By July 6, 2018, beaches on the eastern coast of St. Vincent—an island located in the southeastern Caribbean Sea (Lesser Antilles)—were covered nearly one-meter deep with rotting brown algae (seaweed), known as Sargassum, posing multiple problems for both its human population and its marine ecosystems. St. Vincent was only one of the many Caribbean islands affected both economically (because of loss of tourism) and environmentally by largest Sargassum outbreak since 2011 when this seaweed began washing up on beaches. See also: Algae; Fucales; West Indies
Sargassum found in the Caribbean consists of two species: S. natans and S. fluitans. These are free-floating algae, by virtue of having oxygen-filled bladders (pneumatocysts). Sargassum is transported by ocean currents and winds in the form of consolidated mats (rafts), often extending one meter deep and more than one kilometer long. In the open ocean, Sargassum serves as a habitat for more than 100 species of fish and more than 100 species of invertebrates. However, once Sargassum drifts close to the shore, it dies and begins to decompose, depleting the oxygen content of the water and giving off hydrogen-sulfide gas. As a result, many fish and other marine organisms that live near the shoreline die off and beached Sargassum gives off the sulfurous stench of rotten eggs. See also: Ocean circulation
When rafts of Sargassum began floating up on Caribbean beaches in 2011, it was initially thought that they had come from the Sargasso Sea to the north. However, satellite images showed that the rafts were originating off the coast of Brazil and being transported to the Caribbean by equatorial currents. Scientists are still trying to figure out what is causing these Sargassum blooms. At present, agricultural (nutrient-rich) runoff, originating in Brazil, and warmer ocean temperatures are thought to be contributing factors. See also: Equatorial currents; Ocean warming; Water pollution
A big question has arisen in 2018, for which there is no simple answer, about how to remove and dispose of the huge quantities of decaying Sargassum. In the past, when lesser quantities washed ashore, the best practice was to leave the Sargassum on the beach, where it eventually washed away or was buried after a storm. For now, the government of Saint Vincent and the Grenadines is hiring a company from St. Lucia to convert the collected Sargassum into fertilizer. In addition to fertilizer, other suggested uses of Sargassum include mulch, compost, and biofuel. See also: Fertilizer
