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Sargassum is a genus of brown macroalgae (seaweed) in the order Fucales and class Phaeophyceae, which can form large brown drifting mats that extend for kilometers across the ocean surface, moving with the currents and wind.
Sargassum comes from the Sargasso Sea, which was named after sargassum, due to the large amounts of the macroalgae that grows there. In recent years, Sargassum has been known for arriving in large quantities throughout the Carribbean region. Scientists using satellite data have also found a new hotspot has been forming from the West of Africa and extends into the Carribbean 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 beacase they provide a vital habitat for a variaty of marine species, including fish, crabs, sea trutles, migratory birds and other organims. However, when large amounts of Sargassum accumulates in the shore and starts 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, decreases dissolved oxygen and changes the pH of the coastal waters. As a result, it affects seagrasses meadows, corals, mangroves and coastal communities that depend on tourism.
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 of having encountered great masses of floating algae, where navigation was made to be hard. Sargassum had, however, acquired a legendary reputation as it exapnds through the entire Sargasso Sea, and blocks ships movements , but since then, it has since been discovered that it happens in drifts only.
Most of the species of Sargassum have spherical, gaseous bladders, called pneumatocysts, which give the fronds a sense of lightness 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.
The Sargasso Sea plays a major role in the Fish migration of catadromous eel species such as the European eel, the American eel, and the American conger. The leptocephalus of these species hatch within the sea and as they grow they travel to Europe or the East Coast of North America. Later in life, the matured eel migrates back to the Sargasso Sea to spawn and lay eggs. It is also believed that after hatching, young loggerhead sea turtles use currents, such as the Gulf Stream, to travel to the Sargasso Sea, where they use the Sargassum as cover from until they are mature.
Sargassum also serve as a trophic link between the ocean surface and the seabed. Isopods of the species Bathyopsurus nybelini at depths of 5002–6288 m in the Puerto Rico Trench and Mid-Cayman spreading center have been observed consuming Sargassum. They even exhibit several adaptations for it, such as microbiomes capable of breaking down the seaweed and fixing nitrogen, specialized swimming strokes, and serrated, grinding mouthparts.
Organisms found in the pelagic Sargassum patches,Laffoley, D.d'A., Roe, H.S.J., Angel, M.V., Ardron, J., Bates, N.R., Boyd, I.L., Brooke, S., Buck, K.N., Carlson, C.A., Causey, B., Maureen Conte, Christiansen, S., Cleary, J., Donnelly, J., Earle, S.A., Edwards, R., Gjerde, K.M., Giovannoni, S.J., Gulick, S., Gollock, M., Hallett, J., Halpin, P., Hanel, R., Hemphill, A., Johnson, R.J., Knap, A.H., Lomas, M.W., McKenna, S.A., Miller, M.J., Miller, P.I., Ming, F.W., Moffitt, R., Nelson, N.B., Parson, L., Peters, A.J., Pitt, J., Rouja, P., Roberts, J., Roberts, J., Seigel, D.A., Siuda, A.N.S., Steinberg, D.K., Stevenson, A., Sumaila, V.R., Swartz, W., Thorrold, S., Trott, T.M., and 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. Sargasso Sea Alliance, 44 pp.
Sargassum is commonly found in the beach drift near Sargassum beds, where they are also known as gulfweed, a term that also can mean all seaweed species washed up on shore.
Sargassum species are found throughout tropical areas of the world and are often the most obvious macrophyte in near-shore areas where Sargassum beds often occur near . The plants grow and attach to coral, rocks, or shells in moderately exposed or sheltered rocky or pebble areas. These tropical populations often undergo seasonal cycles of growth and decay in concert with seasonal changes in sea temperature. In tropical Sargassum species that are often preferentially consumed by herbivorous marine fish and , a relatively low level of natural phenol and occurs.
Beginning in 2011, unprecedented quantities of Sargassum began inundating coastal areas in record amounts. Coastlines in Brazil, the Caribbean, Gulf of Mexico, and the east coast of Florida saw quantities of Sargassum wash ashore up to three feet deep. The first major Sargassum inundation event occurred in 2011 and had a biomass increase of 200 fold compared to the previous eight years average bloom size. Since 2011 increasingly stronger inundation events have occurred every 2–3 years. During a Sargassum inundation event in 2018, one Sargassum bloom measured over 1600 square kilometers, more than three times the average size. Recent inundation events have caused millions of dollars of lost revenue in the tourism industry, especially hurting small Caribbean countries whose economies are highly dependent on seasonal tourism.
While the Sargasso Sea is a known source of Sargassum blooms, variations in the Sargassum types composing these inundation events have led researchers to believe that the Sargasso Sea is not the point of origin of inundating Sargassum. Sargassum natans I and Sargassum fluitans III are the dominant Sargassum species found in the Sargasso Sea. Recent net sampling studies have found Sargassum natans VIII, a previously rare type, is constituting a dominating percentage of Sargassum biodiversity in the Western Atlantic and Sargasso Sea.
Recent studies have found three likely drivers of nutrient influx linked to increasing Sargassum biomass: an increase in nutrient output from the Amazon River, increased nutrients in the Gulf of Mexico, and coastal upwelling off the West Africa which transfers deep nutrient-rich waters to the upper water column where Sargassum resides. Nutrient output from the Amazon River has been shown to have a direct delayed effect on large inundation events, which occur one to two years after years of high nutrient output. and iron Saharan dust from North Africa have been reported to have a fertilizing effect on Sargassum growth; further data is required to understand its role in causing inundating blooms. Researchers globally agree that continued research is required to quantify the effect of marine chemical changes and other environmental factors in the recent increase in Sargassum biomass and inundation events.
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.
Sargassum species are cultivated and cleaned for use as an herbal remedy. Many Chinese herbalists prescribe powdered Sargassum—either the species S. pallidum, or more rarely, hijiki, S. fusiforme—in doses of 0.5 grams dissolved in warm water and drunk as a tea. It is called labels=no in traditional Chinese medicine, where it is used to resolve "heat phlegm".
Sargassum ( F. Sargassaceae) is an important seaweed excessively distributed in tropical and subtropical regions. Different species of Sargassum have folk applications in human nutrition and are considered a rich source of , , , and minerals. Many bioactive chemical compounds that are classified as , , sulfated , , sargaquinoic acids, sargachromanol, and pheophytin were isolated from different Sargassum species. These isolated compounds and/or extracts exhibit diverse biological activities, including analgesic, anti-inflammatory, antioxidant, Neuroprotection, Antimicrobial, Chemotherapy, Fibrinolysis, Immunotherapy, anticoagulant, Hepatoprotection, and Antiviral drug activities.
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