Skip to main content

Sargassum Blooms Grow Monstrous, And Researchers Say More Will Come

A Kemps Ridley turtle navigates  the sargassum on a Corpus 
Christi, Texas beach.

A Kemps Ridley turtle navigates the sargassum on a Corpus Christi, Texas beach.

It’s not your imagination. The stuff is worse than ever.

Sargassum, the stinky seaweed that blankets beaches, clogs canals and strangles boat propellers, is piling up at levels and in places that researchers have never seen. What began in 2011 as an annoying increase in sargassum blooms has become a seven-year trend that continues to worsen, to the point that news headlines now sound like doomsday scenarios. “Sargassum a potential natural disaster for Caribbean beaches,” Mexico News Daily warned. “Worst Seaweed Assault on Record,” The Palm Beach Post’s weather expert wrote. “Masses of Seaweed Threaten Fisheries,” NPR reported.

In Barbados, a biologist documented 12-foot-tall sargassum piles along the shoreline. (Consider the height of your boat saloon’s ceiling, and think about that one for a moment.) This past June, researchers found 1,158 square miles of sargassum in the Caribbean Sea — covering about the same area as the state of Rhode Island. That’s three times as much sargassum coverage as in 2015, which held the previous record. In Quintana Roo, Mexico, home to the tourist mecca Cancun, hotels are reportedly paying more than $50,000 a month to clear the beaches of buildups.

“What they’re reporting is real,” Brian Lapointe, a research professor at Florida Atlantic University, told Soundings from Key West, where he was researching sargassum in early August and trying to wrap his mind around the sheer size of a bloom that satellite imagery shows stretching across the width of the Atlantic Ocean. “Where we used to see little patches of it, we’re seeing acres of it. Sometimes it’s the size of islands. Down in the Caribbean, looking down from the plane, it was scary. It was all that sargassum coming in from that huge belt between Africa and the Caribbean. I looked out the window and said, ‘Oh my God.’ I’ve been working in the Caribbean my whole life, and I’ve never seen anything like it.”

Sargassum has been around for centuries, at least since the days of Christopher Columbus. It’s brown or dark green, with little air bladders that look like berries and help it float. It often grows around near-shore coral reefs, and for generations was a mere nuisance, if any problem at all.

Sargassum is piling up on beaches in the Caribbean, Gulf of Mexico and Florida, including Dania Beach.

Sargassum is piling up on beaches in the Caribbean, Gulf of Mexico and Florida, including Dania Beach.

The scope of sargassum on the water has changed dramatically in the past seven years. Massive blooms now create fish kills, ensnare dolphins, smother sea turtle nests, trap commercial boats, gross out tourists, and decompose with a rotten-egg smell and gases so noxious that they’ve forced Caribbean beach-dwellers out of their homes.

Sargassum is also deluging beaches in a way that traditional sand-raking machinery can’t handle. The blooms are like the blizzards that overwhelm snow throwers from Massachusetts to Maine each winter. Beachfront communities are having to bring in bulldozers, backhoes and dump trucks to deal with the mountains of decaying mass. Instead of a surgical strike with the sandraker, it requires more of a wholesale attack where the heavy equipment tears away at the sand, contributing to beach erosion in the process.

Researchers continue to debate the reasons why the blooms have gotten so big and spread so far, with no end in sight. Theories include warmer sea temperatures, changing ocean currents and, according to research by Lapointe and others, runoff from fertilizer used in farming on land.

Lapointe started his career at the Woods Hole Oceanographic Institution in Massachusetts in the 1970s. His mentor did a study on the Sargasso Sea in the North Atlantic, and showed that the waters there didn’t have the nutrients that sargassum needed to grow. The research piqued Lapointe’s curiosity: How could seaweed come from a place where there’s nothing to feed it?

He set off on his own studies in the early 1980s, collecting samples and running tests in Bermuda, the Caribbean and the Gulf of Mexico. Based on that work and all that’s followed, he says manmade fertilizers are a key part of today’s problem. Runoff from agricultural fields gets into rivers and estuaries, which in turn feed into the Gulf of Mexico, Atlantic Ocean and more. The fertilizer nourishes the sargassum, which then grows beyond anything ever documented.

It’s not just American farms that are feeding the seaweed, he says. Runoff is coming from the Amazon and Orinoco rivers in South America too, and dust from the Sahara desert in Africa blows across the ocean surface where the sargassum is afloat. The dust’s phosphorous combines with nitrogen that’s already there, jump-starting the sargassum’s growth.

“It’s coming out of the sky and fertilizing the plants,” Lapointe says. “We’re fertilizing this thing that’s been around forever, and that increases its biomass. It’s getting bigger. It’s fine when it’s out in the blue water, and it’s a fisheries habitat out there, but when it comes into the beach with the winds, and there’s more of it now, it’s making a mess.”

 The fancy scientist term for having excessive nutrients in the water is eutrophication. It’s a word that everyone on Earth is going to have to become familiar with, much like we now know the meaning of the term greenhouse gases. While the global conversation about climate change has focused on carbon emissions, there’s also a compound called reactive nitrogen that, essentially, promotes growth and contributes to eutrophication. In the mid-1800s, humans produced about 15 metric tons of reactive nitrogen. By 2005, it was 185 tons, with some of it coming from industry but most of it coming from crop fertilizers.

In 2008, the journal Science published two articles about reactive nitrogen, with one paper’s author saying humans may have affected the planet’s natural nitrogen cycle even more than the carbon cycle. The researchers warned that a side effect of extra reactive nitrogen getting into the waters and contributing to eutrophication was “blooms of oxygen-gobbling oceanic algae, which can hurt fisheries. Nitrogen pollution could eventually render entire stretches of ocean dead,” Wired magazine reported at the time.

Fast forward a decade, and experts like Lapointe are now tying reactive nitrogen and eutrophication to the sargassum overload being seen everywhere from Texas to Trinidad and Tobago.

Sargassum accumulates on a 
Tobago beachfront near Belmont. 

Sargassum accumulates on a Tobago beachfront near Belmont. 

“It’s a major agent of global climate change,” he says. “You hear a lot about the carbon problem with climate change, but it’s the nitrogen change that’s causing all the algae blooms. We’re having the worst year ever with the blooms in Florida. There’s a trend not just with sargassum, but with algal blooms in general. They’re expanding globally. We believe the sargassum is the most recent example and the largest of all algal blooms at this time.”

Boaters of all kinds are having to adapt to this new reality. In the far southern Caribbean, commercial fishermen are reporting nets so heavy with sargassum that when they try to pull them in, the boat’s engine gets damaged underwater. In St. Lucia, a fisherman is now anchoring his boat far from the dock and using a paddleboard to get out to it, to try and keep the engine’s propeller free of the muck. (When he returns, he carries his catch on his head while paddling, to bring the fish ashore.) And forget about sailing catamarans or kayaking with the family at the St. James’s Club on Antigua; it closed July 1, and will stay closed through at least October 1, because there’s simply too much sargassum to clear away.

Recreational boaters as far north as the Carolinas now have to consider sargassum a potential problem.

“Increasingly, as you cruise up and down the coast, particularly in Florida and the Caribbean, this can foul the boat motor, the water intakes,” Lapointe says. “When you’re in certain anchorages that fill up with this stuff, it’s not going to be safe, really, if you’ve got a lot of hydrogen sulfide gas emanating from the bloom through your boat. A lot of the beaches where cruisers like to go, these remote beaches, guess what: Boaters are going to be on the front line where this problem is being manifested.”

Liveaboard cruisers also are going to have to learn how to adapt, he says, as the blooms get trapped in horseshoe-shaped anchorages and continue to climb higher and higher.

“It’s going to increasingly be an issue for boaters in harbors,” Lapointe says. “I’ve seen harbors in the Abacos, in the Bahamas, that just get stuffed with this stuff, and there’s this odor when it’s rotting and creating these toxic hydrogen sulfide fumes. You’re not going to be able to live on your boat in the harbor with these blooms.”

There are no easy solutions, he and other scientists say.

Chuanmin Hu, a professor of optical oceanography at the University of South Florida, told The Star newspaper on St. Lucia that islanders need to start thinking about sargassum blooms the way they’ve long thought about incoming, and inevitable, Category 4 storms.

“That’s just nature, just like a hurricane,” Hu told the paper. “Can you solve a hurricane? Can you prevent a hurricane? No, there is no way. But you can better prepare for the hurricanes.”

On a bigger scale, Lapointe says the global climate-change initiative has to start including a serious look at the consequences of agricultural runoff dousing the world’s oceans in reactive nitrogen.

“We do have to begin a conversation about the human nitrogen footprint, just like we’re talking about the human carbon footprint,” he says. “I’m kind of surprised we haven’t had more national leadership on this issue. Some states are dealing with it more than others. Florida, now, does have nutrient standards for its waters to try to control this problem of nitrogen.”

The sargassum problem can be turned around, he says, but boaters should not expect progress on that front in upcoming years, and perhaps not for an entire generation.

“It would take decades, just like it took decades to get to this point,” Lapointe says. “It would take international intervention, just like with carbon dioxide and global warming. We would need a similar international action plan to reduce the human-nitrogen program.”

He pauses, and then adds, “We can’t even deal with carbon dioxide yet. Half the people in this country don’t even think it’s real, so I don’t see things getting better anytime soon.”

This article originally appeared in the October 2018 issue.



Researchers Say Slowing Atlantic ‘Conveyor Belt’ Will Bring Rising Sea Levels, Fishery Changes

Two recently published studies in the journal Nature make it seem that the 2004 film “The Day After Tomorrow” was, in fact, more science than fiction.

Whales Return To The Big Apple, Lured By Menhaden And … Times Square?

On an otherwise typical day in August 2015, John Waldman looked around the waters near his home off Hempstead Harbor, on Long Island’s north shore. Usually when he gazed out, he saw the blue shimmer of Long Island Sound. On that day, however, he saw the unmistakable silver glint of menhaden, a fish known locally as bunker.


We’re in the Money

America’s new $1 trillion infrastructure law will fund everything from better roads for boats to New transient docks and boat ramps


Kelp Farms Could Be A Boon To Fishing

No matter how much time Charles Yarish spends aboard his 23-foot Boston Whaler Dauntless, he can’t stop thinking about what’s happening beneath the hull.


Art of the Digital Deal

As the Covid-19 pandemic wears on, the process of buying a boat is moving online. Here’s how to research and shop most efficiently.


Shark-Spotting Boat Owners Wanted

A Massachusetts-based nonprofit is seeking volunteers to report shark sightings from the sea.


The Great Pandemic Escape

From bareboats and crewed charters to learn-to-sail courses, people are flocking to Florida to go boating