Overview

Brief Summary

“[T]halli are highly differentiated into holdfast, cylindrical main axis, leaflike blades, and airbladders in the axil of blades. This genus is widely spread in temperate, tropical, and subtropical waters in both intertidal and subtidal zones. Some forms are free-floating, sometimes occurring in extensive rafts that harbor distinctive communities of organisms adapted to the buoyant Sargassum habitat. These occur in the Sargasso Sea off the western coast of Africa. During the 1940s, Sargassum muticum spread from Japan to the northern pacific coast of the US, and by the 1970s had made its way south to California. This species of Sargassum has also spread to Europe, probably on oysters destined for aquaculture operations. Sargassum forms nuisance growths in harbors and on beaches, and it can quickly spread to new areas due to the floatation capabilities conferred by its many air bladders. Other features contributing to rapid spread include fast growth rate, fertility in the first year and monoecious reproduction.” (Graham & Wilcox, 2000)

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Sargassum is a genus of brown (class Phaeophyceae) macroalga (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. However, the genus may be best known for its planktonic (free-floating) species. While most species within the class Phaeophyceae are predominantly cold water organisms that benefit from nutrients upwelling, genus Sargassum appears to be an exception to this general rule. 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.

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Distribution

“Because of their worldwide distribution and capacity to alter native communities, non-indigenous algae are potentially important agents of global ecological change.” (Britton-Simmons, 2004)

Sargassum occurs in temperate to tropical waters. Since the 1940s, Sargassum muticum has spread from Japan to Canada, the United States, and Europe where it can have a significant impact on the composition of the native flora and fauna, either via direct or indirect effects.

(Critchley et al., 1983; Stæhr et al., 2000; Britton-Simmons, 2004)

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Physical Description

Diagnostic Description

Parenchymatous, with growth from an apical cell

Branching monopodal, with lateral branch systems consisting of leaf-like blades, air bladders, and recepticles

Haploid generation reduced to the egg and sperm

Gametes retained in conceptacles

Gamete union is oogamous

(Lee, 1999; Graham & Wilcox, 2000).

The Sargussum of the Sargasso Sea never develop holdfasts, and all reproduction is vegetative (Graham & Wilcox, 2000).

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Ecology

Habitat

Known from seamounts and knolls
  • Stocks, K. 2009. Seamounts Online: an online information system for seamount biology. Version 2009-1. World Wide Web electronic publication.
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Depth range based on 2 specimens in 2 taxa.

Environmental ranges
  Depth range (m): 1 - 3

Graphical representation

Depth range (m): 1 - 3
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Rocky subtidal and intertidal; also pelagic, creating large rafts floating on the sea surface, e. g., the Sargasso Sea.

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Associations

Sargassum rafts are habitat and/or food for many species of larval and adult fish and invertebrates (Stoner & Greening, 1984; Coston-Clements et al., 1991; Hoffmayer et al., 2005; Casazza & Ross, 2008)

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Life History and Behavior

Life Cycle

Sargassum do not show alternation of generations, as do many other brown algae. Tiny gametophytes (“gametangia”) are retained within the thallus of the larger sporophyte. Gametes are formed in the gametophyte via meios followed by mitotic divisions. The multicellular, macroscopic thalli are diploid (though many cases of polyploidy occur). (Lee, 1999; Graham & Wilcox, 2000)

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Reproduction

Sexual (with gametes as only haploid phase) and/or vegetative (Lee, 1999; Graham & Wilcox, 2000)

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:272Public Records:3
Specimens with Sequences:116Public Species:1
Specimens with Barcodes:115Public BINs:1
Species:40         
Species With Barcodes:25         
          
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Statistics of barcoding coverage: Sargassum cf. cinereum

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Sargassum

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Genomic DNA is available from 16 specimens with morphological vouchers housed at Queensland Museum
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Genomic DNA is available from 11 specimens with morphological vouchers housed at National Institute of Water and Atmospheric Research, Wellington
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Wikipedia

Sargassum

Lines of 'Sargassum can stretch for miles along the ocean surface
The camouflaged sargassum fish has evolved to live among drifting Sargassum seaweed
Close-up of Sargassum, showing its 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. However, the genus may be best known for its planktonic (free-floating) species. While most species within the class Phaeophyceae are predominantly cold water organisms that benefit from nutrients upwelling, genus Sargassum appears to be an exception to this general rule.[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]

History[edit]

Sargassum was named by the Portuguese sailors who found it in the Sargasso Sea after a species of rock rose (Helianthemum) 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.

Sargassum is also cultivated and cleaned for use as an herbal remedy. Many Chinese herbalists prescribe powdered Sargassum in paper packets of 0.5 gm, to be dissolved in warm water and drunk as a tea. It is said[who?] to remove excess phlegm.[citation needed] When sold in this application it is commonly referred to as Seaweed Sargassum Tea.

Description[edit]

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.[4] Some species have berrylike gas-filled bladders which help keep the fronds afloat to promote photosynthesis. Many have a rough sticky texture, which together with a robust but flexible body, helps it to withstand strong water currents.

Ecology[edit]

The thick masses of Sargassum provide an environment for a distinctive and specialised group of marine animals and plants, many of which are not found elsewhere.

Sargassum is commonly found in the beach drift near Sargassum beds where they are also known as gulfweed, a term also used to include 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. 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.[5]

Sargassum muticum[edit]

Sargassum muticum is a large brown seaweed of the class Phaeophyceae. 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 which are shed 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.

References[edit]

  1. ^ C.Michael Hogan. 2011. Brown algae. eds. E.Monosson & C.J.Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC
  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. ^ Abbott, I.A. and Hollenberg, G.J. 1976. Marine Algae of California. Stanford University
  5. ^ Chemical defenses and the susceptibility of tropical marine brown algae to herbivores. Peter D. Steinberg, Oecologia, 1986, Volume 69, Number 4, pages 628-630, doi:10.1007/BF00410374

Further reading[edit]

  • Critchley, A.T., Farnham, W.F. and 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: 799 - 811.
  • Boaden, P.J.S. 1995. The adventive seaweed Sargassum muticum (Yendo) Fensholt in Strangford Lough, Northern Ireland. Ir. Nat. J. 25 111 - 113.
  • 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. No.99/27 ISSN 1367 - 1979.
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