidature’.

Julia Reisser

iv

Abstract

Millimetre-sized plastics are a predominant type of marine debris floating at sea. These

small macroscopic particles are numerically abundant in some marine environments, but

little is known about their spatial distribution and environmental impacts. The goals of

this thesis were to investigate how buoyant plastics are distributed in sea surface waters

(both horizontally and vertically), and characterise organisms and textures on the

surface of millimetre-sized marine plastics. This work is the first to (1) quantify plastic

contamination levels in Australian waters, (2) characterize the biodiversity of organisms

living on millimetre-sized plastics from waters around Australia, and (3) obtain high-

resolution depth profiles (0 – 5 m) of plastic pollution in an oceanic accumulation zone.

I collected 839 pieces of plastic in 171 surface net tows from surface waters around

Australia, and 12,751 pieces of plastic in 12 multi-level tows from an oceanic

accumulation zone in the North Atlantic. Plastics were mostly fragments resulting from

the breakdown of larger objects (e.g. packaging and fishing gear) made of polyethylene

and polypropylene polymers. Contamination levels in waters around Australia were

similar to those in other marine regions (e.g. Caribbean Sea and Gulf of Maine), but

considerably lower than those found in plastic pollution hotspots within subtropical

gyres and Mediterranean Sea. There was a wide range of microbes and a few

invertebrates on the surface of floating plastics from Australia-wide sample collections.

Diatoms were particularly diverse, represented by 14 genera, 11 of which are new

records of ‘epiplastic’ organisms. Plastic pollution levels in the North Atlantic

accumulation zone decreased exponentially with water depth, with decay rates

decreasing as wind strength increased. Plastic mass per cubic metre of water decreased

more rapidly with depth than the number of plastic pieces per cubic metre, as the

smaller plastic pieces were associated with lower rising velocities and were more

susceptible to vertical mixing. This thesis contributed towards the global efforts of

quantifying plastic contamination levels and impacts in surface waters. It highlights the

widespread distribution of anthropogenic polymers, which has created a new pelagic

habitat for microorganisms and invertebrates. Plastic inhabitants seem to be invading

non-native marine regions by plastic transport, and playing an important role on ocean

plastic degradation.

Keywords: microplastics, marine debris, plastic pollution, Australia, garbage patches

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Acknowledgements

Thank you to my main supervisor Chari Pattiaratchi for the opportunity of working

under his guidance over the last years, and to the Australian government, UWA, and

CSIRO for awarding me scholarships that covered my living, study, and research costs.

I also acknowledge my co-supervisors Chris Wilcox and Michele Thums, and

collaborators/mentors Denise Hardesty, Jeremy Shaw, Gustaaf Hallegraeff, David

Barnes, Boyan Slat, Kim Noble, Kate du Plessis, Meredith Epp, Jan de Sonneville, and

Thomas Becker. A special thank you goes to Maíra Proietti, who has been my friend &

mentor since 2002. I also acknowledge my family and friends, specially my dad Carlos

Reisser, mum Helena Wiener, and siblings Tunico and Peteca for all the love, support,

and patience. Finally, but not last, I thank my husband Christopher Phillips for his love

and in-kind support towards my PhD work and failures.

Thanks to the Marine National Facility, Australian Institute of Marine Science, Austral

Fisheries, The Ocean Cleanup, and Pangaea Explorations for providing me sea time.

Thank you staff and crew of RV Southern Surveyor, RV Solander, Comac Enterprise,

and SV Sea Dragon for logistic support during the research voyages. I also

acknowledge the UWA School of Chemistry and Biochemistry, as well as the Centre

for Microscopy, Characterisation and Analysis for their facilities, and technical

assistance. Thank you to Ruth Gongora-Mesas, Don McKenzie, Mark Lewis, Oscar Del

Borrello, Qamar Schuyler, Kathy Townsend, Stephen McCullum, Lisa Woodward,

Alastair Graham, Sara Schofield, Tyrone Ridgway, Kim Brooks, Craig Steinberg, Gary

Brinkman, Martin Exel, Andy Prendergast, Sebastian Holmes, Luana Lins, Dagmar

Kubistin, Murphy Birnberg, Cyprien Bosserelle, Steve Rogers, Susana Agusti, Luana

Lins, Piotr Kuklinski, Paco Cardenas, Pat Hutchings, Anja Schulze, Christopher Boyko,

George Wilson, Marilyn Schotte, John Hooper, Christine Schoenberg, Jean Vacelet,

Andrzej Pisera, Alexander Muir, John Taylor, Martin Thiel, Anthony Richardson,

Carlos Duarte, Deepak Kumaresan, Andy Whiteley, Richard Allcock, Moritz Wandres,

Sarath Wijeratne, Asha de Vos, Shari Gallop, Eric Loss, Shanley McEntee, Winston

Ricardo, Bart Sturm, Beatrice Clyde-Smith, Kasey Erin, Mario Merkus, Max Muller,

Jennifer Gelin, Ruth Thompson, and all the others I forgot to mention for their help and

support towards this work.

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Contents

Thesis Declaration ..................................................................................................... iii

Abstract ....................................................................................................................... iv

Acknowledgements ...................................................................................................... v

Contents ...................................................................................................................... vi

Chapter 1 General Introduction ............................................................. 9

1.1 Plastic: definition and major types ................................................................... 9

1.2 The Plastic Age: plastic production and waste .............................................. 11

1.3 Oceans: the ultimate sink for plastic pollution .............................................. 14

1.4 Marine plastic pollution impacts .................................................................... 20

1.5 Monitoring plastic pollution ............................................................................ 22

1.5.1 Visual surveys ............................................................................................. 23

1.5.2 Surface net tows .......................................................................................... 26

1.5.3 Subsurface net tows .................................................................................... 28

1.6 Goals and aims ................................................................................................. 31

1.7 Structure of the thesis ...................................................................................... 31

Chapter 2 Marine plastic pollution in waters around Australia:

characteristics, concentrations, and pathways ....................................... 33

2.1 Summary ........................................................................................................... 33

2.2 Introduction ...................................................................................................... 34

2.3 Materials and Methods .................................................................................... 36

2.4 Results ............................................................................................................... 40

2.5 Discussion .......................................................................................................... 49

2.5.1 Characteristics of marine plastics ............................................................... 49

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2.5.2 Concentrations and sources ......................................................................... 52

2.5.3 Potential pathways ...................................................................................... 54

2.5.4 Final remarks ............................................................................................... 55

Chapter 3 Millimetre-sized Marine Plastics: A New Pelagic Habitat

for Microorganisms and Invertebrates ................................................... 57

3.1 Summary ........................................................................................................... 57

3.2 Introduction ...................................................................................................... 58

3.3 Material and Methods ...................................................................................... 60

3.4 Results ............................................................................................................... 62

3.5 Discussion .......................................................................................................... 74

Chapter 4 The vertical distribution of buoyant plastics at sea: an

observational study in the North Atlantic Gyre ..................................... 80

4.1 Summary ........................................................................................................... 80

4.2 Introduction ...................................................................................................... 81

4.3 Materials and Methods .................................................................................... 82

4.3.1 At-sea sampling ........................................................................................... 82

4.3.2 Estimating depth profiles of plastic contamination ..................................... 84

4.3.3 Characterising plastic length, type, resin, and rise velocity ........................ 85

4.4 Results ............................................................................................................... 86

4.4.1 Profiles of mass and numerical concentrations ........................................... 86

4.4.2 Lengths, types, resins and rise velocities of plastics ................................... 89

4.5 Discussion .......................................................................................................... 93

Chapter 5 General Discussion ............................................................... 97

5.1 Horizontal distribution of buoyant plastics at sea ........................................ 97

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5.2 Vertical distribution of buoyant plastics at sea . Error! Bookmark not defined.

5.3 Organisms on the surface of millimetre-sized ocean plastics ..................... 101

5.3.1 Ingestion of plastics at sea: does debris size really matter? ...................... 103

5.4 Overall Conclusions ....................................................................................... 108

References ................................................................................................ 111

Appendix 1 Outputs produced during this candidature ..................... 125

Appendix 2 Chapter 2 supplementary material ................................... 128

Appendix 3 Chapter 3 supplementary material ................................... 140

9

Chapter 1 General Introduction

1.1 Plastic: definition and major types

Plastics are a diverse group of synthetic materials predominantly derived from

petrochemicals, such as petroleum and natural gas. They possess a peculiar molecular

architecture consisting of long chainlike macromolecules known as polymers, which are

a sequence of repeating units, called monomers. Plastics can be divided into two major

categories: thermoplastics and thermosets.

Thermosets are used in a few high-volume applications, such as automobile tires. They

can be considered a large molecule that is destroyed with heating, meaning recycling

options are mostly limited to energy recovery and physical grinding into powder

(Pickering, 2006). Environmental impacts of thermosets to marine ecosystems are

outside the scope of this thesis, mainly because nearly all thermosets are heavier than

water. Therefore, these materials do not predominate in the top layer of the world’s

oceans, which is the marine region examined in this thesis.

Thermoplastics, which will be referred here as ‘plastics’, are a group of materials made

of large polymeric molecules held together by relatively weak intermolecular forces.

They soften upon heating and return to their original condition when cooled. This

property makes them suitable for moulding and extrusion into films, fibres and

packaging. It also allows recycling into new products by re-melting and processing into

new shapes. Major thermoplastic types include polyethylene (PE), polypropylene (PP),

polyvinyl chloride (PVC), and polystyrene (PS). These are produced in large volumes

(Figure 1.1) and are therefore of particular environmental significance.

10

Figure 1.1 Major plastic types and their share of the global plastic production.

Source: (Taylor, 2015)

The density of a certain plastic determines a key behaviour in the marine environment:

whether the material will sink or float in seawater. All major polymers containing

elements other than hydrogen and carbon are heavier than water due to their strong

intermolecular forces. As a consequence, the only polymer group containing materials

lighter than water are pure hydrocarbons.

A major group of pure hydrocarbons is polyolefins. They have a density range of

approximately 900 – 960 kg m-3, thus floating in both water (1000 kg m-3) and seawater

(1025 – 1045 kg m-3). Polyolefins are the most common type of synthetic polymer, with

a share of approximately 40% of the global plastic production (Taylor, 2015). This

group includes polypropylene (PP), low-density polyethylene (LDPE), linear low-

density polyethylene (LLDPE), and high-density polyethylene (HDPE) materials.

Polystyrene is also a pure hydrocarbon, but due to the benzene rings in its

11

macromolecule, it commonly sinks in water. The exception is expanded polystyrene

(i.e. Styrofoam), which is highly buoyant due to its air bubbles.

Polyethylenes, an important member of the family of polyolefin resins, are the most

widely used type of plastics in the world (37% of global production). They are made

from the polymerization of ethylene monomers (CH2=CH2) and are used in products

ranging from clear food wrap and shopping bags, to detergent bottles and fish crates.

Polyethylenes’ durability, light-weight characteristics, and high use in single-use

packaging, makes them a major type of floating pollutant that persist for long periods of

time in both freshwater and marine environments, including the sea surface (Hidalgo-

Ruz et al., 2012).

1.2 The Plastic Age: plastic production and waste

Due to the ideal properties of plastic for many applications (e.g. inexpensive,

lightweight, flexible, durable, water resistant), it is displacing materials like paper,

glass, and metal from traditional usages, and is leading to the creation of new products

with high demands. Consequently, the global production of plastics has been growing

exponentially since the 1950-60s, when most basic polymer groups were already

available for use in a diverse range of applications (Thompson et al., 2009) (Figure 1.2).

For instance, in 2012 alone, 288 million tons of plastic were produced (PlasticsEurope,

2013), which is approximately the same weight of the entire human biomass (Walpole

et al., 2012). Approximately 8% of today’s annual fossil fuel production goes towards

plastic production, with 4% of this converted directly into plastic materials and a similar

quantity used as energy for its manufacture (Hopewell et al., 2009).

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Figure 1.2 Plastic production (1950-2012), in millions of tonnes.

Source: PlasticsEurope (PEMRG)/Consultic

One of the key drivers of this plastic production growth is the packaging market.

Approximately 37 - 44% of all plastic produced each year is used in packaging

(Industry Canada, 2011, Plastic Waste Management Institute, 2013, PACIA, 2011,

PlasticsEurope, 2013). This includes the manufacture of products entirely made of

plastic, such as bottles, cups, bags, containers and trays, as well as multilayer structures

containing plastic liners, including aluminium/tin cans and milk/juice cartons. This

packaging, together with agricultural films and other disposable consumer items,

represent half of the plastics produced nowadays, which are predominantly used once

and disposed of in less than one year (Selke, 2003). Packaging also represents the main

source of plastic waste, with 45.8% and 58% of the plastic waste produced respectively

in the UK and Japan coming from packaging (Hopewell et al., 2009, Plastic Waste

Management Institute, 2013).

13

Unfortunately, the vast majority of global plastic winds up in landfills (Hopewell et al.,

2009, Hoornweg and Bhada-Tata, 2012), with only around 3.5 – 15% being recycled. In

the US, 32,000,000 tonnes of plastic waste were generated in 2012, of which 9% was

recycled (EPA, 2013). In Australia, 1,476,690 tonnes of plastic were used in 2011-2012,

of which 20.4% was recycled (PACIA, 2011). Japan, which is a major leader in plastic

waste recovery, recycled 26% of the 95,200,000 tonnes of plastic waste produced in

2011 (Plastic Waste Management Institute, 2013). Among the difficulties to increase the

rates of plastic recycling are the relative high costs of processing waste into recycled

materials, and the challenges to sort domestic waste into single polymer types

(Hopewell et al., 2009). Apart from the small quantities of waste diverted back into the

manufacture system through recycling, disposed plastic is either incinerated (with or

without energy recovery) or disposed in landfills and dumps. Due to low rates of

recycling and high durability, plastics are accumulating in many types of habitats

worldwide, particularly in aquatic environments (Figure 1.3).

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Figure 1.3 Nine-year-old boy collecting aluminium cans for recycling in a Brazilian river full of

plastic.

Source: Diego Nigro/JC Imagem

Particularly concerning issues associated with this sharp rise in plastic production and

waste are (1) the toxicity of certain plastics to human health, leading to adverse effects

such as increased risk for cancer and neurological problems (Breast Cancer Fundation,

2013), and (2) the impacts on marine life arising from the widespread occurrence of

discarded plastics in the oceans (United Nations Environment Programme, 2014). The

latter is the topic of this thesis.

1.3 Oceans: the ultimate sink for plastic pollution

Our massive plastic production and waste, the obstacles to recycle and properly dispose

of plastic products, and the sharp rise in the number of ships and coastal developments,

are all leading to an increase in the amount of plastic items accumulating in the oceans.

Plastics can be transported from populated areas to the marine environment by rivers,

wind, tides, rainwater, storm, drains, sewage disposal, and flooding; or can directly

15

reach the sea from vessels (e.g. fishing gear) and offshore installations (e.g. oil rigs and

aquaculture farms) (Ryan et al., 2009). The relative importance of these different

pathways to the total load of plastics at sea has not yet been quantified. However, some

major sources are evident: (1) rivers, which can connect even inland populated areas to

oceans, (2) vessels, particularly those engaged in fishing activities using plastic gear

(e.g. long and heavy nets), and (3) tides, which takes litter left at beaches by users. It

was recently estimated that around 4.8 to 12.7 million tonnes of plastic waste enters the

oceans from land-based sources (Jambeck et al., 2015).

Once plastics reach the oceans, their fate will depend on their characteristics (e.g.

density, shape and size) and the environmental conditions they are exposed to. Plastics

made of resins denser than seawater (e.g. polyethylene terephthalate water bottles) will

sink to the seafloor, while less dense plastics (e.g. polypropylene water bottle caps) will

float at the sea surface layer for a variable period of time. Floating period will depend

on processes such as hydrodynamics, debris characteristics, and ecology of the

surrounding environment (Cózar et al., 2014, Eriksen et al., 2014). For instance,

buoyant plastics from coastal sources may encounter strong inshore winds and currents

and strand (either permanently or temporarily) in coastal environments such as sandy

beaches, rocky shores, and mangroves (Carson et al., 2011). Furthermore, biofouling,

which is the colonization of the debris surface by microorganisms and invertebrates, can

increase the density of buoyant debris to a point where they sink to the seafloor. This

process is particularly quick (days to months) for plastic items with high surface area to

volume ratios (Ryan, 2015), such as plastic bags and wraps. These biofouled items may

rest on the seafloor permanently and/or return to the water column, depending on the

biofouling dynamics and local sediment rates (Ye and Andrady, 1991).

16

Throughout their marine journey, plastics slowly degrade and become brittle, then break

down into progressively smaller pieces (Andrady, 2011). There are four mechanisms by

which plastics degrade in the environment: photo-oxidative degradation, thermal

oxidation, hydrolysis, and biodegradation (Gregory and Andrady, 2003). Common

plastics encountered in marine environments (e.g. polyolefins), however, break down

primarily through photo-thermal oxidation processes (i.e. mostly due to the effect of

sunlight and heat). Ultraviolet light from the sun gives the energy to begin the

incorporation of oxygen atoms into the polymer (Andrady, 2011), which then causes the

plastic to become brittle and break into progressively smaller pieces. When the polymer

chains reach sufficiently low molecular weight, microorganisms may then convert the

polymer carbon into carbon dioxide or incorporate it into biomolecules (Zheng et al.,

2005). The process explained above can take 50 or more years to be completed (Webb

et al., 2012).

At sea, plastic degradation is particularly slow mostly due to the low temperatures and

low oxygen availability. Furthermore, in the ocean the rate of hydrolysis is insignificant

for most polymers. In the case of negatively buoyant plastics, degradation is likely to be

even slower as ultraviolet wavelengths from the sun are readily absorbed by water,

making the degradation process limited to thermal oxidation. Furthermore, biofouling

on the surface of floating plastics may protect the material from exposure to sunlight,

yielding a slower degradation relative to exposure on land (Gregory and Andrady,

2003).

The fragments resulting from the degradation of plastic objects are known as secondary

microplastics when smaller than 5 mm. In addition to these fragments, plastics can also

be directly manufactured in small sizes (< 5 mm). These are known as primary

microplastics and include: pellets, the raw material used to produce plastic items (Mato

17

et al., 2001); synthetic fibers, including those used in clothing (Browne et al., 2011);

and microbeads, which are plastic spheres found in cosmetics such as toothpaste and

facial scrubs (Fendall and Sewell, 2009).

Buoyant microplastics are widespread across oceans, with well-known hotspots

occurring at surface waters of the Mediterranean Sea and at large oceanic accumulation

zones formed within subtropical gyres (Cózar et al., 2014, Eriksen et al., 2014). It is at

the sea surface that some major and highly visible environmental impacts occur,

including plastic entanglement and ingestion by pelagic animals and wide transport of

fouling organisms across oceans (Barnes, 2002, Derraik, 2002, Mato et al., 2001,

Wilcox et al., 2013).

The ocean’s subtropical gyres are five large continuous loops of flowing water (Talley

et al., 2011b) that occupy around 40% of the Earth’s surface. Their horizontal extension

is from about 10° north and south of the equator to about 45° in each hemisphere; the

water circulating in these massive regions reaches nearly 2 km beneath the sea surface

(Pedlosky, 1990). Those in the North Hemisphere rotate clockwise (North Pacific and

North Atlantic Gyres), while those in the South Hemisphere spin counter clockwise

(South Pacific, South Atlantic, and Indian Gyres). They are shaped by a strong and

narrow “western boundary current” and a weak and broad “eastern boundary current”.

The sea surface interiors of these gyres have low concentrations of nutrients and

biomass throughout the year, but their immense size makes their total biological

productivity significant to the world’s ocean ecosystem (McClain et al., 2004).

Accumulation zones of buoyant plastics within subtropical gyres can exceed 100,000

pieces km-2 and their horizontal extensions have been inferred by numerical (Lebreton

et al., 2012) and statistical modelling using satellite-tracked drifting buoys (Maximenko

18

et al., 2012, van Sebille et al., 2012). Buoyant plastics are transported and accumulated

in these oceanic areas due to a combination of geostrophic current forcing, controlled by

pressure gradients (i.e. by the level “tilt”), and the effect of local wind through (1) direct

wind force applied to the surface of the floating debris - the so-called ‘windage’, (2)

Stokes drift created by local waves, and (3) Ekman currents (Maximenko et al., 2012).

Mean streamlines resulting from this forcing form a large-scale pattern with five well-

defined convergent zones known as accumulation zones or ‘garbage patches’

(Maximenko et al., 2012) (Figure 1.4).

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Figure 1.4 Top map: Mean streamlines as a combination of the mean geostrophic and Ekman

velocities (Maximenko et al., 2009). Bottom map: drifter model solution after 10 years of

integration from an initially homogeneous state. See details in (Maximenko et al., 2012).

Colours in the top map indicate the magnitudes of mean velocities used to compute the streamlines, and colours in the bottom map indicate the relative concentration of drifters/debris. Map sources: Maximenko et al. 2009 and Maximenko et al. 2012.

The main advantage of the statistical modelling approach developed by Maximenko et

al. 2012 is its ability to describe motions of floating objects, even without a full

understanding of the tremendously complex dynamics of the upper ocean. Their model

indicates that tropical and subpolar regions are cleared from buoyant debris within three

20

years, with most of this pollution being transported into the five subtropical gyres. In

ten years time, it predicts that floating debris are redistributed within and between the

subtropical gyres to form more compact accumulation zones, centred at around 30

degrees latitude. The North and South Pacific accumulation zones are located in eastern

parts of the corresponding subtropical gyres, while the North and South Atlantic as well

as the South Indian accumulation zones are elongated zonally across their entire ocean

basin (see Figure 1.4).

1.4 Marine plastic pollution impacts

Animals as small as microscopic zooplankton (Wright et al., 2013) and as large as

whales (Fossi et al., 2012) ingest plastic debris. Plastics can also enter animals’ bodies

through respiration, as has been reported in crabs (Watts et al., 2014). Ingestion of

plastic items by marine animals can lead to gastrointestinal perforation and blockage,

reduction of food intake, reproductive disorders, and death (Derraik, 2002). At least 170

marine species are affected by plastic ingestion, including threatened species of sea

birds, turtles and mammals (Vegter et al., 2014).

Chemical impacts of plastics on organisms, food webs, and ecosystems have also

become a focus of concern over the last decade, e.g. (United Nations Environment

Programme, 2014). One of the main reasons for such concern is that over half of our

plastic objects contain at least one ingredient classified as hazardous (Rochman et al.,

2013a). Many plastic products contain non-polymeric components (e.g. residual

monomers, oligomers, low molecular weight fragments, catalyst remnants,

polymerisation solvents and additives) that can be carcinogenic, mutagenic, and/or toxic

for organisms, with potential long-term effects (Lithner, 2011). Since these substances

are usually of low molecular weight and are weakly/not bound to the polymeric

21

macromolecules, they and/or their degradation products can be released from the plastic

into air, water or other contact media, such as food (Lithner, 2011).

Furthermore, plastics that enter aquatic environments can become increasingly

hazardous by adsorbing persistent organic pollutants and metals on their surface (Rios

et al., 2007, Holmes et al., 2012). Due to the hydrophobic nature of plastics,

hydrophobic pollutants such as polychlorinated biphenyls - PCBs (Mato et al., 2001)

and polycyclic aromatic hydrocarbons - PHAs (Rios et al., 2007) accumulate on their

surfaces. Adsorption of trace metals on plastic debris can also occur through exposure

to environmental conditions that lead to the development of viable surface sites by

photo-oxidation, biofouling and deposition of sediment particles (Holmes et al., 2012).

When plastic enters the body via ingestion or other means, these concentrated pollutants

can be transferred to predators and also up their food chains. Such a bio-magnification

process is more likely to occur when plastics are small enough to be ingested by low

trophic fauna, such as small fish and zooplankton (Browne et al., 2013, Rochman et al.,

2013c).

Entanglement in plastic items, especially discarded fishing gear (e.g. ropes, straps, lines,

pots, traps, nets), are also a serious threat to some species of marine vertebrates

(Derraik, 2002). It can lead to physical injuries, drowning, increased drag, impairment

of abilities to forage and avoid predators, and ultimately death. At least 135 marine

species have been recorded entangled in marine debris (Vegter et al., 2014). Animals

that often occur at the sea surface, such as air-breathing vertebrates (e.g. sea turtles,

birds, and mammals), are particularly prone to this type of adverse interaction. Young

fur seals, which are both curious and playful, are often entangled in nets and packing

bands (Derraik, 2002). Entanglement of juvenile northern sea lions (Eumetopias

jubatus), Hawaiian monk seals (Monachus schauinslandi), and northern fur seals

22

(Callorhinus ursinus) has been listed as one of the factors contributing to the decline of

their populations (Derraik, 2002). Benthic organisms, especially those with branching

morphologies (e.g. gorgonians, sponges, corals), are also affected by tissue abrasion and

mortality caused by entanglement in lost fishing gear (Chiappone et al., 2005).

On the other hand, many marine species can also benefit from the occurrence of plastics

at sea, which is a new long-lasting type of floating habitat. These include fish species

and fouling organisms that can invade non-native waters through plastic drifting

(Barnes, 2002) and ‘epiplastic’ pathogens, which may infect animals that ingest plastics

(Pham et al., 2012). We still know very little about the dwellers of the widely dispersed

and abundant microplastics. The environmental implications of the occurrence of

organisms on the surface of millimetre-sized plastics are discussed in Chapter 3, where

the inhabitants of millimetre-sized plastics from waters around Australia are described.

Another environmental impact of plastic contamination is the alteration of physical

properties of marine environments. It changes light, oxygen and refuge availability, as

well as heat transfer and water movement throughout sediments (Goldberg, 1997,

Carson et al., 2011). Such effects could potentially have consequences to benthic

communities and animals that have offspring sex determined by sand temperature, such

as sea turtles (Goldberg, 1997, Carson et al., 2011). Plastic-induced alterations to

natural environments also lead to social and economic impacts (Vegter et al., 2014),

such as decreased tourism in beaches and diving destinations heavily polluted by marine

litter.

1.5 Monitoring plastic pollution

To gain a better understanding of the environmental hazards associated with marine

plastic pollution, several studies have attempted to quantify marine plastic debris,

23

ranging from several meters to 0.001 millimetres in size (Hidalgo-Ruz et al., 2012,

Pichel et al., 2012). Such investigations have sampled plastics from the shoreline,

seafloor, water column, and sea surface (Thompson et al., 2004, Law et al., 2010,

Browne et al., 2011, Kukulka et al., 2012, Schlining et al., 2013, Van Cauwenberghe et

al., 2013b).

Floating marine plastics have been quantified mostly through visual counts conducted

from vessels and airplanes (Pichel et al., 2007, Hinojosa et al., 2011, Pichel et al.,

2012), and by sampling devices that collect plastics from the oceans. Such instruments

include Continuous Plankton Recorders (Thompson et al., 2004), Niskin bottles

(Gordon, 2000), rotating drum samplers (Ng and Obbard, 2006), and zooplankton nets

(Carpenter and Smith, 1972).

1.5.1 Visual surveys

The most common method of estimating amounts of large plastics in surface waters is

by counting floating objects while aboard vessels. Generally, an observer stands on the

flying bridge looking for floating debris as the ship moves through the area. Binoculars

are sometimes used to confirm the characteristics of the sighted objects (e.g. material,

size, colour). The area that is visually scanned for floating debris varies between

studies. Surveys following the Strip Transect approach stipulate a maximum distance

from the vessel in which the observer should scan for debris. It is a very simple method

that assumes all objects within the scanned area are counted (100% probability

detection). Surveys following the Line Transect approach (Buckland et al., 2005), have

the observers focusing their search effort in the heading line of the vessel, and use the

perpendicular distances between the sighted objects and the vessel’s heading line to

estimate detection probability functions, e.g. (Titmus and Hyrenbach, 2011). To obtain

24

an estimate of abundance, the number of objects observed during a certain time is

divided by the sampled area, which is equal to the distance travelled by the vessel

(transect length) multiplied by the distance from the boat where plastics were counted

(transect width). These plastic concentrations are commonly reported in number of

items per area, but grams per area are also estimated in a few studies that used weights

of beached plastic items to infer the mass of sighted objects and transform numerical

densities into mass densities (Eriksen et al., 2014).

Plastic concentrations in pieces km-2 reported in 18 studies that conducted visual

surveys are plotted in the top panel of Figure 1.5 (Venrick et al., 1973, Morris, 1980a,

Dixon and Dixon, 1983, Dahlberg and Day, 1985, Day and Shaw, 1987, Ryan, 1990,

Dufault and Whitehead, 1994, Aliani et al., 2003, Thiel et al., 2003, Barnes and Milner,

2005, Shiomoto and Kameda, 2005, Hinojosa and Thiel, 2009, Titmus and Hyrenbach,

2011, Zhou et al., 2011, Williams et al., 2011, Ryan, 2013b, Ryan, 2013a, Thiel et al.,

2013). There are many variables that influence these reported estimates, including sea

state, distance from which objects were observed, minimum plastic size counted, etc. As

such, comparisons between studies should be done with caution.

25

Figure 1.5 Mean buoyant plastic concentrations (pieces km-2) in different parts of the ocean.

The currents that form subtropical gyres are displayed as black arrows in the top map, together with mean concentration of meter-sized debris, as estimated by visual surveys. The bottom map shows mean concentrations of millimetre-sized plastics, as measured by net sampling. Circle positions show approximate location of each measurement and letters next to circles indicate the study that reported each mean value. Top map: aVenrick et al. 1973, bMorris 1980a, cDixon and Dixon 1983, dDahlberg and Day 1985, eDay and Shaw 1987, fRyan 1990, gDufault and Whitehead 1994, hAlani et al. 2003, iShiomoto and Kameda 2005, jBarnes and Milner 2005, kThiel et al. 2003, lHinojosa and Thiel 2009, mThiel et al. 2013, nWilliams et al. 2011, oTitmus and Hyrenbach 2011, pZhou et al. 2011, rRyan 2013b, sRyan 2013. Bottom map: aCarpenter and Smith 1972, bShaw 1977, cRyan 1988, dMorris 1980b, eWilber 1987, fGregory 1990, gDay et al. 1990, hMoore et al. 2001, iLaw et al. 2010, jYamashita and Tanimura 2007, kCollignon et al. 2012, lVan Cauwenberghe et al. 2013a, mEriksen et al. 2013, pZhou et al. 2011, qDufault and Whitehead 1994

Generally, centimetre-sized fragments resulting from the disintegration of larger plastic

objects were the most common type of debris observed during these visual surveys,

particularly in offshore regions (Venrick et al., 1973, Dahlberg and Day, 1985, Titmus

and Hyrenbach, 2011). Entire plastic items, such as bags, Styrofoam blocks, bottles,

26

packaging, and fishing gear, were also commonly sighted, especially in coastal waters

(Thiel et al., 2003, Williams et al., 2011).

Sighted plastics were widespread in the sampled marine regions and mean

concentrations higher than 10 pieces km-2 occurred close to coastal populated areas (i.e.

Indonesian, Chilean, Canadian, and South African waters) as well as in oceanic

accumulation zones within subtropical waters of the North Pacific and in the

Mediterranean Sea.

There are still vast areas of the oceans to be sampled, and more data is required to

adequately document the location of large-scale concentrations of plastic objects.

During my PhD, I did a few visual surveys in waters around Australia, but the results

are not presented in this thesis. They were used in a recent global meta-analysis

estimating the distribution and load of plastics at the world’s sea surface (Eriksen et al.,

2014). It was published while this thesis was under review.

1.5.2 Surface net tows

Zooplankton nets, such as Neuston and Manta nets (Brown and Cheng, 1981) are by far

the most common devices used to sample small pelagic plastics (Hidalgo-Ruz et al.,

2012). They are towed from vessels to systematically sample buoyant plastics at the air-

seawater interface, where floating material tend to accumulate (Kukulka et al., 2012). In

comparison to the Neuston net, the Manta net requires more people and logistics to be

deployed. On the other hand, it has two important advantages in relation to the Neuston

net: (1) its paravanes steer the net at an angle to the ship’s path, thus avoiding the

vessel’s wake influence in the sampling, and (2) the top edge of the net always rides on

the surface, ensuring a constant sampling of the sea surface and an easy calculation of

the area and volume sampled by each net tow (Brown and Cheng, 1981).

27

The main advantage of these surface nets is their capacity to concentrate buoyant

material from a relatively large volume of water (Hidalgo-Ruz et al., 2012). After each

net tow, the content captured by the net is carefully examined to separate plastics from

biological material. Detected plastics are then counted and/or weighed and usually

reported in pieces per area (Hidalgo-Ruz et al., 2012), although pieces per volume, mass

per area, and mass per volume are also used.

The findings of 15 studies that conducted surface net tows are shown in the lower panel

of Figure 1.5 (Carpenter and Smith, 1972, Shaw, 1977, Morris, 1980b, Wilber, 1987,

Ryan, 1988, Gregory, 1990, Day et al., 1990, Dufault and Whitehead, 1994, Moore et

al., 2001, Yamashita and Tanimura, 2007, Law et al., 2010, Zhou et al., 2011, Collignon

et al., 2012, Eriksen et al., 2013, Van Cauwenberghe et al., 2013a). These studies report

plastic pollution levels in pieces km-2. There are many variables that influence these

reported estimates, including sampling design, net mesh size, and processing technique

used, as well as efforts towards finding and identifying plastic particles smaller than 1

mm. As such, comparisons between studies should be done with caution.

Fragmented pieces of larger plastic objects were by far the most common plastic type

described in the “net tow” reports considered here. Plastic pellets had a high relative

abundance in reports from the 1970-80s, but decreased thereafter (Law et al., 2010).

This is probably due to both an increase in amounts of secondary microplastics, and a

decrease in pellets being lost during transportation.

Small marine plastics, mostly less than 5 mm across (microplastics), were widespread in

the sampled marine regions, and mean concentrations higher than 10,000 pieces km-2

were present in the Mediterranean Sea and in oceanic subtropical areas of the North

Pacific, South Pacific, and North Atlantic. By considering the estimates from these

28

plastic pollution observations, some recent global studies (Cózar et al., 2014, Eriksen et

al., 2014), and the outputs of global models of plastic dispersal (Lebreton et al., 2012,

Maximenko et al., 2012, van Sebille et al., 2012), it is possible to confidently conclude

that small plastics are concentrated within all large subtropical areas of the oceans

(“oceanic gyres”), as well as in the Mediterranean Sea. There are still several gaps in the

global datasets, particularly in the southern hemisphere and high latitudes. As such,

other large-scale accumulation zones may exist. For instance, the model developed by

Van Sebille et al. (2012) predicted an extra accumulation zone in the Barents Sea, while

the Lebreton et al. (2012) model identified many coastal accumulation zones, most of

which are still unsampled.

1.5.3 Subsurface net tows and depth profile modelling

Most of what is known about at-sea buoyant plastic characteristics and concentrations

comes from surface net sampling. However, buoyant plastics can be transported to

deeper waters due to vertical water movements created by turbulence and other

circulation patterns, such as Langmuir circulation (Kukulka et al., 2012).

Lattin et al. (2004) performed paired manta (surface) and bongo (5 m) net tows in Santa

Monica Bay before and shortly after a storm event, suggesting that high wind conditions

and urban runoff enhance vertical mixing of plastic debris, both at the sea surface and

ocean floor. Doyle et al. (2011) collected surface and subsurface (15 m from the

bottom) samples during four cruises off the US west coast. They found higher quantities

of plastic at the sea surface, with the occurrence of subsurface plastics only during a

winter cruise. They also attributed the presence of plastics in the water column to the

mixing of particles from surface and sediments.

29

Kukulka et al. (2012) conducted the first comprehensive multi-level survey of buoyant

plastics. These authors used a Neuston net and a multiple-net Tucker Trawl (Hopkins et

al., 1973) to sample plastics at the surface, 5 m, 10 m, and 20 m deep. Their

observations were used to validate a model capable of predicting depth-integrated

plastic numerical concentrations (pieces km-2) using surface values and wind conditions.

Their model assumes that buoyant plastics are vertically distributed due to wind-driven

mixing and that the depth-integrated plastic concentrations (Ci, pieces km-2) can be

inferred by applying the following one-dimensional column model:

Where: Cs = surface plastic concentration (pieces km-2); d = immersion depth of

the surface-towed net; wb = buoyant rise velocity of marine plastics; Ao = near-surface

turbulent (eddy) exchange coefficient, which was estimated by the following formula:

Where: k = von Karman constant (equal to 0.4); Hs = significant wave height

(m); u*w = frictional velocity of water (m s-1).

According to this model, one of the main drivers of the vertical distribution of plastic

pollution is the rising velocity of plastic particles (Figure 1.6). Preliminary experiments

conducted in Kukulka et al. 2012 indicated that this velocity ranges from 0.007 – 0.014

m s-1. However, details of this experimental work were not provided in the publication.

Furthermore, their comparison between observed depth profiles and model estimates

was incomplete because their model predicted an exponential depth decay on plastic

Ci =Cs

1− e−dwbAO−1

AO =1.5u*wkHs

30

pollution levels, with the largest decrease in the upper two metres, where no subsurface

measurements were taken (Kukulka et al., 2012) (see Figure 1.6).

Figure 1.6 Observed (dots) and modelled (lines) depth profiles of normalized plastic numerical

concentration for different values of frictional velocity of water (u*w) and debris rising speed (wb).

Note the strong dependence between wb and the depth profile of plastic concentration. Source: (Kukulka et al., 2012)

A better understanding of the vertical transport of buoyant plastics is fundamental for

improving estimates of ocean plastic load, size distribution, and dispersal (Kukulka et

al., 2012, Law et al., 2014, Isobe et al., 2014). In this context, Chapter 4 of this thesis

investigates the wind-driven turbulent transport of buoyant plastics by collecting high-

resolution observations of plastic concentrations and characteristics (e.g. rising speeds)

in the ocean top layer (0 – 5 m).

31

1.6 Goals and aims

Despite growing public awareness of ocean plastic pollution, the abundance, spatial

distribution, and ecological implications of marine plastic debris are still poorly

evaluated. It is clear that plastic pollution is a serious environmental issue occurring in

all oceans, and deserves further research.

The goals of this thesis were to investigate how buoyant plastics are distributed in sea

surface waters (both horizontally and vertically), and characterise organisms on the

surface of millimetre-sized marine plastics.

I collected plastic samples from surface waters around Australia (N = 171 15-minute

surface net tows, 839 pieces), and from an oceanic plastic pollution hotspot (N = 12 1-

hour net tows, 12,751 pieces) to achieve the following aims:

Aim 1: Quantify plastic contamination levels in waters around Australia.

Aim 2: Describe textures and organisms on the surface of millimetre-sized plastics from

Australian waters.

Aim 3: Investigate the vertical profile of plastic pollution in the top layer (0 – 5 m) of

the oceans.

1.7 Structure of the thesis

This thesis was prepared as a ‘series of papers’, following the guidelines of the

University of Western Australia. It has five chapters: this general introduction chapter,

three data chapters, and a general discussion chapter.

32

This chapter covered marine plastic pollution background in order to justify the overall

goals of the thesis. Additional literature reviews, focused on the aims and specific

objectives, are presented in the introduction sections of each data chapter.

The bodies of work related to aims 1, 2 and 3 are described in chapters 2, 3, and 4,

respectively. These chapters were written in standard scientific publication format, so

they can be read individually or as a part of the whole thesis. These three manuscripts

(two published in PLOS ONE and one in Biogeosciences) are generally reproduced

verbatim, except for:

- Acknowledgements, which have been consolidated into one general thesis

acknowledgement section;

- References, which have been consolidated into a general thesis references

section, following the Harvard bibliography style;

- Table and figure numbers, which are now following the thesis structure;

- Citations to the papers arising from this thesis, which have been changed to

references to the corresponding thesis chapters;

- Language, which has been changed from American to British English.

Finally, chapter 5 brings together the main findings of this thesis, highlighting their

scientific significance and limitations, and suggests directions for future research related

to marine plastic pollution.

33

Chapter 2 Marine plastic pollution in waters around Australia:

characteristics, concentrations, and pathways

2.1 Summary

Plastics represent the vast majority of human-made debris present in the oceans.

However, their characteristics, accumulation zones, and transport pathways remain

poorly assessed. We characterised and estimated the concentration of marine plastics in

waters around Australia using surface net tows, and inferred their potential pathways

using particle-tracking models and real drifter trajectories. The 839 marine plastics

recorded were predominantly small fragments (“microplastics”, median length = 2.8

mm, mean length = 4.9 mm) resulting from the breakdown of larger objects made of

polyethylene and polypropylene (e.g. packaging and fishing items). Mean sea surface

plastic concentration was 4256.4 pieces km-2, and after incorporating the effect of

vertical wind mixing, this value increased to 8966.3 pieces km-2. These plastics appear

to be associated with a wide range of ocean currents that connect the sampled sites to

their international and domestic sources, including populated areas of Australia’s east

coast. This study shows that plastic contamination levels in surface waters of Australia

are similar to those in the Caribbean Sea and Gulf of Maine, but considerably lower

than those found in the subtropical gyres and Mediterranean Sea. Microplastics such as

the ones described here have the potential to affect organisms ranging from megafauna

to small fish and zooplankton.

34

2.2 Introduction

Plastics are a diverse group of materials derived from petrochemicals (Thompson et al.,

2009). Their global production has grown exponentially from 1,700,000 tonnes in 1950

to 280,000,000 tonnes in 2011 (PlasticsEurope, 2012). The disposability of plastics,

together with their low recycling rates, has contributed to a significant rise in the

amount of waste produced globally (Hoornweg and Bhada-Tata, 2012). For instance, in

Australia, 1,433,046 tonnes of plastics were used in 2010-2011, of which only 20% was

recycled. Moreover, around 37% of this plastic was for the manufacturing of single-use

disposable packaging (PACIA, 2011). Plastics are transported from populated areas to

the marine environment by rivers, wind, tides, rainwater, storm drains, sewage disposal,

and even flood events. It can also reach the sea from vessels (e.g. fishing gear) and

offshore installations (Ryan et al., 2009). Once in the oceans, they will either float at the

ocean surface, or sink to the seafloor if made from polymers denser than seawater

(Andrady, 2011). Buoyant plastics may be cast ashore by inshore currents or winds

(Thiel et al., 2013), or may enter the open ocean, where they tend to accumulate in

convergence zones such as the ones formed by the five large-scale gyres: South and

North Pacific, South and North Atlantic, and Indian (Moore et al., 2001, Law et al.,

2010, Eriksen et al., 2013).

Marine plastics are known to undergo fragmentation into increasingly smaller pieces by

photochemical, mechanical and biological processes (Andrady, 2011, Davidson, 2012).

Plastics are also directly manufactured in small sizes (< 5 mm), which may find their

way into the oceans. These include virgin plastic pellets (pelletwatch.org) (Mato et al.,

2001), synthetic fibres from clothes (Browne et al., 2011), microbeads from cosmetics

(Fendall and Sewell, 2009), and synthetic ‘sandblasting’ media (Andrady, 2011). There

is increasing awareness that these small plastic particles (often called microplastics

35

when smaller than 5 mm) (Andrady, 2011) represent a significant proportion of the

human-made debris present in the oceans. However, their at-sea spatial and temporal

dynamics remain poorly assessed, mostly due to a lack of data on their characteristics

and at-sea occurrence (Kukulka et al., 2012, Lebreton et al., 2012). In Australia, the

only published information on microplastics comes from a global study that recorded

their occurrence in the sediments of Busselton beach (Western Australia) and Port

Douglas (Queensland) (Browne et al., 2011). Apart from this, our current knowledge on

plastic contamination in the Australian marine environment is restricted to (1) beach

litter clean-ups that record mainly the occurrence of relatively large objects, e.g. (Jones,

1995, Frost and Cullen, 1997, Edyvane et al., 2004); (2) land-based surveys of marine

megafauna impacted by marine debris, e.g. (Jones, 1995, Carey, 2011, Schuyler et al.,

2012, Verlis et al., 2013); and (3) inferences based on plastic pollution reports from

New Zealand, e.g. (Gregory, 2009).

The impacts of plastics on marine vertebrates, such as turtles, mammals and birds, have

been well recognized since the 80s (Carr, 1987, de Stephanis et al., 2013). However,

only recently has concern about the effects of small plastic particles on food webs and

marine ecosystems been raised. More than half of modern plastics contain at least one

hazardous ingredient (Rochman et al., 2013a) and those that end up in aquatic systems

can become increasingly toxic by adsorbing persistent organic pollutants on their

surface (Rochman et al., 2013b). These concentrated toxins might then be delivered to

animals via plastic ingestion and/or endocytosis (Teuten et al., 2009, von Moos et al.,

2012) and transferred up their food webs (Basheer et al., 2004, Choy and Drazen, 2013,

Gassel et al., 2013). This bio-magnification process is more likely to happen when

plastics are small enough to be ingested by organisms that are close to the bottom of the

ocean food web, such as planktivorous fish (Boerger et al., 2010) and zooplankton

36

(Cole et al., 2013). For instance, it was inferred that small plastic particles found in the

stomach contents of Southern Bluefin tuna captured close to Tasmania (Young et al.,

1997) were coming from the guts of their prey: myctophid fish (Eriksson and Burton,

2003). In this scenario, plastic contaminants can be transferred to the affected organism

and then biomagnified up the food chain. If this process is taking place, plastics can

affect the health of food webs, which include humans as an apex predator.

Australia’s acknowledgement of plastic threats to marine ecosystems is mostly limited

to impacts from relatively large debris (e.g. abandoned fishing nets, plastic bags) on

marine megafauna (e.g. turtles, mammals, birds) (Commonwealth of Australia, 2009).

A first step towards a better understanding of the extent of marine plastic hazards to

Australian organisms and environments is a better assessment of the occurrence and

characteristics of plastic debris at-sea. To this end, we characterized (size, type, color,

polymer) and estimated concentration (pieces km-2) of plastics in waters around

Australia using surface net tows. Additionally, potential pathways taken by the collected

plastics were inferred using outputs of a dispersal model and trajectories of satellite-

tracked drifting buoys.

2.3 Materials and Methods

Ethics Statement: Permits to conduct this field research were obtained from the Great

Barrier Reef Marine Park Authority (GBRMPA: permit G11/34378.1). No other special

permitting was required because sampling was limited to the collection of marine

debris.

During seven transit voyages aboard Australian vessels (Figure 2.1), we undertook three

consecutive 15-minute net tows (mean ± standard deviation tow length = 1.3 ± 0.50 km)

at 57 locations (hereafter called “net stations”), while the ship was travelling at a speed

37

of 2 – 4 knots. These net tows sampled the air-sea interface, using a Neuston net (1.2 ×

0.6 m mouth, 335 μm mesh) or a Manta net (1 × 0.17 m mouth, 333 μm mesh). After

each net tow, the collected material was transferred to a container filled with seawater

and examined for floating plastic pieces for at least an hour by a trained observer (J.R.).

Each plastic piece was picked up with forceps and placed in a graduated dish to be

counted, measured (length), photographed and classified into type (hard, soft, line,

expanded polystyrene, pellet), and colour. A random sample of 200 plastic pieces was

selected for polymer composition analysis by Fourier transform infrared spectrometry

(FT-IR; range = 500 - 4000 cm-1). Polymer type was determined by comparing sample

FT-IR spectra against known spectra from a database (Perkin-Elmer ATR of Polymers

Library).

Figure 2.1 Location of the 57 net stations sampled during this study.

Dot colours indicate the voyage when the net station was sampled and numbers follow the chronological order of sampling. Pictures of the two types of net used are shown in the right panel.

To estimate sea surface plastic concentrations (Cs, pieces km-2), we first divided the

number of plastic pieces found in the cod-end of each net tow by its towed area, which

38

was estimated by multiplying net mouth width by tow length (determined from GPS

position data). Mean Cs was then estimated for each of the 57 net stations by averaging

the Cs of its three net tows. To our knowledge, this is the first study to take net tow

replicates for marine plastic sampling. Apart from providing us measurements of Cs

variability, our approach (i.e. execution of 3 short net tows instead of 1 long trawl) also

avoided net clogging by gelatinous zooplankton.

Since buoyant plastics are vertically distributed due to wind-driven mixing, we also

estimated depth-integrated plastic concentrations (Ci, pieces km-2) by applying a one-

dimensional column model (Kukulka et al., 2012):

Where:

d = immersion depth of the surface-towed net; equal to 0.17 m for the Manta net

tows (full immersion of the net frame) and 0.3 m for the Neuston net tows (half

of the frame immersed).

wb = buoyant rise velocity of marine plastics; equal to 0.02 m s-1. Preliminary

experiments indicate that it ranges from 0.005 – 0.035 m s-1 (Kukulka et al.,

2012).

Ao = near-surface turbulent (eddy) exchange coefficient, which was estimated

by:

Where:

Ci =Cs

1− e−dwbAO−1

AO =1.5u*wkHs

39

k = von Karman constant; equal to 0.4.

Hs = significant wave height (m).

u*w = frictional velocity of water (m s-1).

Both Hs and u*w were taken from the ERA-Interim model (Dee et al., 2011). There was

a considerable similarity between wind fields of the ERA-Interim forecast model (U10)

and the wind speed measured by an anemometer (w) on five of our seven voyages (U10

= 0.85 + 1.04w, r2= 0.79, N = 39 net stations), indicating that the use of the model

outputs is adequate.

To infer potential pathways taken by the collected plastics, we used two approaches: (1)

application of the Australian Connectivity Interface Connie2 (csiro.au/connie2), and (2)

trajectories of satellite-tracked buoys from the Global Drifter Program

(aoml.noaa.gov/phod/dac). In our first approach, an area of 0.1° latitude by 0.1°

longitude was created around each net station and particle-tracking models were run

backwards in time. Particles were released within these areas over a 30-day period (25

particles per day), and subsequently tracked for a dispersal time equal to 45 days. These

models were forced by averaged ocean current fields (2002 - 2006) of the month when

the net station was sampled. Details of the particle tracking model, and the eddy-

resolving/data-assimilating ocean general circulation model can be found in (Condie et

al., 2005) and (Schiller et al., 2008), respectively. In our second approach, an area of 4°

latitude by 4° longitude was centred on each net station and drifters (drogued and un-

drogued) that reached these regions were selected. The tracks starting from the drifter

release point until they entered one of the net station areas were then plotted onto maps.

40

2.4 Results

We recorded 839 pieces of plastic, ranging in length from 0.4 to 82.6 mm (median = 2.8

mm, mean ± standard error = 4.9 ± 0.27 mm, Figure 2.2). The majority of these plastic

pieces had low circularity in their shape when compared to manufactured plastic

particles (e.g. pellets and microbeads from cosmetics), suggesting they mostly resulted

from the breakdown of larger items. The main plastic type was hard plastic (N = 633,

median length = 2.4 mm, range = 0.7 - 57.0 mm) followed by soft plastic (N = 142,

median length = 5.0 mm, range = 0.5 - 73.0 mm), plastic line (N = 54, median length =

10.3 mm, range = 2.0 - 82.6 mm), expanded polystyrene (N = 8, median length = 2.9

mm, range = 1.3 - 24.3 mm), and pellet (N = 2, both 4 mm). Most plastics were

white/transparent (84.7 %), but blue (8.3 %) and other colours (7 %) were also present.

Of the 200 pieces subjected to FT-IR, 67.5 % were made of polyethylene, 31 % of

polypropylene, 1 % of expanded polystyrene, and 0.5 % of ethylene vinyl acetate

(Figure 2.3).

41

Figure 2.2 Size and types of marine plastics collected around Australia.

Bars indicate the number of plastic pieces within each size category (< 2.5, 2.5 - 4.9, 5 – 10, > 10 mm) and colours show the amount of each plastic type within size categories. Examples of the types of plastic we collected are shown in the photos, including our biggest fragment of hard plastic (length = 57 mm, net station 32), soft plastic (length = 73 mm, net station 57, note the Indonesian words), and expanded polystyrene (Styrofoam cup fragment, length = 24.3 mm, net station 28).

42

Figure 2.3 Mean infrared spectra of the plastic pieces within each polymer type.

Approximately 80 % of our net tows (136 out of 171), and 93 % of our net stations (53

out of 57), had at least one piece of plastic (range: 0 – 68, median = 2, mean ± standard

error = 4.9 ± 0.63 pieces per net tow). Estimated sea surface plastic concentrations (Cs)

for each net tow ranged from 0 to 48895.6 pieces km-2 (median = 1932.1 pieces km-2,

mean ± standard error = 4256.4 ± 757.79 pieces km-2) and the mean Cs of net stations

varied between 0 and 23610.7 pieces km-2 (Figure 2.4, Appendix 2).

43

Figure 2.4 Mean sea surface plastic concentration (Cs) at the 57 net stations.

White crosses indicate location of major Australian cities (population > 1 million). From west to east: Perth, Adelaide, Melbourne, Sydney, and Brisbane.

Relatively high mean Cs (> 15500 pieces km-2) were estimated only at low wind speeds

(< 7 m s-1, Figure 2.5a). There was an inverse relationship between Cs and wind forcing

(b = -0.77 in Cs = a(u*w)b), which was relatively consistent with the biophysical model

applied here (Figure 2.5b). When taking into account the effect of wind-mixing, net tow

plastic concentrations increased by a mean factor of 2.8 (range: 1.04 – 10.0, median =

1.9). Hence, the amount of plastics collected by our net tows (Cs) represents anywhere

between 10.0 % and 96.1 % (median = 52.7 %, mean ± standard deviation = 50.0 ±

24.47 %) of the estimated total amount of plastic present in the water column (Ci,

Figure 2.6).

44

Figure 2.5 Sea surface plastic concentration (Cs) versus a) wind speed (U10) and b) water friction

velocity (u*w).

In (b) we also show the linear fit (Cs = a (u*w)b) and theoretical model estimates for Cs, when depth-integrated plastic concentration (Ci) is equal to 8966 (mean Ci of the 171 net tows) and significant wave height (Hs) is equal to the mean (1.85 m), maximum (4.78 m) and minimum (0.47 m) values estimated for the 57 net stations.

45

Figure 2.6 Mean and standard error of sea surface (Cs) and depth-integrated (Ci) plastic

concentrations.

Blue represents mean and standard error of Cs and red represents mean and standard error of Ci.

Depth-integrated plastic concentration estimates (Ci) for each net tow ranged from 0 to

105438.6 pieces km-2 (median = 4363.7 pieces km-2, mean ± standard error = 8966.3 ±

1330.75 pieces km-2) and the mean Ci of net stations ranged from 0 to 43194.5 pieces

km-2 (Figure 2.7). In this scenario, plastic concentrations higher than 15500 pieces km-2

(red dots) were quite common, and those higher than 31500 pieces km-2 (dark red dots)

were found close to populated areas (Brisbane and Fiji) as well as in some remote

coastal regions (southwest Tasmania) and oceanic areas (Figure 2.7).

46

Figure 2.7 Mean depth-integrated plastic concentration (Ci) at the 57 net stations.

White crosses indicate location of major Australian cities (population > 1 million). From west to east: Perth, Adelaide, Melbourne, Sydney, and Brisbane.

A wide range of pathways was taken by the virtual particles arriving at the net stations

(Figure 2.8, Appendix 2). The routes taken by real drifters, from their release points to

the net stations, showed similar patterns but covered larger areas due to their longer

drifting time and wider range of release date (Figure 2.9, Appendix 2).

47

Figure 2.8 Cumulative probability distribution of virtual particles arriving at the 57 net stations.

The month when the virtual particles (25 per day) were released is indicated in each panel. Backtracking dispersal time was equal to 45 days and arriving destinations (net stations) are marked with purple dots. See also Appendix 2.

48

Figure 2.9 Real drifter pathways arriving at the 57 net stations.

Purple dots indicate net station locations and asterisks indicate drifter release areas. See also Appendix 2.

49

2.5 Discussion

We found that the surface waters around Australia are contaminated with small plastics

that are mostly a by-product of the degradation of larger objects made of polyethylene

and polypropylene. The high prevalence of plastic fragments smaller than 5 mm in

Australian waters is consistent with other regions of the world’s oceans, where

microplastics were found to be the most abundant type of debris in all types of marine

environment (Moore et al., 2001, Thompson et al., 2004, Browne et al., 2010, Law et

al., 2010, Browne et al., 2011, Eriksen et al., 2013). Plastic pollution levels were

moderate when compared to concentrations in other marine areas (Moore et al., 2001,

Yamashita and Tanimura, 2007, Law et al., 2010, Collignon et al., 2012, Eriksen et al.,

2013). Higher amounts of plastic were found close to cities on Australia’s east coast, as

well as in remote locations (west Tasmania and North West Shelf). Recent studies

reported toxicological effects of these small and contaminated plastics on a host of

organisms, including large marine vertebrates (Fossi et al., 2012) and fish (Basheer et

al., 2004, Choy and Drazen, 2013, Gassel et al., 2013, Wright et al., 2013). As such,

small plastics are a type of harmful marine debris, implying that plastic hazards to

Australian species and ecological communities are likely to be broader than those

officially recognized.

2.5.1 Characteristics of marine plastics

Captured plastic particles ranged in size from 0.4 - 82.6 mm. The frequency distribution

of different sized plastics, which was skewed towards smaller particles, provides

evidence for the existence of smaller plastics. Current methods for assessing plastic

pollution at the ocean surface rely on the use of nets, which omits plastic particles

50

outside the collectible range of their mesh (Hidalgo-Ruz et al., 2012). It will be critical

for future investigations to develop efficient and reproducible techniques capable of

detecting smaller buoyant plastic particles (micro and nanoparticles). In addition, post

processing techniques for sorting particles are also likely to miss small fragments

(Hidalgo-Ruz et al., 2012). An example of a new method with the potential to eliminate

this limitation is the application of molecular mapping by reflectance micro-FT-IR

spectroscopy, which does not rely on visual selection of plastic particles for

characterization (Harrison et al., 2012).

Hard plastics were by far the most common plastic type found (75.4%), but soft plastics

(e.g. fragments of plastic wrappers) and lines (mostly fishing lines) were also relatively

common (16.5% and 6.4%, respectively). It is interesting to note that soft plastics were

more abundant in the larger size class (> 2.4 mm). Our findings are consistent with

recent studies documenting plastic pollution at the ocean surface, although explanations

for variations in hard/soft plastic trends are not given (Moore et al., 2001, Eriksen et al.,

2013, Morét-Ferguson et al., 2010). Plastics gradually lose buoyancy in seawater as a

result of biofilm formation (Ye and Andrady, 1991). We suggest that negative buoyancy

due to biofouling occurs more quickly in soft/thin than in hard/thicker plastic fragments,

resulting in a decline in the occurrence of soft plastics at the ocean surface, as they

become smaller/older and begin to sink. Indirect evidence for this is that the proportion

of soft plastics found in our coastal net stations was higher than that reported in open

ocean settings further away from potential sources (Morét-Ferguson et al., 2010). While

a small number of experimental studies have confirmed that biofilms decrease the

buoyancy of plastic items (Ye and Andrady, 1991, Lobelle and Cunliffe, 2011), none of

them report the magnitude or speed of this process across different types of small

fragments.

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The plastics reported here were mostly white/transparent (84.7 %) or blue (8.3 %),

which is consistent with reports from other investigations on buoyant marine plastics

(Carpenter and Smith, 1972, Morét-Ferguson et al., 2010). Depending on the feeding

ecology of the affected animal, ingested plastic colour proportions can differ from what

is available in the environment (Schuyler et al., 2012). For instance, ingested plastic

colour proportions in Australian shearwaters (Ardenna pacifica and Ardenna

tenuirostris) are different from those reported by this study (Carey, 2011, Verlis et al.,

2013). As these birds are known to use colour vision to select their food (Bowmaker,

1980, Verlis et al., 2013), colour can play a role in the ingestion risk associated with a

certain plastic item. In contrast, the colour proportion of plastics found in scats of fur

seals (Arctocephalus spp.) at Macquarie Island (Australia) reflected what was available

as flotsam in this environment (Eriksson and Burton, 2003). These plastics are likely to

be coming from the stomach contents of their main prey: the myctophid Electrona

subaspera, which are pelagic small fish known to feed at night, selecting their food

based on size rather than colour (Eriksson and Burton, 2003).

The vast majority (98.5 %) of the plastics detected were made of polyolefins

(polyethylene and polypropylene), which is in agreement with what has been found for

this size range of plastics in other marine regions around the world (Morét-Ferguson et

al., 2010, Hidalgo-Ruz et al., 2012). Polyethylene and polypropylene account for most

of our global plastic production (38 % and 24 %, respectively) (Andrady, 2011) and

they are typically applied in the manufacturing of single-use disposable packaging. In

addition to packaging, which reaches the oceans primarily from coastal areas, fishing

equipment made of these polyolefins, e.g. fish crates, nets, ropes, fishing lines (Jones,

1995) are also likely sources of the plastic particles registered here. Other types of

polymers found in this study include two pieces of expanded polystyrene (Styrofoam), a

52

type of plastic also used in packaging and fishing gear, and one fragment of ethylene

vinyl acetate, which has several applications such as the making of shoe soles and foam

mats.

2.5.2 Concentrations and sources

Our overall mean sea surface plastic concentration (Cs) was 4256.4 pieces km-2, which

is similar to mean values reported for other regions outside subtropical gyres, such the

Caribbean Sea (mean Cs = 1414 pieces km-2) and Gulf of Maine (mean Cs = 1534

pieces km-2) (Law et al., 2010). Within subtropical gyres, Cs values tend to be higher

but within the same order of magnitude: 20328 pieces km-2 in the North Atlantic Gyre

(Law et al., 2010), and 26898 pieces km-2 in the South Pacific Gyre (Eriksen et al.,

2013). The exception seems to be the subtropical waters of the North Pacific and

Mediterranean, which present mean Cs values that are an order of magnitude higher

than those reported here: 116000 pieces km-2 in the Mediterranean (Collignon et al.,

2012), 174000 pieces km-2 in Northwest Pacific (Yamashita and Tanimura, 2007), and

334271 pieces km-2 in Northeast Pacific (Moore et al., 2001). The latter is also known

as the “Great Pacific Garbage Patch” (Moore et al., 2001), which is the largest

aggregator of floating marine particles (van Sebille et al., 2012).

Our findings show that the distribution of marine plastics is quite widespread (93 % of

our net stations had at least one plastic piece), patchy (i.e. high variability within and

between net stations’ Cs) and dynamic (Cs ranged from 10% to 91% of Ci). Therefore,

better spatio-temporal data coverage is required in order to identify plastic pollution

hotspots within Australian waters. However, our data already indicate some spatial

patterns: we observed high plastic concentrations close to Sydney and Brisbane cities.

This suggests that plastics along Australia’s east coast are mostly associated with

53

domestic inputs. Since high quantities of plastic were also found close to Viti Levu

(Fiji), we hypothesize that part of the plastics coming from coastal areas remain in the

vicinity of their sources for a long time, while fragmenting into smaller pieces. This

suggestion of local retention of plastic debris is in agreement with findings of recent

studies, e.g.(Thiel et al., 2013), and could be tested by developing high-resolution

models able to simulate plastic transport in coastal environments.

While the relatively high concentrations of plastic found close to the East Australian

coast (net stations 18-20, 22, 37) seem to originate from local sources of plastics, those

found in southwest Tasmania/eastern South Australia (net stations 5, 6, 8), and the

North West Shelf (net station 54) could be associated with international sources and/or

maritime operations. The presence of internationally-based plastics is suggested by (1) a

fragment with Indonesian words that was collected in North West Shelf (see Figure 2.2)

and (2) beach surveys, which registered in South Australia plastic debris from South

Africa and South America (Edyvane et al., 2004). High plastic concentrations in the

southern tip of Tasmania (net station 5) might be caused by convergence effects of the

encounter of the East Australian and Zeehan coastal currents (Edyvane et al., 2004),

whereas those found off the east coast (e.g. net station 37) could be associated with

meso-scale eddies of the East Australian current (Ridgway and Dunn, 2003).

Aside from this study and the one that developed the biophysical model we applied here

(Kukulka et al., 2012), we are not aware of any investigation that quantitatively

considers the effect of vertical mixing processes on plastic concentrations. This effect

needs to be taken into account in future studies assessing at-sea plastic pollution to

allow better comparisons between data collected under different sea states. An

important step towards improved simulations of plastic distribution along the water

column is to better quantify the buoyant rise velocity (wb) of plastic particles from

54

different oceanic and coastal surface waters. This variable has a considerable impact on

the output of the model applied here. Furthermore, other environmental variables that

were not taken into account in our one-dimensional column model (e.g. Langmuir

circulation, breaking waves, mixed layer depth) could be incorporated in this type of

modeling.

2.5.3 Potential pathways

The model outputs and routes taken by real drifters showed that plastics we found could

have moved via a wide range of routes. This is because our net stations are within

regions that experience different hydrodynamics, e.g. North West Shelf, Great

Australian Bright, Coral Sea, and Tasman Sea (Schiller et al., 2008). Plastics have the

potential to reach the sampled sites by travelling with a range of currents, including: (1)

Antarctic Circumpolar current (Talley et al., 2011a), which can carry plastics from a

wide area to several of our net stations, particularly those along the coast of Tasmania,

south coast of Australia, and Tasman Sea (net stations 1-15, 38 and 39); (2) South

Equatorial current in the Pacific Ocean (Webb, 2000, Talley et al., 2011a), which can

bring international plastics to the east coast of Australia (net stations 16-24, 40-45, 36,

37) and areas close to Fiji and New Caledonia (net stations 25-35); (3) East Australian

current (Ridgway and Dunn, 2003, Talley et al., 2011a), which can carry plastics from

domestic highly populated regions (e.g. Brisbane and Sydney) to the net stations along

the coast of Tasmania (net station 5, 15, 38, 39), east coast of Australia (net stations 16-

24, 36, 37) and the Tasman Sea (net stations 1-4); (4) Holloway, Leeuwin, South

Australian, and Zeehan coastal current systems (Ridgway and Condie, 2004, Sandery

and Kämpf, 2007, Condie and Andrewartha, 2008, Pattiaratchi and Woo, 2009), which

can bring plastics from international areas connected to the Indonesian Throughflow

and Indian Gyre, e.g. Southeast Asia/Indonesia (Lebreton et al., 2012), as well as from

55

domestic populated areas, to the net stations of the North West Shelf (net stations 48-

57), off Perth (net station 14), and along the south coast of Australia, Bass Strait,

Tasman Sea, and coast of Tasmania (net stations 1-13, 15-17, 37-39); and (5) West

Australia current (Pattiaratchi and Woo, 2009), which could transport international

marine plastics that accumulated in the Indian Gyre to the net stations in the North West

Shelf (net stations 48-57) and off Perth (net station 14).

It is important to note that running models backwards and using drifter trajectories

arriving at sampled locations can only provide an indication of the directions that the

collected plastics could have taken. To precisely estimate plastic pathways is quite

challenging, mostly because plastic source locations and quantities are still largely

unknown. Moreover, there are still no methods to estimate the “age” (drifting time) of a

certain plastic particle. For instance, only plastics with long drifting times (years) could

have matched the long tracks of drifters. Another limitation of the real drifter approach

is that the resulting pathway formed by all drifter tracks arriving at a certain region is

not only dependent on the ocean current systems, but also on the locations where most

of the drifters were released. For instance, sampled sites in the North West Shelf (net

stations 48-57) had only a few drifters arriving at them. This is mostly due to the non-

existence of drifters in the shallow waters of the Indonesian archipelago. The creation of

a shallow-water drifter - e.g. (Ohlmann et al., 2005) - release program in this area could

bring crucial information to help inform marine plastic pathways and sources.

2.5.4 Final remarks

This investigation shows that the abundant and widespread small marine plastics around

Australia are likely coming from a variety of domestic and international, land- and

ocean-based sources. Even though marine plastic pollution is a global environmental

56

issue, mostly caused by our massive production of plastic single-use disposable items,

there are still no attempts to regulate plastic disposal on land at an international level

(Rochman et al., 2013a). Additionally, dumping of plastics into the oceans remains a

significant issue owing to difficulties with regulation and enforcement (Jones, 1995,

Rakestraw, 2012). We suggest further at-sea studies on the characterization, spatial

distribution, and pathways of marine plastics in coastal and oceanic regions around

Australia, as well as on marine plastic toxin loads and interactions between small plastic

particles and organisms at all trophic levels of the food web. This would improve our

current knowledge on the effects of plastic on the marine ecosystem as a whole.

57

Chapter 3 Millimetre-sized Marine Plastics: A New Pelagic Habitat

for Microorganisms and Invertebrates

3.1 Summary

Millimetre-sized plastics are abundant in most marine surface waters, and known to

carry fouling organisms that potentially play key roles in the fate and ecological impacts

of plastic pollution. In this study we used scanning electron microscopy to characterize

biodiversity of organisms on the surface of 68 small floating plastics (length range = 1.7

- 24.3 mm, median = 3.2 mm) from Australia-wide coastal and oceanic, tropical to

temperate sample collections. Diatoms were the most diverse group of plastic

colonizers, represented by 14 genera. We also recorded ‘epiplastic’ coccolithophores (7

genera), bryozoans, barnacles (Lepas spp.), a dinoflagellate (Ceratium), an isopod

(Asellota), a marine worm, marine insect eggs (Halobates sp.), as well as rounded,

elongated, and spiral cells putatively identified as bacteria, cyanobacteria, and fungi.

Furthermore, we observed a variety of plastic surface microtextures, including pits and

grooves conforming to the shape of microorganisms, suggesting that biota may play an

important role in plastic degradation. This study highlights how anthropogenic

millimetre-sized polymers have created a new pelagic habitat for microorganisms and

invertebrates. The ecological ramifications of this phenomenon for marine organism

dispersal, ocean productivity, and biotransfer of plastic-associated pollutants, remain to

be elucidated.

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3.2 Introduction

Millimetre-sized plastics resulting from the disintegration of synthetic products (known

as ‘microplastics’ if smaller than 5 mm) are abundant and widespread at the sea surface

(Moore et al., 2001, Law et al., 2010, Morét-Ferguson et al., 2010, Hidalgo-Ruz et al.,

2012, Eriksen et al., 2013, Law et al., 2014). These small marine plastics are a toxic

hazard to food webs since they can contain harmful compounds from the manufacturing

process (e.g. Bisphenol A), as well as contaminants adsorbed from the surrounding

water (e.g. polychlorinated biphenyls) (Mato et al., 2001, Rios et al., 2007, Teuten et al.,

2009, Rochman et al., 2013a). These substances can be carried across marine regions

and transferred from plastics to a wide range of organisms, from zooplankton and small

fish to whales (Basheer et al., 2004, Teuten et al., 2009, Boerger et al., 2010, Fossi et

al., 2012, von Moos et al., 2012, Gassel et al., 2013, Choy and Drazen, 2013, Cole et al.,

2013, Rochman et al., 2013c). Furthermore, they can physically damage suspension-

and deposit-feeding fauna (e.g. internal abrasions and blockages after ingestion)

(Wright et al., 2013), and alter pelagic and sediment-dwelling biota by modifying

physical properties of their habitats (Carson et al., 2011). Finally, these small marine

plastics can transport rafting species (Carpenter and Smith, 1972, Carpenter et al., 1972,

Gregory, 1978, Gregory, 1983, Carson et al., 2013, Zettler et al., 2013), potentially

changing their natural ranges to become non-native species and even invasive pests.

Apart from providing long-lasting buoyant substrata that allow many organisms to

widely disperse (Winston, 1982, Jokiel, 1990, Barnes, 2002, Masó et al., 2003, Barnes

and Fraser, 2003, Aliani and Molcard, 2003, Barnes, 2004, Thiel and Gutow, 2005,

Gregory, 2009, Fortuño et al., 2010, Goldstein et al., 2014), marine plastics may also

supply energy for microbiota capable of biodegrading polymers and/or associated

compounds (Sudhakar et al., 2007, Artham and Doble, 2009, Balasubramanian et al.,

59

2010, Harrison et al., 2011, Zettler et al., 2013, Harshvardhan and Jha, 2013), and

perhaps for invertebrates capable of grazing upon plastic inhabitants. The hydrophobic

nature of plastic surfaces stimulates rapid formation of biofilm, which drives succession

of other micro- and macro-organisms. This ‘epiplastic’ community appears to influence

the fate of marine plastic pollution by affecting the degradation rate (Andrady, 2011,

Zettler et al., 2013), buoyancy (Ye and Andrady, 1991, Moore et al., 2001, Lobelle and

Cunliffe, 2011), and toxicity level (Harrison et al., 2011) of plastics. Moreover,

epiplastic microbiota could have impacts on the microflora of its consumers, and

infectious organisms may reach their hosts through plastic ingestion (Harrison et al.,

2011, Pham et al., 2012, Zettler et al., 2013).

Although epiplastic organisms may play an important role in determining the fate and

ecological impacts of plastic pollution, little research has been directed to such study,

particularly on the inhabitants of the widely dispersed and abundant millimetre-sized

marine plastics (Harrison et al., 2011). In 1972, two papers first reported the occurrence

of organisms (diatoms, hydroids, and bacteria) on small plastics (0.1 – 5 mm long)

collected by plankton nets (Carpenter and Smith, 1972, Carpenter et al., 1972). Further

at-sea studies focusing on microplastic fouling biota only emerged in the 2000s (Carson

et al., 2011, Goldstein et al., 2012, Zettler et al., 2013). Zettler et al. (2013) conducted

the first comprehensive characterisation of epiplastic microbial communities, which

they coined the “Plastisphere”. These authors used scanning electron microscopy (SEM)

and next-generation sequencing to analyse three polyethylene and three polypropylene

plastic pieces (approx. 2 – 20 mm long) from offshore waters of the North Atlantic.

This pioneer study revealed a unique, diverse, and complex microbial community that

included diatoms, ciliates, and bacteria.

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Here, we used SEM to examine types of organisms inhabiting the surface of 68 small

marine plastics (length range = 1.7 - 24.3 mm, median = 3.2 mm) from inshore and

offshore waters from around the Australian continent (Figure 3.1). We contributed

many new records of taxa associated with millimetre-sized marine plastics and imaged a

variety of marine plastic shapes and surface textures resulting from the interaction of

polymers with environments and organisms.

Figure 3.1 Sampling locations of the 68 plastics analysed in this study.

Black lines delimit marine regions of Australia (environment.gov.au/topics/marine/marine-bioregional-plans); dots indicate areas where the analysed plastics were collected; numbers represent how many plastics were taken for scanning electron microscopy analyses at these locations. Samples collected were fragments of hard plastic (N = 65), except at locations marked with an asterisk: one piece of Styrofoam cup in Fijian waters, one pellet in South Australia, and one piece of soft plastic in the Australia’s North-west marine region.

3.3 Material and Methods

Ethics Statement: Permits to conduct field research within the Great Barrier Reef area

were obtained from the Great Barrier Reef Marine Park Authority (GBRMPA: permit

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G11/34378.1). No other special permit was required since sampling was limited to

marine debris.

Buoyant plastics were collected using surface net tows in waters around Australia (see

details in Chapter 2) and preserved in 2.5% glutaraldehyde buffered in filtered seawater.

Prior to analysis with a scanning electron microscope, plastics were dehydrated through

a series of increasing ethanol concentrations (up to 100%), critical-point dried using

CO2, mounted on aluminium stubs with carbon tape, and sputter coated with a 20 - 30

nm layer of gold. We used a Zeiss 1555 VP-FESEM scanning electron microscope

operated at 10 - 20 kV, 11 - 39 mm working distance, and 10 - 30 μm aperture. We

randomly selected 65 hard plastics among those small enough to fit onto SEM stubs (<

10 mm) and large enough to be easily handled (> 1 mm). For comparison, a piece of (1)

soft plastic, (2) industrial plastic pellet, and (3) expanded polystyrene (Styrofoam) were

also examined, totalling 68 plastic pieces examined with SEM. These plastics were

collected from offshore waters of the South-west Pacific (N = 19) and from different

Australian marine regions (environment.gov.au/topics/marine/marine-bioregional-

plans): North-west (N = 13), South-west (N = 3), South-east (N = 13), Temperate East

(N = 16), and Coral Sea (N = 4; Figure 3.1).

The different types of organisms detected on each plastic piece were imaged, measured

using ImageJ (length and width, http://rsb.info.nih.gov/ij/), classified into

taxonomic/morphological groups, and the frequency of occurrence (FO) for each type

was calculated. We used online resources, e.g. marinespecies.org,

westerndiatoms.colorado.edu, primary taxonomic literature, e.g (Cheng, 1976, Weise

and Rheinheimer, 1977, Kensley, 1994, Hallegraeff et al., 2010, Magalhães and Bailey-

Brock, 2012), and expert consultation to identify the organisms at the lowest possible

62

taxonomic level. Long filaments were very common but were excluded from the

analysis due to difficulty in determining if they were organisms or mucilage.

For each plastic piece observed, an image of the entire piece was taken at 50x

magnification. These images were uploaded to ImageJ to measure plastic particles’ size

parameters - length, area, perimeter, aspect ratio, and shape parameters - circularity and

solidity indexes (Paulrud et al., 2002, Ferreira and Rasband, 2012). Surface fractures,

pits and grooves (Corcoran et al., 2009, Cooper and Corcoran, 2010) were also

observed, recorded, and imaged while examining the entire surface of the plastics at

magnifications of 100 – 500x. Other peculiar microtextures observed at higher

magnifications, such as those suggesting interactions with biota, were also recorded and

imaged. After SEM analyses, plastics were washed with distilled water and submitted to

Fourier Transform Infrared spectrometry (FT-IR) for polymer identification. Two

plastic pieces were destroyed while being cleaned for FT-IR; as such, we identified the

polymer of 66 out of the 68 plastics examined using SEM.

3.4 Results

We examined 65 hard plastic fragments with lengths ranging from 1.7 to 8.9 mm

(median = 3.2 mm), one 4 mm-wide plastic pellet, one 8.7 mm portion of a 15 mm long

soft plastic fragment, and one 7 mm piece of a 24.3 mm Styrofoam cup fragment. Apart

from the Styrofoam cup fragment (expanded polystyrene), plastics were made of

polyethylene (N = 54) and polypropylene (N = 11). Hard plastics had a diverse range of

shapes (solidity index = 0.87 – 0.98, circularity index = 0.28 – 0.83; Figure 3.2) and

types of surface microtextures, including linear fractures, pits, and scraping marks

(Appendix 3). Diatoms and bacteria (rounded, and elongated cells) were by far the most

frequently observed organisms, being detected in all sampled marine regions (Figure

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3.3). Plastics’ FT-IR spectra, 1143 SEM micrographs, and a matrix containing

information from collection sites, plastics characteristics, and organism/microtexture

presence-absence data are available in (Reisser et al., 2014).

64

Figure 3.2 Overall appearance of marine plastics, as shown by scanning electron micrographs.

Dot colour indicates the marine region where the piece was sampled (see legend and Figure 3.1). Pieces are hard plastic fragments, with the exception of the soft plastic fragment (red dot), pellet (yellow dot), and Styrofoam fragment (green dot) shown at the bottom of the diagram and marked with a white asterisk. All images are at the same magnification (see scale bar at lower right).

65

Figure 3.3 Types of epiplastic organisms detected at each of the marine regions sampled in this

study (see Figure 3.1).

Lines connect types of organisms (squares) to the marine regions (circles) where they were observed. Line colour indicates type of organism, with black lines representing invertebrates. Line thickness is proportional to the organism’s frequency of occurrence (FO = <25%, 25-50%, 50-75%, >75%).

Diatoms were the most abundant, widespread, and diverse group of plastic colonizers

(Figure 3.3 and Figure 3.4). These organisms were frequently observed (FO = 78%, N =

68 plastics) and included symmetrical biraphids/naviculoids (Navicula subgroup

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lineatae, Mastogloia sp., Haslea sp.; Figure 3.4a-c), Nitzschioids (Nitzschia spp.,

Nitzschia longissima; Figure 3.4d-f), monoraphids (Cocconeis spp., Achnanthes sp.;

Figure 3.4g-i), centrics (Minidiscus trioculatus, Thalassiosira sp.; Figure 3.4j), araphids

(Thalassionema nitzschioides var. parva, Microtabella spp., Licmophora spp.,

Grammatophora sp.; Figure 3.4k,l,o), and asymmetrical biraphids (Amphora spp.,

Cymbella sp.; Figure 3.4m,n). Most diatoms were growing flat on the surface (adnate

and motile diatoms), but some were erect, attached to plastics by mucous pads or

stalks/peduncles. The genus Nitzschia was the most frequent diatom (FO = 42.6%),

followed by Amphora (13.2%), Licmophora (11.8%), Navicula (8.8%), Microtabella

(5.9%), Cocconeis (4.4%), Thalassionema (2.9%), and Minidiscus (2.9%). The other six

genera were only detected on a single plastic piece (FO = 1.5%). These frequencies of

occurrence are likely to be underestimated, as many diatoms could not be identified

from girdle-view positions (FO unidentified diatoms = 45.6%).

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Figure 3.4 Examples of epiplastic diatoms.

a: Navicula sp.; b: Mastogloia sp.; c: small naviculoids; d: Nitzschia sp.; e: Nitzschia sp.; f: Nitzschia longissima; g,h: Cocconeis spp.; i: Achnanthes sp.; j: Thalassiosira sp.; k: Thalassionema nitzschioides; l: Microtabella sp.; m,n: Amphora spp.; o: Licmophora sp.

Calcareous coccolithophores were observed only on plastics from southern Australia

(South-east and South-west marine regions; FO = 37.5%, N = 16 plastics; Figure 3.3,

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Figure 3.5a-h). The species identified included Calcidiscus leptoporus (Figure 3.5a),

Emiliania huxleyi (Figure 3.5b,c), Gephyrocapsa oceanica (Figure 3.5d),

Umbellosphaera tenuis (Figure 3.5e), Umbilicosphaera hulburtiana (Figure 3.5f),

Coccolithus pelagicus (Figure 3.5g), and Calciosolenia sp. (Figure 3.5h). Many of these

observations related to detached coccolith scales held in place by mucilage and chitin

filaments resembling those produced by diatoms (e.g. Thalassiosira; Figure 3.5b,f).

However, intact coccospheres were also present (Figure 3.5c,d,f). Additionally, one

specimen of the dinoflagellate Ceratium cf. macroceros was present on a 8.2mm plastic

from South-west Australia (Figure 3.3, Figure 3.5i).

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Figure 3.5 Examples of epiplastic coccoliths (a-h) and dinoflagellate (i).

a: Calcidiscus leptoporus; b, c: Emiliania huxleyi; d: Gephyrocapsa oceanica; e: Umbellosphaera tenuis; f: Umbilicosphaera hulburtiana; g: Coccolithus pelagicus; h: Calciosolenia sp.; i: Ceratium cf. macroceros.

70

We found several unidentified organisms of various morphotypes and sizes, mostly

resembling bacterial, cyanobacterial, and fungal cells (Figure 3.6). After diatoms,

rounded/oval cells (length-width ratio < 1.5; Figure 3.6a-c,i-m) were the most

frequently observed morphotype (FO = 72%, N = 68 plastics; Figure 3.3).

Rounded/oval cells with widths < 1 μm and ≥ 1 μm had an overall FO of 38.2% and

54.4%, respectively.

Elongated cells (length-width ratio ≥ 1.5; Figure 3.6e-h) were also frequently observed,

being detected on 59% of the plastics examined (Figure 3.3). Those with widths < 1 μm

and ≥ 1 μm had an overall FO of 51.5% and 11.7%, respectively. Spiral cells (Figure

3.6d) had similar appearances (resembling spirochaete bacteria) and sizes (0.2 - 0.3 μm

width), and were only observed in the South-west Pacific region (FO = 31.6%, N = 19;

Figure 3.3). Several plastic pits and grooves contained bacteria-like cells closely

resembling their shape (Figure 3.6i-m). They were particularly common on plastics

covered by large rounded cells (Figure 3.6k).

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Figure 3.6 Examples of epiplastic rounded, elongated and spiral cells.

a, b, c: rounded cells; d: spiral “spirochaete” cell; e, f, g, h: elongated cells.; i, j, k, l, m: pits and grooves on plastics with rounded cells.

A few invertebrates were observed on the millimetre-sized plastics (FO = 16.2%, N =

68 plastics; Figure 3.3 and Figure 3.7). Colonies of encrusting bryozoans were the most

common epiplastic animal (FO = 8.8%; Figure 3.7a-d). They occurred on two fragments

from the Temperate East marine region and on four fragments from oceanic waters of

the South-west Pacific (plastic length = 3.2 - 5.4 mm). Four of these bryozoan colonies

were hosting abundant diatom assemblages dominated by Licmophora sp., Nitzschia

longissima (Figure 3.7a), Amphora sp. (Figure 3.7c), and Nitzschia sp. (Figure 3.7d).

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Additionally, lepadomorph barnacles (Lepas spp.; Figure 3.7e,f) were attached to the

24.3 mm Styrofoam cup fragment and to a 8.2 mm-long hard plastic; an Asellote isopod

(Figure 3.7g) was found on the Styrofoam cup fragment; eggs of the marine insect

Halobates sp. (Figure 3.7h) were observed on two plastics (4.6 and 5.5 mm long); and a

unidentified marine worm (Figure 3.7i,j) was found on a 6 mm hard plastic fragment.

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Figure 3.7 Examples of epiplastic invertebrates.

a: Bryozoan colony harboring an abundant assemblage of Nitzschia longissima (zoomed image shows part of this assemblage, scale bar = 20 μm); b: bryozoan colony relatively free of fouling; c: bryozoan-plastic interface displaying an abundant epizoic assemblage of Amphora sp.; d: bryozoan-plastic interface displaying an abundant epizoic assemblage of Nitzschia sp.; e, f: barnacles (Lepas spp.); g: Asellota isopod; h: egg of the marine insect Halobates sp.; i: marine worm; j: zoom on the surface of the unidentified marine worm shown in ‘i’.

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3.5 Discussion

There now exists a large body of evidence that millimetre-sized plastics are abundant

and widespread in marine environments (Carpenter et al., 1972, Carpenter and Smith,

1972, Moore et al., 2001, Law et al., 2010, Morét-Ferguson et al., 2010, Hidalgo-Ruz et

al., 2012, Eriksen et al., 2013) and our study significantly adds to this by conclusively

demonstrating that they are colonized by a wide range of biota, particularly diatom and

bacteria species - Table 1 (Carpenter and Smith, 1972, Gregory, 1978, Gregory, 1983,

Moore et al., 2001, Carson et al., 2013, Zettler et al., 2013). We more than doubled the

number of known diatom genera inhabiting millimetre-sized marine plastics and

provide the first identifications of coccolithophore genera attached to these floating

plastic particles. We also recorded a few invertebrate species living on these small

plastics. As such, our findings provide further evidence that not only large debris

(Winston, 1982, Jokiel, 1990, Aliani and Molcard, 2003, Barnes, 2002, Barnes and

Fraser, 2003, Masó et al., 2003, Barnes, 2004, Thiel and Gutow, 2005, Gregory, 2009,

Fortuño et al., 2010, Goldstein et al., 2014) serve as vehicles for organism dispersal.

Abundant ‘microplastics’ are equally providing a new pelagic habitat to many

microorganism and a few invertebrate taxa.

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Table 1 List of known genera occurring on millimetre-sized pelagic plastics.

Organism groups (first column), their abundance and/or frequency of occurrence (when available; second column), and genera (third column). References are indicated by superscript letters and given at the bottom of the table, along with approximate length range of plastics examined. Genera in bold indicate those first detected in this study.

Group Abundance/FO

Genera

Bacteria a,b,c,d,j d1833 per mm2

Acinetobacterb, Albidovulumb, Alteromonasb, Amoebophilusb, Bacteriovoraxb, Bdellovibriob, Blastopirellulab, Devosiab, Erythrobacterb, Filomicrobiumb, Fulvivirgab, Haliscomenobacterb, Helleab, Henriciellab, Hyphomonasb, Idiomarinab, Labrenziab, Lewinellab, Marinoscillumb, Microscillab, Muricaudab, Nitrotireductorb, Oceaniserpentillab, Parvularculab, Pelagibacterb, Phycisphaerab, Phormidiumb, Pleurocapsab, Prochlorococcusb, Pseudoalteromonasb, Pseudomonasb, Psychrobacterb, Rhodovulumb, Rivulariab, Roseovariusb, Rubrimonasb, Sediminibacteriumb, Synechococcusb, Thalassobiusb, Thiobiosb, Tenacibaculumb, Thalassobiusb, Vibriob

Diatoms a,b,c,d,f a 77.9% d 1188 per mm2

Amphoraa, Achananthesa, Chaetocerosb, Cocconeisa, Cyclotellac , Cymbellaa, Grammatophoraa, Hasleaa, Licmophoraa, Mastogloiaa,c, Microtabellaa, Minidiscusa, Naviculab, Nitzschiaa,b, Pleurosigmac, Sellaphorab, Stauroneisb, Thalassionemaa, Thalassiosiraa

Coccoliths a,d,b a 8.8% Calcidiscusa, Emilianiaa, Gephyrocapsaa, Umbellosphaeraa, Umbilicosphaeraa, Coccolithusa, Calciosoleniaa

Bryozoa a,e,f a 8.8% Membraniporaf, Jellyellae, Bowerbankiae, Filicrisiae Hydroids c,e - Clytiac, Gonothyraeac, Obeliae Polychaete g - Spirorbisg, Hydroidesg Dinoflagellates a,b,d a 1.5% Alexandriumb, Ceratiuma Insect eggs a,h,i a 2.9% Halobatesa,h,i Barnacles a a 2.9% Lepasa Rhodophyta b,g - Fosliellag Foraminifera g - Discorbisg Radiolaria b,d - Circorrhegmad Ciliate b - Ephelotab

aThis study (1.7 – 24.3 mm), bZettler et al. 2013 (2 – 20 mm), cCarpenter and Smith 1972 (2.5 – 5 mm), dCarson et al. 2013 (1 – 10 mm), eGoldstein et al. 2014 (4 – 5 mm), fGregory 1978 (2 – 5 mm), gGregory 1983 (1 – 5 mm), hMajer et al. 2012 (2 – 5 mm), iGoldstein et al. 2012 (1.2 – 6.5 mm), jCarpenter et al. 1972 (0.1 – 2 mm)

We observed fouling diatoms to be diverse and widespread on marine plastics. These

diatoms seemed to firmly attach to the plastic, resisting water turbulence and wave

action. All the identified diatom genera are well known to form biofilms on estuarine

and marine sediments and rocks (epilithic), vegetation (epiphytic), and animals

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(epizoic) (Carpenter, 1970, Totti et al., 2009, Reisser et al., 2010, Congestri and

Albertano, 2011, Tiffany, 2011, Romagnoli et al., 2014); marine plastics thus create a

novel, long-lasting and abundant floating habitat for ‘benthic’ diatoms, in a light and

nutrient-filled environment that is stable and beneficial to these organisms. Future

epiplastic diatom research should focus on the quantitative contribution of these

organisms to enhancing primary and secondary productivity of different marine regions,

such as within subtropical gyres where productivity tends to be low but plastic pollution

level high (Moore et al., 2001, Polovina et al., 2008, Law et al., 2010, Eriksen et al.,

2013). Because of their rapid growth and production of extracellular substances

(Kawamura et al., 1995), epiplastic diatoms may provide an important food source for

invertebrate grazers. As plastic debris can contain harmful substances (Mato et al.,

2001, Rios et al., 2007, Teuten et al., 2009, Gassel et al., 2013, Rochman et al., 2013c),

it remains unclear if such grazer-plastic relationships would have a positive or negative

impact on the populations involved in this new type of food web.

A significant number of coccolithophore species were present on millimetre-sized

marine plastics. These planktonic organisms are not commonly recognized as fouling or

rafting organisms (Thiel and Gutow, 2005), although their occasional occurrence on

marine plastics was briefly mentioned in recent studies (Carson et al., 2013, Zettler et

al., 2013). Some of our observations were of clusters of mixed coccolith species,

resembling zooplankton fecal pellets, and of solitary coccoliths, likely detached from

living coccospheres and stuck to clingy parts of the plastic biofilm. However, entire

coccolithophores were also seen attached to plastics, suggesting that these organisms

could be using ocean plastics as ‘floating devices’. We only observed coccoliths on

plastics from southern Australia; as such, additional studies in these temperate waters

may help better understand this potential coccolith-plastic relationship. Another atypical

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organism detected was the planktonic dinoflagellate Ceratium cf. macroceros. Recent

studies have found plastics heavily fouled by dinoflagellates, including individuals and

cysts of the potentially harmful species Ostreopsis sp., Coolia sp., and Alexandrium

spp. (Masó et al., 2003, Zettler et al., 2013), but here we only detected a single

specimen of this group.

Several unidentified organisms (rounded, oval, elongated, and spiral) resembling

bacterial cells were flourishing on millimetre-sized marine plastics. This supports

previous studies that describe well established bacterial populations growing on plastic

fragments (Carson et al., 2013, Zettler et al., 2013). Many of these unidentified cells

were apparently interacting with the plastic surface by forming pits and grooves. Within

this group of “pit-formers”, colonies of rounded cells (around 5 micron in diameter)

covered large areas of the plastic surface. They were similar to some previously

unidentified epiplastic organisms from the North Atlantic (Zettler et al., 2013). These

SEM observations, along with detections of putative hydrocarbon-degrading bacteria on

marine plastics (Zettler et al., 2013) and experiments demonstrating that marine bacteria

can biodegrade polymers (Sudhakar et al., 2007, Artham and Doble, 2009,

Balasubramanian et al., 2010, Harrison et al., 2011, Zettler et al., 2013, Harshvardhan

and Jha, 2013), strongly suggest that plastic biodegradation is occurring at the sea

surface. Such process could partially explain why quantities of millimetre-sized marine

plastics are not increasing as much as expected (Law et al., 2010, Law et al., 2014).

Studies of the “Plastisphere” from different marine regions worldwide will prove

invaluable for extending our knowledge on epiplastic marine microbial communities,

and may support the development of biotechnological solutions for better plastic waste

disposal practices (Sivan, 2011, Sangale et al., 2012, Webb et al., 2012).

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A number of invertebrates inhabited the small plastics examined here: bryozoans,

barnacles Lepas spp., an Asellota isopod, a marine worm, and eggs of the marine insect

Halobates sp. Even though microplastic-associated animals are rare and less diverse

when compared to those associated with macroplastics (Winston, 1982, Jokiel, 1990,

Barnes, 2002, Aliani and Molcard, 2003, Barnes and Fraser, 2003, Masó et al., 2003,

Barnes, 2004, Thiel and Gutow, 2005, Gregory, 2009, Fortuño et al., 2010, Goldstein et

al., 2014), ecological implications of this phenomenon may be significant, e.g.

(Goldstein et al., 2012), given the large quantities and wide distribution ranges of

millimetre-sized plastics in the marine environment (Carpenter et al., 1972, Carpenter

and Smith, 1972, Moore et al., 2001, Law et al., 2010, Morét-Ferguson et al., 2010,

Hidalgo-Ruz et al., 2012, Eriksen et al., 2013). Among the effects plastic associates may

have is to shape ‘epiplastic’ microbiota by hosting unique epizoic assemblages on their

bodies. For instance, the bryozoan colonies examined here covered a large proportion of

their plastic-host, with some of them harboring unique diatom-dominated assemblages.

Previous studies have shown that bryozoans do not represent neutral surfaces for

microbial colonizers (Scholz and Hillmer, 1995, Kittelmann and Harder, 2005), with

some species offering a favourable habitat for diatoms when compared to the

surrounding substratum, e.g. by protecting against predators and supplying nutrients

through flow generated by polypids (Wuchter et al., 2003). Further studies focusing on

both epiplastic microorganisms and invertebrates have the potential to further elucidate

symbiotic and/or competitive relationships between inhabitants of this new type of

pelagic habitat.

In summary, this study showed that millimetre-sized marine plastics are providing a

new niche for several types of microorganisms and some invertebrates. This

phenomenon has considerable ecological ramifications and deserves further research.

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As discussed here, additional observational and experimental studies on the inhabitants

of these small plastic fragments may better elucidate several key plastic pollution

processes that remain poorly assessed, such as at-sea polymer degradation and

mineralisation, impacts of epiplastic communities on their consumers, and changes in

the distributional range of species by plastic rafting.

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Chapter 4 The vertical distribution of buoyant plastics at sea: an

observational study in the North Atlantic Gyre

4.1 Summary

Millimeter-sized plastics are numerically abundant and widespread across the world’s

ocean surface. These buoyant macroscopic particles can be mixed within the upper

water column due to turbulent transport. Models indicate that the largest decrease in

their concentration occurs within the first few meters of water, where in situ

observations are very scarce. In order to investigate the depth profile and physical

properties of buoyant plastic debris, we used a new type of multi-level trawl at 12 sites

within the North Atlantic subtropical gyre to sample from the air-seawater interface to a

depth of 5 m, at 0.5 m intervals. Our results show that plastic concentrations drop

exponentially with water depth, and decay rates decrease with increasing Beaufort scale.

Furthermore, smaller pieces presented lower rise velocities and were more susceptible

to vertical transport. This resulted in higher depth decays of plastic mass concentration

(milligrams m-3) than numerical concentration (pieces m-3). Further multi-level

sampling of plastics will improve our ability to predict at-sea plastic load, size

distribution, drifting pattern, and impact on marine species and habitats.

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4.2 Introduction

Plastics pose physical and chemical threats to the oceans’ ecosystem. Their widespread

occurrence at the sea surface may be shifting the distribution and abundance of marine

populations due to (1) enhanced ocean drift opportunities and (2) damaging effects on

biota and habitats. Plastics harbour organisms - such as fouling microorganisms,

invertebrates, and fish - that can widely disperse via this new type of habitat, potentially

entering non-native waters (chapter 3) (Winston et al., 1997, Barnes, 2002, Thiel and

Gutow, 2005, Zettler et al., 2013). Plastic objects can also entangle or be

ingested/inhaled by marine animals, leading to impacts such as starvation, death, and

hepatic stress (Derraik, 2002, Browne et al., 2008, Gregory, 2009, Rochman et al.,

2013c, Watts et al., 2014).

Most of what is known about at-sea plastic characteristics and concentrations comes

from surface net sampling, where the top few centimetres of the water column is filtered

to collect plastics larger than 0.2–0.4 mm (Hidalgo-Ruz et al., 2012). These sea surface

samples have shown that the world’s sea surface contains many millimetre-sized plastic

pieces known as ‘microplastics’ when smaller than 5 mm in length (Arthur et al., 2009,

Hidalgo-Ruz et al., 2012). This type of plastic pollution is widespread across oceans,

with higher contamination levels at convergence zones such as those within subtropical

gyres (Carpenter and Smith, 1972, Maximenko et al., 2012, Lebreton et al., 2012, van

Sebille et al., 2012, Cózar et al., 2014, Eriksen et al., 2014). Plastic debris collected by

surface nets are mostly fragments of packaging and fishing gear made of polyethylene

and polypropylene (chapter 2) (Barnes et al., 2009, Morét-Ferguson et al., 2010,

Hidalgo-Ruz et al., 2012). These two resins are less dense than seawater and account for

approximately 62% of the plastic volume produced each year (Andrady, 2011).

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Turbulence in the upper-ocean layer can vertically mix buoyant plastic particles. A

model developed by Kukulka et al. 2012 predicted that the largest decrease in plastic

concentration occurs over the first meters of the water column, where only a few low-

resolution measurements exist (Lattin et al., 2004, Doyle et al., 2011, Kukulka et al.,

2012, Isobe et al., 2014). As studying ocean turbulent transport is heavily dependent on

observations (Ballent et al., 2012, D'Asaro, 2014), high-resolution multi-level plastic

sampling is needed to test this prediction. A better understanding of the vertical

transport of buoyant plastics is fundamental for improving estimates of concentration,

size distribution, and dispersal of plastics in the world’s ocean (chapter 2) (Kukulka et

al., 2012, Law et al., 2014, Isobe et al., 2014).

In this context, the present study aimed at obtaining depth profiles of plastic pollution in

the top layer of the oceans (0-5 m). We performed multi-level sampling with a new type

of equipment to (1) quantify the exponential decay rates of plastic mass and numerical

concentration with depth, and (2) demonstrate how these vary with sea state. We also

provide the first experimental measurements of the rise velocity of plastic pieces,

evaluating its relation to the type and size of pieces.

4.3 Materials and Methods

4.3.1 At-sea sampling

We conducted 12 multi-level net tows that sampled the upper 5 meters of the North

Atlantic accumulation zone (Law et al., 2010, Maximenko et al., 2012, Lebreton et al.,

2012) during day hours, from 19 to 22 May 2014, aboard the sailing vessel Sea Dragon

(Figure 1). We used a new collection device capable of sampling surface waters from

the air-seawater interface to a depth of 5 m, at 0.5 m intervals. This equipment is

composed of eleven frames with 0.5 m height x 0.3 m width fitted with 2.1 m-long 150

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µm mesh polyester nets. These nets were stacked vertically and secured within an

external frame that was dragged in the water from eight towing points, ensuring its

stability and perpendicular position in relation to the sea surface, with the top net

completely above mean water line (see Figure 1). Tow durations ranged from 55 to 60

minutes and were all undertaken while the vessel was travelling at a speed of 1–1.9

knots. The captain, who has 20 years sailing experience, estimated wind speeds and sea

state of each sampling period: Beaufort scale 1 (N = 3 net tows), 3 (N = 4 net tows), and

4 (N = 5 net tows) (Reisser et al., 2015). After each tow, we transferred the collected

contents to a 150 µm sieve and stored them in aluminium bags that were kept frozen

during transportation.

Figure 4.1 North Atlantic map indicating locations sampled during this study (orange dots) using

the multi-level net displayed in the right panel.

The map also shows the expedition departure and arrival location (Bermuda), plastic accumulation zones as predicted by ocean modelling (Lebreton et al., 2012, Maximenko et al., 2012), and a surface net tow dataset (grey dots) (Law et al., 2010).

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4.3.2 Estimating depth profiles of plastic contamination

We calculated plastic numerical and mass concentrations by dividing the number of

plastic pieces and total plastic mass by the volume of filtered seawater of each net

sample (pieces m-3 and milligrams m-3). Filtered volume was estimated using frame

dimensions and readings from a mechanical flowmeter (32 cm per rotation).

Samples were washed into a clear plastic container filled with filtered seawater, and

floating macroscopic plastics were organised into gridded petri dishes for counting and

characterisation. The searches for plastic pieces were of at least one hour per sample,

with the aid of thumb forceps, dissecting needles, magnifying glasses, and LED torches.

The latter was particularly important for detecting thin transparent plastic fragments,

which had low detection probability when not reflecting light. Two thin filaments

resembling textile fibres were discarded due to potential air contamination as noted in

(Foekema et al., 2013). Once all plastics were counted and characterised, they were

washed with deionised water, transferred to aluminium dishes, dried at 60° C, and

weighed.

To quantify the variation of plastic concentration with depth and assess the effect of

changing sea state on these vertical profiles, we first divided plastic concentration of

samples by their corresponding surface concentration value. We then took the average

of these normalised concentrations between adjacent nets to estimate normalised plastic

concentration values at depths of: 0 m (top 2 nets), 1 m (3rd and 4th nets), 2 m (5th and

6th nets), 3 m (7th and 8th nets), 4 m (9th and 10th), and 4.75 m (11th net). Finally,

numerical and mass concentration values from tows collected under the same Beaufort

scale were grouped and fitted to exponential decay models of the form N = e−λz , where

N = normalised plastic concentration, z = depth, and λ = decay rate.

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We also predicted normalised plastic concentration depth profiles using the model

described in Kukulka et al. (2012): N = ezwbA0−1

, where z = depth, wb = plastic rise

velocity, and A0 =1.5u*wkHs with u*w = frictional velocity of water, k = 0.4 (von

Karman constant), and Hs = significant wave height. We considered wb = 0.0053 m s-1

(plastics’ median rise velocity, as estimated in this study), Hs = 0.1 m, 0.6 m, or 1m

(typical wave heights experienced at Beaufort scales 1, 3, and 4, respectively), and used

the wind ranges of Beaufort 1, 3, and 4 (1-3 knots, 7-10 knots, and 11-16 knots,

respectively) to estimate their respective u*w values through the approximation proposed

by (Pugh, 1987): u*w = 0.00012W10, where W10 = ten-metre wind speed in m/s. Thus, the

considered numerical ranges of frictional velocity of water (u*w) were: 0.0006-0.0019 m

s-1 for Beaufort scale 1, 0.0043 – 0.0062 m s-1 for Beaufort scale 3, and 0.0068-0.0099

m s-1 for Beaufort scale 4.

4.3.3 Characterising plastic length, type, resin, and rise velocity

We measured the length of all plastic pieces using a transparent ruler (0.5 mm

resolution), and classified them into the following types: hard plastic - fragments of

rigid plastic; sheet - fragments of thin plastic, with some degree of flexibility; line -

fragments of fishing lines or nets; foam - expanded polystyrene fragments; and pellet -

raw material used to produce plastic items (Fotopoulou and Karapanagioti, 2012). We

also identified the resin composition of 60 pieces using Raman spectroscopy (WITec

alpha 300RA+), and measured the rise velocity of 0-3 plastics from each sample

collected.

Our method of rise velocity measurement is an adaptation of an experiment to examine

the fall velocity of various types of sediment particles in different fluids (Allen, 1985).

Firstly, we made two marks 12.5 cm from the ends of a 1 m long clear plastic tube

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(diameter = 40 mm). Secondly, we filled the tube with filtered seawater, capped both its

ends with rubber stops, and locked it in place with a clamp. One of the tube ends was

then opened, a plastic piece placed inside, the tube closed again (with no trapped air),

and quickly turned upside down and locked in place with a clamp, using a spirit level to

adjust its vertical position. Finally, we recorded the time taken for the plastic piece to

rise from one mark to the other (distance = 75 cm) using a stopwatch. This was

measured 4 times per plastic piece, and the average was used as the estimation of its rise

velocity (wb). Rise velocities of different plastic types were separately plotted against

plastic lengths (l), and linear regressions of the formwb = al + b were applied to assess

the effect of plastics’ characteristics on its rise velocity. We also plotted the rise

velocities of plastic pieces collected at different depths to visualise depth patterns.

Finally, we calculated the fractions of plastics of different size classes (0.5-1 mm, 1.5-2

mm, 2.5-3 mm, 3.5-4 mm, 4.5-5 mm, > 5.5 mm) that were located at the sea surface

(depth < 0.5 m) and in deeper layers (depth > 0.5 m) during sampling at Beaufort scales

1, 3, and 4. We calculated these fractions using all plastics collected, as well as

separated by plastic type.

4.4 Results

4.4.1 Profiles of mass and numerical concentrations

Plastic numerical and mass concentrations both decreased abruptly from their peak

values at the sea surface, where median values were equal to 1.69 pieces m-3 and 1.60

mg m-3 (Figure 4.2). Concentration differences between surface and deeper layers were

higher in terms of mass than number of particles. For instance, median mass and

numerical concentrations at 0.5-1 m were respectively 13.3 and 6.5 times lower than

their median plastic peaks at 0-0.5 m.

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Figure 4.2 Boxplots of plastic numerical (left) and mass (right) concentrations at different depth

intervals (N = 12 multi-level net tows).

The central line is the median value, edges of the box are the 25th and 75th percentiles, whiskers extend to extreme data points not considered outliers, and outliers are plotted individually as crosses.

Exponential models fitted well with both numerical and mass concentrations (R2 =

0.99–0.84), with depth decay rates (λ) consistently higher for mass than numerical

concentration. Furthermore, both numerical and mass concentration decay rates were

inversely proportional to Beaufort state (Figure 4.3). Depth decay rate of numerical

concentration went from 3.0 at Beaufort 1 (95% confidence interval - 95%CI = 2.56-

3.45), to 1.7 at Beaufort 3 (95%CI = 1.51-1.88), and 0.8 at Beaufort 4 (95%CI = 0.62-

0.98). Decay rate of mass concentration went from 3.8 at Beaufort 1 (95%CI = 3.23-

4.33), to 2.4 at Beaufort 3 (95%CI = 1.63-3.14), and 1.7 at Beaufort 4 (95%CI = 1.50-

1.94).

These exponential fits had relatively similar depth decay rates to those predicted by

Kukulka’s model for Beaufort 3 (λ = 2.36–3.37) and 4 (λ = 0.88–1.28). However, for

Beaufort 1 the statistical fit showed much smaller λ (2.56-4.33) than those predicted by

Kukulka’s model (λ = 141.73–47.2492).

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Figure 4.3 Depth profiles of plastic mass and numerical concentration under different Beaufort

scales: 1 (N = 3 net tows), 3 (N = 4 net tows), and 4 (N = 5 net tows).

Black lines show model predictions (Kukulka et al., 2012) using median plastic rise velocity (0.0053 m/s), and the typical range of frictional velocity of water (u*w) at each of the sea states sampled.

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4.4.2 Lengths, types, resins and rise velocities of plastics

We counted and classified 12,751 macroscopic plastic pieces with lengths varying from

0.5 to 207 mm (median = 1.5 mm; Figure 4.4). They were mostly fragments of

polyethylene (84.7%), followed by polypropylene (15.3%) items. Hard plastics (46.6%)

and sheets (45.4%) were predominant, with lower presence of plastic lines (7.9%),

pellets (0.05%) and foams (0.008%).

Figure 4.4 Glass jars with filtered water and plastic samples collected under wind speeds of 1 knot

(top image) and 15 knots (bottom image).

From left to right: 0 – 0.5 m, 0.5 – 1 m, 1 – 1.5 m, 1.5 – 2 m, 2 – 2.5 m, 2.5 – 3 m, 3 – 3.5 m, 3.5 – 4 m, 4 – 4.5 m, and 4.5 – 5 m deep.

Plastic rise velocity ranged from 0.001 to 0.0438 m/s (Figure 4.5a). It was directly

proportional to plastic length, with the slope of this linear relationship differing among

types of plastic (Figure 4.5b). While both hard plastics and sheets had a slope equal to

0.002 (95% CI = 0.0017-0.0026 and 0.0012-0.0023, respectively), plastic lines had a

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flatter slope of 0.00007 (95% CI = 0.00002-0.00013), since their rise velocity increased

only slightly towards longer pieces. Rise velocities differed among sampled depths,

with particles at the surface (0-0.5 m) having a wider range of values and a higher

median value than pieces at greater depths (Figure 4.5c).

Figure 4.5 Histogram of rise velocity of plastics (A), plots of plastic sizes x rise velocities of different

types of plastic (B), and boxplot of rise velocity at different depth intervals (C).

In C, the central dot is the median value, edges of the box are the 25th and 75th percentiles, whiskers extend to extreme data points not considered outliers, and outliers are plotted individually as crosses.

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The vertical mixing process was size-selective, and affected the size distribution of

plastics located at the sea surface (Figure 4.6), with the proportion of plastics at depths

over 0.5 m generally increasing towards smaller plastic lengths (Figure 4.7). For hard

plastics and sheets, this trend was observed at all Beaufort scales sampled. Plastic lines

however, only displayed this trend at Beaufort 1, with different size classes showing

similar and relatively high underwater proportions at Beaufort 3 and 4.

Datasets produced and analysed in this study are available at Figshare (Reisser et al.,

2015).

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Figure 4.6 Size histograms of plastics collected at depths 0-0.5 m and 0.5-5 m during Beaufort scale

1 (top panel), 3 (middle panel), and 4 (bottom panel).

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Figure 4.7 Percentage of plastic pieces of different size classes located at depths higher than 0.5 m

during sampling at Beaufort scale 1, 3, and 4.

Datasets produced and analysed in this study are available at Figshare (Reisser et al.,

2015).

4.5 Discussion

This study describes high-resolution depth profiles of plastic concentrations, which

were shown to decrease exponentially with depth, with decay rates decreasing towards

stronger winds. It also provides the first measurements of the rise velocity of ocean

plastics, which varies with particle size and type. Furthermore, it shows that depth

profiles of plastic mass are associated with higher decay rates than depth profiles of

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plastic numbers. This can be explained by our observation of smaller/lighter plastic

pieces generally associated with lower rising velocities, being therefore more

susceptible to vertical transport.

Predictions of plastic vertical mixing are commonly used to correct numerical

concentrations obtained by surface net sampling (chapter 2) (Kukulka et al., 2012,

Cózar et al., 2014, Law et al., 2014). As determined in our study, the model described in

Kukulka et al. (2012) performed relatively well in estimating the total number of plastic

pieces at the wind-mixed surface layer. The major difference between this model and

our observations occurred at the calmest sea state condition (Beaufort scale 1): while the

model predicted that all plastics would be at the surface, we still observed some

particles submerged at depths greater than 0.5 m below the water surface. This could

have been a consequence of the presence of other types of vertical flow at our sampled

sites (e.g. downwelling) or the occurrence of plastics rising from deeper waters due to

previous wind-driven mixing events.

Our results indicate that plastic numerical concentration decays at a lower rate than

plastic mass concentration, as smaller plastics are more susceptible to vertical transport.

The uncertainties related to how plastic numerical concentration translates into plastic

mass concentration have already led to differences between plastic load estimates

arising from different studies. For instance, Cózar et al. (2014) used a correlation based

on simultaneous surface tow measurements of total mass and abundance of plastic to

convert depth-integrated numerical concentrations into mass concentrations. These

authors estimated that the total plastic load in the world’s sea surface layer is between

7,000 and 35,000 tons. On the other hand, Law et al. (2014) multiplied depth-integrated

numerical concentrations by the average plastic particle mass (1.36 x 10-5 kg), and

estimated that the microplastic load at the North Pacific accumulation zone alone is of

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at least 21,290 tons. Such differences evidence the importance of better predicting the

vertical transport of ocean plastics to develop standard plastic load estimation methods.

More sampling is required to better quantify both profiles of plastic mass and numerical

concentration over a broader range of sea states, and translate these observations into

prediction models. Such models may need to be three-dimensional, and account not

only for wind mixing effects, but also ocean plastic properties (e.g. particle size) and

other types of vertical transport processes (e.g. Langmuir circulation).

As shown here, and in two modelling studies (Ballent et al., 2012, Isobe et al., 2014),

vertical mixing affects the size distribution of plastics floating at the surface. We

observed that the proportion of plastics mixed into deeper waters increases towards

smaller sizes even under low wind speed (1 knot) conditions (see Figure 7). This

observation has implications for studies assessing size distribution of plastics using

surface sampling devices. Cózar et al. (2014) and Eriksen et al. (2014) quantified the

size distribution of ocean plastics from worldwide sampling locations and concluded

that there are major losses of small plastics from the sea surface. Here we show that at

least a fraction of this ‘missing’ plastic could be just under the sampled surface layer (0-

0.5 m). For instance, 20% of 0.5-1 mm, 13% of 1.5-2 mm, and 8% of 2.5-3 mm long

plastics were between 0.5 and 5 m deep during our Beaufort scale 1 net tows. More at-

sea and experimental work is required to further quantify this effect and estimate depth-

integrated size distribution of buoyant plastics drifting at sea.

Predicting the vertical mixing of buoyant plastics is also important as it affects the

horizontal drifting patterns and ecological impacts of plastic pollution. For instance,

larger pieces of plastic coming from land-based sources may stay trapped near the shore

until further fragmentation, due to a combination of their high buoyancy and the effect

of Stokes drift produced by waves parallel to coastlines (Isobe et al., 2014).

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Furthermore, the vertical distribution of plastics will influence the likelihood of animals

inhabiting different depths to encounter, and potentially interact, with plastic. For

instance, sea birds, turtles, and mammals, which breathe air and use the sea surface for

daily activities, present high rates of plastic ingestion and entanglement (Derraik, 2002,

Tourinho et al., 2010). These high interaction rates could be partly explained by the

relatively high concentrations of plastic debris at the sea surface, as shown in this study.

Our findings show that vertical mixing affects the number, mass, and size distribution

of buoyant plastics captured by surface nets, a standard equipment for at-sea plastic

pollution sampling (Hidalgo-Ruz et al., 2012). Subsurface samples are still scarce and

the processes influencing distribution of plastics throughout the ocean’s water column

are poorly understood. Further multi-level sampling across a broader range of sea states

is necessary for better quantifying the vertical mixing of buoyant plastics. This will

improve predictions of ocean plastic concentration levels (Kukulka et al., 2012), size

distributions (Cózar et al., 2014, Eriksen et al., 2014), drifting patterns (Isobe et al.,

2014), and interactions with neustonic and pelagic species of the world’s oceans.

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Chapter 5 General Discussion

Chapters 2, 3, and 4 contain detailed discussions of my PhD results so here I will limit

discussion to the key findings related to the overall goals of this thesis, which were to

investigate how buoyant plastics are distributed in sea surface waters (both horizontally

and vertically), and characterise organisms on the surface of millimetre-sized marine

plastics. Furthermore, I will discuss a few limitations of this thesis and suggest some

future research directions, which complement those mentioned in the discussion

sections of chapters 2, 3, and 4. Finally, the overall conclusions of this thesis are

presented.

5.1 Horizontal distribution of buoyant plastics at sea

In chapter 2, I showed that each square kilometre of Australian surface waters is

contaminated by thousands of small plastic fragments, mostly smaller than 5 mm across

– the so-called “microplastics”. This is the first study to sample plastic debris in waters

around Australia and the data collected here comprise most of the very scarce

measurements of plastic contamination at surface waters of the Indian Ocean and

western South Pacific. This dataset has been made open access in Figshare (Reisser et

al., 2013) and is already being used by a few groups of researchers attempting to

quantify plastic pollution levels and distribution at the world’s ocean, e.g. (Cózar et al.,

2014, Eriksen et al., 2014) (Figure 5.1).

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Figure 5.1 Measurements of plastic numerical concentrations used in Cózar et al. (2014).

Gray areas show accumulation zones as predicted by Maximenko et al. (2012). Dots close to the Australian and Fijian continent are data from this thesis. Source: National Geographic

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I found that the small plastics in surface waters around Australia are mostly a by-

product of the degradation of larger objects made of polyethylene and polypropylene.

The high prevalence of small plastic fragments in Australian waters is consistent with

other regions of the world’s oceans, where microplastics were found to be the most

numerically abundant type of debris in all types of marine environment (Moore et al.,

2001, Thompson et al., 2004, Browne et al., 2010, Law et al., 2010, Browne et al.,

2011, Eriksen et al., 2013). Plastic pollution levels were moderate when compared to

concentrations in other marine areas (Moore et al., 2001, Yamashita and Tanimura,

2007, Law et al., 2010, Collignon et al., 2012, Eriksen et al., 2013), but higher amounts

were found close to cities on Australia’s east coast, as well as in remote locations (west

Tasmania and North West Shelf). Recent studies reported toxicological effects of these

small and contaminated plastics on a host of organisms, from zooplankton, small fish

and turtle hatchlings, to large mammals (Basheer et al., 2004, Choy and Drazen, 2013,

Cole et al., 2013, Fossi et al., 2012, Gassel et al., 2013, Rochman et al., 2013c, Wright

et al., 2013). As such, small plastics are a type of harmful marine debris, implying that

plastic hazards to Australian species and ecological communities are likely to be

broader than those officially recognized, which only includes physical impacts of large

plastic objects on marine vertebrates through entanglement and ingestion

(Commonwealth of Australia, 2009).

Additionally, I found that the abundant and widespread small marine plastics around

Australia are likely coming from a variety of domestic and international, land- and

ocean-based sources. Although marine plastic pollution is a global environmental issue,

mostly caused by our massive production of plastic single-use disposable items, there

are still no attempts to regulate plastic disposal on land and directly at sea at an

international level (Rochman et al., 2013a). Further at-sea studies on the

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characterization, spatial distribution, and pathways of marine plastics in coastal and

oceanic regions around Australia, as well as on marine plastic toxin loads and

interactions between small plastic particles and organisms at all trophic levels of the

food web, are necessary.

Even though the pioneering study described in chapter 2 advanced our knowledge about

plastic pollution in Australian waters, it is important to recognise the limitations of this

opportunistic research aboard Australian vessels. Among them are (1) the relatively

small number of surface trawls conducted, resulting in a very descriptive study; (2) the

use of two types of surface samplers (i.e. Manta and Neuston nets), which may have

brought some sampling bias to the plastic concentration values obtained; (3) the

estimation of plastic numerical concentrations only, as weighing the samples would

have damaged the plastic particles, impeding the conduction of the SEM and FT-IR

analyses described in chapter 3; (4) the use of a mean rising speed different from the

one I obtained two years later, using plastics from the North Atlantic accumulation zone

(chapter 4); (5) the lack of wind measurements in two out of the seven voyages

conducted, which did not allow the use of in-situ wind measurements to calculate the

depth-integrated plastic concentrations; and (6) the quantification of amounts of debris

within a limited size range (i.e. zooplankton size range only), as Manta trawl surveys

are not ideal for the quantification of microscopic plastic and mega debris.

I suggest that researchers continue monitoring plastic pollution levels in Australian

waters and beyond, by taking advantage of transit voyages aboard research vessels (e.g.

RV Investigator, Solander, Falkor). “Underway” data related to plastic debris could

include surface net sampling, as well as visual transects for counting larger items of

marine plastic debris (Eriksen et al., 2014). Furthermore, simple methods using

continuous seawater intake of vessels (Lusher et al., 2014) could be applied during a

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wider range of maritime operations, thus maximising sea time and sampling effort.

Given the limitations of opportunistic sampling, I also suggest the planning and

execution of dedicated voyages to study plastic pollution. These voyages would provide

the plastic pollution research community with the opportunity to conduct robust surveys

with well-planned sampling designs. Plastic pollution research voyages with extensive

sea time, fund, and human resources, could use a range of aerial, sea surface and

underwater surveys to quantify concentrations of plastic debris within a broad range of

debris sizes, from nanometre-sized microplastics to meter-sized ghost nets.

5.2 Organisms on the surface of millimetre-sized ocean plastics

Chapter 3 showed that millimetre-sized plastics contaminating Australian waters are

home of a host of marine life (Figure 5.2), which is being transported by ‘plastic

drifting’, potentially affecting the fate and environmental impacts of plastic pollution. It

contributed 18 new records of taxa living on microplastics, and provided 1,143 open

access high-resolution images of plastic debris shapes, surface textures, and ‘epiplastic’

communities (Reisser et al., 2014).

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Figure 5.2 False-coloured electron micrographs of surface textures and organisms on buoyant

plastic debris. Original images (i.e. black and white) are available in Reisser et al. (2014a)

Top left: diatoms (green) and rounded cells (purple). Top right: Coccoliths (red, blue, yellow) and diatoms (green, turquoise). Bottom left: unidentified marine worm (red). Bottom right: isopod (red). Source: The Conversation

This study evidenced that microscopic plastic-dwellers are everywhere in our oceans.

Organisms ranging from single-celled microbes to invertebrates are all taking advantage

of this new human-made and durable type of floating habitat. Even though the SEM

work described here advanced our knowledge on the types of microbes inhabiting

plastic debris, this visual technique has many limitations, such as the inability to

identify the vast majority of microbes composing the ‘Plastisphere’ (e.g. bacteria and

fungi species). A more detailed study of epiplastic organisms could be achieved by

analysing ocean plastic biofouling with other modern techniques, such as metagenomics

(Thomas et al., 2012) and fluorescence in situ hybridization (Moter and Göbel, 2000).

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Interesting observations of the SEM work described in this thesis included the many

flourishing microbes that appeared to interact with the plastic surfaces. These

observations, together with findings from previous studies (Harrison et al., 2011, Zettler

et al., 2013), suggest that microbes are helping break down plastics at sea. These

putative hydrocarbon-degrading microbes might support biotechnological solutions for

better plastic waste disposal practices on land (Sivan, 2011). For instance, such marine

microbes or their genes might enable the development of industrial ‘composts’ able to

break down plastic waste on land, thus reducing the risk of plastic findings its way to

the sea.

A shipboard three-dimensional survey to collect ocean plastics for functional genome

studies could significantly enhance our understanding of the plastic biofilm in a

relatively quick manner. Microplastics collected at the sea surface, water column, and

seafloor could have their biofilms screened for hydrocarbon-degrading genes, and

results compared with those obtained from the biofilm of natural substrates, such as

sediments, pumice, drifting wood, and floating seaweed. The detection of relatively

high amounts of hydrocarbon-degrading genes in the ‘Plastisphere’ may be the first step

towards the development of a bioremediation solution to some of our plastic waste

management issues.

5.2.1 Ingestion of plastics at sea: does debris size really matter?

Marine microplastics (< 5 mm in length) can contain high loads of additives and

adsorbed pollutants, and may be a threat to marine food webs due to their ingestion by

organisms at the base of the food chain (http://www.unep.org/yearbook/). Most of our

knowledge of plastic ingestion by zooplankton has been obtained through experiments

assuming that plastic particles have to be smaller than the organism’s feeding apparatus

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for this type of interaction to occur (Cole et al., 2013). However, I propose that this is

not a rule.

By examining the surface of millimetre-sized marine plastics using a scanning electron

microscope, I observed a diverse range of fouling organisms, and a variety of intriguing

pits and scraping marks of unknown origin - see details in chapter 3 and SEM images at

(Reisser et al., 2014). I suggest that some of these plastic surface textures are feeding

marks produced by invertebrates grazing upon the plastic biofilm.

I observed sub-parallel linear scrapes with spacing of 5-14 μm (Figure 5.3a,c), which is

similar to typical distances between teeth of the mandibular gnathobases of copepods

(Michels et al., 2012). The thinner and shallower marks around the linear scrapes could

have been formed by filamentous microstructures present on their gnathobases.

Copepods are an abundant planktivorous group and possess strong feeding apparatuses

to feed upon organisms such as diatoms with silica cell walls (Michels et al., 2012).

Some pelagic species have flexible feeding habits, and can feed on sea-ice algae

(Brierley and Thomas, 2002), faecal pellets (Gonzalez and Smetacek, 1994, Noji et al.,

1991), and marine snow particles (Turner, 2002). I suggest that these copepods could

also feed upon biofilm of plastic debris, which is often rich in ‘epiplastic’ diatoms; see

chapter 3 and (Carson et al., 2013).

105

Figure 5.3 Scrapes putatively identified as feeding marks.

a: Linear scrape marks on a 2.3 mm long plastic debris with a high load of diatoms. b: Rounded scrape marks on a 6 mm long plastic with a unidentified marine worm. Arrow indicates unknown structure partially covering the worm. c: zoom on scraping displayed in ‘a’. d: zoom on scraping shown in ‘b’. Scale bars = 10 μm (a, c), 100 μm (b), 20 μm (d)

I also observed peculiar, rounded marks close to an unidentified marine worm (Figure

5.3b,d), which was partially covered by an unknown structure (indicated by the arrow)

possibly secreted by the animal. These unique scraping marks were also noted on two

other plastic pieces that did not have any visible animals, but possessed structures

similar to the one covering the worm in Figure 5.3b. These results suggest that feeding

on plastic biofilm is not restricted to zooplankton, and possibly occurs with rafting

organisms such as amphipods, gastropods, and chitons, which are known to associate

with floating debris such as plastics (Winston et al., 1997).

Small portions of the plastic particles were apparently removed, and perhaps ingested,

during these putative grazing activities (Figure 5.3). Thus, I contend that (1) plastic

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biofouling induces plastic ingestion, and (2) plastic pieces must not necessarily be

smaller than the organism for a feeding interaction to occur. The latter hypothesis has

already been suggested for large items, as 15.8% of drifting plastic objects in Hawaii

displayed a variety of vertebrate bite marks (Carson, 2013).

Experiments exposing zooplanktonic organisms to millimetre-sized plastics with

biofilm may document whether they are capable of handling these particles, creating

such feeding marks. By exposing neustonic zooplankton to fresh pieces of brittle plastic

debris, researchers could possibly document this new type of feeding behaviour (e.g. by

filming) and detect plastic bits co-ingested with biofilm grazing (e.g. by examining

faecal pellets).

Due to their rapid growth and nutritional value, biofilms on plastic debris may be a

significant new food source for invertebrates, particularly in the oligotrophic waters

within subtropical gyres, where plastic contamination levels are particularly high. The

impacts related to this new type of feeding interaction remain unclear, but are likely

negative since plastics pose chemical and physical threats to their ‘predators/grazers’

(Wright et al., 2013). These impacts could include effects on food webs, since plastic-

associated pollutants and additives could be transferred to the biofilm and moved up the

food chain of plastic ‘predators/grazers’. The implications of plastic biofilm ingestion,

particularly in terms of pollutant transfer and health effects, should also be investigated.

5.3 Vertical distribution of buoyant plastics at sea

Chapter 4 is the first study to acquire high-resolution depth profiles of buoyant plastic

concentrations and characteristics across a range of sea states. This study described

high-resolution depth profiles of plastic concentrations, which decreased exponentially

with depth, and provided the first measurements of the rise velocity of ocean plastics,

107

which varied with particle size and type. Furthermore, it showed that depth profiles of

plastic mass are associated with higher decay rates than depth profiles of plastic

numbers. This can be explained by the observation that smaller/lighter plastic pieces

were generally associated with lower rising velocities, being therefore more susceptible

to vertical transport.

My findings show that vertical mixing affects the number, mass, and size distribution of

buoyant plastics captured by surface nets, a standard equipment for at-sea plastic

pollution sampling (Hidalgo-Ruz et al., 2012). Subsurface samples are still scarce and

the processes influencing distribution of plastics throughout the ocean’s water column

are poorly understood. Further multi-level sampling across a broader range of sea states

is necessary for better quantifying the vertical mixing of buoyant plastics. This will

improve predictions of ocean plastic concentration levels (Kukulka et al., 2012), size

distributions (Cózar et al., 2014, Eriksen et al., 2014), drifting patterns (Isobe et al.,

2014), and interactions with neustonic and pelagic species of the world’s oceans.

Models capable of using sea surface measurements of plastic sizes and concentrations to

predict depth-integrated values are of extreme importance to those attempting to

quantify and characterise marine plastic pollution. Kukulka et al. (2012) developed a

simple model to predict depth-integrated numerical concentration (pieces km-2) of

plastics. However, predictive models of depth-integrated mass concentrations and size

distribution still need to be developed. These depth-integrated values would then be

comparable without underestimating plastic loads and amounts of small microplastics

within the mixed layer. More multi-level observations such as the ones described in this

thesis, both in oceanic and coastal waters, will facilitate the creation of such models.

There is an urgent need to develop three-dimensional surveys capable of detecting

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plastic debris thought the water column. Perhaps the unique optical properties of

plastics in the infrared band (e.g. see Figure 2.3) could be used to develop a sensor

capable of detecting ocean plastics, thus making plastic contamination quantification

more efficient and independent of human observers. Since hydrocarbon-bearing

substances such as plastics have typical absorption maxima around 1730nm and 2310

nm (Hörig et al., 2001, Tsuchida et al., 2009), short-wave infrared and Raman

spectroscopy hold promise for such application.

A sampling equipment that may improve the way we sample microplastics at-sea is the

Video Plankton Recorder (Davis et al., 1992), which is an underwater microscope

capable of capturing images of microorganisms and particles while being towed by a

vessel. This equipment could provide valuable information on the horizontal and

vertical distribution of small plastic debris.

5.4 Overall Conclusions

The ocean surface is heavily contaminated by plastic pollution, mostly in the form of

fragments coming from the degradation of plastic objects. The most common types of

items lost or discarded at sea are packaging and fishing gear made of polyethylene and

polypropylene. These are two very common types of plastic resin that are lighter than

seawater and quite resistant to environmental degradation. Such characteristics make

them particularly prone to long-distance dispersion in the ocean surface. Buoyant plastic

represent a major hazard to organisms that live in the top layer of the oceans (e.g. sea

turtles, birds, neuston communities); they are also a new type of vehicle for the

dispersal of pollutants and organisms that live associated with these synthetic floating

habitats.

109

This study set out to explore the spatial distribution and impacts of ocean plastic

pollution. By performing net tows for sampling surface plastics, I was able to

characterize the plastic debris in surface waters around Australia, describe textures and

organisms on the surface of millimetre-sized ocean plastic, and quantify the way

buoyant plastic is distributed in the top layer of the oceans.

The thesis showed that surface waters around Australia have moderate contamination

levels of microplastics, which were mostly fragments of larger objects made of

polyethylene and polypropylene. These millimetre-sized particles harbour a large

variety of organisms, such as bacteria, diatoms, and invertebrates, and are concentrated

at the sea surface, although they can reach deeper depths depending on their buoyancy

and sea state. The information presented in this thesis greatly contributed towards a

better understanding of the distribution and potential impacts of plastic pollution in the

world’s oceans.

It is important that continued research be conducted to further improve this baseline

knowledge for defining regulations and mitigation strategies for this concerning issue.

The findings of this thesis highlight the need for more plastic pollution research,

monitoring, and mitigation efforts within Australian waters, as well as a better

quantification of the depth profile of buoyant plastic debris. This would greatly improve

our capacity to quantify, characterize and search for solutions related to this new type of

marine pollution.

To generate achievable policy strategies and develop targets with regards to plastic

pollution reduction, there is need for more research and monitoring projects at the local,

national, and international scales aiming at assessing the environmental, economical and

human health impacts of plastics. Furthermore, collaborative research and development

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efforts towards better environmental awareness, waste management, packaging designs,

bioplastics, cleanup efforts, and regulation enforcements will help mitigate and solve

this growing environmental issue.

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References

ALIANI, S., GRIFFA, A. & MOLCARD, A. 2003. Floating debris in the Ligurian Sea, north-western Mediterranean. Marine Pollution Bulletin, 46, 1142-1149.

ALIANI, S. & MOLCARD, A. 2003. Hitch-hiking on floating marine debris: macrobenthic species in the Western Mediterranean Sea. Migrations and Dispersal of Marine Organisms. Springer.

ALLEN, J. 1985. Sink or swim? Principles of Physical Sedimentology. Springer. ANDRADY, A. L. 2011. Microplastics in the marine environment. Marine Pollution

Bulletin, 62, 1596-1605. ARTHAM, T. & DOBLE, M. 2009. Fouling and degradation of polycarbonate in

seawater: field and lab studies. Journal of Polymers and the Environment, 17, 170-180.

ARTHUR, C., BAKER, J. & BAMFORD, H. 2009. Proceedings of the International Research Workshop on the Occurrence, Effects, and Fate of Microplastic Marine Debris, September 9-11, 2008.

BALASUBRAMANIAN, V., NATARAJAN, K., HEMAMBIKA, B., RAMESH, N., SUMATHI, C., KOTTAIMUTHU, R. & RAJESH KANNAN, V. 2010. Highdensity polyethylene (HDPE) degrading potential bacteria from marine ecosystem of Gulf of Mannar, India. Letters in Applied Microbiology, 51, 205-211.

BALLENT, A., PURSER, A., MENDES, P. D. J., PANDO, S. & THOMSEN, L. 2012. Physical transport properties of marine microplastic pollution. Biogeosciences Discussions, 9, 18755.

BARNES, D. 2004. Natural and plastic flotsam stranding in the Indian Ocean. The Effects of Human Transport on Ecosystems: Cars and Planes, Boats and Trains. Davenport, D. & Davenport, J.(Eds.). Royal Irish Academy, Dublin, 193-205.

BARNES, D. & MILNER, P. 2005. Drifting plastic and its consequences for sessile organism dispersal in the Atlantic Ocean. Marine Biology, 146, 815-825.

BARNES, D. K. 2002. Biodiversity: invasions by marine life on plastic debris. Nature, 416, 808-809.

BARNES, D. K. & FRASER, K. P. 2003. Rafting by five phyla on man-made flotsam in the Southern Ocean. Marine Ecology Progress Series, 262, 289-291.

BARNES, D. K. A., GALGANI, F., THOMPSON, R. C. & BARLAZ, M. 2009. Accumulation and fragmentation of plastic debris in global environments. Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 1985-1998.

BASHEER, C., LEE, H. K. & TAN, K. S. 2004. Endocrine disrupting alkylphenols and bisphenol-A in coastal waters and supermarket seafood from Singapore. Marine Pollution Bulletin, 48, 1161-1167.

BOERGER, C. M., LATTIN, G. L., MOORE, S. L. & MOORE, C. J. 2010. Plastic ingestion by planktivorous fishes in the North Pacific Central Gyre. Marine Pollution Bulletin, 60, 2275-2278.

112

BOWMAKER, J. 1980. Colour vision in birds and the role of oil droplets. Trends in Neurosciences, 3, 196-199.

BREAST CANCER FUNDATION 2013. Disrupted development: the dangers of prenatal BPA Exposure. 20p.

BRIERLEY, A. S. & THOMAS, D. N. 2002. Ecology of Southern Ocean pack ice. Advances in Marine Biology, 43, 171-IN4.

BROWN, D. & CHENG, L. 1981. New net for sampling the ocean surface. Mar. Ecol. Prog. Ser, 5, 224-227.

BROWNE, M. A., CRUMP, P., NIVEN, S. J., TEUTEN, E., TONKIN, A., GALLOWAY, T. & THOMPSON, R. 2011. Accumulation of microplastic on shorelines woldwide: sources and sinks. Environmental Science & Technology, 45, 9175-9179.

BROWNE, M. A., DISSANAYAKE, A., GALLOWAY, T. S., LOWE, D. M. & THOMPSON, R. C. 2008. Ingested microscopic plastic translocates to the circulatory system of the mussel, Mytilus edulis (L.). Environmental Science & Technology, 42, 5026-5031.

BROWNE, M. A., GALLOWAY, T. S. & THOMPSON, R. C. 2010. Spatial patterns of plastic debris along estuarine shorelines. Environmental Science & Technology, 44, 3404-3409.

BROWNE, M. A., NIVEN, S. J., GALLOWAY, T. S., ROWLAND, S. J. & THOMPSON, R. C. 2013. Microplastic moves pollutants and additives to worms, reducing functions linked to health and biodiversity. Current Biology, 23, 2388-2392.

BUCKLAND, S. T., ANDERSON, D. R., BURNHAM, K. P. & LAAKE, J. L. 2005. Distance sampling, Wiley Online Library.

CAREY, M. J. 2011. Intergenerational transfer of plastic debris by Short-tailed Shearwaters (Ardenna tenuirostris). Emu, 111, 229-234.

CARPENTER, E. J. 1970. Diatoms attached to floating Sargassum in the western Sargasso Sea 1. Phycologia, 9, 269-274.

CARPENTER, E. J., ANDERSON, S. J., HARVEY, G. R., MIKLAS, H. P. & PECK, B. B. 1972. Polystyrene spherules in coastal waters. Science, 178, 749-750.

CARPENTER, E. J. & SMITH, K. 1972. Plastics on the Sargasso Sea Surface. Science, 175, 1240-1241.

CARR, A. 1987. Impact of nondegradable marine debris on the ecology and survival outlook of sea turtles. Marine Pollution Bulletin, 18, 352-356.

CARSON, H. S. 2013. The incidence of plastic ingestion by fishes: From the prey’s perspective. Marine Pollution Bulletin, 74, 170-174.

CARSON, H. S., COLBERT, S. L., KAYLOR, M. J. & MCDERMID, K. J. 2011. Small plastic debris changes water movement and heat transfer through beach sediments. Marine Pollution Bulletin, 62, 1708-1713.

CARSON, H. S., NERHEIM, M. S., CARROLL, K. A. & ERIKSEN, M. 2013. The plastic-associated microorganisms of the North Pacific Gyre. Marine Pollution Bulletin, 75, 126-132.

113

CHENG, L. 1976. Marine insects. University of California, 581p.

CHIAPPONE, M., DIENES, H., SWANSON, D. W. & MILLER, S. L. 2005. Impacts of lost fishing gear on coral reef sessile invertebrates in the Florida Keys National Marine Sanctuary. Biological Conservation, 121, 221-230.

CHOY, C. A. & DRAZEN, J. C. 2013. Plastic for dinner? Observations of frequent debris ingestion by pelagic predatory fishes from the central North Pacific. Marine Ecology Progress Series, 485, 155-163.

COLE, M., LINDEQUE, P., FILEMAN, E., HALSBAND, C., GOODHEAD, R. M., MOGER, J. & GALLOWAY, T. 2013. Microplastic ingestion by zooplankton. Environmental Science & Technology, 47, 6646-6655.

COLLIGNON, A., HECQ, J.-H., GLAGANI, F., VOISIN, P., COLLARD, F. & GOFFART, A. 2012. Neustonic microplastic and zooplankton in the North Western Mediterranean Sea. Marine Pollution Bulletin, 64, 861-864.

COMMONWEALTH OF AUSTRALIA. 2009. Background paper for the threat abatement plan for the impacts of marine debris on vertebrate marine life. Available: http://www.environment.gov.au/biodiversity/threatened/publications/tap/marine-debris.html Accessed 16 July 2013 [Online]. Available: environment.gov.au/biodiversity/threatened/ktp/marine-debris.html.

CONDIE, S. & ANDREWARTHA, J. 2008. Circulation and connectivity on the Australian North West Shelf. Continental Shelf Research, 28, 1724-1739.

CONDIE, S. A., WARING, J., MANSBRIDGE, J. V. & CAHILL, M. L. 2005. Marine connectivity patterns around the Australian continent. Environmental modelling & software, 20, 1149-1157.

CONGESTRI, R. & ALBERTANO, P. 2011. Benthic Diatoms in Biofilm Culture. The Diatom World. Springer.

COOPER, D. A. & CORCORAN, P. L. 2010. Effects of mechanical and chemical processes on the degradation of plastic beach debris on the island of Kauai, Hawaii. Marine Pollution Bulletin, 60, 650-654.

CORCORAN, P. L., BIESINGER, M. C. & GRIFI, M. 2009. Plastics and beaches: A degrading relationship. Marine Pollution Bulletin, 58, 80-84.

CÓZAR, A., ECHEVARRÍA, F., GONZÁLEZ-GORDILLO, J. I., IRIGOIEN, X., ÚBEDA, B., HERNÁNDEZ-LEÓN, S., PALMA, Á. T., NAVARRO, S., GARCÍA-DE-LOMAS, J. & RUIZ, A. 2014. Plastic debris in the open ocean. Proceedings of the National Academy of Sciences, 111, 10239-10244.

D'ASARO, E. A. 2014. Turbulence in the upper-ocean mixed layer. Annual Review of Marine Science, 6, 101-115.

DAHLBERG, M. L. & DAY, R. H. Observations of man-made objects on the surface of the North Pacific Ocean. In: Proceedings of the Workshop on the Fate and Impact of Marine Debris 29p, 1985.

DAVIDSON, T. M. 2012. Boring crustaceans damage polystyrene floats under docks polluting marine waters with microplastic. Marine Pollution Bulletin, 64, 1821-1828.

114

DAVIS, C., GALLAGER, S., BERMAN, M., HAURY, L. & STRICKLER, J. 1992. The video plankton recorder (VPR): design and initial results. Arch. Hydrobiol. Beih, 36, 67-81.

DAY, R. H. & SHAW, D. G. 1987. Patterns in the abundance of pelagic plastic and tar in the North Pacific Ocean, 1976–1985. Marine Pollution Bulletin, 18, 311-316.

DAY, R. H., SHAW, D. G. & IGNELL, S. E. 1990. The quantitative distribution and characteristics of neuston plastic in the North Pacific Ocean, 1985-88. In: Proceedings of the Second International Conference on Marine Debris. pp. 182-211.

DE STEPHANIS, R., GIMÉNEZ, J., CARPINELLI, E., GUTIERREZ-EXPOSITO, C. & CAÑADAS, A. 2013. As main meal for sperm whales: Plastics debris. Marine Pollution Bulletin, 69, 206-214.

DEE, D., UPPALA, S., SIMMONS, A., BERRISFORD, P., POLI, P., KOBAYASHI, S., ANDRAE, U., BALMASEDA, M., BALSAMO, G. & BAUER, P. 2011. The ERA Interim reanalysis: Configuration and performance of the data assimilation system. Quarterly Journal of the Royal Meteorological Society, 137, 553-597.

DERRAIK, J. G. 2002. The pollution of the marine environment by plastic debris: a review. Marine Pollution Bulletin, 44, 842-852.

DIXON, T. & DIXON, T. 1983. Marine litter distribution and composition in the North Sea. Marine Pollution Bulletin, 14, 145-148.

DOYLE, M. J., WATSON, W., BOWLIN, N. M. & SHEAVLY, S. B. 2011. Plastic particles in coastal pelagic ecosystems of the Northeast Pacific ocean. Marine Environmental Research, 71, 41-52.

DUFAULT, S. & WHITEHEAD, H. 1994. Floating marine pollution in ‘the Gully’on the continental slope, Nova Scotia, Canada. Marine pollution bulletin, 28, 489-493.

EDYVANE, K., DALGETTY, A., HONE, P., HIGHAM, J. & WACE, N. 2004. Long-term marine litter monitoring in the remote Great Australian Bight, South Australia. Marine Pollution Bulletin, 48, 1060-1075.

EPA. 2013. Plastics - http://www.epa.gov/wastes/conserve/materials/plastics.htm [Online].

ERIKSEN, M., LEBRETON, L. C. M., CARSON, H. S., THIEL, M., MOORE, C. J., BORERRO, J. C., GALGANI, F., RYAN, P. G. & REISSER, J. 2014. Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea. PLOS ONE, 9, e111913.

ERIKSEN, M., MAXIMENKO, N., THIEL, M., CUMMINS, A., LATTIN, G., WILSON, S., HAFNER, J., ZELLERS, A. & RIFMAN, S. 2013. Plastic pollution in the South Pacific subtropical gyre. Marine Pollution Bulletin, 68, 71-76.

ERIKSSON, C. & BURTON, H. 2003. Origins and biological accumulation of small plastic particles in fur seals from Macquarie Island. AMBIO, 32, 380-384.

115

FENDALL, L. S. & SEWELL, M. A. 2009. Contributing to marine pollution by washing your face: Microplastics in facial cleansers. Marine Pollution Bulletin, 58, 1225-1228.

FERREIRA, T. & RASBAND, W. 2012. RE: ImageJ User Guide. FOEKEMA, E. M., DE GRUIJTER, C., MERGIA, M. T., VAN FRANEKER, J. A.,

MURK, A. J. & KOELMANS, A. A. 2013. Plastic in North sea fish. Environmental Science & Technology, 47, 8818-8824.

FORTUÑO, J., MASÓ, M., SÁEZ, R., DE JUAN, S. & DEMESTRE, M. 2010. SEM microphotographs of biofouling organisms on floating and benthic plastic debris. Rapp. Comm. int. Mer Médit, 39, 358.

FOSSI, M. C., PANTI, C., GUERRANTI, C., COPPOLA, D., GIANNETTI, M., MARSILI, L. & MINUTOLI, R. 2012. Are baleen whales exposed to the threat of microplastics? A case study of the Mediterranean fin whale (Balaenoptera physalus). Marine Pollution Bulletin, 64, 2374-2379.

FOTOPOULOU, K. N. & KARAPANAGIOTI, H. K. 2012. Surface properties of beached plastic pellets. Marine Environmental Research.

FROST, A. & CULLEN, M. 1997. Marine debris on northern New South Wales beaches (Australia): sources and the role of beach usage. Marine Pollution Bulletin, 34, 348-352.

GASSEL, M., HARWANI, S., PARK, J.-S. & JAHN, A. 2013. Detection of nonylphenol and persistent organic pollutants in fish from the North Pacific Central Gyre. Marine Pollution Bulletin, 64, 2374-2379.

GOLDBERG, E. 1997. Plasticizing the seafloor: an overview. Environmental Technology, 18, 195-201.

GOLDSTEIN, M. C., CARSON, H. S. & ERIKSEN, M. 2014. Relationship of diversity and habitat area in North Pacific plastic-associated rafting communities. Marine Biology, 1-13.

GOLDSTEIN, M. C., ROSENBERG, M. & CHENG, L. 2012. Increased oceanic microplastic debris enhances oviposition in an endemic pelagic insect. Biology Letters, 8, 817-820.

GONZALEZ, H. E. & SMETACEK, V. 1994. The possible role of the cyclopoid copepod Oithona in retarding vertical flux of zooplankton faecal material. Marine Ecology Progress Series, 113, 233-246.

GORDON, R. P. 2000. The Vertical and Horizontal Distribution of Microplastics in the Caribbean and Sargasso Seas Along the W-169 Cruise Track, May-June, 2000. http://www.jeffnet.org/~rgordon/Ryan_Gordon/Downloads-Ryan_Gordon_files/Gordon_SEA_2000.pdf.

GREGORY, M. 1990. Plastics: accumulation, distribution, and environmental effects of meso-, macro-, and megalitter in surface waters and on shores of the southwest Pacific. NOAA Technical Memorandum.

GREGORY, M. R. 1978. Accumulation and distribution of virgin plastic granules on New Zealand beaches. New Zealand Journal of Marine and Freshwater Research, 12, 399-414.

116

GREGORY, M. R. 1983. Virgin plastic granules on some beaches of eastern Canada and Bermuda. Marine Environmental Research, 10, 73-92.

GREGORY, M. R. 2009. Environmental implications of plastic debris in marine settings—entanglement, ingestion, smothering, hangers-on, hitch-hiking and alien invasions. Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 2013-2025.

GREGORY, M. R. & ANDRADY, A. L. 2003. Plastics in the marine environment. Plastics and the Environment, 379-401.

HALLEGRAEFF, G. M., BOLCH, C., HILL, D., JAMESON, I., LEROI, J., MCMINN, A., MURRAY, S., DE SALAS, M., SAUNDERS, K. & DE SALAS, M. 2010. Algae of Australia: phytoplankton of temperate coastal waters, Australia.

HARRISON, J. P., OJEDA, J. J. & ROMERO-GONZÁLEZ, M. E. 2012. The applicability of reflectance micro-Fourier-transform infrared spectroscopy for the detection of synthetic microplastics in marine sediments. Science of the Total Environment, 416, 455-463.

HARRISON, J. P., SAPP, M., SCHRATZBERGER, M. & OSBORN, A. M. 2011. Interactions between microorganisms and marine microplastics: a call for research. Marine Technology Society Journal, 45, 12-20.

HARSHVARDHAN, K. & JHA, B. 2013. Biodegradation of low-density polyethylene by marine bacteria from pelagic waters, Arabian Sea, India. Marine Pollution Bulletin, 77, 100-106.

HIDALGO-RUZ, V., GUTOW, L., THOMPSON, R. C. & THIEL, M. 2012. Microplastics in the marine environment: a review of the methods used for identification and quantification. Environmental Science & Technology, 46, 3060-3075.

HINOJOSA, I. A., RIVADENEIRA, M. M. & THIEL, M. 2011. Temporal and spatial distribution of floating objects in coastal waters of central–southern Chile and Patagonian fjords. Continental Shelf Research, 31, 172-186.

HINOJOSA, I. A. & THIEL, M. 2009. Floating marine debris in fjords, gulfs and channels of southern Chile. Marine pollution bulletin, 58, 341-350.

HOLMES, L. A., TURNER, A. & THOMPSON, R. C. 2012. Adsorption of trace metals to plastic resin pellets in the marine environment. Environmental Pollution, 160, 42-48.

HOORNWEG, D. & BHADA-TATA, P. 2012. What a waste: a global review of solid waste management. Urban Development Series Knowledge Papers.

HOPEWELL, J., DVORAK, R. & KOSIOR, E. 2009. Plastics recycling: challenges and opportunities. Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 2115-2126.

HOPKINS, T. L., BAIRD, R. C. & MILLIKEN, D. M. 1973. A messenger-operated closing trawl. Limnol. Oceanogr, 18, 488-490.

HÖRIG, B., KÜHN, F., OSCHÜTZ, F. & LEHMANN, F. 2001. HyMap hyperspectral remote sensing to detect hydrocarbons. International Journal of Remote Sensing, 22, 1413-1422.

117

INDUSTRY CANADA 2011. Industry profile for the Canadian plastic products industry - - http://www.ic.gc.ca/eic/site/plastics-plastiques.nsf/eng/pl01383.html.

ISOBE, A., KUBO, K., TAMURA, Y., NAKASHIMA, E. & FUJII, N. 2014. Selective transport of microplastics and mesoplastics by drifting in coastal waters. Marine Pollution Bulletin.

JAMBECK, J. R., GEYER, R., WILCOX, C., SIEGLER, T. R., PERRYMAN, M., ANDRADY, A., NARAYAN, R. & LAW, K. L. 2015. Plastic waste inputs from land into the ocean. Science, 347, 768-771.

JOKIEL, P. L. 1990. Long-distance dispersal by rafting: reemergence of an old hypothesis. Endeavour, 14, 66-73.

JONES, M. M. 1995. Fishing debris in the Australian marine environment. Marine Pollution Bulletin, 30, 25-33.

KAWAMURA, T., SAIDO, T., TAKAMI, H. & YAMASHITA, Y. 1995. Dietary value of benthic diatoms for the growth of post-larval abalone Haliotis discus hannai. Journal of Experimental Marine Biology and Ecology, 194, 189-199.

KENSLEY, B. 1994. Redescription of Iais elongata Sivertsen & Holthuis, 1980 from the South Atlantic Ocean (Crustacea: Isopoda: Asellota). Proceedings of the Biological Society of Washington, 107, 274-282.

KITTELMANN, S. & HARDER, T. 2005. Species-and site-specific bacterial communities associated with four encrusting bryozoans from the North Sea, Germany. Journal of Experimental Marine Biology and Ecology, 327, 201-209.

KUKULKA, T., PROSKUROWSKI, G., MORÉT FERGUSON, S., MEYER, D. & LAW, K. 2012. The effect of wind mixing on the vertical distribution of buoyant plastic debris. Geophysical Research Letters, 39, 1-6.

LATTIN, G. L., MOORE, C. J., ZELLERS, A. F., MOORE, S. L. & WEISBERG, S. B. 2004. A comparison of neustonic plastic and zooplankton at different depths near the southern California shore. Marine Pollution Bulletin, 49, 291-294.

LAW, K. L., MORET-FERGUSON, S., GOODWIN, D. S., ZETTLER, E. R., DEFORCE, E., KUKULKA, T. & PROSKUROWSKI, G. 2014. Distribution of surface plastic debris in the eastern Pacific Ocean from an 11-year dataset. Environmental Science & Technology.

LAW, K. L., MORÉT-FERGUSON, S., MAXIMENKO, N. A., PROSKUROWSKI, G., PEACOCK, E. E., HAFNER, J. & REDDY, C. M. 2010. Plastic accumulation in the North Atlantic subtropical gyre. Science, 329, 1185-1188.

LEBRETON, L.-M., GREER, S. & BORRERO, J. 2012. Numerical modelling of floating debris in the world’s oceans. Marine Pollution Bulletin, 64, 653-661.

LITHNER, D. 2011. Environmental and health hazards of chemicals in plastic polymers and products. PhD, University of Gothenburg.

LOBELLE, D. & CUNLIFFE, M. 2011. Early microbial biofilm formation on marine plastic debris. Marine Pollution Bulletin, 62, 197-200.

LUSHER, A. L., BURKE, A., O’CONNOR, I. & OFFICER, R. 2014. Microplastic pollution in the Northeast Atlantic Ocean: Validated and opportunistic sampling. Marine pollution bulletin.

118

MAGALHÃES, W. & BAILEY-BROCK, J. 2012. Capitellidae Grube, 1862 (Annelida: Polychaeta) from the Hawaiian Islands with description of two new species. Zootaxa, 3581, 1-52.

MASÓ, M., GARCÉS, E., PAGÈS, F. & CAMP, J. 2003. Drifting plastic debris as a potential vector for dispersing Harmful Algal Bloom (HAB) species. Scientia Marina, 67, 107-111.

MATO, Y., ISOBE, T., TAKADA, H., KANEHIRO, H., OHTAKE, C. & KAMINUMA, T. 2001. Plastic resin pellets as a transport medium for toxic chemicals in the marine environment. Environmental Science & Technology, 35, 318-324.

MAXIMENKO, N., HAFNER, J. & NIILER, P. 2012. Pathways of marine debris derived from trajectories of Lagrangian drifters. Marine Pollution Bulletin, 65, 51-62.

MAXIMENKO, N., NIILER, P., CENTURIONI, L., RIO, M.-H., MELNICHENKO, O., CHAMBERS, D., ZLOTNICKI, V. & GALPERIN, B. 2009. Mean Dynamic Topography of the Ocean Derived from Satellite and Drifting Buoy Data Using Three Different Techniques*. Journal of Atmospheric and Oceanic Technology, 26, 1910-1919.

MCCLAIN, C. R., SIGNORINI, S. R. & CHRISTIAN, J. R. 2004. Subtropical gyre variability observed by ocean-color satellites. Deep Sea Research Part II: Topical Studies in Oceanography, 51, 281-301.

MICHELS, J., VOGT, J. & GORB, S. N. 2012. Tools for crushing diatoms–opal teeth in copepods feature a rubber-like bearing composed of resilin. Scientific reports, 2.

MOORE, C. J., MOORE, S. L., LEECASTER, M. K. & WEISBERG, S. B. 2001. A comparison of plastic and plankton in the North Pacific central gyre. Marine Pollution Bulletin, 42, 1297-1300.

MORÉT-FERGUSON, S., LAW, K. L., PROSKUROWSKI, G., MURPHY, E. K., PEACOCK, E. E. & REDDY, C. M. 2010. The size, mass, and composition of plastic debris in the western North Atlantic Ocean. Marine Pollution Bulletin, 60, 1873-1878.

MORRIS, R. J. 1980a. Floating plastic debris in the Mediterranean. Marine Pollution Bulletin, 11, 125.

MORRIS, R. J. 1980b. Plastic debris in the surface waters of the South Atlantic. Marine Pollution Bulletin, 11, 164-166.

MOTER, A. & GÖBEL, U. B. 2000. Fluorescence in situ hybridization (FISH) for direct visualization of microorganisms. Journal of microbiological methods, 41, 85-112.

NG, K. & OBBARD, J. 2006. Prevalence of microplastics in Singapore’s coastal marine environment. Marine Pollution Bulletin, 52, 761-767.

NOJI, T. T., ESTEP, K. W., MACINTYRE, F. & NORRBIN, F. 1991. Image analysis of faecal material grazed upon by three species of copepods: evidence for coprorhexy, coprophagy and coprochaly. Journal of the Marine Biological Association of the United Kingdom, 71, 465-480.

119

OHLMANN, J. C., WHITE, P. F., SYBRANDY, A. L. & NIILER, P. P. 2005. GPS-cellular drifter technology for coastal ocean observing systems. Journal of Atmospheric and Oceanic Technology, 22, 1381-1388.

PACIA 2011. National plastics recycling survey (2010-11 financial year). PATTIARATCHI, C. & WOO, M. 2009. The mean state of the Leeuwin current system

between North West Cape and Cape Leeuwin. Journal of the Royal Society of Western Australia, 92, 221-241.

PAULRUD, S., MATTSSON, J. E. & NILSSON, C. 2002. Particle and handling characteristics of wood fuel powder: effects of different mills. Fuel Processing Technology, 76, 23-39.

PEDLOSKY, J. 1990. The dynamics of the oceanic subtropical gyres. Science, 248, 316-322.

PHAM, P., JUNG, J., LUMSDEN, J., DIXON, B. & BOLS, N. 2012. The potential of waste items in aquatic environments to act as fomites for viral haemorrhagic septicaemia virus. Journal of Fish Diseases, 35, 73-77.

PICHEL, W. G., CHURNSIDE, J. H., VEENSTRA, T. S., FOLEY, D. G., FRIEDMAN, K. S., BRAINARD, R. E., NICOLL, J. B., ZHENG, Q. & CLEMENTE-COLON, P. 2007. Marine debris collects within the North Pacific subtropical convergence zone. Marine Pollution Bulletin, 54, 1207-1211.

PICHEL, W. G., VEENSTRA, T. S., CHURNSIDE, J. H., ARABINI, E., FRIEDMAN, K. S., FOLEY, D. G., BRAINARD, R. E., KIEFER, D., OGLE, S. & CLEMENTE-COLÓN, P. 2012. GhostNet marine debris survey in the Gulf of Alaska–Satellite guidance and aircraft observations. Marine Pollution Bulletin, 65, 28-41.

PICKERING, S. 2006. Recycling technologies for thermoset composite materials—current status. Composites Part A: Applied Science and Manufacturing, 37, 1206-1215.

PLASTIC WASTE MANAGEMENT INSTITUTE. 2013. Plastic products, plastic waste and resource recovery - - http://www.pwmi.or.jp/ei/siryo/ei/ei_pdf/ei42.pdf [Online].

PLASTICSEUROPE 2012. Plastics - the Facts 2012. An analysis of European plastics production, demand and waste data for 2011.

PLASTICSEUROPE 2013. Plastics - the Facts 2013. An analysis of European latest plastics production, demand and waste data. http://www.plasticseurope.org/Document/plastics-the-facts-2013.aspx?FolID=2.

POLOVINA, J. J., HOWELL, E. A. & ABECASSIS, M. 2008. Ocean's least productive waters are expanding. Geophysical Research Letters, 35.

PUGH, D. T. 1987. Tides, surges and mean sea-level: a handbook for engineers and scientists., Chichester, John Wiley & Sonschichester.

RAKESTRAW, A. 2012. Open oceans and marine debris: solutions for the ineffective enforcement of MARPOL Annex V. Hastings International and Comparative Law Review, 35, 383-451.

120

REISSER, J., PROIETTI, M. & SAZIMA, I. 2010. First record of the silver porgy (Diplodus argenteus) cleaning green turtles (Chelonia mydas) in the south-west Atlantic. Marine Biodiversity Records, 3, e75.

REISSER, J., SHAW, J., HALLEGRAEFF, G., PROIETTI, M., BARNES, D., THUMS, M., WILCOX, C., HARDESTY, B. D. & PATTIARATCHI, C. 2014. Data from 'Millimeter-sized Marine Plastics: A New Pelagic Habitat for Microorganisms and Invertebrates'. Figshare.

REISSER, J., SHAW, J., WILCOX, C., HARDESTY, B. D., PROIETTI, M., THUMS, M. & PATTIARATCHI, C. 2013. Data from 'Marine Plastic Pollution in waters around Australia: characteristics, concentrations, and pathways'. Figshare.

REISSER, J., SLAT, B., NOBLE, K., DU PLESSIS, K., EPP, M., PROIETTI, M., DE SONNEVILLE, J., BECKER, T. & PATTIARATCHI, C. 2015. Data from 'The vertical ditribution of buoyant plastics at sea: an observational study in the North Atlantic Gyre'. Figshare.

RIDGWAY, K. & CONDIE, S. 2004. The 5500-km-long boundary flow off western and southern Australia. Journal of Geophysical Research, 109, 1-18.

RIDGWAY, K. & DUNN, J. 2003. Mesoscale structure of the mean East Australian Current System and its relationship with topography. Progress in Oceanography, 56, 189-222.

RIOS, L. M., MOORE, C. & JONES, P. R. 2007. Persistent organic pollutants carried by synthetic polymers in the ocean environment. Marine Pollution Bulletin, 54, 1230-1237.

ROCHMAN, C. M., BROWNE, M. A., HALPERN, B. S., HENTSCHEL, B. T., HOH, E., KARAPANAGIOTI, H. K., RIOS-MENDOZA, L. M., TAKADA, H., TEH, S. & THOMPSON, R. C. 2013a. Policy: Classify plastic waste as hazardous. Nature, 494, 169-171.

ROCHMAN, C. M., HOH, E., HENTSCHEL, B. T. & KAYE, S. 2013b. Long-Term field measurement of sorption of organic contaminants to five types of plastic pellets: implications for plastic marine debris. Environmental Science & Technology, 47, 1646-1654.

ROCHMAN, C. M., HOH, E., KUROBE, T. & TEH, S. 2013c. Ingested plastic transfers hazardous chemicals to fish and induces hepatic stress. Nature, 3: 3263.

ROMAGNOLI, T., TOTTI, C., ACCORONI, S., DE STEFANO, M. & PENNESI, C. 2014. SEM analysis of the epibenthic diatoms on Eudendrium racemosum (Hydrozoa) from the Mediterranean Sea. Turkish Journal of Botany, 38.

RYAN, P. 1990. The marine plastic debris problem off Southern Africa: types of debris, their environmental effects, and control measures. NOAA Technical Memorandum.

RYAN, P. G. 1988. The characteristics and distribution of plastic particles at the sea-surface off the southwestern Cape Province, South Africa. Marine Environmental Research, 25, 249-273.

RYAN, P. G. 2013a. Litter survey detects the South Atlantic ‘garbage patch’. Marine Pollution Bulletin.

121

RYAN, P. G. 2013b. A simple technique for counting marine debris at sea reveals steep litter gradients between the Straits of Malacca and the Bay of Bengal. Marine Pollution Bulletin.

RYAN, P. G. 2015. Does size and buoyancy affect the long-distance transport of floating debris? Environmental Research Letters, 10, 084019.

RYAN, P. G., MOORE, C. J., VAN FRANEKER, J. A. & MOLONEY, C. L. 2009. Monitoring the abundance of plastic debris in the marine environment. Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 1999-2012.

SANDERY, P. A. & KÄMPF, J. 2007. Transport timescales for identifying seasonal variation in Bass Strait, south-eastern Australia. Estuarine, Coastal and Shelf Science, 74, 684-696.

SANGALE, M., SHAHNAWAZ, M. & ADE, A. 2012. A review on biodegradation of polythene: the microbial approach. J Bioremed Biodeg, 3.

SCHILLER, A., OKE, P. R., BRASSINGTON, G., ENTEL, M., FIEDLER, R., GRIFFIN, D. A. & MANSBRIDGE, J. 2008. Eddy-resolving ocean circulation in the Asian–Australian region inferred from an ocean reanalysis effort. Progress in Oceanography, 76, 334-365.

SCHLINING, K., VON THUN, S., KUHNZ, L., SCHLINING, B., LUNDSTEN, L., JACOBSEN STOUT, N., CHANEY, L. & CONNOR, J. 2013. Debris in the deep: Using a 22-year video annotation database to survey marine litter in Monterey Canyon, central California, USA. Deep Sea Research Part I: Oceanographic Research Papers.

SCHOLZ, J. & HILLMER, G. 1995. Reef-bryozoans and bryozoan-microreefs: control factor evidence from the Philippines and other regions. Facies, 32, 109-143.

SCHUYLER, Q., HARDESTY, B. D., WILCOX, C. & TOWNSEND, K. 2012. To eat or not to eat? Debris selectivity by marine turtles. PloS one, 7, e40884.

SELKE, S. E. 2003. Plastics in packaging. Plastics and the Environment, 137-183. SHAW, D. 1977. Pelagic tar and plastic in the Gulf of Alaska and Bering Sea: 1975.

Science of the Total Environment, 8, 13-20. SHIOMOTO, A. & KAMEDA, T. 2005. Distribution of manufactured floating marine

debris in near-shore areas around Japan. Marine pollution bulletin, 50, 1430-1432.

SIVAN, A. 2011. New perspectives in plastic biodegradation. Current Opinion in Biotechnology, 22, 422-426.

SUDHAKAR, M., TRISHUL, A., DOBLE, M., SURESH KUMAR, K., SYED JAHAN, S., INBAKANDAN, D., VIDUTHALAI, R., UMADEVI, V., SRIYUTHA MURTHY, P. & VENKATESAN, R. 2007. Biofouling and biodegradation of polyolefins in ocean waters. Polymer Degradation and Stability, 92, 1743-1752.

TALLEY, L. D., PICKARD, G. L., EMERY, W. J. & SWIFT, J. H. 2011a. Descriptive physical oceanography: an introduction, Elsevier.

TALLEY, L. D., PICKARD, G. L., EMERY, W. J. & SWIFT, J. H. 2011b. Descriptive physical oceanography: an introduction, Access Online via Elsevier.

122

TAYLOR, M. 2015. The Plastics Indrustry Globally - Challenges and Opportunities. NPE2015 Orlando, FL - http://www.slideshare.net/mdairtaylor/the-plastics-industry-globally-challenges-and-opportunities-npe2015-orlando-fl.

TEUTEN, E. L., SAQUING, J. M., KNAPPE, D. R., BARLAZ, M. A., JONSSON, S., BJÖRN, A., ROWLAND, S. J., THOMPSON, R. C., GALLOWAY, T. S. & YAMASHITA, R. 2009. Transport and release of chemicals from plastics to the environment and to wildlife. Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 2027-2045.

THIEL, M. & GUTOW, L. 2005. The ecology of rafting in the marine environment. II. The rafting organisms and community. Oceanography and Marine Biology: An Annual Review, 43, 279-418.

THIEL, M., HINOJOSA, I., MIRANDA, L., PANTOJA, J., RIVADENEIRA, M. & VÁSQUEZ, N. 2013. Anthropogenic marine debris in the coastal environment: A multi-year comparison between coastal waters and local shores. Marine Pollution Bulletin, 71, 307-316.

THIEL, M., HINOJOSA, I., VÁSQUEZ, N. & MACAYA, E. 2003. Floating marine debris in coastal waters of the SE-Pacific (Chile). Marine Pollution Bulletin, 46, 224-231.

THOMAS, T., GILBERT, J. & MEYER, F. 2012. Metagenomics-a guide from sampling to data analysis. Microb Inform Exp, 2, 1-12.

THOMPSON, R. C., OLSEN, Y., MITCHELL, R. P., DAVIS, A., ROWLAND, S. J., JOHN, A. W., MCGONIGLE, D. & RUSSELL, A. E. 2004. Lost at sea: where is all the plastic? Science, 304, 838-838.

THOMPSON, R. C., SWAN, S. H., MOORE, C. J. & VOM SAAL, F. S. 2009. Our plastic age. Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 1973-1976.

TIFFANY, M. A. 2011. Epizoic and Epiphytic Diatoms. The Diatom World. Springer.

TITMUS, A. J. & HYRENBACH, D. K. 2011. Habitat associations of floating debris and marine birds in the North East Pacific Ocean at coarse and meso spatial scales. Marine pollution bulletin, 62, 2496-2506.

TOTTI, C., POULIN, M., ROMAGNOLI, T., PERRONE, C., PENNESI, C. & DE STEFANO, M. 2009. Epiphytic diatom communities on intertidal seaweeds from Iceland. Polar Biology, 32, 1681-1691.

TOURINHO, P. S., IVAR DO SUL, J. A. & FILLMANN, G. 2010. Is marine debris ingestion still a problem for the coastal marine biota of southern Brazil? Marine Pollution Bulletin, 60, 396-401.

TSUCHIDA, A., KAWAZUMI, H., KAZUYOSHI, A. & YASUO, T. Identification of shredded plastics in milliseconds using Raman spectroscopy for recycling. Sensors, 2009 IEEE, 2009. IEEE, 1473-1476.

TURNER, J. T. 2002. Zooplankton fecal pellets, marine snow and sinking phytoplankton blooms. Aquatic Microbial Ecology, 27, 57-102.

UNITED NATIONS ENVIRONMENT PROGRAMME. 2014. Year Book 2014: Emerging Issues in our Global Environment [Online]. Available: http://www.unep.org/yearbook/2014/.

123

VAN CAUWENBERGHE, L., CLAESSENS, M., VANDEGEHUCHTE, M. B., MEES, J. & JANSSEN, C. R. 2013a. Assessment of marine debris on the Belgian Continental Shelf. Marine Pollution Bulletin.

VAN CAUWENBERGHE, L., VANREUSEL, A., MEES, J. & JANSSEN, C. R. 2013b. Microplastic pollution in deep-sea sediments. Environmental Pollution, 182, 495-499.

VAN SEBILLE, E., ENGLAND, M. H. & FROYLAND, G. 2012. Origin, dynamics and evolution of ocean garbage patches from observed surface drifters. Environmental Research Letters, 7, 044040.

VEGTER, A., BARLETTA, M., BECK, C., BORRERO, J., BURTON, H., CAMPBELL, M., COSTA, M., ERIKSEN, M., ERIKSSON, C. & ESTRADES, A. 2014. Global research priorities to mitigate plastic pollution impacts on marine wildlife. Endangered Species Research.

VENRICK, E., BACKMAN, T., BARTRAM, W., PLATT, C., THORNHILL, M. & YATES, R. 1973. Man-made objects on the surface of the central North Pacific Ocean. Nature, 241.

VERLIS, K., CAMPBELL, M. & WILSON, S. 2013. Ingestion of marine debris plastic by the wedge-tailed shearwater< i> Ardenna pacifica</i> in the Great Barrier Reef, Australia. Marine Pollution Bulletin, 72, 244-249.

VON MOOS, N., BURKHARDT-HOLM, P. & KÖHLER, A. 2012. Uptake and effects of microplastics on cells and tissue of the blue mussel Mytilus edulis L. after an experimental exposure. Environmental Science & Technology, 46, 11327-11335.

WALPOLE, S. C., PRIETO-MERINO, D., EDWARDS, P., CLELAND, J., STEVENS, G. & ROBERTS, I. 2012. The weight of nations: an estimation of adult human biomass. BMC Public Health, 12, 439.

WATTS, A. J., LEWIS, C., GOODHEAD, R. M., BECKETT, S. J., MOGER, J., TYLER, C. R. & GALLOWAY, T. S. 2014. Uptake and retention of microplastics by the shore crab Carcinus maenas. Environmental Science & Technology, 48, 8823-8830.

WEBB, D. J. 2000. Evidence for shallow zonal jets in the South Equatorial Current region of the southwest Pacific. Journal of Physical Oceanography, 30, 706-720.

WEBB, H. K., ARNOTT, J., CRAWFORD, R. J. & IVANOVA, E. P. 2012. Plastic degradation and its environmental implications with special reference to poly (ethylene terephthalate). Polymers, 5, 1-18.

WEISE, W. & RHEINHEIMER, G. 1977. Scanning electron microscopy and epifluorescence investigation of bacterial colonization of marine sand sediments. Microbial Ecology, 4, 175-188.

WILBER, R. J. 1987. Plastic in the North Atlantic. Oceanus, 30, 61-68.

WILCOX, C., HARDESTY, B., SHARPLES, R., GRIFFIN, D., LAWSON, T. & GUNN, R. 2013. Ghostnet impacts on globally threatened turtles, a spatial risk analysis for northern Australia. Conservation Letters, 6, 247-254.

124

WILLIAMS, R., ASHE, E. & O’HARA, P. D. 2011. Marine mammals and debris in coastal waters of British Columbia, Canada. Marine Pollution Bulletin, 62, 1303-1316.

WINSTON, J. E. 1982. Drift plastic—An expanding niche for a marine invertebrate? Marine Pollution Bulletin, 13, 348-351.

WINSTON, J. E., GREGORY, M. R. & STEVENS, L. M. 1997. Encrusters, epibionts, and other biota associated with pelagic plastics: a review of biogeographical, environmental, and conservation issues. Marine Debris. Springer.

WRIGHT, S. L., THOMPSON, R. C. & GALLOWAY, T. S. 2013. The physical impacts of microplastics on marine organisms: A review. Environmental Pollution, 178, 483-492.

WUCHTER, C., MARQUARDT, J. & KRUMBEIN, W. E. 2003. The epizoic diatom community on four bryozoan species from Helgoland (German Bight, North Sea). Helgoland Marine Research, 57, 13-19.

YAMASHITA, R. & TANIMURA, A. 2007. Floating plastic in the Kuroshio current area, western North Pacific Ocean. Marine Pollution Bulletin, 54, 485-488.

YE, S. & ANDRADY, A. L. 1991. Fouling of floating plastic debris under Biscayne Bay exposure conditions. Marine Pollution Bulletin, 22, 608-613.

YOUNG, J. W., LAMB, T. D., LE, D., BRADFORD, R. W. & WHITELAW, A. W. 1997. Feeding ecology and interannual variations in diet of southern bluefin tuna, Thunnus maccoyii, in relation to coastal and oceanic waters off eastern Tasmania, Australia. Environmental Biology of Fishes, 50, 275-291.

ZETTLER, E. R., MINCER, T. J. & AMARAL-ZETTLER, L. A. 2013. Life in the ‘Plastisphere’: Microbial communities on plastic marine debris. Environmental Science & Technology, 47, 7137-7146.

ZHENG, Y., YANFUL, E. K. & BASSI, A. S. 2005. A review of plastic waste biodegradation. Critical Reviews in Biotechnology, 25, 243-250.

ZHOU, P., HUANG, C., FANG, H., CAI, W., LI, D., LI, X. & YU, H. 2011. The abundance, composition and sources of marine debris in coastal seawaters or beaches around the northern South China Sea (China). Marine pollution bulletin, 62, 1998-2007.

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Appendix 1 Outputs produced during this candidature

Peer-reviewed publications published, in press or in prep

1. Thums M, Whiting SD, Reisser J, Pendoley K, Pattiaratchi C, Proietti M, Meekan M

(in prep) Artificial light on water attracts turtle hatchlings during their nearshore transit.

2. Proietti M, Reisser J, Cliff J, Soares L, Monteiro D, Pattiaratchi C, Secchi E (in

prep) Life history in a tortoiseshell: ontogenetic ecological changes of hawksbill turtles

detected through Secondary Ion Mass Spectrometry.

3. Reisser J, Slat B, Noble K, du Plessis K, Epp M, Proietti M, de Sonneville J, Becker

T, Pattiaratchi C (2015) The vertical distribution of buoyant plastics at sea: an

observational study in the North Atlantic Gyre. Biogeosciences 12: 1249-1256

4. Reisser J, Proietti M, Shaw J, Pattiaratchi C (2014) Ingestion of plastics at sea: does

debris size really matter? Frontiers in Marine Science 1: 70

5. Eriksen M, Lebreton LM, Carson HS, Thiel M, Moore C, Borerro JC, Galgani F,

Ryan PG, Reisser J (2014) Plastic Pollution in the World's Oceans: more than 5 trillion

plastic pieces weighing over 250,000 tons afloat at sea. PLOS ONE 9(12): e111913

6. Letessier TB, Bouchet PJ, Reisser J, Meeuwig JJ (2014) Baited videography reveals

remote foraging and migration behavior of sea turtles. Marine Biodiversity 1:2

7. Reisser J, Shaw J, Hallegraeff G, Proietti M, Barnes D, Thums M, Wilcox C,

Hardesty B, Pattiaratchi C (2014) Millimeter-sized Marine Plastics: A New Pelagic

Habitat for Microorganisms and Invertebrates. PLOS ONE 9(6): e100289

126

8. Proietti M, Reisser J, Marins L, Rodriguez-Zarate C, Marcovaldi M, Monteiro D,

Pattiaratchi C, Secchi E (2014) Genetic Structure and Natal Origins of Immature

Hawksbill Turtles (Eretmochelys imbricata) in Brazilian Waters. PLOS ONE

9(2):e88746

9. Proietti M, Reisser J, Marins L, Marcovaldi M, Soares L, Monteiro D, Wijeratne S,

Pattiaratchi C, Secchi E (2014) Hawksbill x loggerhead sea turtle hybrids at Bahia,

Brazil: where do their offspring go? PeerJ 2:e255

10. Reisser J, Shaw J, Wilcox C, Hardesty BD, Proietti M, Thums M, Pattiaratchi C

(2013) Marine Plastic Pollution in Waters around Australia: Characteristics,

Concentrations, and Pathways. PLOS ONE 8(11):e80466

11. Reisser J, Proietti M, Sazima I, Kinas P, Horta P, Secchi E (2013) Feeding ecology

of the green turtle (Chelonia mydas) at rocky reefs in the western South Atlantic.

Marine Biology 160(12): 3169-3179

12. Thums M, Whiting S, Reisser J, Pendoley K, Pattiaratchi C, Harcourt R, McMahon

C, Meekan M (2013) Tracking sea turtle hatchlings - a pilot study using acoustic

telemetry. Journal of Experimental Marine Biology and Ecology 440:156-163

13. Proietti M, Reisser J, Secchi ER (2012) Immature Hawksbill Turtles Feeding in

Brazilian Islands. Marine Turtle Newletter 135:4-6

14. Proietti M, Reisser J, Kinas P, Kerr R, Monteiro D, Marins L, Secchi E (2012)

Green turtle (Chelonia mydas) mixed stocks in the western South Atlantic, as revealed

by mtDNA haplotypes and drifter trajectories. Marine Ecology Progress Series

447:195-209

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Media articles

1. Reisser J, Pattiaratchi C, Proietti M (2015) ‘Missing plastic’ in the oceans can be

found below the surface. The Conversation Link: https://theconversation.com/missing-

plastic-in-the-oceans-can-be-found-below-the-surface-37999

2. Reisser J, Pattiaratchi C, Shaw J (2014) Creatures living on tiny ocean plastic may

be cleaning our seas. The Conversation Link: https://theconversation.com/creatures-

living-on-tiny-ocean-plastic-may-be-cleaning-our-seas-27876

3. Pattiaratchi C, Reisser J (2013) The difficulty of searching for MH370 in a giant

rubbish patch. The Conversation Link: https://theconversation.com/the-difficulty-of-

searching-for-mh370-in-a-giant-rubbish-patch-25083

4. Reisser J, Pattiaratchi C (2013) Australian waters polluted by harmful tiny plastics.

The Conversation link: https://theconversation.com/australian-waters-polluted-by-

harmful-tiny-plastics-20790

5. Duarte C, Reisser J, Thums M, Duarte G (2013) Take a stand on Oceans Day and de-

plastify your life. The Conversation link: https://theconversation.com/take-a-stand-on-

oceans-day-and-de-plastify-your-life-15055

128

Appendix 2 Chapter 2 supplementary material

Net tow data (N = 171) Columns indicate net station number, sampling date (day.month.year), location (degrees minutes), and mean sea surface plastic concentration (Cs; pieces per km-2).

Net Station Date (UTC) Latitude (S) Longitude (E) Sea Surface Concentration (Cs) 1 10.06.11 39 18.663 163 35.799 653.51 1 10.06.11 39 18.663 163 35.799 691.96 1 10.06.11 39 18.663 163 35.799 566.79 2 11.06.11 39 57.089 160 25.080 950.45 2 11.06.11 39 57.089 160 25.080 2198.90 2 11.06.11 39 57.089 160 25.080 1217.12 3 12.06.11 40 38.087 155 53.425 1424.92 3 12.06.11 40 38.087 155 53.425 3254.64 3 12.06.11 40 38.087 155 53.425 0.00 4 13.06.11 41 08.068 152 17.007 785.90 4 13.06.11 41 08.068 152 17.007 0.00 4 13.06.11 41 08.068 152 17.007 1810.17 5 12.08.11 43 34.637 145 47.977 32167.51 5 12.08.11 43 34.637 145 47.977 29582.80 5 12.08.11 43 34.637 145 47.977 9081.73 6 13.08.11 41 55.318 144 32.515 24299.60 6 13.08.11 41 55.318 144 32.515 6077.41 6 13.08.11 41 55.318 144 32.515 0.00 7 14.08.11 39 02.484 142 25.125 3554.15 7 14.08.11 39 02.484 142 25.125 3211.54 7 14.08.11 39 02.484 142 25.125 2477.57 8 15.08.11 37 53.346 139 49.553 931.74 8 15.08.11 37 53.346 139 49.553 2513.76 8 15.08.11 37 53.346 139 49.553 13625.39 9 16.08.11 36 03.358 135 41.202 4177.68 9 16.08.11 36 03.358 135 41.202 2015.15 9 16.08.11 36 03.358 135 41.202 0.00

10 17.08.11 35 28.841 132 10.928 2332.49 10 17.08.11 35 28.841 132 10.928 0.00 10 17.08.11 35 28.841 132 10.928 1381.05 11 18.08.11 35 04.329 127 15.958 0.00 11 18.08.11 35 04.329 127 15.958 0.00 11 18.08.11 35 04.329 127 15.958 0.00 12 19.08.11 34 36.224 121 49.046 0.00 12 19.08.11 34 36.224 121 49.046 1603.96 12 19.08.11 34 36.224 121 49.046 1099.32 13 20.08.11 35 18.893 118 37.370 1540.86 13 20.08.11 35 18.893 118 37.370 0.00 13 20.08.11 35 18.893 118 37.370 2852.58 14 22.08.11 33 06.825 114 29.446 889.63 14 22.08.11 33 06.825 114 29.446 0.00 14 22.08.11 33 06.825 114 29.446 458.30 15 11.04.12 41 53.867 148 26.891 708.09 15 11.04.12 41 53.867 148 26.891 2732.41 15 11.04.12 41 53.867 148 26.891 2355.35 16 12.04.12 39 39.389 148 53.558 0.00 16 12.04.12 39 39.389 148 53.558 0.00 16 12.04.12 39 39.389 148 53.558 0.00 17 13.04.12 37 38.671 150 23.827 3823.59 17 13.04.12 37 38.671 150 23.827 3313.01 17 13.04.12 37 38.671 150 23.827 2840.54

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18 13.04.12 35 24.230 150 50.390 8361.99 18 13.04.12 35 24.230 150 50.390 18324.00 18 13.04.12 35 24.230 150 50.390 6313.02 19 14.04.12 33 52.897 152 0.189 2903.60 19 14.04.12 33 52.897 152 0.189 7374.21 19 14.04.12 33 52.897 152 0.189 3858.96 20 15.04.12 33 10.310 152 41.536 5966.14 20 15.04.12 33 10.310 152 41.536 19119.87 20 15.04.12 33 10.310 152 41.536 33412.23 21 15.04.12 31 01.893 153 22.585 1954.41 21 15.04.12 31 01.893 153 22.585 3818.55 21 15.04.12 31 01.893 153 22.585 4404.43 22 16.04.12 28 20.522 153 55.265 9943.10 22 16.04.12 28 20.522 153 55.265 21021.85 22 16.04.12 28 20.522 153 55.265 32595.07 23 17.04.12 26 43.789 153 22.675 7064.40 23 17.04.12 26 43.789 153 22.675 4327.06 23 17.04.12 26 43.789 153 22.675 6168.01 24 04.05.12 24 55.084 155 12.525 743.14 24 04.05.12 24 55.084 155 12.525 0.00 24 04.05.12 24 55.084 155 12.525 0.00 25 06.05.12 23 52.232 162 20.311 5835.56 25 06.05.12 23 52.232 162 20.311 7695.14 25 06.05.12 23 52.232 162 20.311 10077.88 26 07.05.12 23 12.812 166 37.146 616.07 26 07.05.12 23 12.812 166 37.146 0.00 26 07.05.12 23 12.812 166 37.146 0.00 27 08.05.12 21 46.153 170 37.369 1248.23 27 08.05.12 21 46.153 170 37.369 8821.42 27 08.05.12 21 46.153 170 37.369 6114.52 28 07.06.12 18 33.897 176 30.406 48895.58 28 07.06.12 18 33.897 176 30.406 7857.04 28 07.06.12 18 33.897 176 30.406 3339.76 29 07.06.12 19 58.653 174 59.443 9647.43 29 07.06.12 19 58.653 174 59.443 7519.52 29 07.06.12 19 58.653 174 59.443 3789.07 30 08.06.12 21 16.990 173 34.862 946.73 30 08.06.12 21 16.990 173 34.862 801.95 30 08.06.12 21 16.990 173 34.862 1311.36 31 08.06.12 22 35.700 172 06.689 2575.43 31 08.06.12 22 35.700 172 06.689 2918.15 31 08.06.12 22 35.700 172 06.689 3507.91 32 09.06.12 23 44.992 170 32.263 0.00 32 09.06.12 23 44.992 170 32.263 0.00 32 09.06.12 23 44.992 170 32.263 0.00 33 09.06.12 25 04.307 168 42.713 2119.38 33 09.06.12 25 04.307 168 42.713 0.00 33 09.06.12 25 04.307 168 42.713 0.00 34 10.06.12 26 17.133 167 00.868 1423.41 34 10.06.12 26 17.133 167 00.868 764.70 34 10.06.12 26 17.133 167 00.868 729.39 35 10.06.12 27 31.614 165 11.757 711.58 35 10.06.12 27 31.614 165 11.757 2112.46 35 10.06.12 27 31.614 165 11.757 697.31 36 15.06.12 35 38.607 155 04.472 652.35 36 15.06.12 35 38.607 155 04.472 0.00 36 15.06.12 35 38.607 155 04.472 0.00 37 15.06.12 37 22.370 153 32.457 3594.90 37 15.06.12 37 22.370 153 32.457 9639.55

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37 15.06.12 37 22.370 153 32.457 8349.88 38 16.06.12 42 16.869 148 58.254 5509.05 38 16.06.12 42 16.869 148 58.254 1845.78 38 16.06.12 42 16.869 148 58.254 0.00 39 17.06.12 42 49.848 148 26.515 1651.09 39 17.06.12 42 49.848 148 26.515 3050.52 39 17.06.12 42 49.848 148 26.515 2289.58 40 26.07.12 16 34.596 145 44.605 1960.78 40 26.07.12 16 34.596 145 44.605 5392.16 40 26.07.12 16 34.596 145 44.605 3921.57 41 27.07.12 15 01.649 145 23.440 2304.10 41 27.07.12 15 01.649 145 23.440 5172.33 41 27.07.12 15 01.649 145 23.440 13518.32 42 27.07.12 13 39.306 144 05.270 2398.91 42 27.07.12 13 39.306 144 05.270 956.41 42 27.07.12 13 39.306 144 05.270 1832.08 43 28.07.12 12 01.760 143 16.230 8954.09 43 28.07.12 12 01.760 143 16.230 3588.54 43 28.07.12 12 01.760 143 16.230 6582.30 44 28.07.12 10 44.893 142 20.410 3937.23 44 28.07.12 10 44.893 142 20.410 446.59 44 28.07.12 10 44.893 142 20.410 1382.16 45 29.07.12 12 15.928 141 37.748 2796.53 45 29.07.12 12 15.928 141 37.748 1559.97 45 29.07.12 12 15.928 141 37.748 450.97 46 30.07.12 15 29.180 141 02.689 0.00 46 30.07.12 15 29.180 141 02.689 596.58 46 30.07.12 15 29.180 141 02.689 0.00 47 30.07.12 17 02.883 140 46.650 0.00 47 30.07.12 17 02.883 140 46.650 0.00 47 30.07.12 17 02.883 140 46.650 0.00 48 17.08.12 18 39.076 119 29.745 2747.58 48 17.08.12 18 39.076 119 29.745 1114.00 48 17.08.12 18 39.076 119 29.745 0.00 49 17.08.12 18 51.743 118 40.746 2488.88 49 17.08.12 18 51.743 118 40.746 1110.76 49 17.08.12 18 51.743 118 40.746 534.60 50 17.08.12 18 58.975 118 12.687 4394.68 50 17.08.12 18 58.975 118 12.687 1703.95 50 17.08.12 18 58.975 118 12.687 1143.61 51 17.08.12 19 06.486 117 43.548 0.00 51 17.08.12 19 06.486 117 43.548 612.37 51 17.08.12 19 06.486 117 43.548 1854.75 52 17.08.12 19 25.826 115 55.023 3401.75 52 17.08.12 19 25.826 115 55.023 599.94 52 17.08.12 19 25.826 115 55.023 4049.19 53 19.08.12 20 23.058 116 23.058 7748.76 53 19.08.12 20 23.058 116 23.058 7266.80 53 19.08.12 20 23.058 116 23.058 39225.93 54 19.08.12 20 18.934 115 40.132 3249.67 54 19.08.12 20 18.934 115 40.132 1245.08 54 19.08.12 20 18.934 115 40.132 654.36 55 22.08.12 19 47.716 115 58.478 1241.92 55 22.08.12 19 47.716 115 58.478 2129.73 55 22.08.12 19 47.716 115 58.478 496.75 56 22.08.12 20 22.838 115 08.123 0.00 56 22.08.12 20 22.838 115 08.123 0.00 56 22.08.12 20 22.838 115 08.123 1294.44 57 25.08.12 21 50.655 113 54.765 12846.12

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57 25.08.12 21 50.655 113 54.765 1932.06 57 25.08.12 21 50.655 113 54.765 3462.42

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Probability distribution of virtual particles arriving at the 57 net stations of this study (dispersal time = 45 days). Red dots indicate position of net stations. June 2011

August 2011

April 2012

May 2012

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June 2012

July 2012

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August 2012

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Real drifter pathways arriving at the 57 net stations. Purple dots indicate net station locations and asterisks indicate drifter release areas.

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Appendix 3 Chapter 3 supplementary material

Examples of marine plastic surface textures. a, d: polypropylene plastics with linear fractures and pits; b, c: higher magnification of the plastic surface shown in ‘a’ (note very similar pits – one empty and one with a cell conforming its shape); e: higher magnification of the plastic surface shown in ‘d’ (note three equally spaced deep pits); f: polyethylene soft plastic with linear fractures, producing squared microplastics; g: higher magnification of the plastic surface shown in ‘f’ (note shallow pits likely formed by Cocconeis sp.); h: rounded scrape mark similar to the ones found close to the worm-like animal (see Figure 3.7i); i,k: sub-parallel scrape marks; j: large plastic pit likely formed by an egg of Halobates sp.