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Historically Gigantic Seaweed Blob Threatens Florida (but could it save the world?)
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Historically Gigantic Seaweed Blob Threatens Florida (but could it save the world?)

A mat of seaweed twice the size of the U.S. is headed toward Florida, raising the specter of dirty, stinky beaches and possible harm to coastal ecosystems. Record algal blooms are becoming more common as a result of climate change, while at the same time, farming seaweed might be a powerful weapon in the war against permanent environmental damage.

By Eric Herman

If you think algae is formidable when it takes over a swimming pool, wait until you see what’s headed for the Florida coast. A gargantuan “blob” of sargassum – the most common type of seaweed and a form of algae – measures more than 5,000 miles wide, approximately twice the width of the continental United States, and is slowly drifting toward the Sunshine State.

Although massive algal blooms are nothing new, this one is the largest ever recorded, so massive it can be seen from outer space. Giant mats of algae form in the tropical waters off of Africa’s Atlantic coast and can float for years in the open ocean. Away from shore, the giant growths are harmless and are even beneficial creating habitats for fish and crustaceans, and they absorb huge amounts of carbon dioxide.

However, when currents push the sargassum into coastal waters, it becomes problematic, causing hundreds of tons of seaweed to wash up on beaches, while also blocking sunlight that is crucial to the survival of coral reefs and other marine ecosystems. This unusually huge growth will like make for some very messy beaches throughout the Caribbean and Gulf of Mexico, and especially Florida.

“It’s incredible,” said Brian LaPointe, a research professor at Florida Atlantic University’s Harbor Branch Oceanographic Institute. He told NBC News, “What we’re seeing in the satellite imagery does not bode well for a clean beach year.”


LaPointe, who has studied sargassum growths for four decades, said huge piles typically come ashore in South Florida in May, but beaches in Key West are already being inundated with algae. Parts of Mexico’s Yucatán Peninsula, including Cancun, Playa del Carmen and Tulum, anticipate up to three feet of beached sargassum this spring.

Giant mounds of sargassum are more than a nuisance and an eyesore, said Brian Barnes, an assistant research professor at the University of South Florida’s College of Marine Science. “Even if it’s just out in coastal waters, it can block intake valves for things like power plants or desalination plants, marinas can get completely inundated and boats can’t navigate through,” he said. “It can really threaten critical infrastructure.”

Beached, rotting seaweed releases hydrogen sulfide, which can cause respiratory problems for tourists and residents in the vicinity, LaPointe said. “Following the big 2018 blooms, doctors in Martinique and Guadeloupe reported thousands of people going to clinics with breathing complications from the air that was coming off these rotting piles of sargassum,” he said.

As a result, sargassum invasions can stifle tourism, while removing the aquatic detritus is expensive.

In a 2019 a study published in the journal Science, estimated that more than 20 million metric tons of sargassum blanketed the Atlantic in what has been nicknamed the “Great Atlantic Sargassum Belt.” This year’s growth is expected to exceed the 2019 event.

In investigating the factors driving this dramatic growth in sargassum, scientists, including LaPointe, have found that human activities and climate change are seeding rivers that flow into the Atlantic with nitrogen and other nutrients, which in turn feeds the algae blooms.

“You have the Congo, the Amazon, the Orinoco, the Mississippi — the largest rivers on the planet, which have been affected by things like deforestation, increasing fertilizer use and burning biomass,” LaPointe said. “All of that is increasing the nitrogen concentrations in these rivers and so we’re now seeing these blooms as kind of a manifestation of the changing nutrient cycles on our planet.”


While massive free-floating rafts of seaweed the size of continents can be a problem, controlled seaweed farming might prove a solution to climate-change related issues, including ocean acidification, rising levels of CO2, and even world-wide food shortages.

Every year, sargassum absorbs nearly 200 million metric tons of C02. Aquatic plant life has up to 50 times the capacity to absorb CO2 compared to terrestrial plants. According to a report from the National Oceanic and Atmospheric Administration, “Seaweeds both pull carbon dioxide out of the waters around them and also produce oxygen, greatly benefiting the nearby ecosystem. The harmful effects of ocean acidification on calcium carbonate-dependent species (e.g., oysters, clams, and some plankton) growing near the seaweed is reduced along with the revival of low-oxygen zones that are more prevalent as ocean waters continue to warm.

“By raising shellfish and seaweed, farms improve access to local seafood and mitigate harmful effects of excess nutrients, ocean acidification, and provide habitat for our robust fisheries.”

A recent study by research scientist Seth Theuerkauf explores the habitat value of shellfish and seaweed aquaculture for fish and invertebrates: “A growing body of scientific evidence indicates that the commercial cultivation of bivalve shellfish and seaweed can deliver valuable ecosystem goods and services, including provision of new habitats for fish and mobile invertebrate species.” 

In the long view, the potential benefits of raising seaweed and the species it supports is vast. “[Ocean aquaculture] is nutritious and low-impact,” said Paul Dobbins, who helps lead the aquaculture team at the World Wildlife Fund and has operated both shellfish and kelp farms. “You’re creating food without using arable land, freshwater, fertilizer or pesticides.”

Seaweed also has potential as a fertilizer, animal feed, a packaging replacement for plastics and biofuel, he says. In fact, a type of red seaweed when fed to cattle, reduces the methane in their burps and farts by an estimated 80%.

Supporters say ocean farming can offer economic opportunity to coastal communities that have lost jobs due to declining commercial offshore fisheries. 

“We need to figure out how to transition all these people who have these ocean-based skills and culture and traditions of blue-collar innovation to this really important work of climate solutions,” said Bren Smith, a former fisher who now farms seaweed and shellfish in Connecticut. 

Smith is a co-founder of GreenWave, a nonprofit that supports aspiring ocean farmers. The group has trained 900 farmers and hatchery technicians, and it has a waiting list of 8,000 prospective farmers who want to join its training program.

Opening image by Judith Lienert | Shutterstock.

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