Undaria pinnatifida
Division: Chromophyta
Class: Phaeophyceae
Order: Laminariales
Species name: Undaria pinnatifida (Harvey) Suringer
Synonyms: None
Common name: Wakame (in Japan), Japanese kelp
Date of introduction and origin
Undaria pinnatifida was found attached to floating pontoons in the Hamble estuary in the Solent, Hampshire on 15 June 1994 (Fletcher & Manfredi 1995). It is native to the west coast of Japan. Its introduction to Europe was initially to France where it was found in 1971 in Etang de Thau, a saltwater lagoon on the Mediterranean coast (Perez, Lee & Juge 1981; Boudouresque, Gerbal & Knoepffler-Peguy 1985).
Method of introduction
The most likely vector for the initial introduction of Undaria pinnatifida to Europe was imported spat of Pacific oysters Crassostrea gigas (Perez, Lee & Juge 1981; Boudouresque, Gerbal & Knoepffler-Peguy 1985). However, because of its commercial importance, subsequent introductions in France were intentional, and attempts were made in 1981 to cultivate plants on rope in the Mediterranean (Perez, Lee & Juge 1981) and later, since 1983, successful attempts at cultivation have been made on the Atlantic coast at several sites in Brittany (Perez, Kaas & Barbaroux 1984; Perez et al. 1988; Boudouresque, Gerbal & Knoepffler-Peguy 1985; Castric-Fey, Girard & L'Hardy-Halos 1993; Wallentinus in press). This alga was also reported from Spain in 1990, having been introduced with imported oysters (Wallentinus in press).
Its introduction from France to Britain is thought to have been on ships' hulls (Fletcher & Manfredi 1995). Such spread via boats using ports in the English Channel was predicted by Hay (1990).
Reasons for success
It produces millions of spores with motile periods of up to 5 hours and has a propensity for colonising floating objects (Fletcher & Manfredi 1995) which suggests it can easily be spread locally by natural dispersion and more remotely through the agency of shipping.
Five reasons likely to give competitive edge over native species were listed by Fletcher & Manfredi (1995) from observations on introduced populations in Brittany and the Pacific:
  • its behaviour as an opportunistic weed and its ability to rapidly colonise new or disturbed substrata and artificial floating structures;
  • its occurrence in dense, vigorous stands on benthic shores, forming a thick canopy over the subordinate biota;
  • its occupancy of a wide range of shores varying in exposure;
  • its extensive vertical distribution, from low tide level down to 15 m in suitably clear waters;
  • the extended period of reproductive spore formation and release observed in introduced populations.


Rate of spread and methods involved
Short distance, marginal spread occurs by natural reproductive processes; while spread along the coast and probably across the Channel is likely to be associated with shipping and coastal boat traffic (Hay 1990; Fletcher & Manfredi 1995; Wallentinus in press).
In British waters it was first found in the Hamble estuary in the Solent but has more recently been found at scattered locations on the Isle of Wight, in Torquay in Devon, in a marina on Jersey in the Channel Isles (R.L. Fletcher pers. comm.). Elsewhere in Europe it occurs on the French Mediterranean coast, on the north and south coasts of Brittany, and on the Atlantic coast of Spain around Ria de Arosa (Wallentinus in press).
Factors likely to influence spread and distribution
Fletcher & Manfredi (1995) predicted that coastal boating traffic would be the means of significant spread of this species in northern European waters.
Effects on the environment
It may cause displacement of other native species (Fletcher & Manfredi 1995).
Effects on commercial interests
Undaria is a commercially important edible species. It is a fouling agent.
Control methods used and effectiveness
It is planned to remove all subsequently occurring plants from the marina pontoons in the Hamble. However, this is thought unlikely to eradicate the species or halt its local spread (Fletcher & Manfredi 1995).
Beneficial effects
Undaria is a commercially important species, cultivated for food (Guiry & Blunden 1991).
The intentional introduction of Undaria to the north coast of France and its continued farming has been considered extensively and sanctioned by the International Council for the Exploration of the Sea. Proposals to introduce this species to Ireland were rejected (Wallentinus in press).
Boudouresque, C.F., Gerbal, M., & Knoepffler-Peguy, M. 1985. L'algue japonaise Undaria pinnatifida (Phaeophyceae, Laminariales) en Méditerranée. Phycologia, 24: 364-366.
Castric-Fey, A., Girard, A., & L'Hardy-Halos, M. Th. 1993. The distribution of Undaria pinnatifida (Phaeophyceae, Laminariales) on the coast of St. Malo (Brittany, France). Botanica Marina, 36: 351-358.
Fletcher, R.L., & Manfredi, C. 1995. The occurrence of Undaria pinnatifida (Phaeophyceae, Laminariales) on the south coast of England. Botanica Marina, 38: 355-358.
Guiry, M.D., & Blunden, G. eds.1991. Seaweed resources in Europe: uses and potential. Chichester, John Wiley & sons.
Hay, C.H. 1990. The dispersal of sporophytes of Undaria pinnatifida (Phaeophyta: Laminariales) found in a New Zealand harbour. New Zealand Journal of Botany, 25: 301-313.
Perez, R., Durand, P., Kaas, R., Barbaroux, O., Barbier, V., Vinot, C., Bourgeau-Causse, M., Leclerq, M., & Moigne, J.Y. 1988. Undaria pinnatifida on the French coast. Cultivation method, biochemical composition of the sporophyte and the gametophyte. In: Algal Biotechnology, ed. by T. Staedler, J. Mollion, M.C. Verdus, Y. Karamanos, H. Morvan, & D. Christiaen) 315-328. London, Elsevier.
Perez, R., Lee, J.Y., & Juge, C. 1981. Observations sur la biologie de l'algue japonaise Undaria pinnatifida (Harvey) Suringar introduite accidentellemente dans l'Etang de Thau. Science et Pêche, 315: 1-12.
Perez, R., Kaas, R., & Barbaroux, O. 1984. Culture expérimentale de l'algue Undaria pinnatifida sur les côtes de France. Science et Pêche, 343: 3-15.
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 R.L. Fletcher, University of Portsmouth.