Sargassum

Sargassum is a genus of generally planktonic macroalgae (seaweed) in the order Fucales.

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Description

Species of this genus of algae which 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.^[1] Some species have berrylike gas-filled bladders which help keep the plant afloat thus promoting photosynthesis. Many have a rough sticky texture, which together with a robust but flexible body, helps it to withstand strong water currents.

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, and colloquially as the weed of deceit, 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.

Sargassum muticum (Yendo) Fensholt

Description

Sargassum muticum [1] is a large brown seaweed of the Division Phaeophyta. 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 grows to no more than 4 m long. The holdfast gives rise to a single main axis with secondary and tertiary branches which are shed annually. Numerous small 2-6 mm stalked air vesicules provide buoyancy. The reproductive receptacles are also stalked and develop in the axils of leafy laminae. It is self fertile.

History

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 muticum originally from Japan had by 15 March 1995 been found in Strangford Lough, County Down, Northern Ireland, this is an extension of the distribution of this invasive species. Herbarium specimens are now stored in the Ulster Museum (BEL catalogue numbers: F11241 - F11242; F11182 - F11185). The species was first found in the British Isles in the Isle of Wight in 1973. It is thought to have gained worldwide distribution through being transported with Japanese oysters. There is much concern about its impact on the coastal environment. It has become a great nuisance forming large detached mats, clogging marinas, recreational areas and other sports facilities. It can foul fishing lines, clog pipes of boats and trap debris.

The species is particularly tenacious with fast growth rates, high reproductive rates and an ability to spread vegetatively.

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 drank as a tea. It is said to remove excess phlegm. When sold in this application it is commonly referred to as Seaweed Sargassum Tea.

Distribution

Sargassum muticum has a range stretching from Nanaimo, British Columbia to Baja in California.^[1] In Europe it now extends along the coasts of Great Britain, France, Scandinavia, Baltic Sea, Helgoland, Netherlands, Ireland, the Iberian Peninsula and into the Mediterranean from Italy and the Adriatic. It is recorded from Japan, China and Alaska.^[2]

Life history

Life history [2]

Habitat

Sargassum muticum grows in from just below low-water mark to a depth of 10 m. ^[2]

Further reading

• 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.

• 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 algae Sargassum muticum. Environmental and Heritage Service Research and Development Series. No. 99/27.

References

1. ^ ^{a b} Abbott, I.A. and Hollenberg,G.J. 1976. Marine Algae of California. Stanford University
2. ^ ^{a b} Thomas, D.N. 2002. Seaweeds. The Natural History Museum, London. ISBN

• http://www.marlin.ac.uk/species/Sargassummuticum.htm

• http://www.icais.org/pdf/20Monday/pm/Jamie_Dick.pdf Sargassum in Northern Ireland.

• The SuriaLink Seaplants Handbook - Sargassum

• http://www.irishseaweed.com/startpage.htm

• http://www.habitas.org.uk/invasive/

• http://www.seaweed.ie/sargassum/

• http://www.irishseaweed.com/PDF/smutposter.pdf

• http://www.mbari.org/staff/conn/botany/browns/jacquie/repro.htm Sargassum - reproduction.