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Sargassum weeds closeup.jpg
Scientific classification
Domain: Eukaryota
(unranked): SAR
Superphylum: Heterokonta
Class: Phaeophyceae
Order: Fucales
Family: Sargassaceae
Genus: Sargassum
Lines of Sargassum can stretch for miles along the ocean surface
Sargassum hildebrandtii Grunow, herbarium type specimen, Somalia, before 1889
Close-up of Sargassum, showing the air bladders that help it stay afloat

Sargassum is a genus of brown (class Phaeophyceae) macroalgae (seaweed) in the order Fucales. 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.[1] Any number of the normally benthic species may take on a planktonic, often pelagic existence after being removed from reefs during rough weather; however, two species (S. natans and S. fluitans) have become holopelagic—reproducing vegetatively and never attaching to the seafloor during their lifecycle. The Atlantic Ocean's Sargasso Sea was named after the algae, as it hosts a large amount of sargassum.[2]


Sargassum was named by the Portuguese sailors who found it in the Sargasso Sea 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]).[3]

The Florida Keys and its smaller islands are well known for their high levels of Sargassum covering their shores. Gulfweed was observed by Columbus. Although it was formerly thought to cover the entirety of the Sargasso Sea, making navigation impossible, it has since been found to occur only in drifts.[4]

Sargassum is also 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 gram 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".[5]


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.[6] 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, helps it withstand strong water currents.


Thick masses of Sargassum provide an environment for a distinctive and specialised group of marine animals and plants, many of which don't live elsewhere. 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.[7] In some cases (e.g., the Sargasso Sea) there are floating populations of Sargassum.

In tropical Sargassum species that are often preferentially consumed by herbivorous fishes and echinoids, there is a relatively low level of phenolics and tannins.[8]

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.

Sargassum muticum[edit]

Sargassum muticum is a large brown seaweed of the class Phaeophyceae.[9] It grows attached to rocks by a perennial holdfast up to 5 cm in diameter. From this holdfast the main axis grows to a maximum of 5 cm high. The leaf-like laminae and primary lateral branches grow from this stipe. In warm waters, it can grow to 12 m long, however in British waters it gives rise to a single main axis with secondary and tertiary branches that the plant sheds annually. Numerous small 2–6 mm stalked air vesicles provide buoyancy. The reproductive receptacles are also stalked, and develop in the axils of leafy laminae. It is self-fertile.

Sargassum adrift in Gulf Stream[edit]

The Gulf has the second largest concentration of sargassum of any body of water in the world. A fair amount of it washes out through the Straits of Florida in the Gulf Stream and ends up in the Sargasso Sea in the Atlantic Ocean off the East Coast of the United States.

— Bob Shipp[10]

We rounded Hatteras in fair weather, and saw the line between the brilliant blue Gulf Stream full of gulf weed and the muddy grayish shore water as clearly defined as that between the sidewalk and the roadway in a street.

Sargassum crisis in the Caribbean Sea[edit]

In summer 2015, large quantities of different species of Sargassum accumulated along the shores of many of the countries bathed by the Caribbean Sea. Some of the affected islands and regions include the Caribbean coast of Mexico, the Dominican Republic, Barbados and Tobago.[12] Another large outbreak occurred in 2018.[13]

The algae washes ashore, piles up on beaches, and decays, often causing a foul odor, releasing fumes of sulphur compounds that rust metals, that can turn taps black in shore houses, damages modern conveniences, and causes respiratory problems, particularly for asthmatics. 52 patients were recorded by a single doctor in Guadeloupe with Sargassum-related symptoms. Insurance problems arise for tourist operators and homeowners, where the household and business losses do not fall into previous insurance categories. Wildlife also suffers; for example, sea turtle hatchlings that die on their way to the open water. The affected countries and territories are discussing causes of the outbreak, potential solutions, and the negative effects on tourism.

One method of cleaning is by spade and barrow onshore, and it can be collected by raking boats offshore. Barrages of shallow nets floated by long buoys can be used to ward off algae drifts, depending on wave height and current. On the Caribbean island of Saint Martin, backhoes are also used in the process of clean up once the sargassum weed reaches the shorelines.[14][15]

Researchers say that the Sargassum outbreak started in 2011, but it has become worse over the years. As the sargassum is cleaned up on the shorelines, in a matter of a week the shorelines are once again filled in masses. It is still a recurring problem to this date. There are several factors that could explain the proliferation of Sargassum in the area in recent years. These include the rise of sea temperature and the change of sea currents due to climate change. Also, nutriments from agricultural fertilizers and wastewater from the cities, that end up in the sea, could also make the algae bloom.[12]

See also[edit]


  1. ^ 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. 
  2. ^ "Sargasso". Straight Dope. 
  3. ^ 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.
  4. ^ David McFadden (August 10, 2015). "Stinking mats of seaweed piling up on Caribbean beaches". Retrieved August 10, 2015. 
  5. ^ Xu Li & Wang Wei (2002). Chinese Materia Medica: Combinations and Applications. Donica Publishing Ltd. p. 425. ISBN 1-901149-02-1. 
  6. ^ Abbott, Isabella A.; Hollenberg, George J. (1992). "Phaeophyta § Sargassum". Marine Algae of California. Stanford University Press. pp. 272–. ISBN 978-0-8047-2152-3. 
  7. ^ 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. doi:10.4319/lo.2014.59.1.0156. 
  8. ^ Steinberg, Peter D. (1986). "Chemical defenses and the susceptibility of tropical marine brown algae to herbivores". Oecologia. 69 (4): 628–630. doi:10.1007/BF00410374. PMID 28311627. 
  9. ^ Hardy, F.G.; Guiry, M.D. (2003). A Check-list and Atlas of the Seaweeds of Britain and Ireland. British Phycological Society. ISBN 0-9527115-16. 
  10. ^ Bob Shipp interviewed by Jeff Young (16 July 2010). "Living on Earth: The Need for Seaweed". PRI's Environmental News Magazine. 
  11. ^ Pinchot, Gifford (1930). To the South Seas. New York City: Blue Ribbon Books. p. 14. 
  12. ^ a b "Stinking seaweed piling high on beaches in tourism-dependent Caribbean". CBC News. 
  13. ^ "Sargassum: A Nightmare in the Caribbean". Repeating Islands. 4 April 2018. Retrieved 30 May 2018. 
  14. ^ "Guadeloupe: The invasion of sargassum seaweed". Fr24. 
  15. ^ "Sargassum seaweed, 'greatest single threat to the Caribbean tourism industry'". MercoPress. 

Further reading[edit]

  • Critchley, A.T.; Farnham, W.F.; Morrell, S.L. (1983). "A chronology of new European sites of attachment for the invasive brown alga, Sargassum muticum, 1973–1981". Journal of the Marine Biological Association of the United Kingdom. 63 (1): 799–811. doi:10.1017/S0025315400071228. 
  • Boaden, P.J.S. (1995). "The adventive seaweed Sargassum muticum (Yendo) Fensholt in Strangford Lough, Northern Ireland". Ir. Nat. J. 25 (3): 111–3. JSTOR 25535928. 
  • Davison, D.M. (1999). "Sargassum muticum in Strangford Lough, 1995–1998; a review of the introduction and colonisation of Strangford Lough MNR and cSAC by the invasive brown alga Sargassum muticum". Environment and Heritage Service Research and Development Series (99): 27. ISSN 1367-1979. 

External links[edit]