What is sargassum? The giant blob of seaweed hitting Florida

[NelsonG]

Great news for fans of seaweed that collects on beaches in colossal heaps, and stings people's eyes, nostrils, and throats with a stench like rotten eggs: mass quantities of the algae known as sargassum are once again accumulating on Florida's shorelines. And there's reason to suspect that human-caused environmental havoc may be to blame.

In fact, in live views of Florida's 2023 spring break festivities, you can watch the sargassum pile up in real time. Below, you can see part of a miles-long streak of sargassum running down Fort Lauderdale Beach. If you tune into this livecam early in the morning, you can watch attendants drive farm equipment over it, apparently to break it up and make it more manageable, since there's clearly too much to remove.

Yes, these sargassum accumulations are new

This didn't used to happen.

Historically, sargassum was known to float in giant brown rafts in a section of the North Atlantic named the Sargasso Sea in honor of sargassum. Sargassum beds are established and diverse ecosystems, and they're home to (if you'll excuse my editorializing) the most underrated predator in the ocean in terms of sheer viciousness: the sargassum fish.

But according to a 2015 report by Jeffrey Schell, Deborah Goodwin, and Amy Siuda published in the magazine Oceanography, waters in which sargassum had not previously been dominant were, all at once, producing gobs of the stuff. It was suddenly piling up as high as a meter deep on sections of coastline — including tourist beaches — in the Caribbean and the Gulf of Mexico, as well as on the coasts of West Africa and Brazil.

"We noticed the seaweed looked different from the Sargassum fluitans or S. natans with which we were familiar from 20 years of sailing in the Sargasso Sea, the Caribbean, and Florida Straits," the report said. In other words, this appeared to be an unprecedented accumulation of an unprecedented type of sargassum.

Humanity's ecological havoc may play a role in sargassum accumulation

Further study is needed before anyone can say with confidence exactly what's causing this apparently new phenomenon, but scientists are on the case.

Oceanographers now know from studying satellite views that this sargassum comes not from the Sargasso Sea, but from further south: a patchy stripe the width of an entire section of the ocean dubbed the Great Atlantic Sargassum Belt. In 2018 oceanographers explained to The Atlantic's Ed Yong that the belt seem to draw on river outflows in Brazil and West Africa that dump agricultural fertilizer into the ocean. This in turn may have supercharged seaweed growth, transforming occasional patchy collections of sargassum into the huge, self-perpetuating seaweed monster we have today.

Eckerd College oceanographer Amy Siuda told Yong this state of affairs "is likely the new normal."

Sargassum is a growing problem

NASA satellite photos show bigger and bigger blooms, with an increasing number of record-breaking years since 2011. Last June, over 24 million tons of sargassum materialized in the Atlantic, which broke the previous record set in 2018. University of South Florida oceanographer Brian Barnes told the South Florida NBC news affiliate that 2023 looks like another monster year. "We’ve observed over the last several months that the bloom is getting bigger. It’s likely be as big as or if not bigger than the bloom that we saw last year," he said.

Oh, and that rotten egg smell comes from hydrogen sulfide, which, health officials told the local news in Florida, can do more than just sting people's eyes and noses. Too much exposure can cause "headaches, poor memory, tiredness and balance problems."

And while some sargassum is known to be eaten by humans, according to the Florida Department of Health no one has any business eating this sargassum, "because it may contain large amounts of heavy metals like arsenic and cadmium."

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