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What the Heck Is Sea Snot, Anyway?

And why is it fouling the coast around Istanbul?

The Marmara Sea in Istanbul, Turkey, is plagued by sea snot.Erhan Demirtas/ZUMA Pres

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This story was originally published by Atlas Obscura and is reproduced here as part of the Climate Desk collaboration.

For months, the waters around Istanbul, Turkey, have been coated with a gloopy film. Sometimes creamy, sometimes khaki, it can appear slightly dreamy or superlatively gross, depending on the vantage. From overhead, it’s almost romantic, like clouds glimpsed from space, white squiggles marbling Earth’s blue. Up close, the stuff is much more phlegmy. The shore-hugging substance is sometimes known as “sea snot,” and it’s easy to see why. It looks like the marine equivalent of a big, wet sneeze.

Sea snot is more scientifically known as “marine mucilage,” and it’s an ecosystem of its own. In a 2009 paper in the journal PLOS One, a team of scientists led by Roberto Danovaro, a marine biologist at Italy’s Polytechnic University of Marche, described it as a “gelatinous” stage of marine snow, the jumble of organic material—such as feces and fragments of dead plants and animals—that drifts from the surface to the ocean floor.

The snot is produced by a bunch of microorganisms, one Turkish research team explained in a UNESCO bulletin called Harmful Algae News, especially microalgae known as diatoms. These petite algae are known to exude polysaccharides, sugary carbohydrates that can get quite sticky. Sampling sea snot that clotted several locations in the Sea of Marmara in 2007 and 2008, the researchers also identified species of dinoflagellates and more.

Like the mucus launched from human nostrils, sea snot can smell foul, and slimes whatever it touches. And in addition to discouraging swimmers and deterring fishing, the gunk can be a nuisance for corals, scientists have found. From December 2020 to early March 2021, H. Barış Özalp, a marine biologist at Turkey’s Çanakkale Onsekiz Mart University, measured the effects of sea snot on reefs in the Çanakkale Strait.

Özalp found that some of the creatures were dripping with the stuff. It looked as though they had been blasted with ectoplasm, or wrapped in a spider’s web, and the substance seemed to be killing some of the branches. A thick coating can deprive the corals of oxygen, and other research teams have worked to suss out sea snot’s effect on mussels, crabs, and other sediment-dwellers. Danovaro’s team found that the sticky matrix can also entrap viruses, and potentially ferry them around marine ecosystems.

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