For centuries, pelagic Sargassum, floating brown seaweed, have grown in low nutrient waters of the North Atlantic Ocean, supported by natural nutrient sources like excretions from fishes and invertebrates, upwelling and nitrogen fixation. Using a unique historical baseline from the 1980s and comparing it to samples collected since 2010, researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute and collaborators have discovered dramatic changes in the chemistry and composition of Sargassum, transforming this vibrant living organism into a toxic “dead zone.”

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