The spread of the immigrant brown alga Sargassum muticum ( Yendo) Fensholt, within European waters is chronicled from 1973–1981. New populations of the attached alga are listed together with maps indicating the annual addition of sites. No populations of the alga were known beyond the bounds of the Solent region, southern Britain, until after 1975.
The age of the original Sargassum population found at Bembridge in 1973, and the discovery of drifting S. muticum in 1971, seems to date the initial introduction of the alga in the Channel as possibly the late 1960s.
This paper presents the establishment of Sargassum muticum as a permanent addition to the European marine flora. It is hoped that its future spread will continue to be documented, providing useful information upon the invasion strategy of an ‘aggressive’ introduced marine species.