Long-term changes in the marine macroalgae of Lagaskar, Aland Sea (N Baltic)

Species composition, abundance and depth distribution of marine macroalgae were studied at Lagskar, the Aland Sea, in August 1993. Altogether, 26 species were identified and the most diverse vegetation, comprising 18 species, was recorded at a depth of 4-7 m. Comparison with the results obtained by Andersson in 1956 indicates that the total number of species had decreased by 6, and that the best developed and most diverse algal vegetation was then recorded at a depth of 10-15 m. In 1993 species such as Aglaothamnion roseum, Audouinella efflorescens, Phyllophora pseudoceranoides, Halopteris scoparia and Sphacelaria plumigera had disappeared, or were not recorded. Sphacelaria arctica, Cladophora rupestris, Stictyosiphon tortilis and Polysiphonia fucoides, in the 1950s important and dominating species, were greatly reduced in number. However, Pilayella littoralis, Ectocarpus siliculosus, Fucus vesioculosus and Rhodomela confervoides had increased. Compared with the drastic phytobenthic changes recorded in many coastal areas of the Baltic, the changes in the offshore Lagskar area are of minor extent.