Abstract

The brown alga Sargassum muticum has been found attached in Sweden since 1987. This paper reports the distribution in Swedish waters based on 2 major surveys in 1993 and in 1996. Attached population were found along the entire eastern Skagerrak coast, and as far south as to the middle part of the eastern Kattegat coastline. The number of populations and population size decrease when going south, although the differences had dimished between 1993 and 1996. However, the number of new sites, as well as population numbers still increase. Areas with continuous populations can now be found along the NE Skagerrak coast, and isolated localities may also be found in the inner parts of the archipelagoes. No morphological differences were seen between plants from the more saline Skagerrak and the more brackish Kattegat. The maximum plant length recorded was 4.2 m. Sargassum muticum has definitely become a permanent member of the Swedish algal flora. Although the expansion into the Baltic is slow, it is most likely that, given time, the species will colonize suitable habitats in the entire Kattegat. The possibility of further expansion into the Baltic proper, with its low biodiversity, remains a subject for speculation.