Sargassum seaweed threatens Florida beaches during spring break

Before the spring break season is over, the beaches on the Gulf Coast start to stink.

In mid-April, as businesses in South Florida and on the other side of the Gulf Coast juggle an influx of vacationers, the region’s beaches are likely to encounter another unwelcome visitor: huge mats of decaying sargassum seaweed.

The front of a thousand-mile train of floating sargassum is already beginning to pile up on the beaches of resorts on Mexico’s Yucatan Peninsula, along the Caribbean islands and in Key West, Florida.

But with an estimated 13 million tons of seaweed out there, those early arrivals are just “the tip of the iceberg,” said marine biologist Brian LaPointe.

LaPointe runs one of the largest seaweed laboratories in the country, at Florida American University. He said the bloom was no cause for “panic” – but added that a bloom “that big, that early, just doesn’t bode well.”

But much about the blob, from its origins to its final destination, remains the subject of active scientific debate.

Here’s a list of things we know about the seaweed bloom threats — and what we still don’t.

What is washing up?

Clumps of seaweed that have broken loose from a much larger belt of floating sargassum that has settled in the mid-Atlantic over the past decade.

Unlike kelp or seagrass, types of seaweed that are firmly attached to the seafloor by their roots, sargassum is a form of free-floating seaweed that is most highly concentrated in the Sargasso Sea.

The Sargasso Sea is the only sea in the world that is not bordered by any country. Instead, it’s a part of the Atlantic Ocean surrounded by swirling ocean currents that have long ensnared ships, ocean debris and huge populations of sargassum.

Those swirling currents kept sargassum contained for a long time — until about a decade ago, when the current sargassum crisis began, and cities like Miami and Fort Lauderdale began spending tens of millions a year on tackling it.

What caused the seaweed crisis?

The acute cause appears to be two years of “unprecedented” wind events — in 2009 and 2010 — that blew record amounts of sargassum from its home waters.

While clumps of sargassum had always escaped to wash up on Atlantic and Caribbean beaches, there had never been enough to establish a stable population, said Rick Lumpkin, who directs the division of physical oceanography at the National Oceanic and Marine Observatory’s Observatory Laboratory. Atmospheric Administration (NOAA). in Miami.

Other factors helped the new sargassum colony settle into its new home after 2011, Lumpkin said. Like any plant, sargassum benefits from heat and fertilizer. The heat came from rising ocean temperatures due to climate change. And the fertilizer came from, well, fertilizer.

Many scientists link the bloom of sargassum to the overuse of fertilizers in the basins of the major rivers that flow into the Atlantic Ocean: the Mississippi, Orinoco, Congo and Amazon.

Those fertilizers—pushed far out to sea by the powerful outflow of those rivers—are used in industrial agriculture to compensate for soil depleted by tropical deforestation or season after season of growing the same crops.

But especially in the case of agriculture in the Amazon and Orinoco, this nutrient runoff eventually also increased the floating algae population in the mid-Atlantic and Gulf of Mexico.

Other factors likely contributed, Lumpkin said. The swirling winds off the west coast of Africa that pull nutrient-rich water to the surface, and the colossal dust storms in the Sahara also seem to have played a role.

This led to huge sargassum blooms across the Atlantic in 2018 and 2019 – blooms that may have been even larger than this year’s.

But what’s unusual this year is how much sargassum has entered the western Caribbean, Lumpkin said.

Where Does Sargassum Seaweed Come From?

We don’t really know. Scientists did not discover the incoming sargassum belt until it had already solidified into a mass large enough to be visible from satellites.

But in its broadest sense, the sargassum that began washing up on Caribbean beaches arose from what scientists call the Great Sargasso Belt — that new colony that settled outside the Sargasso Sea in 2011.

The western end of that belt, torn by currents, is now on its long collision course with the Caribbean.

Is the seaweed dangerous?

Not directly – at least not to people.

It may even make the ocean a little safer, says Stephen Leatherman, an oceanographer at Florida International University who specializes in beach health.

Sargassum’s thick floating mats are so thick that they block the action of tidal waves that could otherwise pull people out to sea, Leatherman said.

But few would want to swim among a sargasso flower anyway. As it decays on beaches and among mangroves, it releases foul-smelling chemicals such as hydrogen sulfide – a malodorous chemical reminiscent of rotten eggs that will deter beachgoers.

Leatherman described it as “a floating forest”, with its own unique ecosystem of hundreds of other plants and animals.

A particularly dangerous inhabitant of that forest is the highly venomous Portuguese man-of-war.

But as the seaweed is pulled ashore, all that stuff goes with it, causing a whole new set of problems. Fish, crabs and jellyfish that move among the sargassum wash up on the beach and rot on the beach.

NOAA’s Lumpkin said he pulled a small crab from the sargasso mat that had washed up near Miami. He remembered thinking, “That man had been on a really long drive.”

Could a sargassum colony — or the species that drive it around — eventually establish the kind of permanent presence in the Caribbean that it has in the wider Atlantic?

“That’s a fascinating question,” Lumpkin said. “We don’t know the answer.”

Does it kill coral?

The overwhelming danger of the massive seaweed bloom is ecological. As the floating plants pile on top of each other, they form layered mats several feet deep and sometimes miles long — so big, Leatherman said, that sea turtles sometimes get stuck underneath and drown.

The floating mats can also block all light from reaching the underwater plants below, posing a deadly threat to coral reefs.

The emergence of sargassum blooms occurred alongside a greater loss of stony corals in the Florida Keys, LaPointe said, though he stressed that the cause was still unproven.

And as the floating seaweed decomposes among the mangroves that surround the Gulf of Mexico, hydrogen sulfide and other byproducts suck oxygen out of the water column, creating dead zones that suffocate fish and “anything underwater that can’t swim away,” LaPointe said. .

To make matters worse, those rotting bodies add to the stench.

Where does the seaweed go and when will it get there?

Probably the beaches of the Gulf Coast and the islands of the Caribbean Sea, but there’s not much more to say about them, experts told The HIll.

That belt is “not one single mass — it’s lots and lots of clumps and passages being shaved off,” said NOAA’s Lumpkin.

Some of those clumps have torn away from the larger floating forest and washed up in Cuba, Yucatan and South Florida — and specifically the three east-facing counties of Miami-Dade, Broward and Palm Beach.

“But the mass of it is still going into the Gulf and we will see a steady increase in the amount coming through,” Lumpkin said.

In its current trajectory, a long train of seaweed follows the Caribbean current westward, where it catches the loop current around the Yucatan Peninsula and crosses the 90-mile strait between Cuba and Florida, before the Gulf Stream will carry it back to the Atlantic Ocean.

But while “that’s the path, the wind can blow it off course,” Lumpkin said — a north wind could blow it against Cuba, a south wind against the Florida Keys.

Florida American’s LaPointe returned to the metaphor of a hurricane far from land: its trajectory is too uncertain to warn a specific resort or beach community in time to avoid a wave of disappointed guests.

That could change from July. LaPointe’s lab has received a grant from the Environmental Protection Agency to partner with the Florida National Marine Sanctuary to begin tracking down specific sargassum clumps with enough detail “to tell hotels what’s going on for you.” hands.”

What are places going to do about it?

In the past, Miami plowed algae under the beaches, but it’s become such a problem now that the beach sand can no longer contain it, Leatherman said.

On some of the rockier Caribbean islands, where small beaches sit in a protective bottleneck of peninsulas, the solution to sargassum is simple: pull a boom (of the kind that can be used to stop an oil spill) across a narrow bottleneck .

And in Mexico’s Yucatan, an entrepreneur calling himself Mr. Sargasso, started selling bricks made from clay compacted with the seaweed pulled from beaches – what he calls “sarga blocks.”

But Florida’s long, flat beaches cannot be protected by trees, and the state has no stone industry.

For years, Fort Lauderdale has been getting rid of sargassum by dragging it to giant parking lots, wrapping it in sheets, letting the rain wash away the salt, and then composting it into mulch, which distributes it for free. It’s a solution that essentially recycles and uses the nutrients flowing from the denuded Amazon to feed Florida’s lawns and crops.

But with the seaweed blooms arriving in such quantities so early in the season — months before Florida’s summer rains begin — composting may not be an option, Leatherman said.

That will likely leave the region’s cities with little choice but to tow it to the landfills at a cost of $35 million to $45 million per county.

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