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 mu g 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.

Automated summary

This study examines the kinetics of metal trace elements (MTE) in Sargassum in different coastal environments. It found variations in MTE content and evolution rates among different habitats. The mangrove habitat showed the most rapid evolution of MTE, while Sargassum natans I had a different metal composition compared to other morphotypes. All Sargassum morphotypes rapidly release arsenic (As) when they reach coastal habitats. To prevent the transfer of As to coastal environments, the stranding of Sargassum should be avoided and the As content should be considered in its utilization.