A Giant Blob of Seaweed is Heading to Florida
By Albeck-Ripka and Schmall, March 14, 2023, NY Times

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 seaweed extending in a belt
from West Africa to the Caribbean Sea and Gulf of Mexico, according to a 2019 study.

The immense bloom has continued to grow almost every year.

While scientists are still trying to understand exactly why and how the mass, known as the great Atlantic Sargassum belt, is expanding, it appears to be seasonal — coinciding with the discharge of major waterways, including the Congo, Amazon and
Mississippi rivers.

The runoff from these sources helps to feed the bloom with nitrogen and phosphorus, said Brian Lapointe, a research professor at Florida Atlantic University, who has spent most of his career studying sargassum. Fossil fuel emissions and the burning of
biomass — such as trees after deforestation — also produce nutrients, he added, that could be helping the sargassum to grow.

“These blooms are getting bigger and bigger and this year looks like it’s going to be the biggest year yet on record,” Dr. Lapointe said. In January, scientists measured the largest bloom for that month on record. “This is quite early to see this
much, this soon,” he added. “It just doesn’t bode well for a clean beach summer in 2023.”

According to the NOAA, 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.

https://www.nytimes.com/2023/03/14/us/seaweed-blob-florida-mexico.html

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