A loose raft of brown seaweed spanning about twice the width of the United States crosses the Caribbean. Currently, buckets of floating seaweed are washing up on Florida’s east coast beaches earlier in the year than usual, causing scientists to worry about what the coming months will bring.
Seaweed is composed of species of algae of the genus Sargassum. These species grow as a mat of algal globules that stay afloat via small air-filled sacs attached to leafy structures. Algae form a belt between the Caribbean and West Africa in the Sargasso Sea in the North Atlantic Ocean then ride the currents west. Scientists say reports of a massive mass of seaweed crashing onto shorelines are exaggerated because the Sargassum seaweed is scattered throughout the ocean, and most seaweed will never reach the sandy shores of the coast. But in recent years, researchers have generally observed so-called Sargassum blooms. And once seaweed starts washing up on beaches and rotting, it can cause serious problems, local communities say.
Among the annuals Sargassum censuses in the Atlantic Ocean, “2018 was the record year, and we’ve had several great years since,” says Brian Lapointe, an oceanographer at Florida Atlantic University who has studied algae for decades. “It’s the new normal, and we’re going to have to adapt to it.”
THE seaweed “blob” has been dubbed the Great Sargassum Belt of the Atlantic, and although it’s sprawling, algae in the belt only cover about 0.1% of the water’s surface, says Chuanmin Hu , an oceanographer at the University of South Florida, who has used satellites to study Sargassum For almost 20 years.
Hu and his colleagues estimate the total mass of Sargassum in the Atlantic each month, following an annual cycle that usually peaks in June. To do this, they use data collected by NASA satellites such as Terra and Aqua, as well as National Oceanic and Atmospheric Administration satellites. Algae broke the record for the highest amount ever recorded in the Atlantic last year, with some 22 million metric tons found across the ocean, according to the team’s calculations.
Hu says the team estimated that the Atlantic contained about six million metric tons of Sargassum in February and that he is convinced that the mass in March will be higher. “This month there should be more. There is no doubt,” Hu said. “Even in the first two weeks, I saw increased amounts.”
In the ocean, said Hu, the Sargassum is a critical habitat for fish and turtles, among other marine species. He calls the belt a “moving ecosystem”. And only a small fraction of the algae in the Atlantic will wash up on beaches, adds Hu.
But the beaches of Fort Lauderdale and the Florida Keys are already reporting Sargassum deposits this year, says Lapointe, and it’s on the beaches that algae can be problematic. There, he says, the algae rots and releases chemicals such as hydrogen sulfide gas, which smells like rotten eggs. When inhaled, the gas can also cause headaches and irritate a person’s eyes, nose and throat. People with asthma or other respiratory problems may be more sensitive to the effect, according to Florida Department of Health. The early arrival of seaweed raises concerns about what this summer could bring.
“It’s quite early in the Sargassum season to see that many happen, so I think that also feeds into some of the worry about what’s to come,” Lapointe says.
Hu says that Sargassum quantities cannot be predicted more than two or three months away, so this year’s seasonal peak in summer is still too far away to be predicted. Researchers expect this year to be rich in algae, as even the winter lull has seen higher than average amounts.
And the Atlantic reliably produced much more Sargassum in recent decades than it has historically. Lapointe says that the top Sargassum levels in recent years are probably partly related to nutrient rich water flowing from the land into rivers and to the oceans, where it can fertilize algae. But understanding and solving the problem remains thorny, he adds.
“It’s been going on for over 10 years now, and we haven’t made much progress in understanding all of these nutrient and climate factors better,” he says. “It’s something we’re working on as scientists.”