In August 2006, the ten largest marinas in Scotland were surveyed for the presence of seven non-native species, known to occur at other locations within the UK: the crustaceans Caprella mutica and Eriocheir sinensis, ascidians Perophora japonica and Styela clava, the green alga Codium fragile subsp. tomentosoides, and brown algae Sargassum muticum and Undaria pinnatifida. A variety of structures, including pontoon floats, chains and harbour walls were inspected to a depth of 0.5 m for the presence of these non-native species. Seven of the marinas had one or more of the target species. C. mutica was found at seven marinas; C. fragile subsp. tomentosoides at two marinas; S. muticum and S. clava were each found at a single marina; E. sinensis, P. japonica and U. pinnatifida were not found. The survey suggests that recreational boating is an important vector for the dispersal of marine non-native species, and that marinas may act as a refuge for such species. Further and regular port surveys throughout the UK are recommended to provide an effective early warning system for invasive non-native species.