Distribution of macroalgal communities in the central Baltic Sea

Two brown seaweeds, Fucus serratus and E vesiculosus, are forming stands along the shores of the central Baltic Sea. We studied the regional variations in the abundance of E vesiculosus, E serratus and filamentous algae in the central Baltic Sea. Further, the hypothesis that regional differences in geomorphology and the north-south salinity gradient affect the dominance of the different species was tested. Extended mania tow diving and observations from a skiff with transparent shutters in the hull were used to map the distribution of macroalgae on different substrate types. Estimations of E serratus recruitment and turf biomass were also performed. The results show significant differences in Fucus spp. vegetation among regions and substrate types. Both Fucus species were most abundant in the southern regions as compared with the northern regions. Fucus serratus was significantly more abundant on limestone bedrock than on boulders. The results are discussed in relation to salinity tolerance, eutrophication, life history, and interspecific competition.