An incredible ecosystem, built on golden, floating Sargassum

The Sargasso Sea is a two-million square mile open ocean ecosystem, bounded by the circulating currents of the North Atlantic Gyre.

The foundation of this incredible pelagic ecosystem is the floating, golden Sargassum seaweed for which the sea is named. Sargassum is a free-floating macroalgae that never touches the sea bottom at any stage in its life cycle. It can accumulate into huge rafts on the surface of the ocean and provides an invaluable living matrix for a huge diversity of species. Sargassum supports ten fascinating endemic species, including the Sargassum frogfish, a fearsome ambush predator.

Critical for the breeding and development of many species

Sargassum also acts as critical nursery habitat for many species of pelagic fish that grow to be ocean giants, including dolphinfish, marlin, tripletails, and more. All species of Atlantic sea turtle rely on Sargassum for developmental habitat during their 'lost years' after they leave the nesting beach, sheltering in it, feeding within it and sunbathing on top of it. The rich rafting community found within Sargassum attracts larger predatory fish and gives rise to a thriving ecosystem.

The subtropical convergence zone in the southern part of the Sargasso Sea is also spawning habitat for various species of ecologically and economically important fish including white and blue marlin, swordfish, and albacore tuna.

The only known spawning area for European and American eels

The Sargasso Sea is the only known spawning area for two species of endangered anguillid eel – which perform one of the longest migrations in the animal kingdom, transitioning from marine breeding grounds to freshwater feeding grounds in Europe and the Americas. The eels are threatened by demand for use in the sushi trade and have experienced an 80% decline in fisheries catch since 1960. 

A migratory corridor for marine megafauna

It also acts as a migratory corridor for several species of sharks, rays, and cetaceans. In particular, humpback whales and sperm whales migrate through the area, and the vulnerable Porbeagle shark may pup there.

Threatened by anthropogenic pressures

The Sargasso Sea is threatened by various pressures – including impacts from shipping, fishing, plastic and other pollutants, and climate change.

For more information, see our GEF and FFEM project products page