Sargassum muticum

Division: Chromophyta
Class: Phaeophyceae
Order: Fucales
Species name: Sargassum muticum (Yendo) Fensholt
Synonyms: See Critchley et al. (1990) for discussion of taxonomic identity
Common name: Jap weed, wire weed, strangle weed
Date of introduction and origin
Sargassum muticum was first found attached in Bembridge, Isle of Wight, in 1971 where it had arrived from France (Farnham, Fletcher & Irvine 1973). Critchley, Farnham & Morrell (1983) indicated that it was probably first found in the English Channel in the late 1960s and Farnham (1980) indicated by at least 1966. This species naturally occurs in Japanese and Chinese waters.
Method of introduction
It was an associated unintentional introduction with commercial introductions of oysters from the Canadian state of British Columbia or Japan to France. Spread from northern France is presumed to have occurred by natural means. Spores may be transported in ballast water, on ships' hulls and by rafting or floating of entire plants or detached fragments (Critchley et al. 1990). Marginal dispersal (up to 30 miles) is most likely to occur by the latter method (Farnham et al. 1981).
Reasons for success
This species has a rapid growth rate (Hales & Fletcher 1989). It is highly fecund (Norton & Deysher 1989), producing fertile receptacles which are cast off during the summer months. These float and can survive for up to 3 months (Farnham et al. 1981). The receptacles are androgynous with self-fertilisation; viable germlings are released.
Rate of spread and methods involved
It spread rapidly along the English south coast at about 30 km/year and along the north-west American coast at an average rate of about 60 km/year, mostly by drifting, fertile adults (Farnham et al. 1981).
It is found in the Isles of Scilly, entire Channel coast (Hiscock & Moore 1986; Devon Wildlife Trust 1993) and east coast north to Suffolk, however the Norfolk population appears to be no longer extant (Critchley, Farnham & Morrell 1983; W.F. Farnham pers. comm.). It was recorded from south Wales as drift specimens in 1983 (N.C. Eno pers. obs.) and Lundy in 1993 (Andrew Gibson pers. comm.), and as attached specimens from Strangford Lough, Northern Ireland, in 1995 (Boaden 1995) and Constantine Bay, north Cornwall, in 1991 (K. Hiscock pers. comm.). Plants 2-3 years old were found in Crackington Cove, north Cornwall, in 1992 (W.F. Farnham pers. comm.). Elsewhere in Europe it is known from the Mediterranean and along the North Sea and Atlantic coasts of Portugal, Spain, France, Belgium, The Netherlands, Denmark, southern Norway and Sweden (Critchley, Farnham & Morrell 1983; Rueness 1989; W.F. Farnham pers. comm.).
Factors likely to influence spread and distribution
Higher temperatures are favourable and will encourage its spread further south. Lower temperatures are unfavourable and will limit its spread north. Ideal conditions for growth are 25·C and 34‰ salinity, although this species will grow at temperatures from 10 to 30· and salinities from 6.8 to 34‰.
Effects on the environment
It causes the physical displacement of native species through over-growing and shading underlying species (Critchley, Farnham & Morrell 1986). There is documented replacement of Laminaria saccharina and Zostera marina at Grandcamp on the French Atlantic coast (Givernaud, Cosson & Givernaud-Mouradi 1991). In Britain, there is observed growth of Sargassum on eel-grass beds in the Isles of Scilly (Raines et al. 1992) and in deep pools and channels Halidrys siliquosa can be displaced by Sargassum muticum as the dominant species (George, Tittley & Wood in prep.). Withers et al. (1975) reported a rich epiphytic community associated with Sargassum collected from the east Solent, suggesting that native epiphytic species are not particularly affected.
Effects on commercial interests
This species is a pest and fouling organism which is reported to interfere with recreational use of waterways, particularly when it becomes detached from hold fasts and floats off forming large masses (Farnham 1980). It blocks propellers and intakes (Critchley, Farnham & Morrell 1986). It is also a fouling organism on oyster beds and a nuisance to commercial fishermen, fouling their nets (Critchley, Farnham & Morrell 1981).
Control methods used and effectiveness
Removing Sargassum by hand is extremely time-consuming and needs to be repeated, probably indefinitely (Farnham 1980). Removal by trawling, cutting and suction have also been tried. Chemical methods using herbicide have been tried but failed due to lack of selectivity and the large doses needed. Small germlings can be consumed by molluscs and amphipods but this has no restrictive effect on S. muticum. Whatever method is used the alga always quickly regrows and effective methods for its permanent removal have not been found, although cutting and suction is the preferred method applied (Farnham et al. 1981; Critchley, Farnham & Morell 1986).
Beneficial effects
It is of possible commercial value to the alginate industry.
In its native habitat off the coast of Japan S. muticum is much smaller than in Britain (Rueness 1989). The eradication of this species in British waters has been attempted but has failed.
Boaden, P.J.S. 1995. The adventive seaweed Sargassum muticum (Yendo) Fensholt in Strangford Lough, Northern Ireland. Irish Naturalists' Journal, 25: 111-113.
Critchley, A.T., Farnham, W.F., & Morrell, S.L. 1983. A chronology of the 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.
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.
Critchley, A.T., Farnham, W.F., Yoshida, T., & Norton, T.A. 1990. A bibliography of the invasive alga Sargassum muticum (Yendo) Fensholt (Fucales; Sargassaceae). Botanica Marina, 33: 551-562.
Devon Wildlife Trust. 1993. Marine survey report. Plymouth Sound and approaches. A report on the wildlife resource of Plymouth Sound and the adjacent open coast. Unpublished, Devon Wildlife Trust.
Farnham, W., Fletcher, R.L., & Irvine, L.M. 1973. Attached Sargassum found in Britain. Nature, 243: 231-232.
Farnham, W., Murfin, C., Critchley, A., & Morrell, S. 1981. Distribution and control of the brown alga Sargassum muticum. In: Proceedings of the Xth International Seaweed Symposium, 277-282.
George, J.D., Tittley, I., & Wood, E. In prep. The chalk coasts - final report (working title). (Contractor: Natural History Museum & Dr E. Wood, London & Basingstoke.) Unpublished report to Joint Nature Conservation Committee.
Givernaud, T., Cosson, J., & Givernaud-Mouradi, A. 1991. Etude des populations de Sargassum muticum (Yendo) Fensholt sur les côtes de Basse-Normandie (France). In: Estuaries and coasts: spatial and temporal intercomparisons. ECSA 19 Symposium, Caen, September 1989, ed. by M. Elliott & J.P. Ducrotoy, 129-132. Fredensborg, Olsen & Olsen, for Estuarine and Coastal Sciences Association,. (International Symposium Series No. 19).
Hales, J.M., & Fletcher, R.L. 1989. Studies on the recently introduced brown alga Sargassum muticum (Yendo) Fensholt. IV Effect of temperature, irradiance and salinity on germling growth. Botanica Marina, 32: 167-176.
Hiscock, K., & Moore, J. 1986. Surveys of harbours, rias and estuaries in southern Britain: Plymouth area including the Yealm. Nature Conservancy Council, CSD Report, No. 752.
Norton, T.A., & Deysher, L.E. 1989. The reproductive ecology of Sargassum muticum at different latitudes: 147-152. In: Reproduction, genetics and distributions of marine organisms ed. by J.S. Ryland,.& P.A. Tyler. 147-152. Olsen and Olsen, Fredensberg.
Raines, P., Nunny, R., & Cleator, B. 1992. Isles of Scilly Expedition 1992. Unpublished, Coral Cay Conservation Sub-Aqua Club.
Rueness, J. 1989. Sargassum muticum and other introduced Japanese macroalgae: biological pollution of European coasts. Marine Pollution Bulletin, 20: 173-176.
Withers, R.G., Farnham, W.F., Lewey, S., Jephson, N.A., Haythorn, R.M., & Gray, P.W.G. 1975. The epibiota of Sargassum muticum in British waters. Marine Biology, 31: 79-81.
Acknowledgements (contributions from questionnaire)
Prof. T. A. Norton, Port Erin Marine Laboratory.

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