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.