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Individual study: Attempted control of the introduced brown seaweed, Sargassum muticum, in southern England

Published source details

Critchley A.T., Farnham W.F. & Morrell S.L. (1986) An account of the attempted control of an introduced marine alga, Sargassum muticum, in Southern England. Biological Conservation, 35, 313-332


Since introduction to British coastal waters in the early 1970s, populations of the brown seaweed Sargassum muticum (native to the northern Pacific) have increased rapidly, causing a number of recreational and ecological problems. This present paper summarises and reviews eradication and clearance methods along the southern coat of England.

Handpicking: Clearance, undertaken by volunteers, began in May 1973, at Portsmouth Harbour and Bembridge (Hampshire and Isle of Wight), continuing fortnightly until October 1973. Further clearances were made up to September 1976.

Herbicides: The efficacy of a range of herbicides on S.muticum was evaluated (Lewey 1976, Lewey & Jones 1977).
Biocontrol: At least five studies were identified that investigated various aspects of grazing by marine herbivores of S.muticum as a possible means of control.
Mechanical: Trials were carried out in the mid-1970s using tractors fitted with harrows, cultivators and fore-end loaders in areas accessible at low water. Of these, the harrow method was especially effective at removing S.muticum, but there were problems with containment of collected material and physical damage inflicted to the shore. This was thus abandoned. In 1976 a review was undertaken of available mechanical methods of weed control/collection.Three main techniques were subsequently trialed/developed: trawling, cutting, and suction clearance.

Handpicking: Handpicking was very labour-intensive and time-consuming. When it became obviously ineffective it was abandoned in September 1976.

Herbicide: No herbicide tested was suitable due to lack of selectivity, large doses required, period of time the herbicide needs to be in contact with the seaweed and application problems. The most effective herbicides of those tested were Diquat, Stomp, copper sulphate, sodium hypochlorite, K-lox and Nortron. However, all proved detrimental to other algae tested, including native Ulva and Ceramium.
Biocontrol: It was concluded that no herbivore was likely to restrict S.muticum distribution appreciably within southern England.
Mechanical: Mechanical clearance, although costly, provided the only viable control method. Monitoring of experimental areas highlighted several problems: whilst mechanical clearance rapidly decreases frond length, in the subsequent growth season elongation of primary laterals in cleared and non-cleared areas is similar; plants surviving in cleared areas become fertile sooner; clearance of a mature S.muticum allows regeneration via an increased density of young plants.
Lewey S.A. (1976) Studies on the brown alga Sargassum muticum (Yendo)
Fensholt in Britain. M Phil thesis, CNAA, Portsmouth Polytechnic, UK.
Lewey S.A. & Jones E.B.G. (1977) The effect of aquatic herbicides on
selected marine algae. Journal of Phycology, 13, 40.
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