Piles of rotting seaweed finally clear off South Florida’s beaches, a month earlier than usual

Put your feet in the sand, South Florida. That smelly, unsightly seaweed that’s been rotting on our beaches for the past several months is gone for the year — a month earlier than usual.

The brownish-yellow Sargassum seaweed has been a fixture on South Florida beaches, and was especially bad in 2019, 2018 and 2015.

“We’re done this year,” said Dr. Chuamin Hu, a University of South Florida professor who is an expert on the invasive seaweed.

The Sargassum travels in the Sargasso Sea, a region of the Atlantic Ocean and gets transported by currents that form a large loop around the ocean.

The Sargassum seaweed lives its entire existence on the water’s surface, never attaching to rocks or the ocean’s bottom. It’s useful in the ocean as a home to marine life, including certain breeds of turtles, eels, fish and birds.

But as it makes its way toward shore it gets harmful. If it rots and sinks to the bottom it can smother coral or sea grass. It can also smother sea turtle hatchlings trying to make their way from shore to the water. However, that threat is over for 2020 and when it returns — and how much of it — is somewhat of a mystery.

“If anything bad happens, that would not happen until at least next March or April, at least,” Hu said.

Scientists and researchers still don’t know for certain what makes it bloom. And that’s just one of the mysteries surrounding this unwelcome visitor.

“Why all of a sudden this year the amount decreased in August?” Hu asked. “We don’t know.”

Nitrogen — partly from fertilizer carried in runoff from land — is a leading suspect as a cause for the recent, large blooms, said Dr. Brian LaPointe, a FAU professor who studies marine system eco-health.

“What we’re seeing is that the nitrogen content has gone up in the Sargassum,” said LaPointe, who has studied Sargassum since the 1980s, “and we believe that is probably the primary reason we’re seeing these massive blooms, more biomass than we’ve ever seen before.”

LaPointe will make a presentation to the Florida Chamber of Commerce later this month and will highlight the increased nitrogen content in the water, saying the fertilizer in runoff contributes to Sargassum’s growth. A bloom can double its mass in 10 days when fed by excessive nitrogen, LaPointe said.

The Sargassum seaweed, a macroalgae that features air-filled “grapes” that keep it afloat, has been a local issue since 2011, with the noted exception of 2013.

“It’s almost every year and that’s why we call this a new normal,” Hu said. “Previously there was almost nothing.”

And why was 2013 an exception?

“We actually don’t know,” Hu said.

People are learning to creatively live with the nuisance. In Mexico, one inventive man used the Sargassum seaweed to make bricks and eventually a house. Others have used it as a main ingredient to make shoes.

What’s important to South Floridians right now, however, is clear beaches. The Sargassum is done for 2020.

“We may still get a little bit of it,” LaPointe said, “but I think the big inundations we’ve seen this summer definitely should be ramping down now.”


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