Sargasso Sea: The Current-Bounded Ecosystem, Sargassum Seaweed, and Conservation Efforts

The Sargasso Sea is an elliptical region of the North Atlantic Ocean about 2 million square miles in extent. Unlike other seas, the Sargasso does not have coasts, but is demarcated instead by a series of ocean currents—the North Atlantic Current on the north, the Canary Current on the east, the North Atlantic Equatorial Current on the south, and the Gulf Stream on the west. These currents carry floating material, natural and manmade, into the Northern Atlantic Subtropical Gyre, a slow, clockwise vortex that gives the sea its form.

The Sargasso Sea is noted for the long masses or mats of brown Sargassum seaweed— primarily S. natans and S. fluitans—found in its waters. Both species are holopelagic, meaning that they float freely (because of their small air-filled bladders) and are able to reproduce under the same conditions. Thanks to the Sargassum, a surprisingly large number of animals make the upper levels of the sea their home. These include nearly 150 species of invertebrates (crabs, shrimp, and so on) and more than 100 species of fish, including white marlin, porbeagle sharks, and dolphinfish (mahi-mahi, dorado). At least five species of sea turtles frequent the Sargasso in their early years, and bluefin tuna and humpback whales migrate through its waters on a regular basis. North American and European eels spawn in the sea, and their larvae remain in its upper levels for their first few years of life. The sea’s rich variety of animal life also attracts a number of birds.

Christopher Columbus (1451-1506) crossed the Sargasso Sea on his first voyage across the Atlantic in 1492 and mistakenly took the Sargassum seaweed to be an indication that his ships were approaching land. When his expedition was becalmed for a time, his sailors feared that the weed had taken hold of their ships and that they would be unable to escape. In fact, they had entered what came to be called the “Horse Latitudes,” one of two belts of very light winds that encircle the Earth. The Sargasso Sea’s location fluctuates throughout the seasons in loose coordination with that of an area of high atmospheric pressure within the Horse Latitudes known as the Azores High.

Sargassum seaweed and, in turn, the Sargasso Sea itself are said to owe their names to Portuguese sailors who frequented the Azores Archipelago, which lies to the northeast. According to this theory, the bladders reminded the sailors of a small kind of grape they knew as sargaga or sargacinho.

The French novelist Jules Verne (1828-1905) set one chapter of his 1870 novel Twenty Thousand Leagues Under the Sea in the Sargasso, and the British writer William Hope Hodgson (1877-1918) dramatized the unfounded fears that had grown up around it in several of his short stories and, in particular, his 1907 novel The Boats of the “Glen Carrig.” The fact that the Sargasso Sea overlaps a portion of the Bermuda Triangle, around which a body of folklore has grown more recently, has only added to its sinister, if wholly undeserved, reputation.

The Sargasso Sea is under threat from acidification, climate change, and constant disturbance by shipping—factors that have already led to a depletion of its animal life. Although Bermuda lies within the sea and controls the area near its shores, most of the region’s waters are international. In 2014, five governments—Bermuda, the United States, the Azores, Monaco, and the United Kingdom—signed the Hamilton Declaration of Collaboration for the Conservation of the Sargasso Sea. This declaration led in turn to the creation of the Sargasso Sea Commission, a group intended to encourage and facilitate the protection of the region. In 2016, the British Virgin Islands became the sixth signatory to the declaration, followed by the Bahamas, Canada, the Cayman Islands, and the Dominican Republic. Other governments have expressed interest in signing the agreement.

FURTHER READING: Laffoley, D.d’A., H. S. J. Roe, M. V Angel, J. Ardron, N. R. Bates, I. L. Boyd, . . . V Vats. 2011. “The Protection and Management of the Sargasso Sea: The Golden Floating Rainforest of the Atlantic Ocean.” Summary Science and Supporting Evidence Case. 2011. Sargasso Sea Alliance. http://www.sargassoseacommission.org/storage/documents/Sargasso.Report.9.12.pdf. Accessed August 15, 2016.

Lee, Jane J. 2014. “New International Pact Aims to Protect the Sargasso Sea—Why It’s Worth Saving.” http://news.nationalgeographic.com/news/2014/03/140314-sargasso-sea-nations -bermuda-conservation-science. Accessed August 16, 2016.

McClintock, Jack. 2002. “Sailing the Sea of Life.” http://discovermagazine.com/2002/mar/featsea. Accessed September 30, 2016.

Ryther, John H. 1956. “The Sargasso Sea.” Scientific American 194 (1): 98-104.