Сарғассум: теңіз балдырларының туысы

Genus of brown algae

Sargassum is a genus of brown macroalgae (seaweed) in the order Fucales of the Phaeophyceae class. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral reefs, and the genus is widely known for its planktonic (free floating) species. Most species within the class Phaeophyceae are predominantly cold water organisms that benefit from nutrients upwelling, but the genus Sargassum appears to be an exception. Any number of the normally benthic species may take on a planktonic, often pelagic existence after being removed from reefs during rough weather. Two species (S. natans and S. fluitans) have become holopelagic—reproducing vegetatively and never attaching to the seafloor during their lifecycles. The Atlantic Ocean's Sargasso Sea was named after the algae, as it hosts a large amount of Sargassum. The size of annual blooms in the Atlantic increased by over a hundred fold, starting in 2011, as a result of factors including increased fertilizer runoff in major rivers such as the Amazon and Congo.

Sargassum was named by the Portuguese sailors who found it in the Sargasso Sea. They called it after the wooly rock rose (Halimium lasianthum) that grew in their water wells at home, and that was called sargaço in Portuguese (sɐɾˈɣasu) from the Latin salicastrum. The Florida Keys and mainland South Florida are well known for the high levels of Sargassum covering their shores. Sargassum or gulfweed was observed by Columbus. Although the seaweed acquired a legendary reputation for covering the entirety of the Sargasso Sea, making navigation impossible,
it has since been found to occur only in drifts. 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 c=海藻 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 vitamins, carotenoids, proteins, and minerals. Many bioactive chemical compounds that are classified as terpenoids, sterols, sulfated polysaccharides, polyphenols, 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, neuroprotective, anti microbial, anti tumor, fibrinolytic, immune modulatory, anticoagulant, hepatoprotective, and anti viral activities.

Species of this genus of algae may grow to a length of several metres. They are generally brown or dark green in color and consist of a holdfast, a stipe, and a frond. Oogonia and antheridia occur in conceptacles embedded in receptacles on special branches. Some species have berrylike gas filled bladders that help the fronds float to promote photosynthesis. Many have a rough, sticky texture that, along with a robust but flexible body, help them withstand strong water currents.

In limited amounts, washed ashore Sargassum plays an important role in maintaining Atlantic and Caribbean coastal ecosystems. Once ashore, Sargassum provides vital nutrients such as carbon, nitrogen, and phosphorus to coastal ecosystems which border the nutrient poor waters of the western North Atlantic tropics and subtropics. Additionally, it decreases coastal erosion. 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. 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. 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.

Unprecedented Sargassum inundation events cause a range of biological and ecological impacts in affected regions. The decomposition of large quantities of Sargassum along coastlines consumes oxygen, creating large oxygen depleted zones resulting in fish kills. Decomposing Sargassum additionally creates hydrogen sulfide gas (|H2S|link=Hydrogen sulfide), which causes a range of health impacts in humans. During the Sargassum inundation event in 2018, 11,000 Acute Sargassum Toxicity cases were reported in an 8 month span on just the Caribbean islands of Guadeloupe and Martinique. Massive amounts of floating Sargassum present a physical barrier preventing corals and seagrasses from receiving sufficient light, fouling boat propellers, and entangling marine turtles and mammals. With every Sargassum inundation event, large amounts of nutrients are transported from the open ocean to coastal environments. This greatly increases nutrient transport, and its effect on marine and coastal ecosystems are still unknown. Understanding the causes and drivers of Sargassum inundations is critical as they become more commonplace.

The Sargasso Sea, a known source area for Sargassum blooms, is classified as an oligotrophic region. With warm, oxygen poor waters and low nutrient contents, biomass production is limited by what little nutrients are present. Historically, low nutrient levels in the Sargasso Sea have limited Sargassum production. New influxes of nitrogen and phosphorus are driving factors in increased biomass production. 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 African Coast which transfers deep nutrient rich waters to the upper water column where Sargassum resides. 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.

The effects of deforestation, waste water runoff, and commercial agriculture fertilizer on facilitating the excess accumulation of nutrients in aquatic and marine environments have been well studied and shown to be driving factors in eutrophication. Since detrimental Sargassum inundation events did not begin until 2011, it is likely that an unknown nutrient threshold was reached and surpassed. Given current agricultural policies and practices, it is unlikely these inundation events will disappear on their own without human intervention.

Japanese cuisine as well as Chile have traditionally consumed Sargassum, known as hijiki, although it contains high amounts of arsenic, part of the arsenic cycle from groundwater, waterways, into oceans and back to land. There are methods to process and greatly reduce arsenic from this genus of seaweed, potentially making it a nearly inexhaustible food supply for animals or people.

Variations in sea level, salinity, water temperature, chemical composition, rainfall patterns, and water acidity all play roles in regulating algae blooms. As anthropogenic forces increase the variability of these factors, the frequency, duration, severity and geographic range of harmful algae blooms have increased, causing millions of dollars of lost revenue as well as damaging fragile coastal and coral ecosystems.