Spring development of hydrolittoral rock shore communities on wave-exposed and sheltered sites in the northern Baltic proper

Spring development in the hydrolittoral zone was investigated at five wave-sheltered and five wave-exposed sites on four occasions from late March to late May (every third week). The number of species was higher at the sheltered locations and increased significantly over time. The difference in community structure was significant: over 95% of the Bray-Curtis dissimilarities were due to the biomass of only eleven taxa, and the total Bray-Curtis dissimilarity between exposed and sheltered sites was 75%. Macroalgae made up 70–80% of the total biomass and was dominated by filamentous species. In contrast to previous studies, macroalgal biomass was higher at the exposed sites, which may be due to the fact that this was a spring study, unlike previous studies, which were conducted during summer.