Résumé
The movement of fouled leisure craft is recognized as a major vector for the spread of sessile marine non-indigenous species (NIS) along coastlines. Datasets are presented on the taxa found in the biofouling of the external wetted surfaces of recreational boats (sailing yachts and motor cruisers) in one coastal marina in Devon (SW England) and four coastal marinas in western Brittany (NW France). Visual inspections of the hull surface and ‘niche’ areas (rudder, propeller etc.) for sessile biota were carried out on 71 Devon and 50 Brittany boats immediately upon their removal from the water for maintenance, with field recording of suitable taxa and collection of specimens requiring laboratory identification. Twenty-four sessile NIS (23 invertebrates and one brown alga) were recorded. The distribution of fouling taxa between open-hull surfaces and niche areas was documented. Information was gathered on the recent maintenance regime of the boats studied, particularly with regard to hull cleaningand antifoul treatment, and on the usage patterns of the boats. The fouling dataset characterizes typical loads of NIS carried by marine recreational boats and indicates which particular NIS are colonizing leisure craft, and at what frequency, in the western English Channel. This information can contribute to understanding patterns and mechanisms of the spread of marine NIS, particularly when combined with data on actual leisure-craft traffic volumes and patterns. Knowledge of typi- cal patterns of cleaning and antifouling and their efficacy will help to shape biosecurity advice to marinas and boat owners.