The eradication of the seaweed Sargassum muticum from Britain

  • Published source details Farnham W.F. & Gareth Jones E.B. (1974) The eradication of the seaweed Sargassum muticum from Britain. Biological Conservation, 6, 57-58.


The brown macro-alga Sargassum muticum, originally described from Japan, was accidentally introduced to the Pacific coast of Canada and USA in the 1940s where it subsequently spread and is invasive. In some areas it has drastically altered shallow coastal water ecosystems and reduced species diversity. The alga was first discovered in Britain in February 1973 in intertidal lagoons at Bembridge (Isle of Wight). Scattered plants (up to 1 m long) were observed but on a subsequent visit a dense stand (plants up to 4 m long) was found.Further searches in the area revealed a few plants elsewhere on the Isle of Wight, and another large population within Portsmouth Harbour (Hampshire).

A meeting attended by 18 marine biologists from various institutions in the UK, was held on 4 to 5 May 1973 to discuss what, if any, action need be takenregarding S.muticum. The decision was that it represented an undesirable addition to the British marine flora and should be eliminated. The most acceptable control method was considered removal of plants by hand; although time consuming it is selective, unlike the other main alternative of herbicide treatment.
Those undertaking the clearance (mostly volunteers) were given instruction in the identification of the plants. The necessity to effect complete removal was emphasized, otherwise regeneration could occur. The clearance scheme was started at Bembridge on 9 May 1973. Plants, collected at times of suitable low tides, were disposed of away from the sea in Council refuse-tips made available for the initial large quantities gathered.

During the first two months (May-June) of hand-clearance, 3-4 tonnes of S.muticum were removed from Bembridge. The original large population was rapidly removed and fortnightly visits continued so that sporelings could be cleared. A similar programme commenced in Portsmouth Harbour and a significant proportion of the alga likewise removed. A committee was formed to help continue and guide the eradication campaign.
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