Following the discovery of the newly introduced red alga Heterosiphonia japonica in Loch Sunart, West Scotland in 2008, its local distribution, abundance and dominance within the algal community was examined by in situ observations and algal collections at sites in Loch Sunart and Loch Creran. It was found to be common in both lochs at semi-exposed and sheltered locations, where it was generally one of the dominant species attaining 12% coverage of the seabed below a Laminaria saccharina forest canopy and 28% cover in the shallow circalittoral, where it formed a virtual macroalgal monoculture. Possible vectors for its spread in the area are discussed. The presence of Sargassum muticum is also reported at one of the sites, representing the most northerly UK record of this species in the literature.
