Is a brown seaweed (Sargassum natans) which is a member of a genus with 150 species, nearly all of which live attached to the seabed in shallow water. Sargasso weed is the exception in that it is found floating freely in the tropical oceans, particularly in the Sargasso Sea where it gathers in large accumulations in the centre of a great eddy lined up along slicks and windrows. The Sargasso Sea, the area of the North Atlantic east of the Bahamas Islands bounded by 25° and 30° N. and 40° and 60° W., derived its name from the Portuguese word for grapes sargaco, because of the grapelike floats on the brown fronds of the weed. Clumps of sargasso provide a unique pelagic habitat for an assortment of animals that have become specifically adapted for life within this floating forest. Fishes like the sargassum anglerfish (Histrio histrio) have the same coloration as the weed and bodies covered with protuberances that mimic the fronds of the seaweed. Sargassum muticum, a relative of sargassum weed, is a notoriously aggressive invader. Originating in Japanese waters, it has been accidentally introduced to temperate coastal waters worldwide; such introduction of alien species is an environmental issue. Once introduced it grows so rapidly that it tends to displace the native species of seaweeds and greatly reduces the diversity of inshore habitats.
The Sargasso Sea was mentioned by Christopher Columbus in his accounts of his voyages to the New World, and has given rise to many stories of ships trapped in the weed and unable to make their way out. This was a belief prevalent among many seamen during the days of sail, but it was finally disproved by Sir John Murray's expedition in 1910 that discovered the surface was covered only in patches of weed. It is also the main breeding place of eels, the elvers swimming to Europe in the Gulf Stream.
M. V. Angel
Subjects: Maritime History.