Health Dangers of Florida Seaweed Blob

The gargantuan clump of seaweed that has been slowly floating toward Florida is now washing up on beaches across the state and might be harmful to people and wildlife nearby.

The blob of seaweed is about 5,000 miles across, and is composed of sargassum seaweed, which naturally blooms in the Sargasso Sea but can spread widely across the Atlantic, forming the "Great Atlantic Sargassum Belt."

In March and April, the seaweed clump was estimated by researchers at the University of South Florida's Optical Oceanography Lab to contain about 13 million tons of sargassum, a record amount for that time of year.

Now, however, as the seaweed inundates beaches across Florida and the Caribbean, people and animals might be at risk from the negative health effects of the rotting seaweed.

"Anyone with compromised lung function should avoid areas with sargassum blooms—when the seaweed decomposes, it releases hydrogen sulfide [the smell of rotten eggs] and can be a respiratory irritant," Kait Parker, an atmospheric scientist at the Weather Company, told Newsweek.

Sargassum is a floating brown algae, the National Oceanic and Atmospheric Administration explained, and like any living material, it begins to rot in the right conditions. As the seaweed gathers on the beaches that it's washed up onto, it starts to rot, releasing a horrible smell as well as harmful compounds like hydrogen sulfide.

Hydrogen sulfide is toxic to breathe, the Centers for Disease Control and Prevention said, and can cause respiratory problems and eye irritation. Major exposure to hydrogen sulfide can cause symptoms including convulsions, dizziness, headaches, weakness and nausea.

More than 11,000 cases of acute sargassum toxicity were reported in the eight months after a 20-million-ton sargassum bloom in 2018 across Guadalupe and Martinique, the symptoms of which included heart palpitations, shortness of breath, dizziness, headache and skin rashes.

"Additionally, sargassum should not be consumed, as it contains heavy metals such as arsenic and cadmium. As for cleaning up—it's best left to professionals. While the blooms aren't harmful to touch, the microorganisms living on it can cause skin irritation," Parker said.

The sargassum can wash up in great piles on tourist beaches, which can be a major problem for tourists and locals alike.

"The beaches are narrow and not very wide, so it just covers them up," Stephen Leatherman, a professor of coastal science at Florida International University, previously told Newsweek. "It was so bad in Cancún a couple of years ago that 2,000 people in the Navy had to go out there with pitchforks and other means, just trying to clean it off the beach so they could see the sand."

Those attending sargassum-inundated beaches or clearing the seaweed are urged by the Florida Department of Health to avoid touching or swimming near the seaweed to avoid stinging by organisms that live in it, and to use gloves if you must handle seaweed. People with respiratory issues are warned to stay away from the beaches, or to shut windows and doors if they live close to the coast.

The seaweed can also clog up intakes, which is what happened in July last year, when the U.S. Virgin Islands and the Federal Emergency Management Agency (FEMA) declared a state of emergency after a desalination plant's intakes filled with sargassum.

Wildlife can also be impacted by these huge sargassum blooms. Usually, it provides hundreds of species with shelter and food, including a number of turtles, birds and invertebrates. However, when the blooms get too large or thick, they can starve coral reefs and seagrasses of sunlight they need for photosynthesis, or use up a lot of oxygen in the water, leaving little for fish.

"It can actually kill turtles if the mass is so extensive that turtles have to go up for air every 20 minutes or so," Leatherman said. "They go under it, these huge masses that can go for a mile or so in the worst areas. Then some turtles have actually drowned underneath them. But that's fairly rare."

According to the University of South Florida's Optical Oceanography Lab, the peak of sargassum season is expected to occur in June, with the impacts of the seaweed continuing through July. Additionally, the size of the sargassum blooms has been increasing over the past few years, with the amount of seaweed measured between 2017 and 2022 about double the amount from the previous six years. That might be because of increased release of fertilizers into rivers, which eventually end up in the oceans, triggering blooms of algae like sargassum.

"The Amazon is being deforested to make more agricultural land and to improve agriculture in Brazil," Leatherman said. "But when you do that, you have to add fertilizer, and a lot of fertilizer.

"Unfortunately, it enters the Amazon River, which is one of the largest rivers in the world, and pushes its waters way out in the ocean. And out there it hits the Sargassum belt, and then it multiplies by the billions over days or over time. And so I think that's one of the big problems, that we're getting so much more of it in the Caribbean, in South Florida and the South Atlantic."

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