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
Reasons for success
Lack of grazers has probably contributed to its success. It is
an opportunist, exhibiting vegetative propagation and
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
Effects on commercial interests
Control methods used and effectiveness
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
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:
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.