A 5,000-Mile-Wide Mass of Seaweed Is Heading for Florida and Mexico

Known as sargassum, the algae can hurt tourism as it piles up on beaches and starts to rot

Seaweed piled up on the beach
Sargassum is not a new problem. But the mass of floating seaweed in the Atlantic Ocean is getting bigger, according to scientists. Andre Seale / VW PICS / Universal Images Group via Getty Images

A 5,000-mile-wide blob of brown seaweed is making its way toward North America and could soon wreak havoc on beaches throughout Florida, Mexico and the Caribbean, reports NBC News’ Denise Chow.

The thick raft of seaweed—known as the Great Atlantic Sargassum Belt—is not new, but scientists say it’s especially large now. What’s more, the giant sargassum blanket floating in the Atlantic Ocean appears to be making landfall several months earlier than normal this year, which “doesn’t bode well for a clean beach summer in 2023,” says Brian Lapointe, an ecologist at Florida Atlantic University, to the New York Times’ Livia Albeck-Ripka and Emily Schmall.

Sargassum typically makes landfall in May, then peaks in June and July. But already, the seaweed is starting to pile up on beaches in Florida’s Key West as well as in Mexico’s Cancun, Playa del Carmen and Tulum.

“These blooms are getting bigger and bigger, and this year looks like it’s going to be the biggest year yet on record,” Lapointe tells the Times.

Generally, the sargassum mat bobs harmlessly between West Africa and the Gulf of Mexico. Out in the middle of the Atlantic, it even provides some benefits, such as absorbing carbon dioxide and providing shelter for various marine creatures, including some fish, crustaceans and sea turtles.

But when the tangle of seaweed washes ashore, it starts to cause problems. It piles up on beaches and begins to rot, releasing toxic hydrogen sulfide into the air. Also known as “sewer gas” or “swamp gas,” the colorless hydrogen sulfide smells like rotten eggs and can cause respiratory and neurological issues in humans.

Person holding up clumps of seaweed in hands
Sargassum provides habitat for marine wildlife in the ocean and absorbs carbon dioxide. rjsinenomine via Wikimedia Commons under CC BY 2.0

Sargassum is a big turnoff to tourists, so it can also lead to economic consequences for the hotels, restaurants and other businesses that rely on travelers for their livelihoods. This year, its early arrival adds to the problems of Florida’s Gulf Coast tourism industry, which is already grappling with the harmful effects of a toxic red tide.

“It’s unpleasant,” says Melinda Simmons, a marine scientist at Jacksonville University, to First Coast News’ Robert Speta. “Whether you are swimming or wading in it, it’s going to smell bad. And then people don’t want to come to the beach.”

Beyond that, sargassum can make it challenging for boats to navigate through coastal waters. It can block the intake valves of desalination plants and power plants, which can lead to water shortages and other issues. It can also block light from reaching the plants and animals below the water’s surface and make it difficult for sea turtles to crawl across the sand to their nesting habitats or to the ocean.

Though communities and resorts try to remove as much of the seaweed from the beach as possible, that process is expensive and labor-intensive. And once they remove the sargassum, they then must figure out what to do with it. Sargassum contains heavy metals, including arsenic, that can make it dangerous to compost or use as fertilizer. Entrepreneurs are trying to come up with novel solutions to the sargassum problem—such as sinking it to the bottom of the seafloor or using it for building materials—but have so far struggled to make them commercially viable.

Scientists have been tracking the Atlantic sargassum raft for years. But in 2011, they started to notice that it was ballooning in size annually. The brown blob is now so large that it can be seen from space, and researchers use satellite imagery to keep tabs on it.

They aren’t exactly sure what’s causing the growth, but they suspect that human activities may be at least partly to blame. They’ve noticed that the sargassum mass tends to expand seasonally, around the same time that major rivers like the Congo, the Mississippi and the Amazon are discharging into the Atlantic. From this pattern, they’ve determined that runoff from fertilizers, deforestation and biomass burning may be unintentionally feeding the seaweed. Increasing ocean temperatures, which stem from human-caused climate change, may also be contributing.

“I’ve replaced my climate change anxiety with sargassum anxiety,” says Patricia Estridge, co-founder and CEO of Seaweed Generation, a Scotland-based company that aims to use seaweed to remove carbon emissions, to the Guardian’s Zan Barberton.

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