Giant Seaweed Blob Heading Towards Florida

A 5,000-mile-wide swarm of seaweed may be slowly creeping across the ocean toward Florida.

The enormous mat of seaweed, measuring twice the size of the contiguous United States (New York City to Los Angeles, California is 2,445 miles), is the result of a huge bloom of sargassum seaweed. Mexican news outlet The Cancun Sun reports that the Riviera Maya is preparing to receive 3 feet of sargassum build-up in the coming week.

Sargassum is a type of seaweed algae usually found in the 2 million-square-mile Sargasso Sea—so-named for the seaweed—east of the Gulf of Mexico. During the summer, sargassum usually washes up on beaches along the East Coast of the U.S. and the Caribbean, but occasionally, the seaweed blooms enormously, and a lot more of it makes its way to land.

One 2019 study in the journal Science found that since 2011, the mats of sargassum have been increasing, forming a massive "Atlantic Sargassum belt" stretching across the entire ocean, which as of 2018, weighed over 22 million tons.

Over 8,400 tons of sargassum washed up on a single day at Galveston Island, Texas, which was the most ever recorded in a single 24-hour period.

"In the open ocean, Sargassum provides an essential habitat and refuge for all sorts of marine animals," Mengqiu Wang, a sargassum researcher from the University of South Florida, previously told Newsweek.

Sargassum blooms provide shelter and food for over 100 different species, ranging from sea turtles and insects to marine mammals and birds. Additionally, the seaweed prevents coastal erosion when washed toward the shore.

However, when sargassum blooms, it can cause a number of issues.

"When too much sargassum piles up on the beaches, it can be harmful to the local environment, tourism, and artisanal fisheries, etc., and could also be a public health concern," Wang said.

If the mats of seaweed become too great, they may harm coral reefs by blocking out the sunlight they need to photosynthesize, preventing sea turtles from nesting on beaches, and creating oxygen-dead zones where fish cannot survive.

Brian Barnes, an assistant research professor at the University of South Florida's College of Marine Science told NBC News that the seaweed can entangle boat propellers and block intake valves. When the seaweed gathered on beaches or in the shallows begins to rot, it releases noxious gasses like hydrogen sulfide, which can cause respiratory problems.

Over 11,000 Acute Sargassum Toxicity cases were reported in an 8-month span in Guadalupe and Martinique in the wake of the 2018 sargassum bloom.

The 2019 Science study suggested that the blooms leading to massive mats of sargassum may be caused by agricultural runoff from rivers containing fertilizers.

This could be worsened by increased fertilizer use, as well as climate change, which may increase flooding and runoff into major waterways as a result of increased rainfall. Additionally, higher ocean temperatures due to climate change provide an ideal environment for the blooms to occur.

"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.

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