Surge in nitrogen has turned sargassum into the world's largest harmful algal bloom

Using a unique historical baseline (1983-2019), scientists have discovered dramatic changes in the chemistry and composition of Sargassum, floating brown seaweed, transforming this vibrant living organism into a toxic 'dead zone.' Results suggest that increased nitrogen availability from natural and anthropogenic sources, including sewage, is supporting blooms of Sargassum and turning a critical nursery habitat into harmful algal blooms with catastrophic impacts on coastal ecosystems, economies, and human health. Globally, harmful algal blooms are related to increased nutrient pollution.