Sargassum

Sargassum is a genus of brown macroalgae (seaweed) in the order Fucales of the class Phaeophyceae. This brown macroalgae comes from the Sargasso Sea, which was named because it hosts large amounts of Sargassum. Sargassum can extend for kilometers across the ocean surface, forming golden brown drifting mats that move with the currents and wind; in recent years, Sargassum has been known for arriving in large quantities throughout the Caribbean region. More recently, scientists have found using satellite data that a new hotspot has been forming from western Africa and extends into the Caribbean Sea, called the Great Atlantic Sargassum Belt (GASB).

Most of the macroalgae species inhabit shallow coastal waters and coral reefs, but some are planktonic (free-floating) or pelagic after being detached from reefs during storms. Sargassum includes two holopelagic species, Sargassum natans and Sargassum fluitans, with other species interconnected. These species are distinguished to reproduce solely by clonal reproduction through fragmentation. Sargassum plays an important ecological role in the open ocean because it provides a vital habitat for a variety of marine species, including fish, crabs, sea turtles, migratory birds and other organisms. However, when large amounts of Sargassum accumulate in the shore and start to decompose it forms what is known as Sargassum brown tides (SBT). SBT alters the water column by changing the appearance of the water and in addition alters the water quality by reducing light penetration, decreasing dissolved oxygen and changing the pH of the coastal waters. As a result, it affects seagrass meadows, corals, mangroves and coastal communities that depend on tourism.