Polysiphonia harveyi

Division: Rhodophyta
Class: Rhodophyceae
Order: Ceramiales
Species name: Polysiphonia harveyi Bailey
Synonyms: Polysiphonia insidiosa  P. & H. Crouan
Common name: None
Date of introduction and origin
Polysiphonia harveyi was introduced before 1908 onto the south coast of England, possibly from northern France where it was found in 1832 (Maggs & Hommersand 1993). This species may have originated in the Pacific Ocean and was possibly introduced from Japan.
Method of introduction
It was an associated unintentional introduction with oysters.
Reasons for success
It has a rapid growth rate and is an opportunist.
Rate of spread and methods involved
Its rate of spread is not known. There is a small chance it may have spread through drifting with larger weeds on which it is an epiphyte (Wallentinus in press).
It is found on the south and east coasts of England to Essex and up the western coast to Scotland. European populations occur from Norway to the Mediterranean, including Ireland (Maggs & Hommersand 1993).
Factors likely to influence spread and distribution
It is very tolerant of temperature changes.
Effects on the environment
It possibly displaces native species as it can become very abundant.
Effects on commercial interests
It is a fouling agent as it is abundant in marinas on artificial structures, but as it is small, this is not a significant problem.
Control methods used and effectiveness
None used.
Beneficial effects
None known.
Japanese populations are interfertile with British populations of Polysiphonia harveyi (C.A. Maggs pers. comm.), but the correct taxonomy is still to be determined, possibly involving Polysiphonia strictissima (described from New Zealand). All species of Polysiphonia require microscopic examination to confirm their identification.
Maggs, C.A., & Hommersand, M.H. 1993. Seaweeds of the British Isles. Volume 1: Rhodophyta. Part 3A: Ceramiales. London, HMSO, for Natural History Museum.
Wallentinus, I. In press. Status of introductions of non-indigenous marine species to north Atlantic waters: introductions and transfers of plants. ICES co-operative research report.
Acknowledgements (contributions from questionnaire)
Dr C.A. Maggs, Queen's University of Belfast.