Oceans | Science

The Sargasso Sea – a unique ecosystem protected by seaweed

Located in the area marked under the fabled ‘Bermuda Triangle’, the Sargasso Sea located within the North Atlantic Ocean is the only sea in the world that does not have a land boundary. Unlike other seas, its location is defined using ocean currents. It lies within a large system of rotating ocean currents called the Northern Atlantic Subtropical Gyre.

By compass directions, the Sargasso Sea’s western limit is marked by the Gulf Stream, the eastern by the Canary Current, the northern by the North Atlantic Current, while the southern limit is marked by the North Equatorial Current and the Antilles Current. These borders flow in clockwise motion and are dynamic. They change season after season in accordance with the Azores High Pressure Center.

The Sea is named after the genus of free-floating seaweed called Sargassum, named due to early Portuguese encounters with the seaweed, who named it Sargazzo or kelp in Spanish. Sargassum is a form of free-floating seaweed or algae that is unique in the sense that it reproduces vegetatively in the high seas, unlike other forms of floating seaweed that reproduce and originate in the ocean-floor. As such, Sargassum mats are plentiful on the sea’s surface. On the surface, the Sargassum mats provide habitats for a variety of marine organisms such as turtles, which use their platforms for hatchlings to flourish (NOAA, undated).

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The Sargasso Sea Alliance – a conservation partnership led by the Bermudian government – highlight three interdependent areas that place a case for scientific conservation efforts over the Sargasso Sea (Sargasso Sea Alliance, 2011). These include first, the unique ecosystem based on the floating Sargassum. Second, the area is a junction in the North Atlantic for migratory species that utilize the mats for food, reproduction and safety. Third, the unique conditions, the Sargasso Sea Alliance argues, are pertinent for research and require great vigilance.

The surface ecosystem is based upon two species of Sargassum that reproduce through fragmentation, and is different from all other varieties of seaweed. Golden-brown in colour, the floating mechanism is possible due gas filled bladders in the Sargassum. Sargassum provide critical habitats for many permanent and migratory species. The drifting of the sargassum makes it collect marine organisms, particularly invertebrates that attract other marine species towards the mats.

sargasso sea map

sargasso sea map

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The Sargassum hosts more than 145 invertebrate species and over 127 species of fish. There is variance in this biodiversity owing to the season, location in the gyre and the age of the sea-weed. Larger marine species such as sharks and rays that prey on the spawning fish are also of great conservation value. Many spawning species represent rare species of marine life. Many migrating species of fish such as Bluefin Tuna feed in the Sargassum Sea, which are exploited as a food source but are largely protected in the Sargasso Sea by the natural floating Sargassum.
Sargassum mats have been the source for many myths and legends over the centuries. They led many sailors to believe that their ships would be jammed and trapped in the seaweed in earlier times, which was accompanied with still waters and a lack of surface winds. These myths had an important role in the conceptualization of the southwestern region of the Sargasso Sea as the Bermuda Triangle, as the passage in the ocean where ships would disappear. The floating Sargassum provides a natural barrier to fishing expeditions, and the Sargasso Sea was recently earmarked to be a world heritage site by the UN, and a report was published in 2016 in this regard (UN, 2016).

 

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