Coral Reefs –

An Analysis of the System’s Functioning

and Human Alterations to it

Term Paper

Module “Objects and Dynamics: Global Systems Analysis”

Winter Term 2011/2012

November 6, 2011

Veronika Winkel and Carina Zell

University for Sustainable Development Students of Global Change Management

Eberswalde 1st semester

II

Table of Contents

Abstract ...................................................................................................................................... 1

1 Introduction ........................................................................................................................ 2

2 Methods ............................................................................................................................. 3

3 Results ................................................................................................................................ 4

3.1. The Natural System of a Coral Reef ............................................................................. 5

3.1.1 Major components of the coral reef ecosystem ....................................................... 5

3.1.2 Energy-fluxes and relative closeness ...................................................................... 12

3.2. Human Influences to the Coral Reef System ............................................................. 15

3.2.1 Emergent Properties of the System as Ecosystem Services............................... 16

3.2.2 Interaction between Humans and Coral Reefs .................................................. 19

3.2.3 Trends of Future Change .................................................................................... 27

3.2.4 Management Strategies ..................................................................................... 31

3.2.5 Summary ............................................................................................................ 33

4 Discussion ......................................................................................................................... 34

4.1 The Natural System.................................................................................................... 34

4.2 Human influences ...................................................................................................... 35

5 Conclusion ........................................................................................................................ 37

6 References ........................................................................................................................... i

1

Abstract

Coral reefs are known to be hotspots of biodiversity. They feature extraordinary high bio-

mass production rates and extremely dense populations while being situated in a nutrient-

poor ocean environment.

The following paper depicts a system analysis on coral reefs. The aim of this analysis was to

gain an understanding of coral reefs, applying universal methods of „system-thinking“ which

are not designed for ecosystems in particular but for a general approach towards systems of

any kind.

Based on 12 given questions concerning system properties, we were able to validate the

term „coral reef ecosystem“ as it matches the set criteria for being considered as a system.

Furthermore, we examined biotic and abiotic components of the system, component`s in-

teractions, energy fluxes and dependencies from/to systems of higher order.

Carrying out literature research, we focused on two key aspects. First, the biology of coral

reef systems and its functioning in a hypothesized non-anthropogenic environment and se-

cond the dependencies between the coral reef systems and the anthropogenic system, in-

cluding ecosystem services provided by the coral reefs as well as multiple stresses imposed

on the coral reef systems with a focus on global change issues.

While the ‘biological’ approach showed the high level of self-sufficiency and the remarkable

positive influence coral reefs have on other systems via outwards directed energy flows, the

‘anthropogenic’ approach uncovered a constant and immediate threat of coral reef ecosys-

tems caused by the anthroposystem. This finding is conflicting with the anthroposystem’s

dependence upon the multiple ecosystem services the coral reef ecosystem provides.

We conclude that appropriate management strategies, minimizing the stress load imposed

upon coral reefs, are indispensable to assure the coexistence of coral reef- and anthroposys-

tem to mutual benefit.

2

1 Introduction

Coral reefs fascinate a lot of people with their beauty and stunning biodiversity, featuring

creatures of all shapes, colors and sizes. Thus, coral reefs were subject of a lot of studies for

several hundreds of years and are now even more in the focus of scientific research as coral

cover declines continuously.

With this paper we try to approach coral reefs as systems by analyzing its components and

their interactions to gain an understanding of its underlying principles. Furthermore, we

want to find out how humans as an influential system of higher order alter coral reefs.

Coral reefs cover an area of 2*106 square kilometers in tropical ocean regions (Archituv &

Dubinsky 1990). Although this is just 1.2 per cent of all continental shelf (Allsopp et al. 2009),

they are the biodiversity hotspots of the ocean clearly distinguishing theirselves by their high

biomass production within a nutrient-poor environment. At first, this might sound paradox

but when looking at the system in detail it can be found out that there are loads of symbio-

ses and internal cycles which make coral reefs a self-sustaining and extraordinary effective

system.

Coral reefs provide a lot of services to humans like food, coastal protection, tourist attrac-

tion, pharmaceuticals and building material. Despite these services they are strongly threat-

ened by anthropogenic global change and will irreversibly be damaged if current trends con-

tinue and no management strategies are set up (UNEP-WCMC 2006). That is why we dedi-

cated the second part of our paper solely to anthropogenic influences.

3

2 Methods

We conducted a system analysis to understand the functioning of the coral reef ecosystem

based on literature review. On the basis of the findings within literature we answered the

given questions and drew conclusions on the complex system’s structure and mechanisms.

The following questions were given as guiding questions for this system analysis:

Is it a system? Why?

Components of the system?

Interaction of components and functioning of the system (in coordination with its

environment)?

Relevant emergent properties?

Dependence from systems of higher order?

Effects/impacts on systems of higher order?

Effects/impacts on systems of lower order?

(Thermodynamic) efficiency? Closedness?

Main source of energy?

Trends of change and sustainability?

Vulnerability to global change processes?

The system as contributing/driving force of global change processes?

The answers to the questions do all occur somewhere in the text although the questions are

mostly not directly mentioned again.

4

3 Results

“In its broadest conception, a ‘system’ may be described as a complex of interacting compo-

nents together with the relationships among them that permit the identification of a bound-

ary-maintaining entity or process” (Laszlo & Krippner 1998). As we describe in the following

chapter, coral reefs match these criteria for being considered as a system, more precisely an

ecosystem.

When defining the boundaries of coral reef ecosystems we concluded that there is no uni-

versal interconnected coral reef ecosystem but a number of similar systems scattered across

large distances within different tropical marine regions, all underlying the same principles.

The most famous should be the Great Barrier Reef. All of these coral reefs form clearly dis-

tinguishable nested systems within the higher system of the ocean. Each coral reef system is

defined by the available size of suitable substrate they grow on; therefore coral reef systems

are limited systems.

At first we will describe the natural system of a coral reef before explaining human influ-

ences to coral reefs.

5

3.1. The Natural System of a Coral Reef

„These coral reef ecosystems are undoubtedly so successful […] and so unique in their

boundless diversity, intricate interrelationships and spectacular beauty, that, along with the

tropical rainforest, they demonstrate the upper boundaries which may be reached in the

evolution of life on Earth“ (Dubinsky 1990).

Definition Coral Reef

After Done (in Hopley 2011) a coral reef can be defined as „ a tract of corals growing on a

massive, wave resistant structure and associated sediments, substantially built by skeletons

of successive generations of corals and other calcareous reef-biota“.

Analyzing the system`s components, the fundament on which the whole coral reef ecosys-

tem is based is the calcareous skeleton itself (Sorokin 1993).

3.1.1 Major components of the coral reef ecosystem

The reef structure

The reef structures we find today were built from biogenous calcium carbonate, which has

been incorporated and deposited mainly by scleractinian corals (Lutz-Arend 2005) over 250

millions of years (Hopley 2011).

While various different classifications for coral reefs exist, three main types – fringing reefs,

barrier reefs and atolls - were already identified by DARWIN and are still valid today (Archi-

tuv & Dubinsky 1990).

While fringing reefs and barrier reefs occur in connection to shorelines, atolls can be found

offshore, building ring-shaped reefs enclosing a lagoon. Fringing- and barrier reefs can be

distinguished regarding their distance to the shoreline.

Fringing reefs occur in small distances to the shore, having only narrow lagoons, while barri-

er reefs can be found in bigger distances to the shoreline, such as the Great Barrier Reef

which is located about 100km offshore, building a spacious lagoon (Archituv & Dubinsky

1990).

Reef drills showed that coral skeletons actually built only a fraction of one third of the cal-

careous reef structure, while „the remainder of the reef interior consists of sediment, rub-

ble, and open voids“(Hopley 2011).

6

A reef grows because of the former coral`s carbonate skeletons which will remain after the

polyp died (Purves et. al. 2006). These remaining skeletons built the basis for a new genera-

tion of corals to settle onto them, thereby increasing the accreted volume of the lime reef-

structure by each generation of corals.

The process in which the calcareous skeletons are built-up is called calcification.

It is described by the following chemical equation:

As can be seen in the above formula, carbon dioxide is produced during the calcification pro-

cess. On the other hand, carbon dioxide is taken up by photosynthesis activity within the

coral reef system. There have been long discussions within the research community whether

coral reefs are sinks or sources of carbon but it is now the “current understanding that most

coral reefs operate as sources of atmospheric CO2” (Suzuki & Kawahata 2004). Reef topog-

raphy has proven to be quite important for the carbon balance and also the proximity to

land: “These coastal reefs serve as an active CO2-releasing area due not only to calcification

but also to degradation of land-derived carbon” (Suzuki & Kawahata 2004). To get to this

conclusion, they measured the surface partial pressure of carbon dioxide for atolls and bar-

rier reefs and compared it to the value of the respective offshore waters. The partial pres-

sure was consistently higher within the coral reef area.

So coral reefs can be seen as a contributor to global climate change processes. In 1992 Ware,

Smith & Reaka-Kudla estimated that coral reefs have a share of “approximately 0.4% to 1.4%

of the current anthropogenic CO2 production due to fossil fuel combustion.”

The phenomenon of bioerosion leads to a partial reversion of the lime-accretion-process

because of intensive grazing by reef-biota such as parrotfish (Scaridae) and sea urchins

(Echinoida) (Glynn 1990).

A zonation within the reef-system is mainly attributed to the „interaction of current direc-

tion and intensity“(Done in Dubinsky 1990). Plankton- and thereby nutrient-inflow into the

reef-ecosystem is mediated by waves and currents which constitutes the importance of „lo-

cal flow patterns […] in shaping the mesoscale topography of the riff“ (Archituv & Dubinsky

1990).

Ca²+ + 2HCO3- → CaCO3 + H2O +CO2

7

Within the reef structure, distinctive zones can be found with each zone representing „a def-

inite local ecological unity, characterized by a definite selection of key species in its biota“

(Sorokin 1993). Main regular elements are distinguished as „reef slope, reef crest, reef flat

and lagoon“ (Tropical Marine Biology, Stockholm University).

Within the lagoon, diurnal changes in temperature and salinity are generally small (Andrews

& Pickard 1990).

Hermatypic Corals

As corals had their peak in past times, about 5000 of the 7500 known species are already

extinct (Achituv & Dubinsky 1990).

The reef building scleractinian corals present nowadays belong into the biological class of

anthozoa (phylum cnidaria), which indicates the growth of a coral planulae (larvae-state)

from a fertilized egg, followed by the development of the sessile polyp-form (Purves et. al

2006).

"Although some corals are indeed very long-lived, sexual maturity is reached within 3 to 5

years and most species at all depths rarely live longer than 20 years” (Connell, Hughes &

Wallace 1997).

It is in the larvae-state when the „settlement“ onto the calcareous reef surface takes place.

Figure 1: Reef zonation. Source: US Geological Survey

8

Later on, the fully grown polyp is able to accretiate biogenous calcium carbonate -CaCO3-,

embedding the molecules which where extracted from the surrounding ocean waters into an

excretion layer on the polyps surface (Purves et. al. 2006); the calcareous skeletons are

thereby built in situ (Achituv & Dubinsky 1990).

The actual form of the calcareous skeleton is specific to the species (Purves et. al. 2006),

according to interspecific differences in the coral’s morph.

The amount of accretiated calcium carbonate at modern reefs worldwide is estimated at

about 2.5 x 109 tons per year (Sorokin 1993).

Zooxanthellae

Hermatypic – reef-

building – corals live

in a symbiosis with

dinoflagellates; algal

symbionts from the

genus symbiodinium

which are also called

zooxanthellae

(Purves et. al. 2006,

Hopley 2011).

While the zooxan-

thellae are able to

produce large

amounts of high-

energy assimilates

through photosyn-

thesis, biogenic nitrogen is a restricting factor to their functioning and growth. Thus, within

the established symbiosis between hermatypic coral and zooxanthellae, high-energy carbon

molecules are passed from the algae (more than 90% of the algae’s assimilates) to the coral,

while the coral as a host in return provides the zooxanthellae with nutrients as nitrogen and

phosphorus and their living space (Hopley 2011, Purves et. al. 2006, Sorokin 1993).

Figure 2: A typical hermatypic coral. Many coral polyps of this kind form a layer on the lime-stone substrate, containing autotrophic zooxanthellae in their tissue. Source: Buddemeier, Kleypas & Aronson (2004)

9

The symbiosis between coral and algae is linked with high calcification rates (Sorokin 1993);

this phenomenon is also called „light-enhanced calcification“ after Goreau (in Barnes and

Chalker 1990). It is crucial to the reef`s existence, contributing to the growth of the reef-

structure as a habitat itself as well as propagating coral growth, which can be seen as a nu-

trient pool for many consumers of higher order within the complex ecosystem`s food web.

The temperature optimum for the calcification process has been determined at 27°C (An-

thony et. al. 2011).

The process of photosynthesis is directly dependent upon the amount of light incidences

onto the chloroplasts of autotrophic organisms. According to this, the symbiosis between

coral and zooxanthellae is only effective in oligotrophic waters near the water surface,

where light isn`t easily absorbed by high densities of phyto- and/ or zooplankton. Typical

shallow-water-reefs can therefore only be found in oligotrophic, tropical waters, in average

water depths from 0 to 30 meters, where zooxanthellae reach very high assimilation rates

and metabolism and fast coral growth is promoted by warm temperatures (Purves et. al.

2006, Lutz-Arend 2005, Achituv & Dubinsky 1990). After VAUGHAN coral reef development

would not take place in regions where the ocean`s body annual minimum temperature drops

below 18°C (in Achituv & Dubinsky 1990).

The number of places ocean wide where these prerequisites are met are limited and there-

fore the development of the coral reef ecosystem happened in these places continuously

over large time scales, propagating long-term coevolution leading to extraordinary high bio-

diversity.

Figure 3: Distribution of coral reefs. Source: Buddemeier, Kleypas & Aronson (2004)

10

Beside their ability to feed autotrophic via zooxanthellae, hermatypic corals are also able to

use further heterotrophic food – and thereby energy sources. They are able to filter feed on

plankton as well as to consume dissolved organic matter via their outer tissue membranes.

Lastly, they effectively catch and digest moving prey (Sorokin 1993). With that, „hermatypic

corals possess all the feeding methods known in marine animals and have the necessary

morphological structures for them“ (Odum & Odum 1965, Muscatine & Porter 1977 in So-

rokin 1990). After Sorokin (1993) it is likely that the success and flourishment of hermatypic

corals despite a „remarkably strong competition for solid bottom substrate“ can be attribut-

ed to their multiple feeding mechanisms „using most sources of energy available for sessile

animals: light, plankton and dissolves organic matter“.

The actual amount of energy received by the coral from autotrophic or heterotrophic assimi-

lation is thought to be dependent on the actual species (Sorokin 1993). After LEWIS, around

65% of the coral`s energy demand is covered by photosynthates. Further energy shares were

estimated at about „15% from predatory feeding and 20% by sedimentary feeding on bacte-

ria, and […] dissolved organic matter (Sorokin 1984 in Sorokin 1990). This ratio might also

depend on the water depth, as in deeper parts of the reef, generally less light is available

and therefore the necessity of heterotrophic assimilation by the corals is increased (Sorokin

1993).

The most common way for scleractinian corals to reproduce is by spawning of eggs and

sperm which then fertilize and develop externally. Most species reproduce during so called

„mass spawning events“ which are seasonal and predictable. Beside the sexual reproduction

processes in mass spawning events, asexual reproduction strategies can be observed as well

(Harrison & Wallace 1990).

Reef-fish

Coral reef systems feature unusually dense communities and hold 9% of total stock world-

wide (Sorokin 1993).

A very important example for a symbiosis within these extremely species-rich and diverse

ecosystems is the concept of „cleaning stations“, in which small, brightly colored reef fish

(Labroides spp.) and shrimp „clean“ larger fish by feeding on their parasites (Grutter 1999 in

Hopley 2011).

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Clown fish and large sea anemones also profit mutually from their symbiotic relation in

which the anemone provides protection while the clown fish attracts potential prey which

the anemone will then catch and incorporate, feeding on it heterotrophly (Hopley 2011).

As another important component of the coral reef ecosystem, the „benthic biocenosis of the

soft bottom“ should be mentioned (Sorokin 1993).

Reef-flora

The flora found in a coral reef ecosystem incloses several key components of the systems

nutritional supply such as seaweed and see grasses, free-living phytoplankton as well as zoo-

xanthellae which play an important role as primary producers within the food web (Berner

1990).

Macroalgae form an important system component, especially in the „reef flat“ (D’Elia &

Wiebe 1990).

Nutrients

Nitrogen is an elementary but often limiting factor to organism`s growth and functioning.

Accordingly, processes altering the availability of essential nutrients such as biogenous nitro-

gen have immediate effects on the overall biomass production of the system (D’Elia & Wiebe

1990). For that reason, nitrogen in- and outflows are of special interest in the analysis of the

coral reef system. The major source of bioavailable nitrogen is the process of nitrogen fixa-

tion by bacteria and cyanobacteria (Wiebe 1975, Capone 1977 in Sorokin 1993). Terrestrial

runoff is another influential source of bioavailable nitrogen inflow into the coral reef ecosys-

tem. Bioavailable nitrogen present in the reef’s water columns is rapidly incorporated by

reef-biota such as plankton.

Nitrate removal from the water column by corals could be documented . Nitrogen which is

not incorporated by reef-biota might be deposited on the benthos, where denitrification

processes occur, leading to a loss of former bioavailable nitrogen for the ecosystem (D’Elia &

Wiebe 1990).

Inorganic carbon which is used by zooxanthellae to build up high-energy sugar molecules is

available from „the seawater pool of bicarbonate and metabolically regenerated carbon di-

oxide“. The high-energy fixed-carbon-products are then either trans- and allocated for the

coral`s use or used to cover the zooxanthellae’s own energy demand for respiration and

12

growth. Translocated carbon can be used for biomass built-up and might be released as dis-

solved organic carbon which can be in turn respired by other reef biota (Muscatine 1990). In

the process of calcification „fixed, respired carbon is incorporated into skeletal carbonate“

(Pearse in Muscatine 1990).

3.1.2 Energy-fluxes and relative closeness

To get an overview on the above mentioned components of the coral reef ecosystem and

their interconnectedness, we created a model mapping interactions between system`s com-

ponents in a strongly simplified way.

The vensim-model below shows major components of the coral reef ecosystem and their

interactions, evaluation each connection between two components in either positive or neg-

ative influential impacts.

Figure 4: Vensim model of major system`s components and its interactions. Red arrows designate negative influences while green arrows show positive interdependencies. Major feedback loops are designated by positive/negative circling arrows. Furthermore, solar en solar energy and nutrient-inflow via currents is depicted with larger, straight arrows, designating „energy-inflow“, while „energy outflow“ is depicted in form of roaming fish.

13

As can be seen in Figure 4, corals play a fundamental role for the energy-supply and there-

fore flourishment of the system. Due to their ability as a host to incorporate zooxanthellae,

they are able to provide large amounts of fixed-carbon-compounds to the ecosystem which

were fixed in an autotrophic way by their symbionts. As corals are closely linked to zooxan-

thellae as well as the calcareous substrate they live on, any disturbance of these two funda-

mental component`s will have direct consequences on the energy-balance of the whole eco-

system. A dependency between the density of corals and the presence of microbial popula-

tions has also been observed (1993). Corals are as well as excellent example of intra- and

interspecific interaction, as high competitive pressure for solid substrate occurs (Lang &

Chornesky 1990, Sorokin 1993).

The coral reef ecosystem shows a very high level of interconnectedness and closeness.

Due to their high autotrophic production (Sorokin 1993), coral reefs can be seen as high-

level energy stocks, influencing their adjoining systems via outwards directed energy fluxes.

„The export of organic matter and combined nitrogen“ (Sorokin 1993), for example in form

of fish and other organisms, roaming between reef and off-reef ocean domains is an exam-

ple of the coral reef ecosystem’s positive influence upon the ocean (Sorokin 1993) as a sys-

tem of higher order. Another aspect of the coral reef`s significant influence upon systems of

higher order is the outflow of lime sediments into the surrounding ocean and its influence

on oceanic sediment composition (Sorokin 1993).

The biomass production within the coral reef system can be regarded as „ actually inde-

pendent of the nutrient concentration in surrounding waters“ (Sorokin 1993).

The symbiosis between hermatypic corals and zooxanthellae is crucial to the existence of the

whole coral reef ecosystem, as it provides the main energy-inflow into the system from

which other ecosystem-components profit and on which they inevitably depend.

Therefore, light energy and the consequential storage of this energy in chemical carbon-

bonds can be recognized as the main energy source for the system, with smaller inflows of

organic nutrients via currents from the out-reef ocean realms.

While the coral reef ecosystem is a highly independent system regarding its self-generated

autotrophic energy-supply which is the base for the florishment of its prominently diverse

biocenosis, it forms at the same time nested sub-systems within systems of higher order.

14

The lime reef construction itself for example „represents an important geomorphological

element of the sea floor in tropical regions“ (Sorokin 1993) and with that is part of the high-

er-order ocean system or other possibly circumscribable larger scale systems.

The coral reef ecosystem is in many ways directly dependent on their surrounding environ-

ment, which is in terms of direct interaction the „ocean“ as a system of higher order. The

calcium carbonate molecules abundant in the sea water are indispensable for the reef struc-

ture itself and are therefore a system`s component of highest priority on which all other

reef-biota and -abiota depend. Changes in the density of biogenous Calcium carbonate will

in turn have all-embracing consequences on the whole coral reef ecosystem.

On the other hand the reef provides the prerequisites for multiple systems of lower order to

exist and flourish as nested systems within the coral reef. The sheltered lime-stone structure

in interaction with its biotic inhabitants creates an unique microclimate which provides shel-

tered space for reproduction for large numbers of organisms participating in „predictable

mass spawning events“ (Harrison & Wallace 1990). All these are emergent properties of the

coral reef ecosystem. The unique microclimate, which provides appropriate habitat for lar-

vae to settle on the solid substrate as well as for many organism which normally live off-reef

but roam in to reproduce, emerges from the multiple influences each organism living in the

ecosystem causes to its environment.

Coral reefs might be considered as „high-energy-islands“ building hotspots of biodiversity as

nested systems within the comparably nutrient-poor water body of the surrounding envi-

ronment – the ocean as a system of higher order. While the buildup of biomass is only possi-

ble when more energy is available to the growing organisms than is needed by them to

maintain their metabolic basic requirements (D’Elia & Wiebe 1990), the importance of the

autotrophic acquisition of high-energy molecules becomes clear, as well as the high level of

independency coral reef ecosystems possess.

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3.2. Human Influences to the Coral Reef System

Humans always interact with their environment, so do they with the coral reef system.

Hence this very efficient and well-working system is “opened” by humans because there is a

lot of interaction between the human system and its activities and the coral reef system. In

Figure 5 you can see how human activity is influencing coral reef systems. Due to this large

impact we want to address a whole chapter to human influences to the coral reef system

and explain all interactions in detail in the following subchapters.

Figure 5: Model of how the human system influences the coral reef ecosystem; made by Veronika Winkel and Carina Zell using “Vensim”, 3.11.2011

For the coral reef system interaction with the human system means a loss in efficiency be-

cause a lot of system components cannot work properly anymore and have to recover or to

be repaired which costs energy. The input of additional energy from humans in forms of nu-

trients and heat and the outtake of energy in forms of fish and carbonate is in most cases

not beneficial to coral and is likely to lead to their destruction. Normally, coral reefs are not

too vulnerable and can recover from destruction but the human top-down interactions are

often too frequent and intense so coral reefs cannot cope with these strong alterations.

16

Humans on the other hand benefit from coral reefs and their ecosystem services; wanted or

unwanted they use the emerging properties of the coral reef and profit from them.

For example, 30 million people, all living either on islands or at the coast, fully depend on

coral reefs in terms of food and income (Gomez et al. 1994, Wilkinson 2004). According to

TEEB (2010), even half a billion people make their living with coral reefs but are, in terms of

food, not just dependent on them. Additionally, a huge number of other people also profits

from coral reefs like tourists and people needing medical treatment (UNEP-WCRC 2006).

Some scientists and well-known institutions like UNEP and the WRI calculated the economic

value of reefs; this is described in the first following subchapter.

To a certain degree, human interaction with and influence on coral reefs may be sustainable,

meaning that internal cycles are just disrupted a bit but can recover and continue to work

more or less normally. It is always a question of the degree of influence – like the degree of

fish taken out of the reefs, the degree to which additional nutrients and sediments are put in

or the degree to which carbon dioxide is added to the atmosphere – and also a question of

the speed of change (Buddemeier, Kleypas & Aronson 2004). Most human activities are very

intense and increasing fast so humans are altering coral reef systems in a non-sustainable

way and causing large damage (Buddemeier, Kleypas & Aronson 2004, Millennium Ecosys-

tem Assessment 2005, UNEP-WCRC 2006, TEEB 2010). The damages to coral reefs caused by

humans are described in the second following subchapter and future predicted impacts are

described in the third one. In the fourth subchapter, management strategies for coral reefs

are presented and it is described how they try to combat human influence.

3.2.1 Emergent Properties of the System as Ecosystem Services

Besides their services to marine organisms like recycling nutrients and providing food, shel-

ter and nursery habitat (Buddemeier, Kleypas & Aronson 2004), coral reefs also play a major

role in a lot of ecosystem services to humans. These non-intended but favorable emergent

properties for humans can even be valued with a prize (see Constanza et al. 1997, Cesar,

Burke & Pet-Soede 2003, UNEP-WCMC 2006, TEEB 2010). The Millennium Ecosystem As-

sessment report (2005) defines four categories for the different services: regulating, provi-

sioning, cultural and supporting. In the following subchapters, the services of the three cate-

gories humans can profit directly from are shortly described and their economic values, as

17

stated in the above mentioned papers and reports, are given directly or in the “summary”

subchapter.

Regulating (Coastal Protection and Erosion Prevention)

Reefs are able to protect coastal areas from waves and storms, thus act as natural breakwa-

ters (Buddemeier, Kleypas & Aronson 2004). They can absorb between 70 and more than 90

per cent of wind-generated wave energy, depending on their characteristics and health.

Their ability to protect coastal areas from storms or tsunamis is less good because they have

a much larger force and affect the whole water column, not just the surface waters. Anyhow,

also the force of storms and tsunamis is weakened by coral reefs with the effect that reefs

themselves suffer significantly from destruction (UNEP-WCMC 2006).

Berg et al. (1998) estimated for Sri Lanka, that one square kilometer of reef can, per year,

protect 2000 square kilometers from erosion. If the reef is lost, costs will arise from the con-

struction of artificial breakwaters and the restoration of eroded beaches.

Provisioning (Fishery and Pharmaceuticals)

Although corals just cover 1.2 per cent of the world’s continental shelfs, they provide habitat

for about one to three million species, with more than a quarter of all marine fish species

(Allsopp et al. 2009). So there is a high potential for fisheries: Depending on the value of the

fish, each square kilometer of coral reef is potentially worth 15,000-150,000 dollars per year.

But also for non-commercial use coral fish are important, for example in the Philippines

there are about one million fishers who sustain their livelihood directly with coral reefs, get-

ting most proteins from eating their self-caught fish (UNEP-WCMC 2006).

The aquarium trade also makes up for large revenues from coral reef fish as they can often

be sold more expensive than food fish. In Sri Lanka, around 50,000 people profit directly

from selling aquarium fish, thereby earning about 5.6 million dollars (UNEP-WCMC 2006).

Coral reef species have proven to contain some pharmaceutically active compounds which

can be used for HIV treatment and as a painkiller. Furthermore, researchers believe that

there is potential to find more substances which can be used as pharmaceuticals like cancer

drugs (UNEP-WCMC 2006).

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Cultural (Tourism)

Tourism is the largest industry in the world. Especially coral reefs attract a lot of tourists and

account for huge revenues from diving and other tourism activities. For example, incomes

from the whole tourist sector in Egypt make up eleven per cent of the country’s GDP (UNEP-

WCMC 2006). For Hawaii, the annual recreational value of one Marine Management Area

including a coral reef was calculated to be up to 35 million dollars (Millennium Ecosystem

Assessment 2005). For the Caribbean, a loss from dive tourism revenue of two to five per

cent is predicted if the reef health continues to deteriorate (Burke & Maidens 2004).

Summary

Although it is quite difficult to calcu-

late the monetary value of all ecosys-

tem services of coral reefs adequate-

ly, the value of a square kilometer of

coral reef, accepted by a lot of scien-

tists and organizations like UNEP, lies

between 100,000 and 600,000 US

dollars, calculated by Cesar, Burke &

Pet-Soede (2003) and Constanza et

al. (1997). In Figure 6 there is an

overview of the most valuable ecosystem services according to Cesar, Burke & Pet-Soede

(2003).

Especially the economies of small island states are dependent on income and services from

coral reefs. In Indonesia and the Philippines reef degradation by blast fishing, overfishing and

sedimentation is predicted to account for a net economic loss of at least 2.5 billion US dol-

lars in 20 years per country (Burke, Selig & Spalding 2002). In the whole Indian Ocean, the

total cost of damages over the same period of time is estimated to be at least 608 million

dollars but up to 8 billion dollars if tourism, employment, fishery and coastal protection are

severely affected (Millennium Ecosystem Assessment 2005).

Figure 6: Economic value of the main ecosystem services of coral reefs, according to Cesar, Burke & Pet-Soede (2003)

19

3.2.2 Interaction between Humans and Coral Reefs

Coastal areas are especially affected by humans because the population density there com-

pared to inland population density is 2.6 times larger with nearly 50% of the world’s large

cities (having at least 500,000 inhabitants) being located not more than 50 kilometers from

the coast (Millennium Ecosystem Assessment 2005).

There are different monitoring programs assessing of how severely humans have so far af-

fected coral reefs. Burke, Selig & Spalding (2002) estimate that 88 per cent of the South-East

Asian reefs are threatened by human activities, most of them at high or very high risk. Wil-

kinson states in his “Status of the World’s Reefs Report” (2004) that some 30 percent of all

reefs are already seriously damaged and that 60 per cent could be lost by 2030 (see also Fig-

ure 7). In the Millennium Ecosystem Assessment report (2005) it can be read that about 20

per cent of all coral reefs were already lost by now. Buddemeier, Kleypas & Aronson (2004)

name this a „coral reef crisis“.

Figure 7: Overview of lost and threatened reefs by region, from Wilkinson (2008)

Anthony et al. (2011) divide anthropogenic disturbances into two main categories which are

“major global threats” and “local-scale disturbances”. Buddemeier, Kleypas & Aronson

20

(2004) categorize the threats to coral reefs in “climatic and nonclimatic stresses”. Both defi-

nitions fit together quite well as global threats such as global warming, coral bleaching, acidi-

fication as well as sea level rise, all triggered directly or indirectly by an increase in atmos-

pheric CO2 concentration, are climatic stresses. On the other hand, local-scale disturbances

such as nutrient loading, contaminant input, fishing, invasive species, diseases, sediment

loading, coastal zone modification, mining and tourism are nonclimatic stresses. Other

threats to coral reefs like ocean circulation changes, storms and changes in precipitation

patterns cannot be categorized that easily because they appear due to climatic reasons but

only have a local impact. Another difference between the threats is that some are chronic

and some are acute meaning that some cause gradual environmental degradation over a

long period of time while others cause rapid damage but occur only during a short time.

Normally, coral reefs can recover from acute damages but if they are additionally affected by

chronic stress, they are less likely to recover (Buddemeier, Kleypas & Aronson 2004). All

mentioned human impacts are explained in the following paragraphs according to the above

mentioned categorization of Buddemeier, Kleypas & Aronson (2004).

Climatic Change Stresses

Climatic Change Stresses are the ones which are either caused directly by an increase in at-

mospheric CO2 concentration or by indirect effects of CO2 like global warming, glacier melt-

ing and increased evapotranspiration.

Acidification

The ocean absorbs about one

third of the atmospheric car-

bon dioxide. This leads to an

increase in ocean acidity, thus

a lower pH value because the

absorbed carbon dioxide mol-

ecules react with water to

form carbonic acid (H2CO3)

but this state is not stable so Figure 8: Ocean acidification and coral reef buffering / dissolution of carbonate substrate, Hoegh-Guldberg et al. 2007

21

the carbonic acid dissolves to bicarbonate (HCO3-) and a proton (H+) which makes the water

more acidic. About 85 per cent of the carbonic acid dissolves into bicarbonate, the other 15

per cent further dissolve from bicarbonate into carbonate (CO32-) and another proton, again

leading to an increase in acidity (Buddemeier, Kleypas & Aronson 2004, see Figure 8).

Since industrialization the pH has dropped from 8.2 to 8.1 which at first does not seem to be

much but it actually is because the pH is given on a logarithmic scale, which means a change

of 0.1 in pH is a 30 per cent difference in acidity. Additionally, surface ocean pH is already

very low at the moment, it has probably not been this low for more than 20 million years,

certainly not for the last 800,000 years (Wilkinson, 2008).

Reefs act as natural buffer systems for oceans, so they are able to slow down global change

processes by neutralizing the water: When the amount of protons increases, calcium car-

bonate, the molecule reefs are made of (CaCO3), dissociates into a calcium ion (Ca2+) and a

carbonate ion (CO32-). The carbonate ion will then merge with the proton to neutralize the

acid and form bicarbonate and also other available carbonate ions will from bicarbonate

with a proton. Although this process is good for keeping the acidity of the ocean water low,

it has severe consequences for coral reefs because they are dissoluted and the carbonate

needed to build up reefs is no longer available (Kleypas et al. 1999). But coral reefs need the

calcification process to counteract erosion, to be able to compete for space with algae and

to maintain a stable and dense skeleton which is important to withstand storms and bioero-

sion and to provide coast protection (Buddemeier, Kleypas & Aronson 2004). For one coral

species in the Great Barrier Reef it was shown that a reduction in growth rate of 20 per cent

within a 16-year time period occurred due to acidification. Furthermore, if corals have to

invest a lot in their structure, they cannot put as much energy in reproduction anymore

(Hoegh-Guldberg et al. 2007).

Not only corals get problems with acidification, also coralline algae which are very sensitive

to pH. These algae are a key substrate for corals to grow on so coral recruitment is also af-

fected through a reduction in coralline algae (Hoegh-Guldberg et al. 2007). In general, re-

duced calcification rates will lead to a shift in species composition and increase non-

calcifying organisms (Kleypas et al. 1999).

22

Global Warming and Coral Bleaching

Carbon Dioxide in the atmosphere not only causes an increase in global mean temperature

but also an increase in sea surface temperature. It has increased by 0.7°C during the last cen-

tury (Wilkinson 2008). This will on the one hand make other areas potentially accessible for

corals, the threshold for tropical reefs is 18°C, and could lead to an expansion of coral reefs

into higher latitudes. But it will on the other hand endanger reefs situated in already very

warm tropical waters because they are more likely to bleach (Buddemeier, Kleypas & Ar-

onson 2004).

A bleaching event occurs when the local sea surface temperature exceeds the average tem-

perature of the hottest months by 0.5–1° Celsius for one month (Millennium Ecosystem As-

sessment 2005). During years when extreme bleaching events occurred, there have always

been El Niño or La Niña events which cause temperature anomalies. So if there is an El Niño

event in the season with the highest temperature anyway plus global warming, coral bleach-

ing is very likely to occur (Buddemeier, Kleypas & Aronson 2004).

Buddemeier, Kleypas & Aronson (2004) state that widespread coral bleaching was not

known before the 1980s and in the UNEP-WCMC report (2006) one can read that there have

been significantly more bleaching events since 1975. In 1998 there was a severe coral

bleaching event which lead to a death of 16 per cent of the world’s coral reefs, there was

one in 2003/2004 in the North of Australia as well as in the Central Pacific, one in 2005 in the

Caribbean and in 2010 there was another one which for example killed 80 per cent of the

corals in the Indonesian province Aceh (Masters 2011).

When the water is too warm, zooxanthellae pigment proteins degrade leading to a break-

down of the photosynthetic system through incoming light. In reaction to that, zooxanthel-

lae produce reactive oxygen species which damage cellular structures. But as these radicals

threaten the coral tissue, the symbiosis between the coral and the zooxanthellae does no

longer work and corals expel their zooxanthellae. This makes the coral look white because

just the carbonate structure remains and the colorful zooxanthellae have gone (Sprenger

2009). Bleaching is not just a reaction to temperature, also other stresses like chemicals,

acidity or very intensive light can degrade pigments but bleaching is in most cases and on a

larger scale observed with temperature anomalies (Buddemeier, Kleypas & Aronson 2004).

23

Coral bleaching does not necessarily mean death of corals because they can host new zoo-

xanthellae after the bleaching. But during the time they are bleached they are more suscep-

tible to diseases and only have low rates of growth and sexual reproduction what makes

them vulnerable to being outcompeted by algae (Buddemeier, Kleypas & Aronson 2004).

There is the “Adaptive Bleaching Hypothesis” by Buddemeier & Fautin (1993) saying that

corals bleach to adapt to a new temperature situation. There are different clusters of symbi-

otic zooxanthellae which all have a different temperature optimum for doing photosynthe-

sis. So corals could, if the actual zooxanthellae are not working efficient anymore due to an

increased sea surface temperature, expel them and attract a different, more heat-resistant

cluster or have more than one cluster at the same time. This means that corals can maybe

actively adapt to different temperatures. Hughes et al. (2003) state, that “bleaching suscep-

tibilities may also change over time as a result of phenotypic and genetic responses”.

Coral bleaching always leads to a change in coral species composition because some species

are more susceptible to bleaching than others. After a bleaching there will be more massive,

slow-growing species because branched, fast-growing ones are more likely to bleach (Bud-

demeier, Kleypas & Aronson 2004).

An increase in temperature can also affect the calcification rate. The optimum temperature

for calcification is about 27°C so for corals in colder water global warming could be beneficial

in terms of an increase in the calcification rate. But for corals in tropical warm waters, warm-

ing will decrease the calcification rate (Anthony et al. 2011).

Others (Sea Level Rise, Precipitation Patterns and Storms)

Sea level rise is not always a threat, it can be positive for corals which already grew close to

the sea level and could expand upwards when the sea level rose. The main problem with a

rising sea level is that the erosion of coastal zones would increase as well which leads to sed-

imentation of coral reefs and the effects which will be described in the next subchapter in

the section “Sediment Loading” (Buddemeier, Kleypas & Aronson 2004).

Heavy rainfalls cause the same problems for coral reefs: more erosion and more sedimenta-

tion. And also droughts can lead to these problems because they trigger a less vegetated

land where the soil can more easily be eroded (Buddemeier, Kleypas & Aronson 2004). The

amount of additional freshwater through runoff and direct input is another threat to coral

24

reefs. Bates et al. (2008) state that this will significantly lower the reef quality and increase

susceptibility to diseases.

From time to time, reefs are partly destroyed by storms. In general, they are adapted to dis-

turbance from storms, so they start growing again and fish recolonize them after only one or

two years following a disturbance. Recovery time takes in general several decades. However,

there was a study in the Caribbean showing that a reef did not start to recover for at least

eight years after a hurricane decreased coral cover by 17 per cent (UNEP-WCMC 2006, Bates

et al. 2008).

Nonclimatic Stresses

Contrarily to the climatic stresses, the nonclimatic ones described in the following are espe-

cially influencing reefs on a local scale and are mostly caused by activities near the coast, so

their cause and impact relationship is more obvious than it is for climatic stresses. This also

increases the possibility to control and eradicate nonclimatic stresses (Buddemeier, Kleypas

& Aronson 2004).

Nutrient Loading and Contaminant Inputs

Coral reefs are affected by nutrient inputs such as nitrogen and phosphorus because they

promote algae growth what can finally lead to a shift towards algae-dominated reefs. Fur-

thermore, nutrients deplete available oxygen in the water, lead to an increase in phytoplank-

ton which makes the water less clear thus a smaller amount of light will reach the corals and

it promotes the growth of bioeroding species which weaken the carbonate skeleton of corals

(Hughes et al. 2003, Buddemeier, Kleypas & Aronson 2004). In 2004, the effects nutrient

input has on coral reefs could be observed quite well: There was a huge dust storm in Africa

which blew large amounts of minerals like iron into the Pacific, even up to Florida. In the

Caribbean, this lead to a bloom of toxic algae which affected the coral reef health (Millenni-

um Ecosystem Assessment 2005). Nutrients can also boost the population of coral predators

like the crown-of-thorn starfish which feeds on coral tissue. On the Great Barrier Reefs there

have been repeated mass breakouts which could be a result of agricultural run-offs or over-

fishing of starfish predators (Buddemeier, Kleypas & Aronson 2004, Sprenger 2009).

The amount of nitrogen in the water has globally increased by about 80 per cent and also

other nutrients are largely added to the sea for example by the discharge of sewage and by

25

agriculture through the use of fertilizers (Millennium Ecosystem Assessment 2005, Bud-

demeier, Kleypas & Aronson 2004).

Humans also add non-natural, toxic substances from industry to oceans that will kill corals if

the concentration is too high (Buddemeier, Kleypas & Aronson 2004). In 2010 for example, a

Chinese container ship crashed into the Great Barrier Reef and lost oil (Spiegel 2010).

Fishing, Invasive Species and Diseases

Fish abundance plays an important role within coral ecosystems. For example, parrot- and

rabbitfish control algae growth by feeding on them and triggerfish control sea urchin popula-

tions. Sea urchins are good to a certain degree because they prevent corals from being over-

grown by algae but they also cause bioerosion and thus reef degradation. A lot of fish being

good for the reef health are commercial fish we like to eat or are nice and colorful ones we

like to keep in aquaria (UNEP-WCMC 2006, Buddemeier, Kleypas & Aronson 2004). So over-

fishing can be a severe problem for corals if there are not enough fish left to protect them

from being overgrown by algae. Hoegh-Guldberg et al. (2007) report, that today there is al-

ready 64% more fished than is sustainable and that 15.600 square kilometers of reef were

needed to provide food for all humans with the predicted population growth. Looking at

overfishing, the characteristic of time delays inherent in most systems can be seen: If fish

with a long reproduction cycle are fished then their population will, after some time, sud-

denly decrease rapidly.

Especially in South-East Asia, people still do dynamite or cyanide fishing what is prohibited in

most of the world’s countries because it destroys a lot of corals and other, non-commercial

fish. Further destructive elements in fishing are anchors, small-mesh nets and trawling the

net on the sea floor causing physical damage to corals (Buddemeier, Kleypas & Aronson

2004, UNEP-WCMC 2006).

With globalization and long-distance transportation of goods the spread of species and

pathogens threatening corals has increased; they can for example be in ballast water of con-

tainer ships. Furthermore, global warming helps coral pathogens to reproduce (Buddemeier,

Kleypas & Aronson 2004). It has been proven that also bacteria from human feces can cause

coral disease. In the Caribbean, a certain bacterium responsible for some human infections

was also responsible for white pox among corals leading to their death (Sutherland et al.

2011).

26

A well-studied example for coral depletion after overfishing and disease happened in Jamai-

ca in 1983/84. Herbivores had been overfished for several centuries and there was just one

species of sea urchin left to control the algae cover of the corals. When a new pathogen at-

tacking this species of sea urchin occurred, the population collapsed leading to a soon phase-

shift from a coral- to an algae-dominated environment which has still not recovered to its

original or a similar state. This is also very bad for local fishers because just very little fish live

in an algae-dominated environment (Millennium Ecosystem Assessment 2005).

Sediment Loading, Coastal Zone Modification and Mining

Coastal development often goes together with land reclamation, construction activities,

shoreline protection and dredging, resulting in sediment being mixed into the water and

changes in coastal currents. Agriculture and deforestation are as well responsible for sedi-

ment loading to water and reefs because they lead to an increase in surface runoff and ero-

sion. This sedimentation causes a reduction in light available for zooxanthellae to conduct

photosynthesis and smothers corals. Smothering is bad for the corals because it costs energy

to get rid of the sediment, polyps have a harder time to feed and it reduces the chance of

new polyps to settle down because they need hard substrate (UNEP-WCMC 2006, Bud-

demeier, Kleypas & Aronson 2004, Riegl & Branch 1995).

According to Burke, Selig & Spalding (2002) 21 per cent of all reefs are threatened by sedi-

mentation and McCulloch et al. (2003) found out that sedimentation of the Great Barrier

Reef increased five to ten fold within the years 1750 till 1998 after the Europeans introduced

their agricultural methods to Australia.

Another threat to coral reefs is mining. Although forbidden in most countries, some people

are still doing it to use carbonate reef substrate as building material, especially on atolls

where almost no other building material exists (Wilkinson 2004).

Tourism

Diving and snorkeling tourism is increasing so is the impact of divers and snorkelers on coral

reefs. Barker & Roberts (2004) quantified this impact and found out, that divers without a

camera have 0.1 contacts with the reef per minute, the ones using a camera have 0.4 con-

tacts per minute and during night dives, there is even 1 reef contact per minute. Allison

(1996) measured for the Maldives that on the most impacted section, snorkelers broke off

27

7% of total coral cover in one month. Hawkins et al. (1999) state in their paper that abrasion

of corals by tourists could make them more susceptible to being affected by a disease.

3.2.3 Trends of Future Change

As explained in chapter 3.2.1, coral reefs are quite important ecosystems and provide a lot of

ecosystem services to humans. That is why a lot of studies were conducted to assess the

future of coral reefs, to predict how they will look like in the future and if they in general are

able to sustain their system facing all the above mentioned threats. Wilkinson (2008) pre-

dict, that within the next 40 years 35 per cent of corals could be lost even without taking

into account all impacts of climate change. But still, predictions are quite difficult to make as

there have never been comparable conditions of surface ocean chemistry and temperature

within the 50 million year history of modern corals (Buddemeier, Kleypas & Aronson 2004).

In the following paragraphs, the future predicted impacts of the already mentioned threats

to coral reefs are described.

Ocean Warming and Coral Bleaching

“Corals are vulnerable to thermal stress and have low adaptive capacity. Increases in sea

surface temperature of about 1–3°C are projected to result in more frequent coral bleaching

events and widespread mortality, unless there is thermal adaptation or acclimatization by

corals”. This statement in the IPCC Synthesis Report on Climate Change in 2007 (page 65)

shows that coral reefs will be one of the losers of climate change.

Even without an addition of more greenhouse gases into the atmosphere, global tempera-

ture would almost certainly rise by about another 1°C and bleaching events would increase

(Wilkinson 2008).

Additionally, some scientists say that El Niño events have increased and will increase in the

future in frequency and intensity what means that also bleaching events will become more

frequent and intensive (Stahle et al. 1998, Mann, Bradley & Hughes 2000, Rayner et al.

2000). Hughes et al. (2003) predict that bleaching will become an annual event in the Carib-

bean because the temperatures are already in the upper threshold for coral survival. This

would mean that corals were not able to recover between the bleaching events anymore.

Even though some evidence shows that not everything about global warming is bad, in the

end the negative effects always dominate the positive ones: Through the increase in sea sur-

28

face temperature realistic chances for new coral reef establishments arise at the coast of

South Africa, in Australia and in Southern China. But practically an expansion will be difficult

due to factors like cloudy water, river deltas with a lot of nutrient and sediment input and

cold currents. Furthermore, human activities at the coast make it very difficult for corals to

establish so the potential positive effects will quite certainly not (over-)compensate the neg-

ative effects coral reefs face (Buddemeier, Kleypas & Aronson 2004).

Some people argue that warmer than present temperatures also occurred in the past, like in

the Mid Holocene. But in these times there were no human activities at the coast what

makes it very difficult to compare the past to the future. Due to human activities like de-

scribed above, the chances of corals to settle at new spots and to withstand multiple stress-

es at their current location are very low today (Buddemeier, Kleypas & Aronson 2004).

Acidification

The carbon dioxide concentration in the ocean is

predicted to reach two times its pre-industrial level

within 40-50 years from now. This will lead to a fur-

ther acidification of the seawater and a drop in pH

by another 0.2 units (Wilkinson 2008). Calcification

rates are predicted to decrease by 17-35 per cent

compared to pre-industrial rates within this century

(Kleypas et al. 1999, see Figure 9).

This is due to the fact that with an increase in acidi-

ty the amount of carbonate, which is needed for

calcification, decreases from a 15 per cent share of

ion species to a 10 per cent share (Buddemeier,

Kleypas & Aronson 2004). In Figure 10 these chang-

es can be seen.

If carbonate saturation drops below 200µmol/kg,

the decrease in carbonate material could be larger

than the build-up of new material thus reefs would

decrease in volume. The carbon dioxide threshold

Figure 9: Projected changes in reef calcification rate based on average calcification response of two species of tropical marine algae and one coral (Kleypas et al. 1999)

29

for this concentration of carbonate lies between 450 and 500 ppm according to Hoegh-

Guldberg et al. (2007), see also Figure 11. Evidence for him is that the fossils from the Trias,

when carbon dioxide levels were five times as high as today, contain no calcium carbonate.

Acidification plays a more important role in cold waters as they take up more carbon dioxide

from the air than warm water. This effect will more than overcompensate the benefit coral

reefs in colder regions have from global warming; they will be more threatened from a de-

crease in the calcification rate (Buddemeier, Kleypas & Aronson 2004).

Figure 10: Changes in the speciations of the carbonate ions due to an increased CO2 level in the atmosphere (from Wil-kinson 2008)

Figure 11: Thermal and carbonate thresholds for coral-dominated environments (Hoegh-Guldberg et al. (2007))

30

Nutrification

Nutrification of coastal waters is predicted to increase in the future especially in developing

countries because there, just little regulations and knowledge about the impacts of nutrient

loading exist. Three out of the four scenarios calculated within the Millennium Ecosystem

Assessment report project that the global flux of nitrogen to coastal ecosystems will increase

by 10–20% by 2030 with a medium certainty. The result will be toxic algae blooms, human

health problems, fish kills and habitat damages (Millennium Ecosystem Assessment 2005).

Other Trends of Change

Especially in the tropics, the frequency and intensity of heavy rains and storms will increase

thus increasing the sediment and nitrogen loading to coral reefs, increasing the direct de-

struction and giving them less time to recover (Buddemeier, Kleypas & Aronson 2004, Tren-

berth 2005). As described above this will lead to a reduction in calcification rates, an in-

crease in susceptibility to diseases, a phase-shift towards algae-dominated environments

and finally coral reef mortality.

In the Third Assessment Report of the IPCC, a sea level rise of 0.1 to 0.9 meters is predicted

until 2100, so between one and four millimeters per year (Houghton et al. 2001). The net

upward growth of reefs is about 4 mm per year, taking into account erosion. So reefs can

only keep pace with a sea level rise of not more than 4 mm per year otherwise they will suf-

fer from a lack in light availability (UNEP-WCMC 2006).

Summary

Above, just single stresses and their effects are described but in reality there will be several

of them at the same time effecting coral reefs. The most urgent question is where tipping

points within the complex system are and when the adaptive capacity will be reached before

there is a shift towards algae-dominated reefs (Hoegh-Guldberg et al. 2007).

In contrast to reefs in other areas, the reefs in South-East Asia will be in favor because they

cover a large area, have a good water flow through it and have a large biodiversity thus it is

more likely and easier for polyps from neighboring reefs to settle there. So even if there is

destruction in one area within South-East Asia, the surrounding reefs will help this area to

recover faster (Buddemeier, Kleypas & Aronson 2004).

31

3.2.4 Management Strategies

Reefs are normally not dependent on humans, they would be even healthier without them,

but to restore, recover and to be protected from future destruction, they are now very much

dependent on humans.

There are different ideas on how to manage coral reefs: Installing Marine Protection Areas

(MPAs), no-build areas, coastal erosion control, low-impact aquaculture, Integrated Coastal

Management (ICM), laws and regulations for the construction industry, sustainable fishery

and sustainable tourism (UNEP-WCMC 2006, Wilkinson 2008), some of these measures are

described in more detail in the following subchapters. Furthermore, there needs to be re-

search on the adaptive capacity of corals, on their recovery mechanisms, on breeding re-

sistant varieties and on monitoring (Buddemeier, Kleypas & Aronson 2004, Hoegh-Guldberg

et al. 2007).

To put reef management into action several cooperations between states and regions with

coral reefs have formed. There is for example the Coral Triangle Initiative, the Micronesia

Challenge and the Caribbean Challenge. Some areas including coral reefs are even within

World Heritage Areas to protect them.

Management of coral reefs and prevention of coral reefs is worth it because repairing dam-

ages of reefs after destruction is difficult and quite expensive. This is due to the fact that the

processes leading to a healthy and diverse reef ecosystem are not fully understood yet and

restoration always takes its time. UNEP calculated that the cost per square kilometer to

manage a marine protected area (MPA) is just 0.2 per cent of the global value of one square

kilometer of intact coral reef that would be lost (UNEP-WCMC 2006).

Marine Protected Areas

Wilkinson (2004) proved in his study that coral reefs within protected areas or remote areas

with limited human impact recover faster from disasters such as bleaching events. Following

the proposal of the Convention on Biological Diversity, the states agreed at the World Sum-

mit in 2002 on reducing the loss in biodiversity and on “establishing networks of marine pro-

tected areas (MPAs) encompassing 20% of marine resources by 2012” (see Wilkinson 2008).

In 2004 there were 660 MPAs containing coral reefs worldwide but Burke & Maidens state in

their report (2004) that most of them within the Caribbean are not effectively managed.

32

Sustainable Fishery and Mariculture

The FAO has a “Code of Conduct for Responsible Fisheries” which includes among others the

elimination of destructive fishing gear, the establishment of no-take areas and management

plan. Additionally, breeding fish in maricultures can reduce overfishing (see UNEP-WCMC

2006, Sprenger 2009). The management of fishing is probably the most important compo-

nent in reef management because the abundance of fish feeding on algae is directly related

to a phase shift, so if corals are overgrown by algae or not (Hughes et al. 2007).

Diver supervision

Reducing the damage of divers and snorkelers is also a question of management. Barker &

Roberts (2004) found out that people do not change their behavior when there is just a no-

tice about not touching corals included in the briefing right before the dive starts. People

only had fewer contacts with corals when dive leaders intervened so Barker & Roberts con-

clude that divers must be closely supervised to prevent corals from damage.

Artificial reefs

There are a lot of projects going on to establish reefs on artificial substrate either to attract

tourists, as artwork or just to get rid of some used-up stuff it seems. In Cancún, Mexico, in

2010, the British artist Jason de Caires Taylor installed his exhibition “the silent evolution” in

the sea which consists of 400 live-sized figures. He says that they are made out of material

promoting coral growth and shall act as habitat for a variety of plants and animals (Smets

2010).

In Florida in the 1970s, two million old car tyres were dumped in front of the coast to estab-

lish a new reef and attract tourists. But fish and corals did not like them so the wheels had to

be taken out for a lot of money after a few years (Kremp 2011). In 2006 there was a new trial

in front of Florida’s coast: They dumped the US aircraft carrier USS Oriskany which was used

before in the war in Vietnam. This is until now the largest potential artificial reef. In Dela-

ware, they used the old underground trains of New York and in Thailand they put garbage

trucks and tanks into the water to establish reefs (Kremp 2011).

30 years ago a German architect developed the “biorock-method” with which artificial reefs

can be made more effective. He uses a metal cage and sends a direct electric current

through it so there is electro deposition of minerals like calcium carbonate and magnesium

33

hydroxide forming limestone. Coral polyps are more likely to settle on them (UNEP-WCMC

2006, Hilbertz 2009).

There are also trials to breed corals on tiles: coral fragments are transplanted from living

corals and glued onto the tiles to start growing there (UNEP-WCMC 2006).

3.2.5 Summary

One single species – homo sapiens – can have a very large impact on coral reefs as we saw in

this chapter. It is difficult to predict what will happen to coral reefs in the future because

“Projected increases in carbon dioxide and temperature over the next 50 years exceed the

conditions under which coral reefs have flourished over the past half-million years” (Hughes

et al. 2003).

Coral reefs always seem to be the part which is influenced but never influences for example

the human system. Some scientists recently stated that coral reefs can be the driving force

of global change thus influencing the human system (Donnadieu et al. 2011). During the

Mesozoic there have been several 1 million year-long cooling periods. During or before these

periods carbonate platforms vanished which lead to an increase in calcium ions. This made

the pH value rise thus increasing the concentration of carbonate ions and decreasing the

concentration of carbonic acid. Due to that there was a “massive dissolution of atmospheric

carbon dioxide into seawater” which lowered its concentration in the air inducing a global

cooling. The scientists result that there is a “high sensitivity of the Earth system to perturba-

tions in carbonate system deposition”.

But before this happens there will be strong alterations to the coral reef system through new

interactions as described in the chapters before. The original system cannot work efficient

and self-sustaining anymore but has now large in- and outflows of energy. It gets vulnerable

through multiple stressors and coral-dominated environments are not sustainably there be-

cause the likeliness of algae-dominated environments increases. Furthermore, coral reefs

become dependent on the human system concerning management and recovering efforts.

34

4 Discussion

In this chapter we want to discuss a few aspects of the results, combine single findings and

state our own opinion.

4.1 The Natural System

Coral reefs are amongst the most species-rich ecosystems on our planet (Lutz-Arend 2005).

Their productivity is 50-100 times higher than in the tropical ocean waters they are sur-

rounded by with zooxanthellae as a dominant primary producer, despite their nutrient-poor

ocean-environment (Sorokin 1993, Muscatine 1990).

HUISMAN and WEISSING (2001) discuss in their paper on „biological conditions for oscilla-

tions and chaos generated by multispecies competition“ population dynamics that might

occur when several species compete for abiotic essential resources. As they designate their

model as being „particularly relevant for phytoplankton communities [...]“ it seems applica-

ble for the coral reef ecosystem as well, as many different species compete for essential abi-

otic elements such as light, nitrogen and phosphor within the nutrient-restricted ocean-

environment.

The chaotic interactions within the food web might lead to higher flexibility and resilience of

the system, as nutrient-pathways are heterogenic and unpredictable and might therefore

Figure 12: Multispecies competition may lead to the phenomenon of „competitive chaos“ as shown above.

35

easier adapt to changes in nutrient supply or changes in competitive pressure through

changes in species composition.

Beside the extraordinarily and permanently high primary production (Sorokin 1993) they

also show „a high efficiency of the use of primary energy resources in the heterotrophic pro-

cesses“ which lead to extremely dense populations (Sorokin 1990, 1993).

The „recycling of nutrients within a system is a mechanism to retain nutrients and increase

primary production“ (D`Elia & Wiebe 1990) and might contribute to the coral reef system’s

property of being „generally self-maintaining“ (Sargent & Austin 1954). Still „the extremely

high production of reef systems at a low nutrient supply […] remains one of the most excit-

ing enigmas in marine biology“ (Sorokin 1990).

After KAUFFMANN (1995) „The complex whole, in a completely nonmystical sense, can often

exhibit collective properties, „emergent“ features that are lawful in their own right.“

The extraordinary and not yet fully understood energy- and nutrient efficiency of coral reef

ecosystems promoting their remarkable primary production can therefore be seen as an

emergent property of the system itself.

4.2 Human influences

It seems to be paradox: The people most dependent on a system are often the ones most

destroying it thus creating their own vicious circle. With coral reefs, there is exactly this

problem. In the poor countries where people often live from fish they catch in coral reefs,

methods like dynamite fishing are still used (Buddemeier, Kleypas & Aronson 2004). Educa-

tion and a better understanding of the system’s functioning and interconnections would be

helpful to understand for example the effects fishing methods like this have on the ecosys-

tem. So management strategies should always have the component of education included.

In general, management strategies are quite important to counteract the decline in coral

reefs. Anyhow, some do not seem to really help and do not get down to the root of the

problem. For example there is a lot of energy needed for the cages with “biorock-method”,

additionally algae and other unwanted species have to be removed regularly. The technique

with which corals should grow on tiles is quite expensive and will never be suitable for large

areas as well (UNEP-WCMC 2006). When ships, carriers and other stuff are dumped into the

ocean this can also be harmful for corals. In Honolulu, anemones spread on a sunken ship

36

thereby reducing biodiversity and coral cover. Probably the anemones were promoted by

iron coming from the corroding ship (Löfken 2008).

Mariculture does not only show positive effects. A lot of organic material is released by the

bred fish which influences the marine habitat. Escaping invasive species and pathogens can

be problematic and affect the surrounding natural fish. Furthermore, these fish also need

food so the problem of overfishing is not solved (Sprenger 2009).

A mechanism to pay coral reef management seems to be fees from tourists and divers. Stud-

ies showed that most of them are willing to pay if they can preserve the wonderful reef they

see (UNEP-WCMC 2006, Burke & Maidens 2004).

37

5 Conclusion

Through this analysis we understood the coral reef system better and are now even more

fascinated of the complex self-sufficient nested system and its functioning.

Coral reefs are important ecosystems for biodiversity which provide services to us that can-

not only be expressed monetarily but are also immaterial. Normally, they are disturbance-

adapted but experiencing multiple anthropogenic stresses they are getting more and more

vulnerable with nobody really knowing when the adaptive capacity of them to sustain their

population will be reached.

Coral reefs are worth protecting them so management activities should be carried out wide-

spread and negative anthropogenic influence should be stopped immediately.

i

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