http://www.sciencemag.org/news/2018/06/mysterious-masses-seaweed-assault-caribbean-islands

Deep drifts of Sargassum seaweed swept ashore on Guadeloupe in April.

In retrospect, 2011 was just the first wave. That year, massive rafts of Sargassum—a brown seaweed that lives in the open ocean—washed up on beaches across the Caribbean, trapping sea turtles and filling the air with the stench of rotting eggs. “We had some really massive turtle kills,” says Hazel Oxenford, a fisheries biologist at The University of the West Indies in Cave Hill, Barbados. Before then, beachgoers had sometimes noticed “little drifty bits on the tideline,” but the 2011 deluge of seaweed was unprecedented, she says, piling up meters thick in places. “We’d never seen it before.”