It’s brown, it weighs millions of tons, it stretches over 5,000 miles and it is headed for Florida’s beaches. An enormous clump of seaweed circulating the Gulf of Mexico and Atlantic is set to coat beaches in a spongy goop, bringing with it a pungent odor similar to rotting eggs.
The huge mass of sargassum is the latest in a series of massive blooms scientists have noticed in the Atlantic since 2011 but could be the largest yet. It is pushing west through the Caribbean and beaches in Cancún, Mexico, and Key West, Florida, have already seen large mats wash ashore.
The brown morass has doubled in size every month from November to January, forming a belt wider than the continental US. It is expected to hit beaches elsewhere in Florida and along the Gulf of Mexico this summer, potentially causing problems for tourists.
The seaweed is a floating type of algae that has berry-like bubbles filled with oxygen that keep it buoyant. When it reaches shore, it decays in the sun and releases hydrogen sulfide, which smells like rotten eggs and can aggravate respiratory problems such as asthma.
“It smells very bad and chases away tourists,” said Chuanmin Hu, an oceanographer at the University of South Florida who tracks the sargassum blooms via satellite.
Sargassum has always naturally formed in the Atlantic and, out at sea, provides a huge floating habitat for animals such as turtles, birds, crabs and shrimp. Some animals, like the sargassum fish, live their whole lives in the floating brown armada. The seaweed also soaks up carbon dioxide.
However, sargassum can pose problems once it has washed ashore and scientists have noticed a large increase over the last decades in the amount now routinely clogging up shorelines in piles five or six feet deep.
In Barbados, authorities deploy hundreds of dump trucks to clear the beaches for tourist season. Last year, the US Virgin Islands declared a state of emergency after being inundated by sargassum.
“The low season of the cycle is now higher than the high point of the cycle five or six years ago,” Brian Barnes, a researcher with the University of South Florida’s College of Marine Science, told NPR.
“What we thought was just a massive bloom has only gotten bigger.”
The exact reason for the monster formations of seaweed is still debated but researchers suspect the seasonal nature of the outgrowths is linked to discharges of pollution from major waterways. Phosphorus and nitrogen, which the algae feed on, are routinely washed into the oceans as runoff from fertilizers used in agriculture.
The climate crisis may also be contributing to the problem by causing stronger storms that stir up more seaweed and cause flash flooding that washes pollution into the sea.
What is clear, though, is that the big brown blobs appear here to stay.
“It’s only getting bigger and bigger and bigger each year,” Barnes said.
