The largest Seaweed Bloom ever detected spanned the Atlantic in 2018

During the summer, vast, floating islands of Sargassum algae can blanket entire parts of the tropical Atlantic Ocean. The algae reached their largest extent on record in June 2018, forming a giant brown belt that extended for 8,850 kilometers from the west coast of Africa into the Gulf of Mexico. At least 20 million metric tons of Sargassum made up the belt, the largest bloom of seaweed ever detected, researchers say.

Satellite data tracking the extent of the mats over the last 19 years reveal a sudden, dramatic increase in the summer of 2011, and recurring almost every year since, the scientists report in the July 5 Science. This paper is authored by Mengqiu Wang and colleagues.

These annual massive mats of seaweed, which the researchers have dubbed the great Atlantic Sargassum belt, have been fueled in part by increasing nutrients pouring into the ocean from the Amazon River, the study suggests. Forests can both filter and regulate the flow of water from land to ocean. But with increasing fertilizer use and deforestation anticipated in the coming decades along the Amazon’s tributaries, such colossal blooms may become a new normal.

The floating algae islands have long provided an important shelter for turtles, fish, crabs, eels and other marine species. But there can be too much of a good thing, particularly when Sargassum mats crowd coastlines.