Sargassum
Scientific classification Edit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Gyrista
Subphylum: Ochrophytina
Class: Phaeophyceae
Order: Fucales
Family: Sargassaceae
Genus: Sargassum
Species

See list

Lines of Sargassum may stretch for miles along the ocean surface
Sargassum hildebrandtii Grunow, herbarium type specimen, Somalia, before 1889

Sargassum is a genus of brown macroalgae (seaweed) in the order Fucales of the Phaeophyceae class.[1] 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.[2] 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.[3]

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.

History

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 (Portuguese pronunciation: [sɐɾˈɣasu])[4] - 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,[5] it has since been found to occur only in drifts.[6]

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 海藻; hǎizǎo in traditional Chinese medicine, where it is used to resolve "heat phlegm".[7]

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.[8]

Description

Close-up of Sargassum, showing the air bladders that help it stay afloat.

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.[9] 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.

Ecology

Large, pelagic mats of Sargassum in the Sargasso Sea act as one of the only habitats available for ecosystem development; this is because the Sargasso Sea lacks any land boundaries.[10] The Sargassum patches act as a refuge for many species in different parts of their development, but also as a permanent residence for endemic species that can only be found living on and within the Sargassum.[11] These endemic organisms have specialized patterns and colorations that mimic the Sargassum and allow them to be impressively camouflaged in their environment. In total, these Sargassum mats are home to more than 11 phyla and over 100 different species.[12] There is also a total of 81 fish species (36 families represented) that reside in the Sargassum or utilize it for parts of their life cycles.[13] Other marine organisms, such as young sea turtles, will use the Sargassum as 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.[11] Below is a list of organisms that are associated with the Sargassum in the Sargasso Sea.

The Sargasso Sea plays a major role in the migration of catadromous eel species such as the European eel, the American eel, and the American conger eel. The larvae 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 predators until they are mature.[14][15]

Organisms found in the pelagic Sargassum patches,[16][17][11]

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 coral reefs. The plants grow subtidally 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.[18] In tropical Sargassum species that are often preferentially consumed by herbivorous fishes and echinoids, a relatively low level of phenolics and tannins occurs.[19]

The camouflaged Sargassum fish (left) has adapted to live among drifting Sargassum seaweed. It is usually a small fish (center).
Some other small fish, such as this juvenile puffer (right), are also found in Sargassum.

"Coastal inundations" by washed-ashore Sargassum

Large patches of Sargassum adrift near the island of Saint Martin.

In limited amounts, washed-ashore Sargassum plays an important role in maintaining Atlantic and Caribbean coastal ecosystems.[20] 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.[21][22] Additionally, it decreases coastal erosion.[22]

Beginning in 2011, unprecedented quantities of Sargassum began inundating coastal areas in record amounts.[23] 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.[24][20] 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.[25] 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.[25][26] 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.[25]

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.[25][27] Sargassum natans I and Sargassum fluitans III are the dominant Sargassum species found in the Sargasso Sea.[28] 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.[28][29][30]

Biological impacts

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.[31] Decomposing Sargassum additionally creates hydrogen sulfide gas (H2S), which causes a range of health impacts in humans.[32] 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.[33] 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.[34][35] 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.[36]

Nutrient factors

The Sargasso Sea, a known source area for Sargassum blooms, is classified as an oligotrophic region.[37] With warm, oxygen-poor waters and low nutrient contents, biomass production is limited by what little nutrients are present.[38] 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.[39][40][41]

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.[42][43][41] 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.[42] Phosphates and iron transported via the trade winds 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.[25] 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.[42]

Currents and winds

The physical drivers behind Sargassum inundation events are prevailing winds and ocean surface currents.[44] 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.[45] Trade winds additionally play a critical role in the annual hurricane season in the Western Atlantic.[46] The Caribbean Current and Antilles branch of the Atlantic North Equatorial Current are the major current transporters of Sargassum in the region.[47][48]

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.[49]

Human effects

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.[50][51] 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.

As food

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.

Climate change

Variations in sea level, salinity, water temperature, chemical composition, rainfall patterns, and water acidity all play roles in regulating algae blooms.[52] 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.[53]

References

  1. ↑ Guiry, M.D.; Guiry, G.M., eds. (2023). "Sargassum C.Agardh, 1820, nom. et typ. cons". AlgaeBase. National University of Ireland. Retrieved 4 July 2023.
  2. ↑ Hogan, C. Michael (2011). Monosson, E.; Cleveland, C.J. (eds.). "Algae § 1.3 Brown_algae". Encyclopedia of Earth. Washington DC: National Council for Science and the Environment.
  3. ↑ "Sargasso". Straight Dope.
  4. ↑ Gómez de Silva, Guido 1988. Breve diccionario etimológico de la lengua española. Fondo de Cultura Económica, Mexico City, ISBN 968-16-2812-8, p. 627.
  5. ↑ Padilla, Michael J. (2000). Earth's Waters. Prentice Hall. p. 114. ISBN 9780134349404. Retrieved 11 July 2022. Since Columbus's time, many legends about the Sargasso Sea have spread. The seaweed covering its surface was believed to be so thick that no ship could escape from it. Early writers described ancient ghost ships, rotting away as they remained trapped forever in the seaweed.
  6. ↑ David McFadden (August 10, 2015). "Stinking mats of seaweed piling up on Caribbean beaches". Archived from the original on August 13, 2015. Retrieved August 10, 2015.
  7. ↑ Xu Li & Wang Wei (2002). Chinese Materia Medica: Combinations and Applications. Donica Publishing Ltd. p. 425. ISBN 978-1-901149-02-9.
  8. ↑ Rushdi, Mohammed I.; Abdel-Rahman, Iman A. M.; Saber, Hani; Attia, Eman Zekry; Abdelraheem, Wedad M.; Madkour, Hashem A.; Hassan, Hossam M.; Elmaidomy, Abeer H.; Abdelmohsen, Usama Ramadan (2020). "Pharmacological and natural products diversity of the brown algae genus Sargassum". RSC Advances. 10 (42): 24951–24972. Bibcode:2020RSCAd..1024951R. doi:10.1039/D0RA03576A. ISSN 2046-2069. PMC 9055232. PMID 35517468.
  9. ↑ Abbott, Isabella A.; Hollenberg, George J. (1992). "Phaeophyta § Sargassum". Marine Algae of California. Stanford University Press. pp. 272–. ISBN 978-0-8047-2152-3.
  10. ↑ US Department of Commerce, National Oceanic and Atmospheric Administration. (2013, June 01). What is the Sargasso Sea? Retrieved November 28, 2017
  11. 1 2 3 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., Conte, M.H., 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.
  12. ↑ Stoner, AW; Greening, HS (1984). "Geographic variation in the macrofaunal associates of pelagic Sargassum and some biogeographic implications". Marine Ecology Progress Series. 20: 185–192. Bibcode:1984MEPS...20..185S. doi:10.3354/meps020185.
  13. ↑ Casazza, T.L.; Ross, S.W., PhD. "Sargassum: A Complex 'Island' Community at Sea". NOAA Ocean Explorer. Retrieved 27 September 2018.{{cite web}}: CS1 maint: multiple names: authors list (link)
  14. ↑ "Turtles return home after UK stay". BBC News. 2008-06-30. Retrieved 2010-05-23.
  15. ↑ "Satellites track turtle 'lost years'". BBC News. 2014-03-05. Retrieved 2014-03-05.
  16. ↑ "NOAA Ocean Explorer: Life on the Edge: Sargassum". oceanexplorer.noaa.gov. Retrieved 2021-11-22.
  17. ↑ Huffard, C. L.; von Thun, S.; Sherman, A. D.; Sealey, K.; Smith, K. L. (December 2014). "Pelagic Sargassum community change over a 40-year period: temporal and spatial variability". Marine Biology. 161 (12): 2735–2751. doi:10.1007/s00227-014-2539-y. PMC 4231207. PMID 25414525.
  18. ↑ Fulton CJ, Depczynski M, Holmes TH, Noble MM, Radford B, Wernberg TH, Wilson SK (2014). "Sea temperature shapes seasonal fluctuations in seaweed biomass within the Ningaloo coral reef ecosystem". Limnology & Oceanography. 59 (1): 156–166. Bibcode:2014LimOc..59..156F. doi:10.4319/lo.2014.59.1.0156.
  19. ↑ Steinberg, Peter D. (1986). "Chemical defenses and the susceptibility of tropical marine brown algae to herbivores". Oecologia. 69 (4): 628–630. Bibcode:1986Oecol..69..628S. doi:10.1007/BF00410374. PMID 28311627. S2CID 19551247.
  20. 1 2 "Sargassum Seaweed: An important element for beaches and shoreline stability. | Government of the Virgin Islands". bvi.gov.vg.
  21. ↑ Read "Managing Wastewater in Coastal Urban Areas" at NAP.edu. 1993. doi:10.17226/2049. ISBN 978-0-309-04826-2 – via www.nap.edu.
  22. 1 2 Crist, Carolyn (July 26, 2019). "Toxic seaweed a menace to Caribbean tourists". Reuters – via www.reuters.com.
  23. ↑ Schell, Jeffrey; Goodwin, Deborah; Siuda, Amy (September 1, 2015). "Recent Sargassum Inundation Events in the Caribbean: Shipboard Observations Reveal Dominance of a Previously Rare Form". Oceanography. 28 (3): 8–10. doi:10.5670/oceanog.2015.70.
  24. ↑ "Fact sheet" (PDF). www.nps.gov. Retrieved 2020-09-29.
  25. 1 2 3 4 5 "The Great Sargassum Disaster of 2018". essa.com. February 7, 2019.
  26. ↑ "The Sargassum Mass-Bloom of 2018". nereusprogram.org.
  27. ↑ Schell, Jeffrey M.; Goodwin, Deborah S.; Siuda, Amy N. S. (2015). "Recent Sargassum Inundation Events in the Caribbean". Oceanography. 28 (3): 8–11. doi:10.5670/oceanog.2015.70. JSTOR 24861895.
  28. 1 2 Schell, Jeffrey; Goodwin, Deborah; Siuda, Amy (1 September 2015). "Recent Sargassum Inundation Events in the Caribbean: Shipboard Observations Reveal Dominance of a Previously Rare Form". Oceanography. 28 (3): 8–10. doi:10.5670/oceanog.2015.70.
  29. ↑ Martin, Lindsay Margaret (6 May 2016). Pelagic Sargassum and Its Associated Mobile Fauna in the Caribbean, Gulf Of Mexico, and Sargasso Sea (Thesis). hdl:1969.1/157125.
  30. ↑ "Ramlogan et al 2017 sargassum influx barbados fish". 2018-06-15. Archived from the original on 2018-06-15. Retrieved 2021-11-22.
  31. ↑ Burton, Rebecca (2018-07-15). "Sargassum: Seaweed or Brown Algae". Florida Museum. Retrieved 2020-09-29.
  32. ↑ "Sargassum seaweed: limit the exposure of residents and workers to hydrogen sulphide - Agence nationale de sécurité sanitaire de l'alimentation, de l'environnement et du travail". Anses. 9 November 2018. Retrieved 2020-09-29.
  33. ↑ Crist, Carolyn (2019-07-26). "Toxic seaweed a menace to Caribbean tourists". U.S. Retrieved 2020-09-29.
  34. ↑ "Tracking Sargassum's ocean path could help predict coastal inundation events". University of Maryland Center for Environmental Science. 2018-08-22. Retrieved 2020-09-29.
  35. ↑ "The Great Sargassum Disaster of 2018". ESSA. 2019-02-07. Retrieved 2020-09-29.
  36. ↑ Smetacek, Victor; Zingone, Adriana (2013). "Green and golden seaweed tides on the rise" (PDF). Nature. 504 (7478): 84–88. Bibcode:2013Natur.504...84S. doi:10.1038/nature12860. PMID 24305152. S2CID 4389919.
  37. ↑ Lundgreen, Regitze B. C.; Jaspers, Cornelia; Traving, Sachia J.; Ayala, Daniel J.; Lombard, Fabien; Grossart, Hans-Peter; Nielsen, Torkel G.; Munk, Peter; Riemann, Lasse (20 June 2019). "Eukaryotic and cyanobacterial communities associated with marine snow particles in the oligotrophic Sargasso Sea". Scientific Reports. 9 (1): 8891. Bibcode:2019NatSR...9.8891L. doi:10.1038/s41598-019-45146-7. PMC 6586830. PMID 31222051.
  38. ↑ Bulger, Faith. "Functionality of World Ocean". Sargasso Sea Commission.
  39. ↑ "Satellite Data Reveal Growth and Decline of Sargassum". Eos. 29 July 2019.
  40. ↑ Kornei, Katherine (2019-07-29). "Satellite Data Reveal Growth and Decline of Sargassum". Eos. Retrieved 2020-09-29.
  41. 1 2 Lapointe, Brian E. (1995). "A comparison of nutrient-limited productivity in Sargassum natans from neritic vs. oceanic waters of the western North Atlantic Ocean". Limnology and Oceanography. 40 (3): 625–633. Bibcode:1995LimOc..40..625L. doi:10.4319/lo.1995.40.3.0625.
  42. 1 2 3 "Scientists discover the biggest seaweed bloom in the world". phys.org.
  43. ↑ "Tracking Sargassum's ocean path could help predict coastal inundation events". ScienceDaily.
  44. ↑ "Tracking Sargassum's ocean path could help predict coastal inundation events". phys.org.
  45. ↑ News, Chelsea Harvey, E&E. "Saharan Dust Plume Slams U.S., Kicking Up Climate Questions". Scientific American. {{cite web}}: |last= has generic name (help)CS1 maint: multiple names: authors list (link)
  46. ↑ "Movement of Hurricanes: steered by the global winds". ww2010.atmos.uiuc.edu.
  47. ↑ "Antilles Current | current, Atlantic Ocean". Encyclopedia Britannica.
  48. ↑ "The Caribbean Current". oceancurrents.rsmas.miami.edu.
  49. ↑ Wang, Mengqiu; Hu, Chuanmin (16 April 2017). "Predicting Sargassum blooms in the Caribbean Sea from MODIS observations: Sargassum Bloom Prediction". Geophysical Research Letters. 44 (7): 3265–3273. doi:10.1002/2017GL072932.
  50. ↑ "The Effects of Deforestation on Nutrient Concentrations in Tributaries of Lake Tanganyika" (PDF). www.geo.arizona.edu. Retrieved 2020-09-29.
  51. ↑ US EPA, OW (March 12, 2013). "The Sources and Solutions: Agriculture". US EPA.
  52. ↑ US EPA, OW (September 5, 2013). "Climate Change and Harmful Algal Blooms". US EPA.
  53. ↑ "Impacts of Climate Change on the Occurrence of Harmful Algal Blooms" (PDF). www.epa.gov. 2013. Retrieved 2020-09-29.

Further reading

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