An account of the attempted control of an introduced marine alga, 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.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:


Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 20

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered speciesVincet Wildlife Trust