What’s Fueling Florida’s Seaweed Blooms?

by Ashira Morris, ODP Staff Writer

The Atlantic Ocean’s Sargasso Sea, the only sea without a land boundary, is named for the brown free-floating seaweed that’s unique to its waters. Over the past decade, the sargassum seaweed has proliferated and spawned massive blooms beyond the Sargasso Sea’s boundaries, inundating Caribbean, Gulf of Mexico and Florida coastlines. The blooms are a result of Saharan dust clouds, warming temperatures and the growing human nitrogen footprint.

Giant “rafts” of it first hit the Caribbean in 2011, and the largest marine algae bloom was of sargassum in 2018, when over 22 million tons of seaweed stretched from the west coast of African into the Gulf of Mexico. This year, there are “abnormally high” amounts similar in size to the record-topping 2018 outbreak. 

Why This Matters: When contained within its usual area of the ocean, sargassum seaweed is a biodiverse ecosystem that’s home to crabs, seabirds, shrimp, and whales–as ocean explorer Sylvia Earle calls it, “a golden floating rainforest.” But when it blooms out of control, it harms fishing communities and blocks beaches, requiring intense cleanup efforts. On a bigger scale, it can suck oxygen from the water, killing off other marine life. These seaweed outbreaks illustrate the overlapping impacts of too much nitrogen from agriculture amplified by hotter ocean temperatures due to climate change. 

Where Does the Seaweed Go?: When there are mountains of brown seaweed on your city’s beach, what do you do? The seaweed isn’t harmful but does block beach and boat access and smells like rotten eggs as it bakes in the sun.

As Stephen P. Leatherman, a professor of coastal science at Florida International University put it succinctly for The Conversation, “There is currently no good way to dispose of such great volumes of seaweed.” In 2019, it cost $45 million to get rid of sargassum from just 15 miles of Florida beaches. 

Given the high costs, communities have turned to other repurposing solutions: some rotate it under the sand, while others convert it into fertilizer or mulch. Entrepreneurs in Mexico have taken to collecting the seaweed and making bricks from it to use in construction.

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