Scientists Are Puzzled Over Record Amounts of Sargassum

A record amount of sargassum piled up across the Caribbean and nearby areas in May, and more is expected this month, according to a new report. The amount—about 41 million tons, tallied through May—is the biggest quantity of algae observed across the Caribbean Sea, the western and eastern Atlantic, and the Gulf of Mexico since scientists began studying the Great Atlantic Sargassum Belt in 2011, said Brian Barnes, an assistant research professor at the University of South Florida who worked on the report published on Monday by the school's Optical Oceanography Lab. The previous record was set in June 2022, with some 24 million tons, and the new record is hardly stationary—experts said they expect even more sargassum in June. More from the AP:

• The issue: The brown prickly algae is suffocating shorelines from Puerto Rico to Guyana and beyond, disrupting tourism, killing wildlife, and even releasing toxic gases that forced one school on the French Caribbean island of Martinique to temporarily close.
• The puzzle: "The peaks just seem to keep getting bigger and bigger year after year," Barnes said. But scientists don't know why yet. "It's the million-dollar question," he said. "I don't have a supremely satisfying answer."
• The science: Three different types of sargassum exist in the Caribbean and nearby areas, reproducing asexually as they remain afloat thanks to tiny air sacs. They thrive in different ways depending on sunlight, nutrients, and water temperature, factors that scientists are currently studying, Barnes said.
• The science II: While large clumps of algae in the open ocean are what Barnes called a "healthy, happy ecosystem" for creatures ranging from tiny shrimp to endangered sea turtles, sargassum near or on the shore can wreak havoc. It can block sunlight that coral reefs need to survive, and if the algae sinks, it can smother reefs and seagrasses. Once it reaches shore, the creatures living in the algae die or are picked off by birds, Barnes said.
• The tourism angle: Huge piles of stinky seaweed also are a headache for the Caribbean, where tourism often generates big money for small islands. In the Dutch Caribbean territory of St. Maarten, crews with backhoes were dispatched in late May as part of an emergency cleanup after residents complained of strong smells of ammonia and hydrogen sulfide, which can affect a person's respiratory system. "It is a challenge, but it's certainly not affecting every single inch of the Caribbean," said Frank Comito, special adviser to the Caribbean Hotel and Tourism Association.
• One countermeasure: Officials in the French Caribbean expect to soon use storage barges and an upgraded special vessel that can collect several tons of seaweed a day. The sargassum "disfigures our coasts, prevents swimming, and makes life impossible for local residents," French Prime Minister Francois Bayrou recently told reporters. But Comito said such vessels are "massively expensive" and not a popular option.