In the South Pacific

Marine Pollution Bulletin 137 (2018) 119–128

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Marine Pollution Bulletin

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Travelling light: Fouling biota on macroplastics arriving on beaches of remote Rapa Nui (Easter Island) in the South Paciﬁc Subtropical Gyre T ⁎ Sabine Recha, , Martin Thielb,c,d, Yaisel J. Borrell Pichsa, Eva García-Vazqueza a Department of Functional Biology, University of Oviedo, 33006 Oviedo, Asturias, Spain b Universidad Católica del Norte, Coquimbo, Chile c Millennium Nucleus of Ecology and Sustainable Management of Oceanic Island (ESMOI), Coquimbo, Chile d Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Coquimbo, Chile

ARTICLE INFO ABSTRACT

Keywords: Marine anthropogenic debris was sampled from two beaches on the remote South Pacific island Rapa Nui (Easter Non-indigenous species Island). Abundance, composition, and the attached fouling assemblages on stranded litter were analysed. Most Fouling assembly litter (n = 172 items found) was composed of plastic material, and 34% of all litter items were fouled. The main Long-distance rafting fouling species was the encrusting bryozoan Jellyella eburnea. Transporting vectors were exclusively made from Marine anthropogenic litter plastics and were mainly small items and fragments, probably stemming from the South Pacific Subtropical Gyre. South Pacific Subtropical Gyre We present the first report of Planes major, Halobates sericeus, and Pocillopora sp. on anthropogenic litter in the Oceanic islands South Pacific.

1. Introduction everyday items, its production has risen to 335 × 109 kg in 2016 (PlasticsEurope, 2018). Due to the high influx of discarded plastic items Non-indigenous species (NIS) and pollution of marine and coastal to the oceans worldwide, rafting opportunities for marine species have environments are amongst the most important threats to biodiversity increased dramatically (Barnes, 2002; Kiessling et al., 2015). Plastics that should be urgently treated (Regulation (EU) No 1143/2014, 2014; make for particularly stable and persistent rafts. Such floating substrata Bergmann et al., 2015). One of the manifold impacts of marine an- and their attached communities can float over wide distances. Several thropogenic litter on the environment is its role as a transport vector for trans-oceanic rafting events are known. A recent major event was the attached biota, amongst them non-native invasive species (Kiessling trans-Pacific rafting from Japan to North America of nearly 300 marine et al., 2015; Rech et al., 2016). Although this phenomenon has received coastal species on anthropogenic rafts detached by the 2011 tsunami in very little scientific and public attention in the past, floating rafts are Japan (Calder et al., 2014; Carlton et al., 2017; McCuller and Carlton, now considered to play an important role in biota introduction and 2018; Miller et al., 2018). Another example worth to be mentioned is dispersal, even in areas where there are several other vectors known to the trans-Atlantic rafting of non-indigenous molluscs and barnacles to generate a high risk of introducing NIS, like aquaculture or shipping British and Irish shores (Minchin et al., 2013; Holmes et al., 2015). and ports (e.g. Rech et al., 2018a, 2018b). Examples are British brackish Plastic debris and flotsam/jetsam are not distributed homo- and marine waters, where floating debris is listed as the third most geneously in the oceans. The floating items are moved with oceanic common vector for NIS transport (Minchin et al., 2013); in the Medi- currents and accumulate in oceanic divergence zones. The biggest and terranean region, > 80% of NIS might have arrived or dispersed on most important of them are the five principal oceanic gyres, situated in flotsam of anthropogenic origin (Galgani et al., 2014). This vector may the North- and South Pacific, North-and South Atlantic and Indian be especially important in remote regions, particularly remote islands, Ocean. Contrary to widespread popular opinion, these accumulations where other vectors of NIS introduction, like aquaculture, transport in are not visible litter islands, but are defined by significantly higher ballast water, or hull fouling are absent or scarce. Species transport by concentrations of litter items and particles compared to oceanic waters natural floating material, like pumice or algal rafts, is well known, and outside the gyres (Eriksen et al., 2013, 2014; Ryan, 2014; Miranda- has importantly influenced biotic communities on islands (Thiel and Urbina et al., 2015). Not only debris, but also attached micro and Gutow, 2005a; Fraser et al., 2011; Nikula et al., 2013; Kiessling et al., macrobiota are travelling in the gyres and have been increasingly stu- 2015). Since the introduction of plastic as a common material for died in the last years (e.g. Goldstein et al., 2012, 2014; Bryant et al.,

⁎ Corresponding author. E-mail address: [email protected] (S. Rech). https://doi.org/10.1016/j.marpolbul.2018.10.015 Received 2 July 2018; Received in revised form 1 October 2018; Accepted 4 October 2018 Available online 11 October 2018 0025-326X/ © 2018 Elsevier Ltd. All rights reserved. S. Rech et al. Marine Pollution Bulletin 137 (2018) 119–128

2016). within small bays (Fig. 1). The main sampling area was proportional to A significant rise of marine debris accumulation over the last the length of the beach and was 480 m2 on Anakena beach and 160 m2 30 years has been documented from remote islands of the southern on Ovahe beach. hemisphere, and it has been shown that South Pacific islands accumulate exceptionally high quantities of marine debris (Barnes, 2005; 2.2. Sampling strategy Lavers and Bond, 2017; Hidalgo-Ruz et al., 2018). The highest density of debris reported worldwide was found on unpopulated and rarely Each beach was sampled during approximately two hours, at low visited Henderson island in the South Pacific gyre region (Lavers and tide and daylight in the beginning of April 2017. All anthropogenic Bond, 2017). This suggests that many remote islands, which are usually litter was counted along the most recognizable tideline +1 m to both thought to be rather protected from human impact, are particularly sides on both beaches. Non-fouled and fouled anthropogenic litter items impacted by anthropogenic marine debris accumulation and its dele- were counted separately, to estimate the abundance of both types of terious consequences. Rapa Nui is an inhabited, but remote island, lo- litter and to calculate the percentage of fouled items. At Ovahe beach, cated in the South Pacific Subtropical Gyre (SPSG). Marine litter rapidly an opportunistic sampling of a marine litter accumulation patch (area: accumulates within the Easter Island ecoregion, with items coming 6m2) at the rocky backshore of the beach was done additionally. As no from the South American continent reaching the area within < 2 years such backshore litter patch was present at the Anakena beach, there (Martinez et al., 2009). In a citizen-science study carried out on the was a total of three sampling points in this study: (1) Ovahe – tideline island‘s beaches, accumulation of microplastics was found to be almost (OVA-TL), (2) Anakena – tideline (ANA-TL), and (3) Ovahe – backshore thirty times higher than on Chilean continental beaches (Hidalgo-Ruz (OVA-BS). The minimum size of debris items counted in this study was and Thiel, 2013) and also floating macrolitter in the waters of the SPSG of 5 cm in either length, width, height, or diagonal. Fouled litter items reaches much higher abundances than in continental waters (Miranda- were photographed with a size reference and taken to the lab for Urbina et al., 2015). Little is known about native and non-native biota measuring and further analysis. of Rapa Nui; however, one non-native fouling bryozoan species, Jelly- ella eburnea, has been found on plastic debris stranded on the island‘s 2.3. Data analysis beaches and is thought to have been introduced via this vector (Moyano, 2005). All litter items were sorted according to the categories and codes The aim of this work was to investigate the extent of arrival of established by United Nations Environment Programme (UNEP; fouling biota on floating items on beaches of this remote island. Cheshire et al., 2009; Table 1). Fouled items as well as encrusting Particularly, the objectives were to (i) characterize the abundance and bryozoan colonies, if present, were measured and the total surface area, composition of macrolitter deposited at Rapa Nui, (ii) infer its origin (as as well as surface area encrusted by bryozoans was calculated for each local versus imported via the oceanic gyre), and (iii) determine its role item by SR. The percentage of surface covered by encrusting bryozoans as vector of fouling biota. The investigation is based on the hypothesis was then calculated for each item. Afterwards, the biota attached to that macrolitter items and fragments from the currents of the South each item were scraped off, counted, and identified to the lowest Pacific Subtropical Gyre (SPSG) and the marine litter accumulation taxonomic level possible. The taxonomic diversity of the fouling as- zone in the center of the SPSG arrive on Rapa Nui. As such items and semblage as well as the percentage of bryozoan cover on litter items fragments are known to travel for prolonged periods of time with the was compared between the three sampling points (OVA-TL, ANA-TL, oceanic currents, we predicted to find highly persistent plastic items of OVA-BS) and UNEP item categories using permutational analysis of high floatability, and in an advanced state of fragmentation. We ex- variance (PERMANOVA; Anderson et al., 2008), based on Bray-Curtis pected such items to serve as dispersal vectors of fouling biota. similarities. The analyses were carried out with PRIMER 6 software (Clarke and Gorley, 2006). Results were regarded as statistically sig- 2. Material and methods nificant at a p-value < 0.05.

2.1. Sampling site 2.4. Genetic analysis and visual identiﬁcation

The study presented here was carried out on two beaches of the All biota attached to litter items in this study were identified to the South Pacific island Rapa Nui (English: Easter Island): Anakena beach most specific taxonomic level possible using state of the art taxonomic (27°04′23.8”S 109°19′23.6”W, north-western orientation) and Ovahe guides and literature (Herring, 1961; Foster and Newman, 1987; beach (27°04′26.0”S 109°18′51.0”W, eastern orientation). They are the Hayward and Ryland, 1995; Møller Andersen and Cheng, 2004; island's only accessible sandy beaches, both situated on the island's Heckman, 2008; Fernández et al., 2014; Chan and Cheang, 2015; northern coast, frequently used by beach goers, and relatively protected Harada et al., 2016). Taxon nomenclature follows World Register of

Fig. 1. Map of Rapa Nui island and the surrounding currents of the South Paciﬁc Subtropical Gyre.

120 S. Rech et al. Marine Pollution Bulletin 137 (2018) 119–128

Table 1 one fragment of paper/cardboard (PC05, Fig. 2; Table S1). The majority Assignment of litter items found in the present study to United Nations of litter items were unidentified fragments and objects (PL24), followed Environmental Programme (UNEP) litter categories and codes. by ropes (PL19) and plastic sheeting (PL16, only found at Anakena UNEP code Material Category UNEP Items present study beach). The composition of fouled items was less diverse than non-fouled PL01 Plastic Bottle caps & lids Bottle caps & lids beach litter. All fouled vectors were made from plastics and belonged to PL02 Bottles < 2 L Non-beverage bottle only 6 categories: PL01, PL03, PL13, PL17, PL19 and PL24 (Fig. 3; PL03 Bottles, drums, Jerrycans, detergent fi jerrycans, buckets container Table S1). The most frequent were PL24 (non-identi ed items and >2L fragments, 69%) and PL19 (ropes, 13.8%; Fig. 3; Table S1). PL06 Food containers Lolli stick Most fouled items were fragments of broken items and were rather PL13 Baskets, crates, trays Crates (fragments) small, with a surface area of ≤100 cm2 (Figs. 4 and 5). There were no PL16 Sheeting Foil, packaging material fi ff PL17 Fishing gear Light stick, grid from signi cant di erences in the average surface area of fouled litter items trap, cap of fishing rod amongst the three sampled points (Anakena tideline: PL18 Monofilament line Monofilament line 128 cm2 ± 118 cm2; Ovahe tideline: 479 cm2 ± 1017 cm2; Ovahe PL19 Rope Rope backshore accumulation: 216 cm2 ± 288 cm2; Table 2, PERMANOVA fi PL24 Other Unidenti ed items and 1). In fact, tidelines along the beaches were mainly defined by small fragments FP05 Foamed Other Foam, not further litter items and so-called microplastics (Fig. 5). An exception are ropes plastic identified (UNEP code PL19): 4 of the 8 ropes found had a length of 1.5 m to 20 m OT02 Other Sanitary Cotton swab stick, rests and were therefore not small fragments. of wet wipes PC05 Paper & Other Paper, cardboard, not cardboard further identified 3.2. Species identified upon visual inspection and barcoding

Eleven taxa, with at least 650 individuals (not counting colonial Marine Species database (WoRMS editorial board, 2017). For the gen- biota, like hydrozoans and bryozoans) were identified by visual analysis eration of genetic barcodes, deoxyribonucleic acid (DNA) was extracted on Rapa Nui beached litter and 9 barcodes were generated by genetic 2 from a piece of tissue (~ 4mm ) using Chelex (Bio Rad BT Chelex 100 analysis (Table 3). The barcode sequences are available in GenBank Resin). DNA from very small individuals with non-tissue parts (e.g. (https://www.ncbi.nlm.nih.gov/genbank/) with the accession numbers ® sessile barnacles) was extracted with E.Z.N.A. Mollusc DNA Kit. Mul- MH536243 - MH536251. Sequence matches with a nucleotide identity fi tiplication of a species-speci c gene (cytochrome oxidase I) fragment of over 96% were obtained for two individuals of flotsam crabs Planes (genetic barcode) by polymerase chain reaction (PCR) was performed major, two individuals of the pelagic gooseneck barnacle Lepas anatifera using the primers jgLCO1490 and jgHCO2198 (Geller et al., 2013). The and two individuals of sea skaters Halobates sericeus. For three se- sequencing of those genetic barcodes was performed by Macrogen quences obtained from chthamalid barnacles there were no matching Europe, Amsterdam, Netherlands. The sequences so generated were sequences available. No barcodes could be generated from cnidarians, uploaded in GenBank BLAST nucleotide (Clark et al., 2016) and BOLD bryozoans and polychaetes, as well as from unidentified encrusting (Ratnasingham and Hebert, 2007) databases. colonies, as these biota were completely dried out and DNA extraction was not possible. Photographs of encrusting colonies that could not be 3. Results identified beyond the phylum level can be found in the supplementary material (Fig. S2). 3.1. Beach litter and fouled items Although no genetic identification of the obtained material was possible, Jellyella eburnea could be identified and distinguished from The abundance of beach litter was 0.18 items per m2 at Anakena other genera and from the only other species in its genus (J. tuberculata) beach and 0.29 items per m2 at Ovahe beach (see supplementary ma- by morphologic characteristics, on the basis of descriptions and pictures terial, Table S1). The percentage of fouled items (sampled along the from several authors (Gordon, 1984; Stevens et al., 1996; Taylor and tideline) was similar on both beaches: 27.9% on Anakena beach and Monks, 1997; Tilbrook et al., 2001; Moyano, 2005; McCuller and 19.1% on Ovahe beach. It was notably higher in the zone of litter ac- Carlton, 2018). The colonies found in our study are particularly similar cumulation found at the backshore of Ovahe beach: 64.1% of litter to those described by Moyano (2005) from Rapa Nui and by McCuller items were fouled there. At all three sites the vast majority of items was and Carlton (2018) from the North Pacific. A coral, attached to a plastic made of plastics (> 97%). The only non-plastic items were one rest of rope, was identified as Pocillopora sp. by Bert Hoeksema and Peter wet wipe, which contains natural as well as synthetic fibers (OT02) and Glynn. It is most likely P. damicornis, however the identification on

Fig. 2. Litter items (fouled + non-fouled) found on Rapa Nui beaches per category. For explanation of litter categories based on United Nations Environmental Programme (UNEP) codes, please see Table 1. N = 172 total litter items.

121 S. Rech et al. Marine Pollution Bulletin 137 (2018) 119–128

Fig. 3. Fouled litter items found on Rapa Nui beaches per category. Litter categories are represented by symbols taken from https://iconos8.es/. PL01 = caps/lids; PL03 = containers > 2 L; PL13 = crates; PL17 = ﬁshing gear; PL19 = ropes; PL24 = non-identiﬁed fragments or objects. N = 58 fouled litter items.

(Table 3). The colony of Pocillopora sp. as well as two fragments of Jellyella eburnea have been deposited in the reference collection of Naturalis Biodiversity Center (collection numbers: RMNH.COEL.42334 and RMNH.BRY.20900).

3.3. Fouling assembly by beach, material, and items surface area

The biota fouling beached litter items on Rapa Nui beaches represented several phyla (Fig. 6). Bryozoans were the most frequent biota – they were present on 87.9% of all fouled items found in this study. They were followed by arthropods, cnidarians and annelids (present on 31%, 5.2%, and 1.7% of fouled vectors, respectively; Fig. 6). Other, not identifiable animal species or algae were found on 3.4% and 15.5% of all fouled items, respectively. Fig. 4. Total number of fouled litter items of different surface area (n = 58 The composition of the fouling assemblage was not related to the fouled items). sampling point (Table 2, PERMANOVA 2), but differed between item categories (Fig. 7; Table 2, PERMANOVA 3 main). The three items of fi species level is uncertain, due to the specimen being a juvenile, worn, shing gear found in this study (PL17) were exclusively fouled by and being attached to a floating object (not the natural habitat) and a bryozoans, while all other item categories were associated with at least ff high morphologic plasticity of Pocillopora species (B. Hoeksema, pers. two di erent taxa (Fig. 7). The most diverse (by number of taxa) fouling communication; Schmidt-Roach et al., 2013, 2014). All identified taxa assemblage was observed on items of the categories PL19 (ropes) and fi are common colonizers of plastic litter in the marine environment PL24 (non-identi ed fragments and objects). These two categories contained the highest numbers of fouled vectors (PL19: 7 items; PL24:

Fig. 5. Tidelines, mainly deﬁned by small debris and microplastics, at Ovahe beach (left) and examples of broken down plastic items found on Rapa Nui beaches (right).

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Table 2 Permutational MANOVAs (PERMANOVAs). ID = Identification, Df = degrees of freedom, SS = sum of squares, MS = mean sum of squares, Pseudo-F = F value by permutation, perms = permutations. * = significant p-value. Bold = Factor. Item categories: PL03 = containers > 2 L; PL19 = ropes; PL24 = unidentified fragments and objects. Sampling points: Anakena tideline, Ovahe tideline and Ovahe backshore.

ID PERMANOVA Dependent variable Source of variation df SS MS Pseudo-F/t p-Value Unique perms.

1 Surface area of fouled items Sampling point 2 702.77 351.39 0.6369 0.594 999 Residuals 55 30,341 551.66 Total 57 31,044 2 Composition of fouling assemblage Sampling point 2 2184.2 1092.1 0.7876 0.529 999 Residuals 55 76,263 1386.6 Total 57 78,447 3 - main Composition of fouling assemblage Item category 5 17,895 3579 3.0735 0.01* 999 Residuals 52 60,552 1164.5 Total 57 78,447 3 - pairwise Composition of fouling assemblage Item category Groups PL19, PL24 3.3592 0.002* 474 Groups PL03, PL24 1.9176 0.04* 92 4 - main Surface area covered by bryozoans Item category 5 83.694 16.739 2.7286 0.02* 999 Residuals 49 300.59 6.1345 Total 54 384.29 4 - pairwise Surface area covered by bryozoans Item category 3.4573 0.001* 945 Groups PL24, PL19 Groups PL19, PL03 2.8181 0.03* 36

24 items; see also Fig. 3), which may be a reason for their elevated 3.3.1. Encrusting bryozoan colonies taxonomic diversity. Statistical analysis showed significant difference The most common fouling organisms found on Rapa Nui beach litter between the fouling assemblages of these two item categories, as well as were encrusting bryozoans (Figs. 6–9). The grade of encrustation varied between PL24 and PL03 (bottles > 2 L; Table 2, PERMANOVA 3 pair- between objects and ranged from 0% to 100% of the item's surface area, wise). While at least 90% of items of all other categories were fouled by with a mean value of 21%. The colonies found in our study were all encrusting bryozoans, those organisms were only found on 50% of fo- dead and dried out. Since it is not known for how long they had been uled ropes. Arthropods, algae and cnidarians, on the other hand, ap- afloat and for how long they had been stranded before this survey, it is peared with a higher frequency on ropes than on not-identified frag- possible that parts of the encrusting colonies have been lost from their ments and items (PL24; Fig. 7). The number of taxa attached to a fouled transporting vectors before we found them. Notwithstanding, there was item of litter was positively and significantly correlated with the item's a positive and significant correlation between the surface area of litter surface area (Pearson Correlation Coefficient: R = 0.3166; 56 d.f.; items and the percentage of bryozoan cover (Pearson Correlation p = 0.016; Fig. 8). Coefficient: R = 0.2943; 53 d.f., p = 0.02; Fig. 8).

Table 3 List of animal taxa identified on stranded litter on Rapa Nui with numbers of genetic barcodes obtained and closest match in the genbank database (with nucleotide identity > 96%) and prior reports of the listed taxa on floating or stranded anthropogenic debris in several marine regions. x = does not apply, n.i. = not further identified. * = see supplementary material (Fig. S2) for photographs. Rev. = reviewed in.

Phylum Order Visual identiﬁcation # Ind. # Seq. Closest match Prior reports Locality

Annelida Sabellida Spirorbinae 80 x x Gregory, 1990; A (N), (polychaetes) Winston et al., 1997; P(N+S) Goldstein et al., 2014 Serpulidae 10 x x rev: A (N), (polychaetes) Kiessling et al., 2015 P (N + S), Med Arthropoda Decapoda Planes major 2 2 MF490112 Pons et al., 2011; A (S), (ﬂotsam crab) Planes major Carlton et al., 2017 P (N) Hemiptera Halobates sericeus 3 2 MH795807 Goldstein et al., 2012 P (N) (water strider) H. sericeus Lepadiformes Lepas anatifera 400–500 2 GU993619 Astudillo et al., 2009; A (N + S), (gooseneck barnacle) L. anatifera Whitehead et al., 2011; P (N + S), Cabezas et al., 2013; Ind, Goldstein et al., 2014; Med Rech et al., 2018b Sessilia Chthamalidae 33 3 x Carlton et al., 2017; P (N), (acorn barnacles) Rech et al., 2018a A (N) Bryozoa Cheilostomatida Jellyella eburnea xxx Moyano, 2005; P(N+S) (encrusting bryozoan) McCuller and Carlton, 2018 Cnidaria Scleractinia Pocillopora sp. xxx Jokiel, 1984, P (N) (cauliﬂower coral) Carlton et al., 2017 n. i. Hydrozoa x x x rev: A (N), (colonial hydrozoan) Kiessling et al., 2015 P (N + S), Med n.i. n. i. Colonies, encrusting* 120 x x x x Algae x x x rev: Kiessling et al., 2015, A (N), Hansen et al., 2018 P (N + S), Ind, Med

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oceanic gyres, floating items trapped in the SPSG cannot escape (Martinez et al., 2009). While floating in the gyre, litter items could complete several cycles of biofouling, subject to decline in buoyancy, sinking and defouling, and resurfacing (Ye and Andrady, 1991), which can make it difficult to estimate for how long beached litter items have been afloat. The majority of marine litter from the South Pacific region, however, reaches the SPSG's main accumulation area within only two years (Martinez et al., 2009). As the larger items found in our study are still recognizable, it seems probable that they have not been floating for a much longer time. Stranded litter on beaches of Rapa Nui consisted almost exclusively of plastic items, which is consistent with findings from all over the world (e.g. Kiessling et al., 2015). There are several possible reasons to Fig. 6. Frequency (counted as presence/absence) of phyla on fouled litter items explain why only six of the 13 litter categories in this study contained (n = 58) found on Rapa Nui beaches. fouled items. This might be a stochastic effect, as several of the categories that did not contain fouled items, were represented by very few The percentage of bryozoan cover differed between object types litter items in general. On the other hand, some of the non-fouled items (Table 2, PERMANOVA 4 main), with the lowest percentages on ropes may stem from local land-based sources and have spent only a short (PL19; Fig. 10). Statistically significant differences were found between period of time in the sea (e.g. lolli stick (PL06) or sanitary items PL19 (Ropes) and PL24 (other), as well as between PL19 and PL03 (OT02)). Finally, several non-fouled items are rather small and/or not (bottles > 2 L) (Table 2, PERMANOVA 4 pairwise). very resistant (e.g. plastic sheeting, fragments of paper/cardboard), thus not very suitable for long-distance transport (Ryan, 2015; Vlachogianni et al., 2015). 4. Discussion All fouled vectors found in this study were made from hard, durable plastics. Ropes were found to be less fouled by encrusting bryozoans, The hypothesis that fouled items arrive on Rapa Nui beaches from both in terms of surface area cover and percentage of items fouled and fi the South Paci c Subtropical Gyre was supported by the results of our instead have a relatively high frequency of attached arthropods. In clear study. Stranded litter items were mainly broken fragments of formerly contrast to our results, Campbell et al. (2017) found ropes from aqua- larger items, in some cases in an advanced state of erosion (as indicated culture activities to be the main vectors of fouling biota in a New by rounded shapes) and with high rates of fouling by encrusting Zealand-based study. Other studies show that polypropylene ropes do bryozoan colonies. The advanced state of fragmentation and the con- become fouled by encrusting bryozoans (Ye and Andrady, 1991; sistently small size of many stranded items may indicate that the litter Fernandez-Gonzalez and Sanchez-Jerez, 2017), but these colonies only fl found on Rapa Nui beaches has been a oat (and breaking down) for become abundant after several months at sea (Ye and Andrady, 1991). some time, before arriving at Rapa Nui. Hidalgo-Ruz and Thiel (2013) The significantly smaller coverage of encrusting bryozoans on ropes found exceptionally high amounts of small debris (microplastics) on might indicate that these items have been travelling at sea for less time Rapa Nui beaches and proposed that the litter fragments and items than the majority of fouled items at Rapa Nui beaches. This is also stranding there might have been travelling in the currents towards the consistent with the low grade of degradation of several ropes found in fi centre of the SPSG. Floating litter from several South Paci c source our study. The length of the ropes also points to a relatively shorter stay regions ultimately accumulates in the SPSG's eastern-centre region, at sea, or a higher resistance to breakage. Another possible explication where Rapa Nui is located (Martinez et al., 2009; Miranda-Urbina et al., for the difference observed between ropes and other fouled litter items fl 2015). Litter items or fragments oating in the oceanic gyres may spend might be the different surface structure and morphology of ropes in long periods of time, even years, travelling in these current systems contrast to other items, as pointed out by Thiel and Gutow (2005a).In (e.g. Hoeksema et al., 2012; Carlton et al., 2017). In contrast to other

Fig. 7. Frequency (counted as presence/absence) of phyla on fouled litter items found on Rapa Nui beaches, by item category. PL01 = caps/lids (n = 2); PL03 = containers > 2 L (n = 3); PL13 = crates (n = 2); PL17 = ﬁshing gear (n = 3); PL19 = ropes (n = 8); PL24 = not identiﬁed fragments or objects (n = 40).

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Fig. 8. Number of taxa comprising the rafting assemblage of a stranded item and percentage of item's surface covered by encrusting bryozoan colonies against the item's surface area.

Fig. 9. Examples of bryozoan colonies encrusting beach litter on Rapa Nui beaches. Left: Colony on black Nescafé lid. Right: Colony on grey plastic crate.

Fig. 10. Percentage of fouled litter items' surface covered by encrusting bryozoans by litter category (represented by symbols taken from https://iconos8.es/). PL01 = caps / lids (n = 1); PL03 = containers > 2 L (n = 3); PL13 = crates (n = 2); PL17 = ﬁshing gear (n = 3); PL19 = ropes (n = 8); PL24 = not identiﬁed fragments or objects (n = 38).

125 S. Rech et al. Marine Pollution Bulletin 137 (2018) 119–128 concordance with this, a study on Caribbean beaches showed that goose locally abundant (Glynn et al., 2003, 2007; National Geographic barnacles were mostly found attached to rough woody debris, while Society, 2011). Although pocilloporids are common in the whole Pa- encrusting bryozoan colonies mostly fouled smoother surfaces, like cific, there is little connectivity across the Eastern Paci fic Barrier hard plastics, glass, or mangrove propagules (Gracia et al., 2018). On (Romero-Torres et al., 2018). Even though the potential importance of the other hand, the cylindric shape of ropes may make a difference in rafting for dispersal over extended time and distance exceeds that of their floating behaviour and positional changes, which also influences larval dispersal, as highlighted by Jokiel (1984, 1990) and Hoeksema the attached fouling community (Bravo et al., 2011). (2018), this might not be a major factor for the dispersal of Rapa Nui The positive correlation between size of raft and taxonomic di- populations. However, our finding of Pocillopora sp. on plastic debris is versity of the rafting assemblage found in our study is in concordance the first report from the South Pacific and the ongoing increase in with the results of previous studies on anthropogenic debris, algae, and plastic debris in the oceans might strongly enhance long-distance pumice (Thiel and Gutow, 2005b; Bryan et al., 2012; Clarkin et al., rafting opportunities for these corals and other organisms. 2012; Goldstein et al., 2014; Gil and Pfaller, 2016), and is logically The dominating species on plastics found in our study, the cosmo- explained from a larger habitat sheltering a more diverse community. politan bryozoan Jellyella eburnea, is a common rafter and is frequently This correlation was also seen in large rafts, which were detached from found on anthropogenic litter (Taylor and Monks, 1997; Goldstein Japanese shores during the 2011 tsunami and transported to Northern et al., 2014; McCuller and Carlton, 2018). Jellyella sp. has been found American shores (Carlton et al., 2017). Possible reasons for this corre- before attached to pumice that had travelled over 5000 km from Tonga lation are the higher rate of migration to larger objects, as well as their island to Eastern Australia in the South Pacific(Bryan et al., 2012), as higher stability on the sea surface (Goldstein et al., 2014). The share of well as on anthropogenic objects that were detached by a tsunami in fouled items found in our study is in concordance with the results of Japan and had travelled across the North Pacific to Hawaii and North other studies conducted at this latitude (Barnes and Milner, 2005). American shores (McCuller and Carlton, 2018). Jellyella eburnea had not The diversity of attached biota found in our study was rather low, been reported from Rapa Nui before 1999, when it was found in high compared to other studies on beached and/or floating litter (e.g. abundance on stranded plastic litter on Anakena beach (Moyano, Goldstein et al., 2014; Rech et al., 2018a). This again might be due to 2005). This points to the importance that floating plastic debris can the small size of most fragments and items found in our study. Indeed, have for the introduction of non-native species on remote islands. Apart Goldstein et al. (2014) point out that small fragments from the North from the finding in the present study, no further strandings and no Pacific gyre hosted few taxa and were often fouled by the encrusting settlement of this species on Rapa Nui have been reported. However, bryozoans Jellyella and Membranipora. Another reason might be the this does not necessarily mean that colonization has not taken place, as remoteness of Rapa Nui, and the possible loss of coastal species with such findings may depend on time and research effort (Hoeksema, distance from the continental shore or travelling time, although such a 2018). relationship was not observed for fouled floating litter items from the None of the species identified in this study is known to be invasive. North Pacific gyre (Goldstein et al., 2014). Carlton et al. (2017) found a However, several attached biota that could not be identified to species decline in the arrival of tsunami-debris with a high species richness level belong to taxonomic groups containing invasive species. Examples with time, possibly due to loss of coastal species in the unsuitable are the serpulid tubeworms Ficopomatus enigmaticus and F. miamiensis, oceanic environment. Apart from that, studies on stranded litter gen- which are invasive in the Eastern Pacific region (Bastida-Zavala, 2008), erally tend to underestimate mobile species, as these may leave their as well as the Caribbean barnacle Chthamalus proteus, an invader in the raft rapidly during or after its stranding (Kiessling et al., 2015). North Pacific Hawaiian Islands (Zardus and Hadfield, 2005). The taxa identified in this study on plastic litter on Rapa Nui bea- Last but not least, genetic barcodes were not sufficient to identify ches are common colonizers of anthropogenic and/or natural flotsam most of the species found in our study, as there were no matching se- and jetsam. The crab Planes major, for example, is also known as flotsam quences available from Genbank and BOLD databases. Enhancing bar- crab, which due to its ability to opportunistically colonize a wide range coding of less studied species, as well as improving databases elim- of floating substrata is common both in the Atlantic and Pacific Ocean inating not curated sequences and discrepancies, should be encouraged (Chace, 1951; Pons et al., 2011; Pfaller et al., 2014; Kiessling et al., (Darling et al., 2017). This finding also shows the importance of species 2015). Similarly, Lepas anatifera, as well as other species of this genus, identification based on morphologic criteria, especially in areas where are obligate rafters and have a cosmopolitan distribution (Thiel and few genetic data are available. Gutow, 2005b; Kiessling et al., 2015). This species is particularly known from tropical and subtropical environments. Along the Chilean coast, 5. Conclusion for example, L. anatifera abundances decline with increasing latitude and decreasing sea surface temperature (Hinojosa et al., 2006). Sea Our results confirm that there is a high accumulation of plastic skaters of the genus Halobates are the only true marine insects and have debris, particularly smaller fragments, probably stemming from the repeatedly been reported on floating plastics. They also rely on them, as SPSG, on Rapa Nui beaches. The rafting biota found on these items are well as on other floating surfaces for oviposition (Møller Andersen and mainly well-known rafters which seem to commonly use the increased Cheng, 2004; Goldstein et al., 2012; Majer et al., 2012). High density availability of floating substrata for their dispersal. Anthropogenic areas of different Halobates species are separate, with H. sericeus ex- marine litter transports non-native biota to Rapa Nui and may be a clusively occurring in the Pacific Ocean and having an amphitropical vector of introduction for them, which holds the risk of biotic invasions distribution, from 10° to 35° N and S (Cheng, 1997). Our finding con- on this remote island that has a high level of endemism. Substantial firms previous reports of this species around Rapa Nui (Prado, 2008; monitoring effort will be needed to investigate if and where such non- Comité Oceanográfico Nacional, 2017). native species have established in the island's marine and coastal ha- Several coral species are known to colonize anthropogenic marine bitats. litter items in general and lost fishing gear in particular (Hoeksema and Hermanto, 2018; Valderrama Ballesteros et al., 2018). Corals of the Acknowledgments genus Pocillopora are frequently found on natural (e.g. logs, pumice) as well as on anthropogenic flotsam and jetsam (Thiel and Gutow, 2005b). We would like to thank Stephen Cairns, Peter W. Glynn, Dennis P. Pocilloporids are abundant in Rapa Nui's sublittoral habitats and Po- Gordon, Bert Hoeksema, Tim Kiessling, Vivian Macaya and William cillopora verrucosa is the dominating species (Hubbard and Garcia, Newman for their help with species identification, as well as Luis 2003). Together with the coral Porites lobata it is estimated to constitute Arregi, Oihane Cabezas, Phillip Haubrock and Iñigo Onandia for their 95% of the island's live coral cover. Pocillopora damicornis can also be help with litter object identification. This project has received funding

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