Sargassum

Sargassumis a genus of brown macroalgae (seaweed) in the orderFucalesof thePhaeophyceaeclass.Numerous species are distributed throughout the temperate and tropicaloceansof 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 genusSargassumappears to be an exception.The species within Sargassum are normallybenthic, but some of the species may take on aplanktonic, oftenpelagicexistence after being removed from reefs during rough weather. Two species (S. natansandS. fluitans) have become holopelagic—reproducing vegetatively and never attaching to the seafloor during their lifecycles. TheAtlantic Ocean'sSargasso Seawas named after the algae, as it hosts a large amount ofSargassum.
The size of annualbloomsin the Atlantic increased by over a hundred-fold, starting in 2011, as a result of factors including increasedfertilizer runoffin major rivers such as theAmazonandCongo.
Sargassumwas named by the Portuguese sailors who found it in theSargasso Sea. They called it after the wooly rock rose (Halimium lasianthum) that grew in their water wells at home,and that was calledsargaçoin Portuguese (Portuguese pronunciation:[sɐɾˈɣasu])- from the Latinsalicastrum.
TheFlorida Keysand mainland South Florida are well known for the high levels ofSargassumcovering their shores.Sargassumorgulfweedwas observed byColumbus. 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.
Sargassumspecies are cultivated and cleaned for use as an herbal remedy. Many Chinese herbalists prescribe powderedSargassum—either the speciesS. 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海藻;hǎizǎointraditional 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 ofSargassumhave folk applications in human nutrition and are considered a rich source ofvitamins,carotenoids,proteins, and minerals. Many bioactive chemical compounds that are classified asterpenoids,sterols, sulfatedpolysaccharides,polyphenols, sargaquinoic acids,sargachromanol, andpheophytinwere isolated from differentSargassumspecies. These isolated compounds and/or extracts exhibit diverse biological activities, includinganalgesic,anti-inflammatory,antioxidant,neuroprotective,anti-microbial,anti-tumor,fibrinolytic,immune-modulatory,anticoagulant,hepatoprotective, andanti-viralactivities.
Species of this genus ofalgaemay grow to a length of several metres. They are generally brown or dark green in color and consist of aholdfast, astipe, and afrond.Oogoniaandantheridiaoccur inconceptaclesembedded inreceptacleson special branches.Some species have berrylike gas-filled bladders that help the fronds float to promotephotosynthesis. Many have a rough, sticky texture that, along with a robust but flexible body, help them withstand strong water currents.
Large,pelagicmats ofSargassumin the Sargasso Sea act as one of the only habitats available for ecosystem development; this is because the Sargasso Sea lacks any land boundaries.TheSargassumpatches act as a refuge for many species in different parts of their development, but also as a permanent residence forendemicspecies that can only be found living on and within theSargassum.These endemic organisms have specialized patterns and colorations that mimic theSargassumand allow them to be impressively camouflaged in their environment. In total, theseSargassummats are home to more than 11 phyla and over 100 different species.There is also a total of 81 fish species (36 families represented) that reside in theSargassumor utilize it for parts of their life cycles.Other marine organisms, such as young sea turtles, will use theSargassumas shelter and a resource for food until they reach a size at which they can survive elsewhere. This community is being affected by humans due to overfishing, trash and other types of pollution, and boat traffic, which could eventually lead to the demise of this diverse and unique habitat.Below is a list of organisms that are associated with theSargassumin the Sargasso Sea.
The Sargasso Sea plays a major role in themigrationofcatadromouseelspecies such as theEuropean eel, theAmerican eel, and theAmerican conger eel. Thelarvaeof 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 layeggs. It is also believed that after hatching, youngloggerhead sea turtlesuse currents, such as theGulf Stream, to travel to the Sargasso Sea, where they use theSargassumas cover frompredatorsuntil they are mature.
Sargassumalso serve as a trophic link between the ocean surface and the seabed. Isopods of the speciesBathyopsurus nybeliniat depths of 5002–6288 m in thePuerto Rico TrenchandMid-Cayman spreading centerhave been observed consumingSargassum. 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 pelagicSargassumpatches,
Sargassumis commonly found in the beach drift nearSargassumbeds, where they are also known asgulfweed, a term that also can mean all seaweed species washed up on shore.
Sargassumspecies are found throughout tropical areas of the world and are often the most obvious macrophyte in near-shore areas whereSargassumbeds often occur nearcoral reefs. The plants growsubtidallyand 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 tropicalSargassumspecies that are often preferentially consumed byherbivorousfishesandechinoids, a relatively low level ofphenolicsandtanninsoccurs.
In limited amounts, washed-ashoreSargassumplays an important role in maintaining Atlantic and Caribbean coastal ecosystems.Once ashore,Sargassumprovides vital nutrients such ascarbon,nitrogen, andphosphorusto coastal ecosystems which border the nutrient-poor waters of the western North Atlantic tropics and subtropics.Additionally, it decreasescoastal erosion.
Beginning in 2011, unprecedented quantities ofSargassumbegan inundating coastal areas in record amounts.Coastlines inBrazil, theCaribbean,Gulf of Mexico, and the east coast ofFloridasaw quantities ofSargassumwash ashore up to three feet deep.The first majorSargassuminundation event occurred in 2011 and had abiomassincrease 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 aSargassuminundation event in 2018, oneSargassumbloom 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 ofSargassumblooms, variations in theSargassumtypes composing these inundation events have led researchers to believe that the Sargasso Sea is not the point of origin of inundatingSargassum.Sargassum natans IandSargassum fluitans IIIare the dominantSargassumspecies found in the Sargasso Sea.Recent net sampling studies have foundSargassum natans VIII, a previously rare type, is constituting a dominating percentage ofSargassumbiodiversity in the Western Atlantic and Sargasso Sea.
UnprecedentedSargassuminundation events cause a range of biological and ecological impacts in affected regions. The decomposition of large quantities ofSargassumalong coastlines consumes oxygen, creating large oxygen-depleted zones resulting in fish kills.DecomposingSargassumadditionally createshydrogen sulfidegas (H2S), which causes a range of health impacts in humans.During theSargassuminundation event in 2018, 11,000 AcuteSargassumToxicity cases were reported in an 8-month span on just the Caribbean islands ofGuadeloupeandMartinique.Massive amounts of floatingSargassumpresent a physical barrier preventingcoralsandseagrassesfrom receiving sufficient light, fouling boat propellers, and entangling marine turtles and mammals.With everySargassuminundation 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 coastalecosystemsare still unknown. Understanding the causes and drivers ofSargassuminundations is critical as they become more commonplace.
Sargassum can harm wildlife and water quality. But companies like Algas Organics clean beaches and use it to make plant fertilizer and pulp. The company said Georgia Pacific and Procter & Gamble work with it.
The Sargasso Sea, a known source area forSargassumblooms, is classified as anoligotrophicregion.With warm, oxygen-poor waters and low nutrient contents, biomass production is limited by what little nutrients are present.Historically,low nutrient levelsin the Sargasso Sea have limitedSargassumproduction. New influxes ofnitrogenandphosphorusare driving factors in increasedbiomassproduction.
Recent studies have found three likely drivers of nutrient influx linked to increasingSargassumbiomass: an increase in nutrient output from theAmazon River, increased nutrients in theGulf of Mexico, and coastalupwellingoff theWest African Coastwhich transfers deepnutrient-rich waters to the upper water column whereSargassumresides.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.Phosphatesandirontransported via the trade windsfrom North Africa have been reported to have a fertilizing effect onSargassumgrowth; 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 inSargassumbiomass and inundation events.
The physical drivers behindSargassuminundation events are prevailing winds and ocean surface currents.TheCaribbeanis located in a region heavily affected byTrade winds. Trade winds are strong, consistent northeasterlies winds which blow dust-filled dry air from theSaharaacross the Atlantic.Trade winds additionally play a critical role in the annualhurricaneseason in the Western Atlantic.TheCaribbean CurrentandAntillesbranch of the Atlantic North Equatorial Current are the major current transporters ofSargassumin the region.
Researchers have recently begun usingModerate Resolution Imaging Spectroradiometersatellite imageryandocean currentdata to track and forecast inundation events with a high level of accuracy.
The effects ofdeforestation, waste-waterrunoff, and commercial agriculturefertilizeron facilitating the excess accumulation of nutrients in aquatic and marine environments have been well studied and shown to be driving factors ineutrophication.Since detrimentalSargassuminundation 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 cuisineas well asChilehave traditionally consumedSargassum, known ashijiki, although it contains high amounts ofarsenic, part of the arsenic cycle from groundwater, waterways, into oceans and back to land.  There aremethodsto process and greatly reduce arsenic from this genus of seaweed, potentially making it a nearly inexhaustiblefood supplyfor animals or people.
Variations insea level,salinity, water temperature, chemical composition, rainfall patterns, and water acidity all play roles in regulatingalgae 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 andcoralecosystems.