Sargassum is a genus of brown macroalgae (seaweed) in the order Fucales of the class Phaeophyceae. This brown macroalgae is spread predominantly in tropical and subtropical areas. It 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.
History
Sargassum was named after sargaço, the Portuguese word for grape, after Portuguese sailors who found the floating macroalgae in the Sargasso Sea noticed the small air-filled bladders that keep the seaweed afloat. The earliest mention in history of the Sargassum may be traced to the times of Cristobal Columbus in his maritime letters "Relaciones y Cartas" of the first voyage, where he mentions having encountered great masses of floating algae that made navigation difficult. Sargassum had, however, acquired a legendary reputation as it expands through the entire Sargasso Sea, and blocks ships movements, but since then, it has since been discovered that it happens in drifts only.
Taxonomy and classification Sargassum is a genus of over 300 species of brown macroalgae (seaweed) in the order Fucales of the class Phaeophyceae. It is one of the members of the proposed Chromista kingdom. Sargassum is spread predominantly in tropical and subtropical areas of the world. The species vary in size, shape and location. There are those that are attached (benthic) and others that are free floating (holopelagic). As mentioned before, the Caribbean receives two interconnected species, Sargassum natans and Sargassum fluitans.
Evolution Fossils of a floating brown algae reminiscent of modern Sargassum are common in certain layers of the Early Oligocene-aged Menilite Formation of Poland, in what was once the Paratethys Sea, suggesting that floating Sargassum mats have been a dominant feature of certain oceanic ecosystems for tens of millions of years. In addition to providing a minimum age for Sargassum, associated with these fossil algae are fossils of shallow-water fishes and crabs, despite these fossil deposits otherwise preserving deepwater fish fossils. This species assemblage closely resembles that found in the modern Sargasso Sea, and has been nicknamed a "quasi-Sargasso" assemblage.
Description
Species of this genus of brown algae may reach up to several metres in length. They are brown or dark olive green in color, and consist of a holdfast, a stipe, and fronds or branches. Oogonia and antheridia occur in conceptacles embedded in receptacles on special branches. Most of the species of Sargassum have spherical, gaseous bladders, called pneumatocysts, which provide buoyancy to the fronds and keep them close to the surface so they can get the maximum amount of light to carry out photosynthesis. The fronds are frequently rough and slightly sticky in feel, and their structure is loose yet strong allowing the algae to endure the waves and the great force of the water currents. The morphological difference within the genus is also significant and tends to change according to the environmental factors, including the water flow, nutritional supply, and the light intensity.
Distribution and ocean currents The physical drivers behind Sargassum inundation events are prevailing winds and ocean surface currents. The Caribbean is located in a region heavily affected by trade winds. Trade winds are strong, consistent northeasterlies winds which blow dust-filled dry air from the Sahara across the Atlantic. Trade winds additionally play a critical role in the annual hurricane season in the Western Atlantic. The Caribbean Current and Antilles branch of the Atlantic North Equatorial Current are the major current transporters of Sargassum in the region. Researchers have recently begun using Moderate Resolution Imaging Spectroradiometer satellite imagery and ocean current data to track and forecast inundation events with a high level of accuracy.
… excerpt ends here. Continue reading the full article.
