The next time you vacation to a Caribbean beach like Cancún, you might be greeted with a smell of rotten eggs! Since 2011, blooms of a brown seaweed called Sargassum have been piling and decomposing on the Caribbean beaches where they make landfall. Decomposing algae remove oxygen from the water, killing marine life and affecting the businesses that depend on those beaches.

But how much marine death has been caused by the massive influxes of Sargassum? A team of researchers in the Yucatán region of México recently published an article in the Marine Pollution Bulletin that quantifies the mortality of marine life from 2018’s Sargassum bloom season. They counted the number of marine animals that had washed up on the east coast of the Yucatán, which includes popular tourist spots Puerto Morelos and Cancún. They also collected water samples to assess the water quality in the affected areas. 

The dead animals they found comprised 78 species. Over half were fish (59%), followed by crustaceans (28%) many of which came from shallow coral reef habitats close to the seaweed-strewn beaches. They also found that water quality was poor, with low-oxygen conditions and increased ammonium and hydrogen sulfide in the water. Conditions like that combined with the high amount of toxins have made a perfect storm of massive mortality from a decomposing seaweed. 

Managing the Sargassum in those coastal areas will be of utmost importance, as these heavy influxes of Sargassum will affect the local coastal environment and the economies that depend on those areas.