The Japanese brown alga Undaria pinnatifida on the coast of France and its possible establishment in European waters

The first observations of the seaweed Undaria pinnalifida (Harv.) Sur. in France were made in 1971 in the Etang de Thau in the Mediterranean, after the alga had been accidentally introduced with oysters from Japan. Since the species is of commercial interest, the prospect of cultivating it on the French Atlantic coast was explored. The risk of its dispersal from the farm site was considered minimal by the French authorities. Field experiments with farming on ropes have been conducted by IFREMER at three sites since 1983, two of which were soon abandoned. On the island of Ouessant, Brittany, the experiments with rope cultivation in the field have continued with plantules raised in a local hatchery. Based on the literature, an evaluation of the possible establishment of the species on the European Atlantic coast was made by the ICES Working Group on Introductions and Transfers of Marine Organisms. It was suggested that a control programme including a study of the main grazers should be carried out by French algologists. Since 1987, after a visit to the Asian seaweed communities including Undaria (in Korea, Japan, and China), a survey of fertile plants and naturally settled sporophytes has been undertaken by the first two authors at Ouessant. In 1987, Undaria sporophytes were found in the bay of Lampaul on the west coast of Brittany, growing vigorously on immersed supporting structures of a mussel farm, both old and newly built. A few plants were also recorded from rocks down to a depth of 5 m, occasionally down to 18 m. The occurrence of mature sporophytes and the colonization in the autumn of 1987 on structures built that summer indicated that the species had reproduced on the French Atlantic coast. However, the significance of natural reproduction for the native seaweed communities in the area will depend also on competition with other species and on the grazing pressure. An experimental control programme was begun in May 1988 to check the competition between the newly introduced Undaria and the native seaweed communities on the rocky shore of Ouessant. Thus the ecological importance of the species in these waters will have to be evaluated after the final results of the control programme are available.