Contributions of several litter sources to the differences between the general beach litter counted in a standardized area (group General) and litter used as biota raft (group Rafts), calculated by SIMPER analysis.

<p>Contributions of several litter sources to the differences between the general beach litter counted in a standardized area (group General) and litter used as biota raft (group Rafts), calculated by SIMPER analysis.</p

Composition and likely source of anthropogenic beach litter from standardized beach litter counts (in white, at left), and fouled litter items along the whole beach area (in grey, at right).

<p>Composition and likely source of anthropogenic beach litter from standardized beach litter counts (in white, at left), and fouled litter items along the whole beach area (in grey, at right).</p

Sampled beaches as shown in Fig 1, with geographic position.

<p>Sampled beaches as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191859#pone.0191859.g001" target="_blank">Fig 1</a>, with geographic position.</p

Overview of species attached to stranded litter, identified in the present study.

<p>Overview of species attached to stranded litter, identified in the present study.</p

Anthropogenic marine litter composition in coastal areas may be a predictor of potentially invasive rafting fauna

<div><p>Anthropogenic plastic pollution is a global problem. In the marine environment, one of its less studied effects is the transport of attached biota, which might lead to introductions of non-native species in new areas or aid in habitat expansions of invasive species. The goal of the present work was to assess if the material composition of beached anthropogenic litter is indicative of the rafting fauna in a coastal area and could thus be used as a simple and cost-efficient tool for risk assessment in the future. Beached anthropogenic litter and attached biota along the 200 km coastline of Asturias, central Bay of Biscay, Spain, were analysed. The macrobiotic community attached to fouled litter items was identified using genetic barcoding combined with visual taxonomic analysis, and compared between hard plastics, foams, other plastics and non-plastic items. On the other hand, the material composition of beached litter was analysed in a standardized area on each beach. From these two datasets, the expected frequency of several rafting taxa was calculated for the coastal area and compared to the actually observed frequencies. The results showed that plastics were the most abundant type of beached litter. Litter accumulation was likely driven by coastal sources (industry, ports) and river/sewage inputs and transported by near-shore currents. Rafting vectors were almost exclusively made up of plastics and could mainly be attributed to fishing activity and leisure/ household. We identified a variety of rafting biota, including species of goose barnacles, acorn barnacles, bivalves, gastropods, polychaetes and bryozoan, and hydrozoan colonies attached to stranded litter. Several of these species were non-native and invasive, such as the giant Pacific oyster (<i>Crassostrea gigas</i>) and the Australian barnacle (<i>Austrominius modestus)</i>. The composition of attached fauna varied strongly between litter items of different materials. Plastics, except for foam, had a much more diverse attached community than non-plastic materials. The predicted frequency of several taxa attached to beached litter significantly correlated with the actually observed frequencies. Therefore we suggest that the composition of stranded litter on a beach or an area could allow for predictions about the corresponding attached biotic community, including invasive species.</p></div

Primers used for DNA amplification in different taxa.

<p>Primers used for DNA amplification in different taxa.</p

Abundance of anthropogenic litter, counted in a standardized area at the sampled beaches.

<p>Data are presented in a box-and whisker plot, with the middle box representing 50% of the values and the upper and lower whiskers representing the values outside of the 50% range. The median and outliers are indicated by a middle line and a circle (◦), respectively. Litter items were counted in a standardized area at each beach.</p

Multi-dimensional plot of the sampled beaches, based on abundance and composition of anthropogenic litter counted in a standardized area at each beach.

<p>HPl = hard plastics, OPl = Other plastics, Mix = beaches with mixed litter composition and less than 25 litter items in the standardized sampling area (> 0.35 items×m²).</p

Phylogenetic trees reconstructed from sequences obtained in this study and reference sequences from GenBank database (bold style).

<p>a) molluscs, b) crustaceans, c) polychaetes, d) hydrozoans. Frame = Species not native to the study area; * = Species listed in the invasive species database; + = Terrestrial species; # = reference without species voucher.</p

Particular profile of attached biota for each litter material.

<p>Particular profile of attached biota for each litter material.</p