Codium fragile

Division: Chlorophyta
Class: Chlorophyceae
Order: Codiales
Species name: Codium fragile (Suringar) Hariot subsp. atlanticum (A. Cotton) Silva
Synonyms: None
Common name: Green sea fingers
Date of introduction and origin
Codium fragile subsp. atlanticum  arrived in southwest Ireland in about 1808, from where it may have spread through rafting or floating (Silva 1955). It was found on the west coast of Scotland before 1840. This species is considered to have originated in the Pacific Ocean around Japan, and Silva (1955) considered it was introduced from there.
Method of introduction
It was unintentionally introduced to Ireland with shellfish.
Reasons for success
Lack of grazers has probably contributed to its success. It is an opportunist, exhibiting vegetative propagation and perennation.
Rate of spread and methods involved
It spread the length of Britain, including Shetland, since 1840 by marginal, natural dispersion. It spread from Berwick-upon-Tweed to St. Andrews, Fife, between 1949 and 1955, a distance of 80 km.
Populations occur mainly in the north of Britain (C.A. Maggs pers. comm.). It is found from Dorset up the western coast of Britain, in Shetland (Irvine et al. 1975) and in east Scotland and Northumberland (Norton 1985; South & Tittley 1986). Elsewhere in Europe it is recorded only from Norway.
Factors likely to influence spread and distribution
Spread of this species is limited by cool summer temperatures, particularly on the east coast (Hardy 1981). This species is being displaced by C. fragile subsp. tomentosoides in Berwickshire (Hardy 1990).
Effects on the environment
It displaces the native species Codium tomentosum (Farnham 1980).
Effects on commercial interests
Control methods used and effectiveness
None used.
Beneficial effects
It is eaten in the Far East.
The subspecies of C. fragile found in Britain are only distinguishable microscopically. This has resulted in uncertainty as to when they were introduced and how they have spread. A third subspecies, scandinavicum, was introduced to Denmark in 1919 and Norway from Asiatic coasts of the Pacific.
Burrows, E.M. 1991. Seaweeds of the British Isles. Volume 2. Chlorophyta. Natural History Museum, London.
Farnham, W.F. 1980. Studies on aliens in the marine flora of southern England. In: The shore environment, volume 2: ecosystems, ed. by J.H. Price, D.E.G. Irvine & W.F. Farnham, 875-914. London, Academic Press. (Systematics Association Special Volume, No. 17B.)
Hardy, F.G. 1981. Codium on the Northumbrian coast. Transactions of the Natural History Society of Northumbria, 43: 59-60.
Hardy, F.G. 1990. The green seaweed Codium fragile on the Berwickshire coast. History of the Berwickshire Naturalists' Club, 44: 154-156.
Irvine, D.E.G., Guiry, M.D., Tittley, I., & Russell, G. 1975. New and interesting marine algae from the Shetland Isles. British Phycological Journal, 10: 57-71.
Norton, T.A., ed. 1985. Provisional atlas of the marine algae of Britain and Ireland. Huntingdon, Institute of Terrestrial Ecology, Biological Records Centre.
Silva, P.C. 1955. The dichotomous species of Codium in Britain. Journal of the Marine Biological Association of the United Kingdom, 34: 565-577.
South, G.R., & Tittley, I. 1986. A checklist and distributional index of the benthic marine algae of the North Atlantic Ocean. St Andrews & London, Huntsman Marine Laboratory & British Museum (Natural History).
Acknowledgements (contributions from questionnaire)
Dr F.G. Hardy, University of Newcastle Upon Tyne.
Mr I. Tittley, Natural History Museum, London.