Huge Seaweed Clump Seen From Space as It Moves Toward Florida

A 5,000-mile-wide blob of seaweed that is slowly creeping toward the Florida coast has been recorded from space by NASA.

The enormous mat of seaweed is composed of sargassum, floating brown algae that usually blooms in a region called the Sargasso Sea. It spreads across the Atlantic from the west coast of Africa to the Gulf of Mexico in what is known as the "Great Atlantic Sargassum Belt."

Last month marked one of the largest sargassum blooms ever recorded, with the mat of seaweed measuring twice the size of the mainland United States.

The NASA images show a map of sargassum density developed by scientists at the University of South Florida's (USF) College of Marine Science, using data from the Moderate Resolution Imaging Spectroradiometer instruments on NASA's Terra and Aqua satellites. The red and orange areas show where sargassum densities were the highest.

Around 13 million tons of the seaweed are estimated to have been floating across the ocean during March, a record size for this time of year, with the seaweed doubling every month from November to January, according to USF.

The seaweed is now beginning to wash up on beaches on Florida's east coast and in the Florida Keys. While the seaweed itself is not harmful to humans, as it begins to rot it can cause a very unpleasant smell and potentially harmful chemicals.

"People hate the smell. It's like rotten eggs," Stephen Leatherman, a professor of coastal science at Florida International University, previously told Newsweek. "You know how rotten eggs smell. Because it's not just the seaweed itself but there are bits and pieces, there's little crabs in there, small fish get caught up. It's a natural ecosystem in its own way. But all that stuff gets beached, and it rots and stinks."

As the seaweed rots, it can also release harmful compounds like hydrogen sulfide, which can cause respiratory problems in animals and humans that breathe it in. Previous sargassum blooms have resulted in large numbers of respiratory irritation problems, with over 11,000 cases of acute sargassum toxicity reported in an eight-month period in the aftermath of a sargassum bloom in Guadalupe and Martinique in 2018.

Acute sargassum toxicity includes symptoms like heart palpitations, shortness of breath, dizziness, headache and skin rashes. The bloom was especially massive, measuring an estimated 20 million tons as of July 2018.

This can pose large problems for beaches and coastal communities, especially during the tourist season.

"The beaches are narrow and not very wide, so it just covers them up," Leatherman said. "It was so bad in Cancún a couple of years ago that 2,000 people in the Navy had to go out there with pitchforks and other means, just trying to clean it off the beach so they could see the sand."

In the wild, sargassum is usually a boon for wildlife, providing shelter and food for many species, including turtles, birds and marine mammals. However, in massive blooms the seaweed can block out the sunlight reaching the ocean floor, starving coral reefs and seagrass meadows of light. It also can alter the pH of the water and sap oxygen from the water, causing fish to die.

The massive mats can even cause turtles to suffocate.

"It can actually kill turtles if the mass is so extensive that turtles have to go up for air every 20 minutes or so," Leatherman said. "They go under it, these huge masses that can go for a mile or so in the worst areas. Then some turtles have actually drowned underneath them. But that's fairly rare."

A 2019 study published in the journal Science found that agricultural runoff from rivers containing nitrogen and phosphorus fertilizers, especially the Amazon, may be contributing to the massive blooms of sargassum across the Great Atlantic Sargassum Belt.

The effects of climate change may further worsen the size of the sargassum blooms, with increased rainfall causing excess runoff from agricultural land into waterways. Additionally, climate change may result in altered ocean currents because of changes in air and water temperatures, which will affect the movement of the sargassum as well as its access to nutrients.

"Based on the last 20 years of data, I can say that the belt is very likely to be a new normal," Chuanmin Hu, a professor of optical oceanography at the University of South Florida, previously told Newsweek.

According to NASA, sargassum density usually peaks in June or July, meaning that this already record-breaking glob of seaweed may continue to grow and, as a result, drown beaches across Florida and the Caribbean in thick, stinky seaweed. In the meantime, local communities have plans to remove the seaweed from their beaches if it reaches overwhelming levels in the coming months.

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