Sargassum seaweed blob on the way to Florida explained

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A giant blob of seaweed, twice the width of the mainland United States, is heading for the coasts of Florida and other Gulf of Mexico coastlines, threatening to dump smelly and potentially harmful piles over beaches and dampen the tourism season .

Sargassum – the specific variety of seaweed – has long formed large blooms in the Atlantic Ocean, and scientists have been tracking huge aggregations since 2011. But this year’s bloom could be the largest ever, spanning more than 5,000 miles (8,047 kilometers) from the coasts of Africa to the Gulf of Mexico.

This year’s sargassum blooms started forming early and doubled in size between December and January, said Dr. Brian Lapointe, a researcher at Florida Atlantic University’s Harbor Branch Oceanographic Institute. The crowd “was bigger in January than at any time since this new region of sargassum growth began in 2011,” he told CNN International’s Rosemary Church.

Workers remove sargassum from a beach in Punta Cana, Dominican Republic, in June.

Traveling west, the blob will push through the Caribbean and into the Gulf of Mexico in the summer. The seaweed is expected to appear on Florida beaches around July, Lapointe said.

“This is an entirely new oceanographic phenomenon that creates such a problem — a truly catastrophic problem — for tourism in the Caribbean, where it’s piling up on beaches up to 5 or 6 feet deep,” Lapointe said.

Here’s what you need to know about why these masses occur and how they affect both humans and ocean life.

Sargassum is a collective term that can be used to refer to more than 300 species of brown algae, although Sargassum natans and Sargassum fluitans are the two species most commonly found in the Atlantic Ocean.

When floating at sea, the algae may have benefits for ocean life.

“This floating habitat provides food and shelter for fish, mammals, seabirds, crabs and more,” said the Sargassum Information Hub, a joint project of several research institutions. “It serves as a critical habitat for endangered loggerhead turtles and a nursery for a variety of commercially important fish such as mahi mahi, jacks and amberjacks.”

The problems with sargassum arise when it hits the beaches, accumulating in hills that are difficult to navigate and emitting a gas that can smell like rotten eggs.

Sargassum can also quickly turn from an asset to a threat to ocean life.

It comes in such “large amounts that it basically sucks the oxygen out of the water and creates what we call dead zones,” Lapointe said. “These are normally breeding grounds for fisheries…and once they’re deprived of oxygen, we’ve lost that habitat.”

Sargassum can also be dangerous to humans, Lapointe added. The gas emitted by the decaying algae – hydrogen sulfide – is toxic and can cause breathing problems. The seaweed also contains arsenic in its flesh, making it dangerous if ingested or used as fertilizer.

“You have to be very careful when you clean the beaches,” Lapointe said.

Like plants and crops on the ground, seaweed proliferation can shift from year to year depending on ecological factors, influenced by changes in nutrients, rainfall and wind conditions, said Dr. Gustavo Jorge Goni, an oceanographer at the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory.

Ocean currents also affect sargassum growth and how much it accumulates, Goni added. Phosphorus and nitrogen in the sea can serve as food for the algae.

Those elements can be dumped into the ocean from rivers, which acquire concentrations of phosphorus and nitrogen through human activities such as agriculture and fossil fuel production, according to the U.S. Environmental Protection Agency.

For now, researchers are exploring ways to thwart the seaweed’s impact on beaches, possibly sinking it to the bottom of the ocean or harvesting it for use in commercial products like soap, Goni said.

Goni cautioned that research on these buildups of sargassum is new, and it’s likely that scientists’ understanding of how the algae grow will change over time.

“Whatever we think we know today,” he said, “may change tomorrow.”

Before you travel to coastal areas this spring or summer, research whether sargassum is at your destination or might appear there, Lapointe said. Plan ahead so your vacation won’t disappoint.

There are sargassum Facebook groups, with members posting about what they’ve recently seen on beaches, Lapointe said.

“It has already affected the travel industry,” he said.

Tourists enjoy the beach despite sargassum algae buildup in Cancun, Mexico, in May 2021.

Unfortunately, sargassum can build up overnight, so you may not be able to predict its effects on a trip, Lapointe said.

“That’s why we’re trying to work on these early warning systems — high resolution in coastal areas, which would require higher resolution satellite imagery to better show what’s actually hitting a beach within the next 24 or 48 hours,” he added .

Satellite images from the past week show that sargassum is not an amorphous mass moving across the ocean, but rather teardrop-shaped blobs followed by long, thin strands of seaweed.

In the past week, sargassum blobs have been spotted about 346 kilometers from Guadeloupe, between the islands of St. Vincent and Bequia, 914 meters from Martinique and off the coast of Key Largo, Florida.

Algae piles that have built up on beaches cost millions of dollars to clean up, and removal efforts can also harm marine life, according to the Sargassum Information Hub.

In Barbados, locals “used 1,600 dump trucks a day to clean the beaches of this seaweed to make it suitable for tourists and recreation on the beaches,” Lapointe said.

In shallow waters, sargassum can be removed using fishing nets pulled by light boats or by hand, according to the Dutch Caribbean Nature Alliance.

In the U.S., cleanup is often done with Barber beach rakes pulled by a tractor, Lapointe said. But once there’s a buildup of more than a foot of sargassum, the rakes don’t work as well, he added. That’s when front loader dump trucks can be useful, but they can be detrimental to the health of the beach.

Using dump trucks to remove sargassum can become problematic.

“Often you have sea turtle nests on beaches that get run over by tires from this heavy equipment that crushes the eggs,” Lapointe said.

If sargassum isn’t cleaned from beaches or used as fertilizer, the arsenic in its flesh can leach into groundwater, which could pose a health hazard to humans, Lapointe said.

An excessive amount of rotting sargassum can also support the growth of fecal bacteria.

And in 2018, a massive bloom that hit South Florida beaches coincided with the largest red tide ever seen on that coast, Lapointe said. Red tides occur when toxin-producing algal blooms get so out of control that they discolor coastal waters. Red tide organisms can live on and be transported by sargassum.

The toxins in red tides can harm marine life, and sargassum buildup on beaches can prevent sea turtles and adults from reaching the sea, Lapointe said.

Experts don’t know if a sargassum bloom of this size will happen every year, Lapointe said.

“It’s hard to project because we don’t know everything we need to know about the drivers[behind this],” he said. “We know it varies from year to year and the trajectory is generally going up. So based on what we’ve seen in the past, we think we could continue to see this worsen in the coming years. What will it be like in 10 years? Will it be twice as big as it is now?”

More money is needed to do the research that can answer these questions, he added.

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