Detached aquaculture buoys in the SE Pacific: potential dispersal vehicles for associated organisms

Throughout the world's oceans a wide variety of floating plastics are found, among which buoys stand but for their high floatability and diversity and abundance of associated organisms. Between 2001 and 2005, we conducted 25 ship surveys in the Bay System of Coquimbo (BSC), during which we registered 34 detached buoys floating between 1 and 45 km from the coast. The objective of this study was to infer the possible origin of these buoys, identify the associated biota and characterize their biological traits. Short-term drift experiments (30 min) showed that buoys without rope responded primarily to the velocity and direction of the wind, while buoys with ropes (3 m length) followed surface currents. Using the wind velocity and direction during the 12 h before capture of the detached buoys, we estimated the hypothetical trajectories of these buoys during that time period. Results indicated that most buoys originated from aquaculture facilities in the BSC. A total of 134 different species from 14 phyla was found on 18 anchored (91 species) and 22 detached (116 species) buoys sampled. Community composition was similar among buoys - 54 % of all species were common for anchored and detached buoys-but a higher number of rare species occurred on detached buoys. Buoys do not seem to lose but rather gain organisms after detachment. The most common functional groups on these buoys were mobile species, suspension-feeders and species with sexual reproduction, separate sexes, internal fertilization and direct or very short larval development. Fouling communities on detached buoys were mostly in advanced successional stages, comprising diverse species (including several non-indigenous species) adapted to the conditions at the sea surface. These results suggest that floating buoys may transport associated species over extensive distances, thereby also contributing to the spread of non-indigenous species.