A massive “seaweed blob” that is part of the Great Sargassum Belt is once again making headlines and could have beachgoers wondering if their upcoming sand-filled getaways along the Gulf of Mexico and Atlantic Ocean in the Caribbean and Florida might be plagued with a layer of rotting, stinking algae.
At the start of this year, University of South Florida scientists released data showing that the amount of seaweed in the Great Sargassum Belt—a 5,000-mile-long area containing a loose collection of patches of the brown floating seaweed, located between West Africa and the Gulf of Mexico—had doubled in size in two consecutive months (December 2022 and again in January 2023). But in a new report released at the end of May, the same team of researchers found that the amount of seaweed in the belt had decreased by 15 percent during May when compared to April 2023.
“The reasons behind such a sharp decrease remain to be investigated,” the new report stated, adding that “looking ahead, because of the unexpected sharp decrease in the eastern Atlantic and the relatively stable amount elsewhere, it is difficult to predict whether sargassum quantity in the individual regions will increase or decrease.” The researchers noted that the amount of sargassum is expected to remain “relatively high” this year compared to past years.
To better understand what the rapidly growing mass of seaweed will mean for some of our favorite beach destinations in the coming months, we reached out to some experts.
What is sargassum?
Chances are if you’ve ever been on a beach lapped by the Atlantic Ocean or Gulf of Mexico, you’ve already encountered sargassum, in whatever small amount, along the shoreline or in the water.
The naturally occurring brown seaweed floats freely on the ocean’s surface, extending as deep as 10 feet below the surface, and sometimes makes its way to shore with currents and wind.
“It’s a floating brown macroalgae, related to kelp, but it’s always afloat, never attached to the bottom,” explains Brian Barnes, an expert on marine sciences and assistant professor at the University of South Florida, which collects data on sargassum blooms in the Caribbean Sea.
Sargassum is composed of gas-filled structures that look like berries called pneumatocysts that keep it buoyant.
Visible from outer space, the Great Sargassum Belt that’s making headlines of late is a 13-million-ton mass that stretches 5,000 miles long and 300 miles wide in an area of the Atlantic Ocean between the Gulf of Mexico and the coast of West Africa.
“It’s a good thing when it’s out offshore,” says Brian LaPointe, a research professor with Florida Atlantic University Harbor Branch Oceanographic Institute in Fort Pierce, Florida. “Sargassum provides habitat for hundreds of species and invertebrates and even endangered sea turtles, supporting pelagic fisheries like mahi mahi and other fish that feed on prey items.” (Pelagic fish are fish that live and eat near the water’s surface.)
“It’s when it comes ashore in mass, that’s when it becomes a problem,” LaPointe says about the seaweed.
Sargassum can emit a strong, rotten egg–like odor when it decomposes on shore.
Photo by Shutterstock
Can you swim in the water when there is sargassum present?
Depending on how thick it is, swimming in water where sargassum is present may require pushing it out of the way to clear a route. And sargassum can feel scratchy, kind of like a loofah sponge, when it rubs up against you. (Dolphins have been reported to play with sargassum and may even use it to scratch themselves, according to the Wild Dolphin Project.) But for humans, there can be some unpleasant conditions associated with swimming where sargassum is abundant, says LaPointe.
“You can swim in the water if there’s sargassum and people do, but I have seen some reports of sea lice associated with sargassum in water with big mats of it floating around,” he says, referring to small jellyfish larvae, which can cause the skin to erupt in a red, itchy rash.
Additionally, “There are some risks of stinging organisms to be aware of,” LaPointe says, referring to jellyfish that can also often be present among sargassum.
The odor of sargassum—which can smell like rotten eggs when it decomposes due to the production of the hydrogen sulfide gas—can be off-putting. LaPointe notes that there have been reports of respiratory issues in areas with large amounts of decomposing sargassum on the shore due to the hydrogen sulfide released.
Why is there so much sargassum right now?
Barnes says that scientists are currently studying why there is so much sargassum right now. From his perspective, he says it comes down to current conditions being ideal for it to grow.
“Just like land plants, you need the right light environment, the right temperature,” for growth, he says, as well as a seed (the seed in this case is the population of sargassum that’s already out in the Great Sargassum Belt). Nutrients rising from the ocean depths or from rivers flowing into the region act as fertilizers, adding to the ideal conditions for growth.
LaPointe says the scale of the current bloom is “all about the nutrients.”
“The more you feed it, the bigger it gets,” he says, adding that there’s evidence that nutrient runoff (in the form of nitrogen and phosphorus from human activities and sources such as fertilizers, wastewater, automobile exhaust, and animal waste) from rivers—including the Mississippi River, Amazon River, and Congo River—are feeding sargassum blooms all along the Atlantic Basin.
Which beaches and destinations will be most affected by the growing sargassum belt?
“This is not the first time we’ve seen major blooms,” Barnes says, pointing to record blooms in 2018 and 2022. However, there were no such major blooms prior to 2011, he adds, saying there is no clear explanation for why.
All of the islands in the Caribbean are in the target zone for where sargassum might wash shore, he says, with the Southern Lesser Antilles (which includes islands such as Aruba, Bonaire, Curaçao, Margarita Island, and Trinidad and Tobago) likely to be slightly less impacted than elsewhere in the Caribbean. “But that’s not to say they’ll see no impact,” he says of those places.
Other areas in the sargassum belt’s target zone include the Yucatan (on the Gulf of Mexico coasts of Belize and Mexico), the Gulf of Mexico (from Florida’s panhandle west into Texas), and southeast Florida, from the Florida Keys northwest to around Fort Pierce, says Barnes.
“Despite the fact that Florida has previously been hit pretty hard, sargassum is a much bigger problem in the Caribbean than Florida,” he says. “That’s true this year, so far, and in previous years.” The reason why the problem looms larger in the Caribbean is due to currents there that deliver sargassum to the area in more abundance and keep it circulating there for longer.
“We can’t predict what’s going to happen this summer, but in past years Mexico has been impacted quite heavily, as well as the eastern Caribbean, including places like Barbados and Martinique,” says LaPointe.
LaPointe says it’s important to remember, too, that where sargassum accumulates is highly variable.
“It can come in on one day with strong winds and pile up, and the next day the wind may shift and currents can change and will carry this stuff offshore,” he says.
Is there anything destinations and beachfront hotels and resorts can do to mitigate the problem?
Keeping sargassum at bay from a beach where it’s determined to wash ashore is like fighting a rising tide. And scenes of workers pitchforking and shoveling piles of seaweed into waiting wheelbarrows around the clock have, unfortunately, become a somewhat standard oceanfront backdrop in recent years at beaches in popular warm-weather destinations like Playa del Carmen and Tulum in Mexico and Barbados in the Caribbean.
Apart from removing what washes ashore as it arrives, Barnes says a hotel might consider installing a floating boom offshore (usually made of PVC and deployed parallel to the shoreline) with the goal of preventing sargassum from coming ashore. But again, it represents a small measure against a monumental task.
Booms are not 100 percent effective, he says, and can only be implemented in relatively small areas in the context of the larger bloom. Because booms can’t be infinitely long, sargassum can seep in at their ends and still make its way to the sand.
“They work, but not perfectly,” Barnes says.
However, one place that’s likely to be perfect on a sunny day no matter what the Great Sargassum Belt and ocean currents and winds are doing? That’s your hotel pool, preferably one with ocean views.
After all, it never hurts to have a beach day backup plan.
This story was originally published on March 24, 2023, and has been updated to include current information.
