Reduced transfer of metals and metalloids from pelagic Sargassum spp. accumulated in artificial floating barrier.

Since 2011, holopelagic Sargassum have been massively stranding in the coastal environments of the Caribbean Islands inducing damages to coastal ecosystems, public health and the economy. To limit the risks associated with Sargassum stranding, floating barriers with nets can be placed in front of sensitive areas, to divert Sargassum away from the coast. To evaluate the potential transfer of metallic trace element (MTE) from Sargassum to adjacent marine life, seagrasses (Halophila stipulacea, Thalassia testidinum) and urchin (Lytechinus variegatus) were sampled, both close (0 m) and far (200 m) from barriers installed during 4 years in two bays: Baie Cayol (BC) and Cap Est (CE) in Martinique (FWI). A bay without barriers Baie-Tresor (BT) was also sampled in order to compare the effects of Sargassum accumulated in a natural environment versus an environment with floating barriers. The short-term effects of barriers were evaluated by measuring the evolution of MTE after four days, in the algae (Dictyota spp.), located close to Sargassum accumulations. All sampling was realized during two periods of active (July 2021) and reduced (January 2022) Sargassum stranding. The measured concentrations of 19 metal(loid)s trace elements revealed that the proximity of Sargassum to the barriers did not increase MTE concentration. The absence of increase in MTE was observed all sites (BT, BC and CE) and during periods of limited and important Sargassum stranding. Similarly, translocations of Dictyota close to Sargassum accumulations did not reveal any increase in MTE concentrations in the algae after 4 days. The present study suggests that the use of barriers to manage Sargassum stranding would not constitute an important threat of MTE contamination of marine environments.