Here’s the real story behind the massive blob of seaweed heading towards Florida

A loose raft of brown seaweed stretching twice the width of the United States is inch by inch across the Caribbean. Currently, bucket loads of the floating seaweed are washing up on beaches on Florida’s east coast earlier in the year than usual, raising scientists’ concerns for the coming months.

The seaweed consists of algae species of the genus Sargassum. These species grow as a mat of clumps of algae that stay afloat by small air-filled sacs attached to leaf structures. The algae form a belt between the Caribbean and West Africa in the Sargasso Sea in the North Atlantic and then ride west with the currents. Scientists say reports of a massive clump of seaweed slamming into shorelines are exaggerated because the sargassum algae are scattered across the ocean and much of the algae will never reach the shore’s sandy shores. But in recent years, researchers have generally seen larger so-called sargassum flowers. And once the seaweed starts washing up on beaches and rotting, it can cause serious problems, local communities say.

Among the annual Atlantic sargassum censuses, “2018 was the record year, and we’ve had several big years since then,” says Brian Lapointe, an oceanographer at Florida Atlantic University who has studied algae for decades. “It’s the new normal and we have to adapt to it.”

The algae “blob” has been dubbed the Great Atlantic Sargassum Belt, and though it’s spreading, the algae in the belt only cover about 0.1 percent of the water’s surface, says Chuanmin Hu, an oceanographer at the University of South Florida who used Satellites to study Sargassum for almost 20 years.

Estimating the total mass of sargassum in the Atlantic each month, Hu and his colleagues track an annual cycle that typically peaks in June. To do this, they use data collected by NASA satellites such as Terra and Aqua, as well as satellites from the National Oceanic and Atmospheric Administration. Last year, the seaweed broke the record for the highest amount ever measured in the Atlantic, with about 22 million tons of the material found across the ocean, the team calculated.

Hu says the team estimated the Atlantic contained about six million tons of sargassum in February, and he’s confident the mass will be higher in March. “There should be more this month. There’s no doubt about it,” says Hu. “Already in the first two weeks I saw increased amounts.”

In the ocean, Hu says, the sargassum is a crucial habitat for fish and turtles, among other marine life. He calls the Belt a “mobile ecosystem.” And only a small fraction of the algae present in the Atlantic ever washes up on beaches, Hu adds.

But beaches in Fort Lauderdale and the Florida Keys are already reporting sargassum occurrences this year, Lapointe says, and the algae can be a problem on beaches. There, he says, the algae rot and release chemicals like hydrogen sulfide, which smell like rotten eggs. When inhaled, the gas can also cause headaches and irritate a person’s eyes, nose, and throat. According to the Florida Department of Health, people with asthma or other breathing problems may be more sensitive to the effects. The seaweed’s early arrival raises concerns about what this summer may bring.

“It’s pretty early in the sargassum season to see that much coming in, so I think that also fuels concern about what’s to come,” says Lapointe.

Hu says sargassum levels can’t be predicted more than two or three months in advance, so this year’s summer seasonal peak is still too far away to predict. However, researchers have expected this year to be rich in algae, with above-average levels seen even in the winter doldrums.

And the Atlantic has reliably produced far more sargassum in recent decades than it has in the past. Lapointe says the high levels of Sargassum in recent years are likely related in part to nutrient-rich water flowing from the land into rivers and out to the oceans, where it can fertilize the algae. But understanding and addressing the problem remains difficult, he adds.

“It’s been going on for over 10 years now, and we haven’t made much progress to better understand all these nutrient and climate drivers,” he says. “That’s what we’re working on as scientists.”