A Giant Blob of Seaweed Is Heading to Florida

According to the National Oceanography and Atmospheric Administration, the sargassum blooms will continue to disrupt Caribbean waters into mid-October.

While floating sargassum can benefit marine animals by providing shade and shelter, the problems begin once it comes ashore. As the sargassum begins to die, it degrades the water quality and pollutes beaches, scientists say. It can also choke vital mangrove habitats and suck oxygen out of the water. The decaying algae also releases hydrogen sulfide, a colorless gas that smells like rotten eggs, and can cause respiratory problems in humans.

Last summer, the U.S. Virgin Islands declared a state of emergency, after “unusually high amounts” of sargassum piled up on its shores, affecting a desalination plant on the island of St. Croix. And in 2018, after a mass bloom that sprawled across about 5,500 miles in the Atlantic Ocean, doctors on the Caribbean islands of Guadeloupe and Martinique reported thousands of cases of “acute” exposure to hydrogen sulfide, according to a study published that year.

In the past, besieged beach towns have turned to various measures to rid themselves of sargassum: In Mexico, the navy has been recruited to scoop the seaweed from the ocean, and rake the country’s beaches. Meanwhile, some entrepreneurs have proposed transforming the seaweed into animal feed, fuel or construction materials.

But Dr. Lapointe, the research professor, warned that anyone experimenting with new uses for the seaweed should exercise extreme caution: sargassum contains arsenic, which, if used in fertilizer, could potentially make its way up the food chain.

The most immediate threat, however, is to tourism. “It’s having catastrophic effects,” he said.