For months, Florida’s normally picturesque coastline has been plagued by a rotting tangle of seaweed, known as sargassum. Then, as quickly as the stinking mass had arrived, it began to disappear.
Beachgoers rejoiced, posting pictures of white sands and sparkling waters to social media. Scientists said they expected the sargassum in the Gulf of Mexico to eventually decline — but not that fast, or that much.
“That’s a surprise,” said Chuanmin Hu, a professor of oceanography at the University of South Florida, noting that there is still “a lot of sargassum” in the Tropical Atlantic. “The good news is that the sargassum season for Florida is very likely to end this year. But for the Eastern Caribbean, it’s not over yet,” he said.
Last month, the amount of sargassum in the Gulf of Mexico dropped by 75 percent, noted Dr. Hu and colleagues from the University of South Florida’s Optical Oceanography Laboratory in newsletter published last week.
Sargassum – a type of macroalgae that is naturally abundant in the Sargasso Sea – has long been seen floating in mats across the North Atlantic. But in 2011, scientists began to observe extraordinary accumulations of the algae extending in a zone from West Africa to the Caribbean Sea and Gulf of Mexico, according to 2019. to study.
The huge bloom continued to grow almost every year.
In March, scientists said they expected the blob to come ashore in Florida and elsewhere along the Gulf of Mexico. At sea, the blob provides habitat for fish, crabs and sea turtles, but on land it has begun to rot, emitting toxic fumes and fouling the region’s beaches during the busiest summer months.
“Avoid touching or swimming near seaweed,” the city of Deerfield Beach, Fla., warned residents about Facebooknoting research this suggested that the bloom may contain bacteria. In Miami-Dade Countytractors with rear-mounted blades traversed 17 miles of shoreline each day to “mix and mix” the algae, the county said.
Like other plants, sargassum has a natural life cycle, Dr. Hu said, and scientists expected it to decline in the Gulf of Mexico around September.
But scientists don’t know why the decline was so rapid. One theory is that strong winds caused by recent tropical storms could have dissipated the sargas into smaller clumps, or sunk it to the ocean floor, Dr. Hu said, making it difficult to see by satellite. “There could be other reasons, we just don’t know,” he added.
While floating sargassum can benefit marine animals by providing shade and shelter, it begins to die once it comes ashore, degrading water quality and polluting beaches, scientists say. The decaying algae also release hydrogen sulfide, a colorless gas that smells like rotten eggs, and can cause respiratory problems in humans. Certain types of bacteria can colonize rafts of sargassum and marine plastics that, once ashore, can pose a risk to public health, according to a recent study published by researchers from Florida Atlantic University.
Sarah Collier, who works for Seabird Key, a private island vacation rental in Key West, said her community has been on edge since hearing about the sargassum patch earlier this year. “It’s such a relief,” she said of news that it’s breaking up in the Gulf of Mexico, noting that she personally hasn’t seen more algae than usual.
But while tour operators, vacationers and locals in Florida enjoy sargas-free beaches, the situation is not so rosy further south.
The beaches of the Dominican Republic, Haiti, Puerto Rico, US Virgin Islands, British Virgin Islands, Lesser Antilles, Barbados and Trinidad are likely to remain threatened by algae for the next one to two months, Dr. Hu said.
He and his colleagues predict that for the next two to three months, the amount of sargassum in the Gulf of Mexico will remain minimal, and that it will either decrease or remain stable in the Caribbean Sea. While that’s good news for residents of Florida’s east coast, as well as the Florida Keys, sargassum is still likely to wash ashore in parts of the Caribbean, they said in the bulletin, noting that it is “difficult to predict an exact time and location for individual shore events.”