Sargassum

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

Description

The plants , which may grow to a length of several metres, are generally brown or dark green in colour and are differentiated into holdfast, stipes, fronds and fruiting bodies. Some species have berrylike gas-filled bladders to keep the plants afloat, thus promoting photosynthesis. Many plants have rough sticky textures, which together with robust but flexible bodies, help to withstand strong currents.

The thick masses of Sargassum provide an environment for a distinctive and specialised group of marine forms, 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

Sargassum muticum originally from Japan has now, 15th 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: F11182 - F11185). The species was first found in the British Isles in the Isle of Wight in 1973. In Europe it now extends from the Mediterranean to Norway. There is much concern about its impact on the coastal environment.

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 whole Sargasso Sea, making navigation impossible, it has since been found to occur only in drifts.

References

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
The SuriaLink Seaplants Hankbook - Sargassum
http://www.surialink.com/HANDBOOK/Genera/browns/Sargassum/Sargassum.htm
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.

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