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A seaweed mass expands, reaching record tonnage. Messy Florida beaches are 'inevitable'

 Beached sargassum surrounds a pair of sunbathers.
Robyn Wishna
Beached sargassum surrounds a pair of sunbathers in Boca Raton on March 31, 2023.

13 million tons of seaweed are bobbing off the coast as this year’s Great Atlantic Sargassum Bloom sets new records.

We already knew South Florida beaches were bracing for a surge of seaweed, but the mass of seaweed looming in the Atlantic Ocean is now officially record-breaking.

The Great Atlantic Sargassum Belt — the official name for the collection of floating brown seaweed that sprawls across 5,000 miles from the Gulf of Mexico to the west coast of Africa — contained about 13 million tons of seaweed by the end of March, according to researchers at the University of South Florida’s Optical Oceanography Lab who have been monitoring the sargassum belt via satellite.

Map shows the sargassum bloom as of March 2023
USF Optical Oceanography Laboratory
This map from the University of South Florida Optical Oceanography Laboratory shows the sargassum bloom as of March 2023. Red areas have a higher density of seaweed. Read more at: https://www.miamiherald.com/news/local/environment/climate-change/article273912380.html#storylink=cpy

That’s a new record for this time of year. Though it remains strung out over thousands of square miles of open ocean, it’s an omen of smelly, slimy beach days to come. In some places, including Boca Raton and Fort Lauderdale, large masses have already washed ashore or been spotted by boaters just offshore.

“Major beaching events are inevitable around the Caribbean, along the ocean side of Florida Keys and east coast of Florida, although the exact timings and locations are difficult to predict,” the USF researchers wrote in their latest monthly sargassum bulletin.

Robyn Wishna
A mat of sargassum bobs in the water off the coast of Fort Lauderdale just north of the Port Everglades inlet on April 2, 2023.

We only have ourselves to blame. Human activity and climate variability have caused sargassum blooms to get bigger since about 2011, according to Chuanmin Hu, a USF oceanography professor who is part of the sargassum observation team. Fertilizer runoff and sewage dumped into the ocean have fed sargassum more nutrients, while climate change has warmed ocean waters and given the seaweed a more hospitable environment in which to grow.

Sargassum on the beach with people in the background
Robyn Wishna
Beachgoers step around a mat of sargassum that washed ashore at Fort Lauderdale Beach near Sunrise Boulevard on March 31, 2023.

So far this year, South Florida beaches have only been hit sporadically with seaweed pileups. But it’s still early: The local seaweed season typically runs from May to October, with the peak coming in June and July, according to Tom Morgan, chief of operations at Miami-Dade County Parks, Recreation and Open Spaces.

Miami-Dade County’s spending on seaweed cleanup has risen from $2.8 million during the 2020 sargassum season to $3.9 million during last year’s season. Now the county is asking the state Legislature for an extra $2 million to fund sargassum removal, which would bring this year’s total spending on seaweed cleanup to about $6 million.

“I was just up there [in Tallahassee] a couple of days ago talking about this,” said Miami-Dade County Mayor Daniella Levine Cava, “because we’re spending in the range of $4 million per year and we are anticipating the need to spend more with the additional arrival” of seaweed on the beaches this year.

A piece of heavy equipment cleaning seaweed off a beach
Pedro Portal
Miami Herald
Heavy equipment starts cleaning seaweed from the seashore after a press conference by Miami-Dade County and City of Miami Beach elected officials announcing the county’s removal operation for sargassum/seaweed on Miami Beach on Friday, Aug. 2, 2019.

Most of Miami-Dade County’s seaweed budget goes toward removing the sargassum that piles up in four hot spots: beaches in Haulover just north of Haulover Cut; beaches in Bal Harbour just south of Haulover Cut; Miami Beach between 26th Street and 31st Street; and the beaches alongside South Pointe jetty.

Last year, the county cleared 18,000 cubic yards of sargassum from these four areas. Most of it wound up in the county’s rapidly filling landfills. “Obviously, that’s not a great solution because the landfills have limited space,” Levine Cava said.

The county is looking into the idea of composting the seaweed rather than dumping it, but has concerns about sargassum’s reportedly high concentrations of arsenic and other heavy metals, according to Lisa Spadafina, who runs the county’s Department of Environmental Resource Management. “Those are the things that we’re looking to address so that we’re not creating another problem by composting,” Spadafina said.

 Sargassum washes ashore at Fort Lauderdale Beach
Robyn Wishna
Sargassum washes ashore at Fort Lauderdale Beach near Sunrise Boulevard on March 31, 2023.

To be clear, sargassum itself is harmless to humans. It does harbor jellyfish, sea lice, and other stinging creatures that can irritate the skin — and the hydrogen sulfide it releases when it rots in the sun can aggravate breathing problems for people with pre-existing respiratory conditions, in addition to smelling like rotten eggs and making the beaches generally unpleasant for swimmers and sunbathers.

But it’s also an important habitat and food source for many sea creatures and poses no threat to human health when beach maintenance crews promptly remove it or use machines to cut it up and mix it into the sand. During the peak of the sargassum season, Miami-Dade County crews do this each morning just after sunrise, after they’ve made sure there are no sea turtle nests nearby that might be disturbed by the heavy machinery.

The 13 million tons of seaweed currently bobbing in the Atlantic Ocean won’t all come ashore on Florida beaches, and the fraction that does land here won’t come all at once — not even in hot spots. “Even Miami Beach won’t receive sargassum every week or every month,” said Hu. “That will depend on the tides and the wind.”

In their latest sargassum bulletin, Hu and his colleagues also stressed that the sargassum belt isn’t one giant blob of uninterrupted seaweed, but rather a collection of “clumps and mats scattered randomly within the 5,000-mile Sargassum belt.” Within the belt, seaweed covers less than 0.1% of the ocean surface, on average. Because it’s so scattered, it can be hard to pinpoint how big the sargassum bloom is; for instance, the researchers said that their February estimate was low because of “persistent cloud cover in the eastern Atlantic” that blocked their satellites’ view of the sea.

This climate report is funded by Florida International University, the Knight Foundation and the David and Christina Martin Family Foundation in partnership with Journalism Funding Partners. The Miami Herald retains editorial control of all content.

This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative formed to cover the impacts of climate change in the state.