In the Antilles, sargassum is smothering mangroves and marine seagrass beds, making these spaces uninhabitable for wildlife and plants. Research by the University of the Antilles highlights the severe impact of these brown algae on biodiversity, following a 2025 request from the Guadeloupe prefecture. This issue, intensified since 2011, stems from climate change and shifts in ocean currents.
Sargassum, invasive brown algae, represents a major scourge for Caribbean islands and North American coastlines. They cause eye and respiratory irritations in populations exposed to toxic gases such as hydrogen sulfide and ammonia released by these decomposing mats.
Since 2011, their proliferation has intensified due to changes in ocean currents, climate disruption, and rising sea temperatures. In 2025, the Guadeloupe prefecture commissioned marine biologists from the University of the Antilles to assess the effects on biodiversity.
Initial findings show that mangroves and marine seagrass beds – these underwater plant formations vital as shelters and food sources for many species – are severely altered. "Overall, the bacteria that decompose sargassum when it reaches the shores consume all the oxygen, making the space uninhabitable for fauna and flora," summarizes Charlotte Dromard, a marine biology lecturer-researcher at the university.
These observations highlight the need to better understand the consequences for crucial ecosystems, as the impacts on natural environments remain partly unexplored.