Date of introduction and origin
Pleurosigma simonsenii was first detected in the
English Channel during 1966 and is thought to originate from the
Indian Ocean (Simonsen 1974; Boalch & Harbour 1977a;
Wallentinus in press).
Method of introduction
The method of introduction is not known, but ballast transport
cannot be ruled out (Wallentinus in press).
Reasons for success
Rate of spread and methods involved
It was found in the English Channel (off Ushant, on the French
coast) in 1966; and off The Netherlands by 1974 (Wallentinus in
press). The method of spread is unknown.
It has been sporadically reported in the English Channel and
southern North Sea, but it may have more or less disappeared since
these reports were received (Wallentinus in press; Smayda 1990;
Interrnational Council for the Exploration of the Sea 1983).
Factors likely to influence spread and distribution
Effects on the environment
Presumably Pleurosigma simonsenii has displaced
native species at times since it was reported dominant in the
Plymouth area in 1973; it has since 'settled down' to a minor
constituent of the plankton (Boalch & Harbour 1977b; Boalch
1987; Wallentinus in press).
Effects on commercial interests
Control methods used and effectiveness
Currently it is considered a minor constituent of the British
phytoplankton (Boalch & Harbour 1977a).
Boalch, G.T. 1987. Changes in the phytoplankton of the western
English Channel in recent years. British Phycological
Journal, 22: 225-235.
Boalch, G.T., & Harbour, D.S. 1977a. Observations on the
structure of the planktonic Pleurosigma. Nova Hedwigia,
Beiheft, 54: 275-280.
Boalch, G.T., & Harbour, D.S. 1977b. Unusual diatom off
the coast of south-west England and its effect on fishing.
Nature, 269: 687-688.
ICES, 1983. Report of the Working Group on Introductions
and Transfers of Marine Organisms, Bergen, Norway, 10-13 May
1983. CM 1983/F:27. International Council for the Exploration of
Simonsen, R. 1974. The diatom plankton of the Indian Ocean
Expedition of R/V "Meteor" 1964-1965. "Meteor"
Forschungsergebnisse, Reihe, D. 19:
Smayda, T.J. 1990. Novel and nuisance phytoplankton blooms in
the sea: evidence for a global epidemic. In: Toxic
marine phytoplankton, Granéli, E, Sundström, B., Elder, L.,
& Anderson, D.M. eds. Proceedings of the Fourth
International Conference on Toxic Marine Phytoplankton, 26-30 June
1989, Lund, Sweden. Elsevier, New York, p29-40.
Wallentinus, I. In press. Status of introductions of
non-indigenous marine species to north Atlantic waters:
introductions and transfers of plants. ICES co-operative
Prof. G.R. Hasle, University of Oslo.