Marine Pollution Bulletin 71 (2013) 307–316

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Marine Pollution Bulletin

journal homepage: www.elsevier .com/locate /marpolbul

Anthropogenic marine debris in the coastal environment: A multi-yearcomparison between coastal waters and local shores

M. Thiel a,b,⇑, I.A. Hinojosa a,c, L. Miranda a, J.F. Pantoja a, M.M. Rivadeneira a,b, N. Vásquez a

a Facultad Ciencias del Mar, Universidad Católica del Norte, Larrondo 1281, Coquimbo, Chileb Centro de Estudios Avanzados en Zonas Áridas, CEAZA, Coquimbo, Chilec Institute for Marine and Antarctic Studies, University of Tasmania, Nubeena Crescent, Taroona, Tasmania 7053, Australia

a r t i c l e i n f o

Keywords:Anthropogenic marine debrisLocal shoresCoastal watersPlasticsSE Pacific

0025-326X/$ - see front matter � 2013 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.marpolbul.2013.01.005

⇑ Corresponding author at: Facultad Ciencias del MNorte, Larrondo 1281, Coquimbo, Chile. Tel.: +56 51 2

E-mail address: thiel@ucn.cl (M. Thiel).

a b s t r a c t

Anthropogenic marine debris (AMD) is frequently studied on sandy beaches and occasionally in coastalwaters, but links between these two environments have rarely been studied. High densities of AMD werefound in coastal waters and on local shores of a large bay system in northern-central Chile. No seasonalpattern in AMD densities was found, but there was a trend of increasing densities over the entire studyperiod. While plastics and Styrofoam were the most common types of AMD both on shores and in coastalwaters, AMD composition differed slightly between the two environments. The results suggest that AMDfrom coastal waters are deposited on local shores, which over time accumulate all types of AMD. Thetypes and the very low percentages of AMD with epibionts point to mostly local sources. Based on theseresults, it can be concluded that a reduction of AMD will require local solutions.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Anthropogenic marine debris (AMD) can be found in all majoroceans, reflecting widespread sources and post-entry dispersal.Sources of AMD can be from activities at sea, on the shore, or fromfarther inland. Activities that contribute AMD are tourism, agricul-ture, aquaculture, fisheries and industry (Golik and Gertner, 1992;Corbin and Singh, 1993; Nagelkerken et al., 2001; Claereboudt,2004; Fujieda and Sasaki, 2005; Oigman-Pszczol and Creed,2007). Large quantities of AMD are initially deposited on the shorebut can later be pulled into the sea by tides, wind or rain run-off(Nagelkerken et al., 2001). In coastal waters with large rivers animportant fraction of AMD comes from land-based activities,which can be far away from the coast (Williams and Simmons,1997; Galgani et al., 2000; Araújo and Costa, 2007; Shimizuet al., 2008; Neto and da Fonseca, 2011). Large amounts of AMDfrom land-based sources are also flushed into coastal waters byhurricanes, storms, or tsunamis (Cunningham and Wilson, 2003;Abu-Hilal and Al-Najjar, 2004; Ramachandran et al., 2005; Wora-chananant et al., 2007; Shimizu et al., 2008; Ribic et al., 2012a).Sea-based activities such as shipping, fishing, aquaculture or oil/gas extraction also contribute much AMD (e.g. Dixon and Dixon,1983; Vauk and Schrey, 1987; Dufault and Whitehead, 1994; Jones,1995; Haynes, 1997; Santos et al., 2005; Hinojosa and Thiel, 2009).

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ar, Universidad Católica del09776; fax: +56 51 209812.

After reaching the sea, some AMD will quickly sink and thusaccumulate in the areas where they first enter the sea (Galganiet al., 2000; Barnes et al., 2009; Mordecai et al., 2011). However,a large fraction of AMD will float at the sea surface and conse-quently may be transported away from its original sources (Win-ston, 1982; Benton, 1995; Aliani et al., 2003; Barnes and Fraser,2003). This AMD can float for extended time periods at the sea sur-face, during which it may cause substantial ecological harm, due toingestion or entanglement by sea turtles, seabirds or marine mam-mals (Gregory, 2009). Furthermore, floating AMD could potentiallytransport invasive species to distant areas where these species didnot previously occur (Barnes, 2002; Gregory, 2009; Astudillo et al.,2009). It is thus especially important to identify the sources andthe potential pathways of floating AMD.

After the initial arrival in the sea, several factors contribute tothe post-entry displacement of floating AMD. Wind, tides, wavesand ocean currents can carry floating AMD over long distancesfrom their original point of entry to the sea (Ryan, 1988; Haynes,1997; Aliani et al., 2003; Maximenko et al., 2012). After voyagesof variable extension, floating AMDs may finally sink, fragmentinto smaller pieces, or become deposited on the shore. The largeamounts of AMD on the seafloor (Mordecai et al., 2011) and thehigh proportion of plastics among this litter (Galgani et al., 2000;Koutsodendris et al., 2008) suggest that a considerable fraction ofAMD might sooner or later sink to the seafloor. However, manyplastics are known to float for long time periods and disintegrateinto ever smaller particles (e.g. Andrady, 2011). A large proportionof this floating AMD accumulates on shores around the world.

308 M. Thiel et al. / Marine Pollution Bulletin 71 (2013) 307–316

Sedimentary shores are generally considered important sinks forfloating AMD, which after stranding generally becomes trappedin/under sand or might be blown farther inland (Merrell, 1980;Williams and Tudor, 2001; Kusui and Noda, 2003). The role ofrocky shores in trapping floating AMD is less well known. Observa-tions from Eriksson and Burton (2003) suggest that on exposedrocky shores floating AMD might be battered into smaller pieceswhich can then be pulled back into the sea. Wave-exposed rockyshores functioning as grinding mills for AMD have also been sug-gested by Debrot et al. (1999) and Convey et al. (2002). Interest-ingly, few studies have compared the types and abundances ofAMD on sandy beaches and nearby rocky shores.

While AMD can be found throughout the world’s oceans, thehighest concentrations of AMD are often observed on shores closeto the main sources. This pattern has been reported repeatedlyfrom many shorelines around the world. For example, in IndonesiaAMD concentrations on local beaches are highest near the mainpopulation center, but decrease substantially at distances of 20–50 km (Uneputty and Evans, 1997; Willoughby et al., 1997), a sim-ilar situation to that reported for Caribbean beaches in Panama(Garrity and Levings, 1993). A close relationship between AMDabundances and population centers is often used to infer thatAMD on local shores comes from nearby sources (Gabrielideset al., 1991).

Another important indicator for the origin of AMD on the shoreis overgrowth by marine life. AMD heavily fouled by marine organ-isms is indicative of long floating times at the sea surface, andtherefore likely comes from distant sources (Benton, 1995; Frostand Cullen, 1997; Cunningham and Wilson, 2003). In contrast,AMD without fouling probably has spent only very little (or no)time at sea and is thus suggestive of very local sources. The litteritself can also serve as indicator for potential sources. For example,if a large fraction of floating AMD carries foreign labels, this is oftenused as indicator to infer sea-based activities, in particular ship-ping (Santos et al., 2005; Kei, 2005). The type of litter can also hintat the possible sources, e.g. plastic cups, beverage bottles, sun lo-tion and other items likely come from touristic activities on thebeach (e.g. Gabrielides et al., 1991; Nagelkerken et al., 2001).

Depending on the sources and the dynamics in the sea, the tem-poral patterns of floating AMD in coastal waters and on shores canbe highly variable. For example, on touristic beaches, the amountsof AMD are often highest during the summer months, the periodwith intense touristic activities (Gabrielides et al., 1991; Arizaet al., 2008; Martinez-Ribes et al., 2007; Portz et al., 2011). Stormsalso influence the amounts of AMD in local waters and on shores(Ryan, 1988; Gabrielides et al., 1991; Moore et al., 2002; Cunning-ham and Wilson, 2003; Browne et al., 2010; Ribic et al., 2012a).Wind-exposed beaches often have substantially higher amountsof AMD than wind-protected beaches (e.g. Debrot et al., 1999;Cunningham and Wilson, 2003). On South African beaches the den-sities of plastic debris were high in summer while at the same timethe densities in coastal waters were low (Ryan, 1988). Strong on-shore winds could sweep coastal waters clean while accumulatinglarge quantities of floating AMD on local beaches (e.g. Aliani et al.,2003). Indeed, on a Japanese beach, the abundances of AMD werestrongly correlated with onshore winds (Kako et al., 2010). Theseexamples suggest that the types and amounts of AMD on localshores might be closely related to those in adjacent coastal waters.However, few studies have systematically examined the abun-dances and proportions of AMD simultaneously at sea and on theshore.

Herein we surveyed AMD on the shores and in the coastalwaters of the Coastal System of Coquimbo (CSC), northern-centralChile. In this area sea-based (fishing and aquaculture) and shore-based (tourism) activities are common. The main goal of this studywas to reveal the spatio-temporal dynamics of AMD and to identify

the main sources of AMD in the study area. The objectives of thisstudy were (i) to identify the different categories of AMD in coastalwaters and on local shores, (ii) characterize the temporal dynamicsof AMD abundances and categories, (iii) determine the spatial dis-tribution (coastal waters versus shores, sandy versus rocky shores),and (iv) examine whether there is a relationship between AMD incoastal waters and on local shores.

2. Materials and methods

2.1. Study area and potential sources of litter

The Coastal System of Coquimbo (CSC) is located in northern-central Chile (Fig. 1). It extends over approximately 150 km dis-tance in north–south direction and comprises several smaller bays.There are several small fishing ports with a numerous fleet of arti-sanal fishermen (>600 small boats, each with 2–4 crew members),and seven industrial shrimp trawlers. In the southern part of theCSC there are extensive scallop cultures covering about 25 km2.In the city of Coquimbo there is a large shipping port that is fre-quently visited by cruise and container ships, especially duringaustral summer. The coastal population in the study area has about500,000 inhabitants. However, during the summer this populationapproximately doubles, because the villages and cities along theCSC are important touristic centers. Rivers in the study area aresmall and during normal years contribute little freshwater (andAMD) to the coastal system. However, during El Niño years, whenrainfalls are very intense, more AMD might be flushed into thecoastal waters through river and drainage runoff.

2.2. General sampling strategy

Seasonal sampling was conducted in the CSC during the years2002–2005 to determine the temporal and spatial composition ofAMD on local shores and in coastal waters.

Ship surveys (coastal waters): 12 seasonal ship surveys (12 tran-sects in the northern sector, and 10 transects in the southern sec-tor) were conducted in the CSC. All surveys were conductedbetween dawn and dusk because light was necessary to identifyAMD at the sea surface. During navigation a team of three skilledobservers surveyed the sea surface around the vessel. Two observ-ers continuously focused on the sides of the vessel reporting theobserved AMD items to the third observer who recorded the type,number, position and distance to the vessel. The perpendicular dis-tance of each item to the vessel was estimated using known dis-tances (e.g. width or length of vessel).

To estimate the total density of AMD, we used the strip transectmethod, based on the number of items seen, the perpendicular dis-tance to the vessel for each item, and the transect length (Thielet al., 2003). Density (D = items km�2) was calculated using the fol-lowing equation:

D ¼ n=ð2� ðw=1000Þ � LÞ

where n is the number of AMD observed, w is the maximum dis-tance perpendicular to the transect (here: 10 m), and L is the totallength of the transect (in km). The densities (D) for AMD were ex-pressed as the number of items per km2. A transect width of 10 mto each side of the vessel was considered, since previous samplingsof AMD had shown that this was a conservative estimate to preventobservation errors; any items seen beyond that distance were notconsidered in the calculations because their abundance most likelyis underestimated (see Thiel et al., 2003).

For the purpose of this study we evaluated ship transectsthrough the northern and southern parts of the study area sepa-rately (Fig. 1). In order to determine whether higher densities of

Fig. 1. Study area and sampled beaches. The main shipping ports are in Coquimbo; most of the smaller villages have fishing ports with small artisanal fishing boats;aquaculture activities consist of suspended scallop cultures.

M. Thiel et al. / Marine Pollution Bulletin 71 (2013) 307–316 309

AMD were found in the immediate vicinity to the shore, we alsodistinguished the nearshore (0–10 km) and the offshore (>10 km)zone where water depth is more than 500 m.

Beach surveys (local shores): In general, the shore sampling wasconducted within 2 weeks after the coastal water sampling. Be-tween Spring 2002 and Autumn 2005, a total of 10 seasonal sur-veys were completed. We surveyed one rocky shore and onesandy beach each in the northern (Punta Teatinos, 29�4902300S;71�1702500W) and southern part of the study area (El Frances,30�0601600S; 71�2203600W) (Fig. 1). AMD (all items <1 kg and/or <1 m) from the most recent drift line was collected and broughtback to the laboratory where it was identified, counted andweighed. Items >1 kg and/or >1 m in length or cramped betweenrocks were recorded and weighed (when possible) in situ. The den-sity of AMD on the local shores was calculated as the number ofitems per km1.

2.3. Identification of Anthropogenic Marine Debris categories

All items of Anthropogenic Marine Debris (AMD) were identi-fied and categorized according to the type of material into eightmajor categories (plastic, Styrofoam, metal, paper, fabric/fiber,glass, manufactured wood and organic matter). All AMD items inthose categories were counted and weighed. Additionally, AMDitems were classified according to their origin in ‘‘household’’and ‘‘fisheries and aquaculture’’ items. AMD items considered ashaving their origin in fisheries and aquaculture activities werethose clearly identified as being used in those marine activities

such as fishing lines, fishing lures, hooks, floats, plastic and Styro-foam buoys, plastic ropes, pieces of wetsuits, light sticks, oil and lu-bricant bottles, fishing nets, among others (e.g. Edyvane et al.,2004; Hess et al., 1999; Jones, 1995). Among household AMD weidentified plastic bags, food bags and wrappers, pieces of packagingStyrofoam, cans, beverage bottles, plastic pieces, toys, shoes,clothes, etc. (e.g. Gabrielides et al., 1991; Keller et al., 2010). Thisclassification was included to evaluate a potential relationship be-tween the main activities developed in the southern and northernparts of CSC and the type and/or density of AMD items found inthose areas.

2.4. Statistical analyses

For each shore type (rocky, sandy), coastal waters (nearshore,offshore) and sector (southern, northern) we determined the meandensity of all items, the mean number of different types of AMD(richness), and the mean dominance (Simpson’s k) based on all sea-sonal surveys. Differences in the composition of AMD categorieswere evaluated using a permutational analysis of variance (PER-MANOVA, 10,000 runs) and a posteriori tests, based on the Bray–Curtis index of similarity. AMD densities were transformed usingthe fourth root of the proportions of density in order to meet theassumption of homoscedastic variances. Differences were visual-ized through a 2D non-metric multidimensional scaling. The rela-tive contribution of each particular AMD category to differencesin composition was evaluated using a similarity percentage analy-

Fig. 2. Composition of AMD in nearshore and offshore coastal waters from thenorthern and southern sectors of the study area.

310 M. Thiel et al. / Marine Pollution Bulletin 71 (2013) 307–316

sis (SIMPER). Analyses were carried out using the free softwarePAST v. 2.12 (Hammer et al., 2001).

3. Results

3.1. Composition of AMD in coastal waters and on local shores

The proportions of the different items of AMD found in thisstudy are relatively similar between sandy beaches, rocky shoresand the sea surface in coastal waters (Table 1). Plastics dominatedboth on the shore as well as at the sea surface. The most commonplastic items were shopping bags, wrappers, ropes and pieces ofhard and soft plastic (>75%). Styrofoam reached high percentageson rocky shores and manufactured wood was commonly foundon both rocky shores and sandy beaches (Table 1). All other items,including glass and metal, were relatively rare, and only metal, pa-per, and fabric/fiber on rocky shores, and paper at the sea surfacereached slightly higher proportions (>2%). Organic matter, com-prising mainly fruits and vegetables (e.g. lemons and onions),was found in comparatively low proportions at the sea surfaceand on both types of shore.

On the sandy beaches, no clear differences were found in thecomposition of the AMD between the northern and southern partsof the study area, but on the rocky shores there were slight differ-ences in AMD composition between the northern and southernsectors, with Styrofoam and organic materials being comparativelyhigher on the southern rocky shores (Fig. 2). Also there were differ-ences in AMD composition between sandy beaches and rockyshores, with the proportions of Styrofoam and metal being com-paratively higher on the rocky shores (Fig. 2). Manufactured woodwas commonly found on all types of shores. The proportion of AMDwith clear signs of overgrowth by marine organisms was low(0.15%).

At the sea surface, the proportion of plastics was higher in thenorthern than in the southern sector of the study area, where Sty-rofoam reached comparatively high proportions. Also, the propor-tion of organic matter was higher in the northern than thesouthern sector. The composition of floating AMD was similar inthe offshore and nearshore waters of the northern sector but dif-fered in the southern sector, where AMD in offshore waters wasdominated by Styrofoam and plastics, while in nearshore watersplastics were by far the most common AMD (Fig. 2).

3.2. Temporal dynamics of AMD in coastal waters and on local shores

Densities of AMD were generally higher on sandy beaches thanon rocky shores (Fig. 3). There was an increase in AMD density overthe years and the highest densities were observed in the last sam-pling year (2005), with the exception of the northern sandy beach,

Table 1Categories and composition of AMD on sandy beaches, rocky shores and in coastalwaters of the Coastal System of Coquimbo between summer 2002 and autumn 2005.

Categories Shores Coastal waters

Sandy beach Rocky shore Sea surface

No. item % No. item % No. item %

Plastic 5742 83.1 791 68.8 225 84.3Styrofoam 204 3.0 187 16.3 13 4.9Glass 42 0.6 10 0.9 0 0.0Metal 53 0.8 36 3.1 1 0.4Manufactured wood 553 8.0 71 6.2 16 6.0Paper 108 1.6 26 2.3 7 2.6Organic matter 146 2.1 3 0.3 4 1.5Fabric/fiber 58 0.8 25 2.2 1 0.4

Total 6906 1149 267

where the highest density was already observed during the lastsurvey (spring) of the year 2004. AMD densities on sandy beachesranged from about 10 items km�1 up to >250 items km�1. On rockyshores the minimum densities of AMD were 9 items km�1 andmaximum densities were 138 items km�1. No seasonal trend wasobserved on either of the sampled shores. AMD comprised mostlyhousehold items, and items from fisheries and aquaculture activi-ties (ropes and buoys) usually did not exceed 22% on a given shoreand sampling date (Fig. 3).

Densities of floating AMD in coastal waters ranged from1 item km�2 to 130 items km�2 (Fig. 4). Maximum densities wereobserved in nearshore waters, but also in offshore waters high den-sities could be observed. No clear temporal trend was recognizablein either of the sampling sectors. Floating AMD comprised mostlyhousehold items such as plastic bags and food bags, but items fromfisheries and aquaculture activities were also common in thesouthern sector (Fig. 4).

3.3. Relationship between AMD in coastal waters and on local shores

The mean densities of AMD were higher on sandy beaches thanon rocky shores (Fig. 5a). Floating AMD was more abundant innearshore waters than in offshore waters (Fig. 5a). The mean rich-ness of AMD categories was substantially higher on the shore thanin coastal waters (Fig. 5b). The average number of different AMDcategories found on the shore was �6–7 on sandy beaches andup to 5 on rocky shores. In contrast, in the coastal waters on aver-age fewer than two different categories of AMD were found.Accordingly, the average dominance of AMD was lower on theshores than at the sea surface (Fig. 5c). AMD dominance wasslightly lower in nearshore waters where plastics dominated morethan in offshore waters. Interestingly, the AMD dominance incoastal waters was consistently higher in the southern sector.

The PERMANOVA revealed significant differences (p < 0.0001) inthe composition of AMD categories across study sectors and envi-ronments, where coastal waters differed from the shores (Table 2).Within coastal waters no significant differences were detected, butwithin shores, sandy beaches and rocky shores showed significantdifferences, independent of the sector. When data were pooled, dif-ferences between shores and coastal waters were more evident(PERMANOVA, p < 0.0001, Fig. 6a). The differences in compositionbetween coastal waters and shores were mostly driven by Styro-foam and manufactured wood (SIMPER >16%, Fig. 6b), whereasplastic was the AMD category contributing most to the similaritiesbetween those environments. Nevertheless, the marked differencein type composition of AMD between coastal waters and shores

Fig. 3. Density (items km�1) of AMD on sandy beaches and rocky shores from the northern and southern shores of the study area. Sampling was done seasonally from spring2002 until autumn 2005; � – no data available.

Fig. 4. Density (items km�2) of AMD in nearshore and offshore coastal waters from the northern and southern sectors of the study area. Sampling was done seasonally fromspring 2002 until autumn 2005; � – no data available.

M. Thiel et al. / Marine Pollution Bulletin 71 (2013) 307–316 311

was not detected when all the information was aggregated (see Ta-ble 1); the observed Bray–Curtis percent of similarity (58%) washigher than expected under a null random model (95% CI = 9–57%, 10,000 runs).

4. Discussion

4.1. Composition of AMD

The different categories of AMD collected during the entirestudy in the Coastal System of Coquimbo (CSC) were very similarbetween the shores and coastal waters. The proportions of AMDon the shores of the CSC differed from that reported for the entireChilean coast by Bravo et al. (2009), who found substantially high-er proportions of metal, and in particular of glass than observed inthe present study. This is most likely due to the different samplingmethods between the two studies. Herein we sampled AMD fromthe flotsam left behind after the last high tide. In contrast, the

study by Bravo et al. (2009) is based on transect samples perpen-dicular to the shoreline that include sampling stations betweenthe last tideline and the dunes. This is the area where most beachusers settle down, leaving behind also many items that do not floatat the sea surface, and where litter accumulates over time (Veland-er and Mocogni, 1999; Silva-Iñiguez and Fischer, 2003; Cla-ereboudt, 2004; Oigman-Pszczol and Creed, 2007). The samplingsreported by Bravo et al. (2009) were conducted on beaches nearcoastal cities and villages, which might receive higher numbersof visitors than the sandy beaches sampled in our study. Further-more, glass and metal might last longer in the upper zone of thebeach than paper and plastics, which are blown away from theupper beach by strong onshore winds (common along the Chileancoast), thus ending up in the dunes or behind the shoreline (Garrityand Levings, 1993; Cunningham and Wilson, 2003; Portz et al.,2011). The close similarity in AMD composition between localshores and coastal waters in the CSC further indicates that a largefraction of the floating AMD from coastal waters might relativelyquickly end up on local shores without any major sorting at sea.

Fig. 5. (a) Mean density (items km�2 or km�1) of total AMD, (b) richness of AMDtypes, and (c) dominance of AMD types on shore types (sandy, rocky) and coastalwaters (nearshore, offshore) from the northern and southern sectors of the studyarea. Also shown the mean values for coastal waters and shores aggregating valuesacross different environments. Bars indicate the standard errors associated. Eightdifferent AMD types were considered for the analysis: plastic, Styrofoam, glass,metal, manufactured wood, paper, organic matter, fabric/fiber. Data based on allseasonal surveys.

Fig. 6. (a) Ordination analysis, showing the first two axes of a non-metricmultidimensional scaling (nMDS) comparing the type composition of the AMDbetween coastal waters and shores. One outlier point excluded to improve thevisualization of the results. (b) Similarity percentage analysis (SIMPER) showing thepercent contribution of each AMD type to overall differences in composition.

312 M. Thiel et al. / Marine Pollution Bulletin 71 (2013) 307–316

This similarity, however, was only evident in the pooled data set(Fig. 6a), suggesting that AMD floating in coastal waters accumu-lates on the shores over time.

Plastics are almost always the dominant AMD on shores world-wide, where they often reach similarly high proportions asobserved herein (>50%) (Table 3). The main reason for this is theextensive use of plastic for a variety of purposes and its longpersistence in the marine environment (Derraik, 2002). In some

Table 2A posteriori tests (p-values with sequential Bonferroni correction) of a permutational analysstudy sectors. Significant values (p < 0.05) in bold.

Shores

Sandy Rocky

N S N

ShoresSandy N

S 0.1682Rocky N 0.0206 0.0001

S 0.0008 0.0001 0.7996

Coastal watersNearshore N 0.0001 0.0001 0.0004

S 0.0002 0.0001 0.0001Offshore N 0.001 0.0001 0.0004

S 0.0025 0.0009 0.0057

studies, other items (e.g. Styrofoam, metal or wood) were morecommon, most likely due to specific sources or local customs. Forexample, large quantities of Styrofoam were often observed inareas with extensive aquaculture installations (Fujieda and Sasaki,2005; Hinojosa and Thiel, 2009).

In the CSC, AMD from fishing and aquaculture debris reached�21%, while AMD derived from household items represented�79%. On the Caribbean coast of Panama household items domi-

is of variance (PERMANOVA) comparing the type composition of AMD across different

Coastal waters

Nearshore Offshore

S N S N S

0.00020.0001 0.62860.0008 0.948 0.66260.0015 0.9365 0.7928 0.8579

M. Thiel et al. / Marine Pollution Bulletin 71 (2013) 307–316 313

nated the AMD, while fishing and boating only comprised 3% ofanthropogenic litter (Garrity and Levings, 1993). On beaches fromthe greater Sydney region (East Australia), similarly low percent-ages of AMD from fishing activities were found (Cunningham andWilson, 2003). In contrast, in Oman, where user items comprisedalmost 70%, fishing contributed >25% of all AMD (Claereboudt,2004), a value very similar to those reported by Edyvane et al.(2004) for South Australia and by Hess et al. (1999) for Alaska. Der-elict fishing gear often reaches very high proportions (>50%) of allAMD in remote areas where contributions from other sources aresmall (Slip and Burton, 1990, 1991; Jones, 1995; Walker et al.,1997; Convey et al., 2002). While in the CSC the contribution offishing and aquaculture debris is high, it is substantially surpassedby that of household-related AMD.

4.2. Temporal dynamics of AMD in coastal waters and on local shores

The overall densities of floating AMD (reaching up to70 items km�2) in the CSC were within the same range as valuesreported for other areas (Mediterranean Sea – Aliani et al., 2003;western N Atlantic – Dufault and Whitehead, 1994; eastern N Pa-cific – Titmus and Hyrenbach, 2011; East China Sea – Kim, 2011).However, these densities remain far below those observed incoastal waters of Indonesia (Willoughby et al., 1997).

The densities of AMD on the shores of the CSC are within thelower range of those reported for beaches around the globe (Edyv-ane et al., 2004; Taffs and Cullen, 2005; Santos et al., 2009). Theselow abundances could be due to several reasons. The present studyis only based on the most recent flotsam, i.e. the AMD deposited onthe shore during the last high tide. It thus does not include thehigher parts of the shore, where AMD is usually most abundant(see above). Furthermore, AMD densities on the shore might bemoderate because the beaches in the CSC only receive local debris(see also below), without major inputs of AMD from inlandsources, which would have reached coastal waters via river or rainrun-off.

No seasonal trend was observed in AMD densities, but thereseemed to be a tendency of increasing densities during the studyperiod. The fact that high densities of AMD could be observed onthe local shores throughout the year, irrespective of the season,suggests that activities that generate AMD occur throughout theyear. If AMD would be mainly contributed by touristic activities,one should expect highest densities during the summer months,as reported for example from beaches in Brazil (Portz et al.,2011), Spain (Martinez-Ribes et al., 2007; Ariza et al., 2008), Italy(Gabrielides et al., 1991), and Israel (Golik and Gertner, 1992).Abu-Hilal and Al-Najjar (2004) also suggested seasonal changesin visitors to the coastal regions as an important driver for seasonalvariations in AMD densities. This pattern can be further enhancedby winter storms which wipe the main beach clean, pushing AMDfurther up behind the beach or into the dunes (Golik and Gertner,1992; Thornton and Jackson, 1998) or pulling it back out to sea(Ivar do Sul et al., 2011). Higher numbers of AMD during wintercompared to summer led Williams and Simmons (1997) to suggestthat tourism is not the major source of litter on beaches in Wales.However, seasonal variation in currents and wind might also leadto a lacking relationship between visitor frequency and AMD num-bers (Otley and Ingham, 2003).

Herein we observed no clear summer peak of AMD densitiesand it is likely that this is due to consistent input of AMD from fish-eries and aquaculture or year-round beach visitors. Intense clean-up activities during the main tourist season could also suppressthe abundances of AMD during the summer months (e.g. Golikand Gertner, 1992; Oigman-Pszczol and Creed, 2007; Storrieret al., 2007; Khairunnisa et al., 2012), thereby obscuring any sea-sonal patterns (see also Ivar do Sul et al., 2011). However, the local

shores studied herein are not regularly cleaned, and thus cleaningactivities are unlikely to affect the observed seasonal pattern.

The temporal dynamics of AMD were very similar on rockyshores and on sandy beaches in the CSC, suggesting similar supplyand removal dynamics for both types of shore. Both rocky shoressurveyed herein were adjacent to sandy beaches and beach visitorswere frequently observed to venture along these rocky shoreswhere they were fishing or searching for shellfish (personal obser-vations). Furthermore, some of the AMD deposited directly on thesandy beaches may have been moved onto the nearby rocky shoresby wind and currents. Merrell (1980) also reported similar num-bers and categories of AMD from boulder shores and sandy bea-ches of the NE Pacific, albeit in that case the similarity mostlikely is due to homogeneous supply from pelagic sources (fishery),because the shores surveyed by him were too remote for beach vis-itors. On rocky shores a large fraction of the incoming AMD mightalso be destroyed by wave battering (Eriksson and Burton, 2003),leading to the lower abundances observed herein during most sur-veys; smaller fragments might not be easily visible on rocky shoreswhere they are filtered down below the upper boulder and rocklayers (Abu-Hilal and Al-Najjar, 2009).

Also the densities of floating AMD did not vary seasonally in theCSC, similar to what was reported by Lecke-Mitchell and Mullin(1997) for the Gulf of Mexico. Seasonal variation of AMD densitiesand composition might not only be influenced by seasonal differ-ences in human activities (see above), but also by seasonal changesin climate or current regimes (Garrity and Levings, 1993; Frost andCullen, 1997). Episodic events and storms occurring during partic-ular oceanographic and climatic situations might push floatingAMD onto local beaches (Edyvane et al., 2004; Shimizu et al.,2008; Viehman et al., 2011), thereby cleaning out coastal waters.In contrast, strong rainfalls may flush large amounts of AMD intocoastal waters (Cunningham and Wilson, 2003; Abu-Hilal and Al-Najjar, 2004). Herein we observed no clear seasonal variation infloating AMD, which probably is due to the fact that no major cli-matic events (e.g. strong El Niño with heavy rainfalls) occurredduring the study period.

4.3. Potential sources of AMD in the Coastal System of Coquimbo

The very small fraction (<0.2%) of AMD with marine overgrowthsuggests that most of the AMD stranded on beaches in the CSC haspassed very little time at the sea surface (see also Santos et al.,2005, 2009). Widmer and Hennemann (2010) reported a propor-tion of about 4.7% of all AMD to be encrusted by organisms, whichthey considered low. Nevertheless those values are substantiallyhigher than those found herein, indicating that a comparativelyhigh proportion of AMD arrives on Brazilian shores after prolongedpassage at the sea surface. Also, on beaches from Sydney, Australia,up to 4% of all AMD had signs of attached marine organisms (Cunn-ingham and Wilson, 2003). The proportions of encrusted AMD onremote coasts and islands were substantially higher (>20%), indi-cating that most AMD reaching these shores comes from distantsources (Gregory, 1991; Barnes and Milner, 2005; Eriksson et al.,2013).

In some countries, foreign labels indicate that AMD has beentransported to local beaches by coastal currents, but this occurredmost commonly on beaches close to national borders (e.g. Golikand Gertner, 1992) or on remote islands (Kei, 2005). Based onthe high proportion of foreign labels, Santos et al. (2005) concludedthat most AMD on beaches in central Brazil came from shipping.Herein, no AMD with foreign labels was found, possibly due tothe fact that in either direction along the shore the national borderis >1300 km away.

The type of AMD found herein strongly indicates that it has lo-cal sources, which point mostly at recreational beach visitors, fish-

Table 3Proportions of different types of AMD in studies conducted on shorelines throughout the world; percentage values >50% marked bold.

Plastic Styrofoam Glass Metal Wood Paper Others

Rocky ShoreMacquarie Island 58.1 1.4 0.8 33.5 6.2 Slip and Burton (1990)Goto Islands, Japan 74.0 9.0 0.3 1.0 1.0 0.3 14.5 Nakashima et al. (2011)German Bight, Germany 19.0 56.6 2.7 4.4 11.6 3.8 1.9 Vauk and Schrey (1987)

SaltmarshNorth Carolina, USA 45.6 31.9 4.3 4.1 9.1 4.7 Viehman et al. (2011)Georgia, USA 25.6 33.0 7.5 26.0 3.4 4.5 Gilligan et al. (1992)

Sandy BeachWales, UK 82.0 1.0 17.0 0.0 Williams and Simmons (1997)N. Devon/Somerset, UK 58.0 2.0 40.0 0.0 Williams and Simmons (1997)Irish Sea, UK 51.0 8.0 37.0 4.0 Williams and Simmons (1997)Halifax harbor, Canada 53.8 12.0 8.4 12.4 5.2 5.2 3.0 Ross et al. (1991)New Jersey, USA 73.8 16.4 2.2 2.4 1.3 1.7 2.2 Ribic (1998)Firth of Forth, UK 46.9 5.3 9.4 5.4 3.8 4.7 24.5 Storrier et al. (2007)Sta Lucia (Caribbean) 51.3 10.2 1.6 9.8 1.2 25.9 Corbin and Singh (1993)Panama, Caribbean 56.0 31.0 8.0 4.0 2.0 0.0 Garrity and Levings (1993)Curacao, wind-exposed 64.2 4.1 3.8 1.1 15.1 0.9 10.8 Debrot et al. (1999)Curacao, wind-protected 40.0 1.9 19.4 7.3 21.9 4.0 5.5 Debrot et al. (1999)Brazil, Buzios 36.8 1.8 3.0 0.9 50.6 6.9 Oigman-Pszczol and Creed (2007)Coqueiros, Brazil 69.8 0.4 2.7 14.0 0.3 12.8 0.0 Santos et al. (2005)Bahia, Brazil 75.0 14.0 1.0 1.0 2.0 0.0 7.0 Santos et al. (2009)Rio Grande, Brazil 47.9 1.3 1.6 4.4 3.6 41.2 Tourinho and Fillmann (2011)Guanabara Bay, Brazil 47.8 7.0 8.1 8.1 4.7 6.7 17.6 Neto and da Fonseca (2011)Falkland islands, UK 74.0 11.0 3.0 12.0 Otley and Ingham (2003)Transkei, S Africa 83.4 8.6 3.1 0.5 0.3 1.0 3.1 Madzena and Lasiak (1997)Balearic Islands, Spain 54.0 1.5 1.5 3.0 2.5 37.5 Martinez-Ribes et al. (2007)Mediterranean 60.0 8.0 4.0 4.0 10.0 14.0 Gabrielides et al. (1991)Jordania 54.2 8.1 9.0 4.7 14.5 4.4 5.1 Abu-Hilal and Al-Najjar (2004)Israel 71.0 3.5 2.8 4.8 8.4 9.5 Golik and Gertner (1992)Oman 61.8 2.7 3.4 18.9 2.1 11.1 Claereboudt (2004)Jayapura, Indonesia 22.5 8.3 0.9 1.0 0.5 66.9 Nash (1992)1000 Islands, Indonesia 50.3 37.7 0.3 2.0 9.7 Willoughby et al. (1997)Port Dickson, Malaysia 55.7 16.1 1.6 0.8 0.1 10.4 14.6 Khairunnisa et al. (2012)Bootless Bay, Papua New Guinea 89.7 2.3 1.1 1.7 1.6 3.5 Smith (2012)Fog Bay, N Australia 32.2 8.7 15.6 35.1 1.0 1.5 5.9 Whiting (1998)Great Barrier Reef, Australia 43.3 10.8 15.8 2.2 27.8 Haynes (1997)NS Wales, Australia 39.4 11.6 14.1 14.1 6.8 14.1 Frost and Cullen (1997)Sydney, Australia 74.1 12.7 0.7 1.6 5.0 5.9 Cunningham and Wilson (2003)S Australia 70.4 21.0 8.6 0.0 Edyvane et al. (2004)South China Sea 42.0 6.6 2.4 1.4 33.7 4.2 9.7 Zhou et al. (2011)Japan 72.9 19.3 2.2 1.0 1.0 3.6 Kusui and Noda (2003)Midway Atoll, USA 91.1 7.3 1.6 Ribic et al. (2012b)Orange County, California 37.9 43.9 1.3 1.4 1.6 4.0 9.9 Moore et al. (2001)Baja California, Mexico 43.8 7.7 31.8 1.8 12.3 2.6 Silva-Iñiguez and Fischer (2003)

Sea SurfaceUS harbors 55.0 28.0 0.5 1.0 3.0 1.0 11.5 Redford et al. (1992)South China Sea 44.9 23.2 4.3 0.5 13.0 7.6 6.4 Zhou et al. (2011)Kuroshio current 52.5 5.7 41.8 Yamashita and Tanimura (2007)Chilean coast 84.3 1.4 0.5 7.4 2.3 4.2 Thiel et al. (2003)Patagonian fjords 26.0 68.5 0.2 0.1 0.7 0.0 4.6 Hinojosa and Thiel (2009)German Bight 61.8 4.0 0.4 0.5 1.8 0.4 31.1 Thiel et al. (2011)

Mean percentage 55.8 15.9 5.5 7.3 6.8 5.2 11.7

314 M. Thiel et al. / Marine Pollution Bulletin 71 (2013) 307–316

ing and aquaculture activities. The composition of AMD on the bea-ches also suggested local sources, e.g. tourism, as reported frommany other studies (Golik and Gertner, 1992; Madzena and Lasiak,1997; Martinez-Ribes et al., 2007). Herein, fishing and aquaculturecontributed substantial AMD, but did not reach the high propor-tions observed in other studies, most likely due to the high inputfrom other sources (beach users) in the CSC. Similarly, no indica-tion was found that some of the examined shorelines accumulatesubstantially more AMD than others. This is different from otherareas where some beaches receive large quantities of AMD thatare transported there via currents or coastal winds (e.g. Gabrielideset al., 1991; Oigman-Pszczol and Creed, 2007; Browne et al., 2010;Smith, 2012). Most AMD found in the CSC comes from shore-based(beach users) and nearshore activities (artisanal fishery and aqua-culture), and is quickly deposited on local shores as can also be in-ferred from the fact that the composition of AMD in coastal watersis very similar to that on local shores.

Similar as observed for many other coastal areas (e.g. Garrityand Levings, 1993; Oigman-Pszczol and Creed, 2007; Storrieret al., 2007; Santos et al., 2009; Viehman et al., 2011), all presentlyavailable evidence strongly indicates that most AMD in the CSCcomes from very local sources, mostly without passing much timeat the sea surface. The results also suggest that a high proportion ofthe AMD on local shores has been directly deposited there bybeach users without ever coming in contact with the seawater.This underlines the strong need for local solutions in the questfor keeping local beaches along the SE Pacific clean.

Acknowledgements

We are grateful to all the members of the BEDIM lab whohelped with the collection and sorting of marine debris, and thecrew of RV Stella Maris for their good company during the researchcruises. The English of the manuscript was kindly improved by T.

M. Thiel et al. / Marine Pollution Bulletin 71 (2013) 307–316 315

Manzur and L. Eastman. Funding for this study was obtainedthrough FONDECYT 1010356.

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