Sargassum Shift

Some coastal areas along the Caribbean Sea and the Gulf of Mexico have had a big, stinky problem over the past decade or so. Big mats of seaweed have been washing ashore. It can harm other marine life, while making the beaches unpleasant.

The seaweed is called sargassum. In the open ocean it provides habitat, shelter, and hunting grounds for fish, sea turtles, and other creatures.

It’s been concentrated in the Sargasso Sea—a wide area that extends from the southeastern coast of the United States into the Atlantic Ocean. But over the past decade, the amount of sargassum in that region has dropped dramatically. That might be a result of changes in the Gulf, where annual blooms of the seaweed begin. At the same time, a new region started to develop—the Great Atlantic Sargassum Belt, populated by a different species of sargassum.

The belt stretches from West Africa to Brazil and into the Caribbean. It’s grown larger and denser over the years. It might be fed by nutrients from the Amazon River and other sources. Or it might be fed by changes in circulation patterns in the Atlantic, which dredge more nutrients from the deep ocean.

As the sargassum reaches shore, it can choke seagrass beds and reef systems. As it decays, it produces a gas that smells like rotten eggs. And it can contain high levels of arsenic and other nasty compounds. So the new area of sargassum is providing great habitat in the open ocean, but a headache for many coastal regions.