Kinetics of metal and metalloid concentrations in holopelagic Sargassum reaching coastal environments.

Since 2011, the Caribbean Islands have experienced unprecedented stranding of a pelagic brown macroalgae Sargassum inducing damages for coastal ecosystems and economy. This study measures the kinetics of metal trace elements (MTE) in Sargassum reaching different coastal environments. In July 2021, over a period of 25 days, fixed experimental floating cages containing the three Sargassum morphotypes (S. fluitans III and S. natans I and VIII) were placed in three different coastal habitats (coral reef, seagrass, and mangrove) in Guadeloupe (French West Indies). Evolution of biomasses and their total phenolic content of Sargassum reveals that environmental conditions of caging were stressful and end up to the death of algae. Concentrations of 19 metal(loid) trace elements were analyzed and three shapes of kinetics were identified with the MTE that either concentrate, depurate, or remains stable. In the mangrove, evolution of MTE was more rapid than the two other habitats a decrease of the As between 70 and 50 µg g-1 in the mangrove. Sargassum natans I presented a different metal composition than the two other morphotypes, with higher contents of As and Zn. All Sargassum morphotype are rapidly releasing the metal(oid)s arsenic (As) when they arrive in studied coastal habitats. In order to avoid the transfer of As from Sargassum to coastal environments, Sargassum stranding should be avoided and their valorization must take into account their As contents.

Metals and metalloids concentrations in three genotypes of pelagic Sargassum from the Atlantic Ocean Basin-scale.

Since 2011, the Caribbean Islands have witnessed unprecedented massive stranding of a pelagic brown algal Sargassum spp. inducing damages for coastal ecosystems and economy. By accumulating heavy metals, Sargassum can play a role in contaminant transportation from offshore to the coast. In 2019, three genotypes of Sargassum (S. fluitans III, S. natans I, and VIII) were sampled in seven stations along a 3400 km transect in the Atlantic Ocean. Concentrations of 15 heavy metal(loid)s elements were analyzed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). Mean metal concentrations were ranked following descending order: As >Fe > Al > Mn > Cd > Zn > Ni > V > Cu > Cr > Hg. The metalloid As was the most abundant contaminant with a maximum value of 115 ppm, previously observed in the Caribbean area (80-150 ppm). At Atlantic Ocean Basin-scale, metallic element concentrations do not present spatial longitudinal gradients. Genotypes S. fluitans III and S. natans (I and VIII), present differents metal(loid)s contamination distinct patterns.

First assessment of Atlantic open ocean Sargassum spp. metal and metalloid concentrations.

Over the last decade, increasing proliferations of Atlantic Sargassum populations have led to massive beaching with disastrous environmental consequences. This study is a preliminary assessment of open ocean Sargassum spp. element concentration to assess their potential contribution on coastal ecosystems. Sargassum spp. samples from seven sites, collected along a transect from the center of the Atlantic Ocean to near the coast of Martinique (French West Indies), were analyzed to determine their potential metal and metalloid enrichment. Mean element concentrations from the Sargassum spp. samples were ranked in the following descending order: As > Fe > Mn > Al > Zn > V > Ni > Cu > Cr > Cd > Hg. Element concentrations are relatively low compared to previous results of beached Sargassum spp. except for As that need to be carefully considered before reusing Sargassum spp.