2008), which continuously replenishes food particles for suspension-feeding animals ( Leigh et al. 1987). Differences in predation pressure between wave-exposed and wave-sheltered sites are probably not very important at our study sites, since critical predators, such as starfish and crabs, are not found in the northern Baltic Sea. In the present study, the biomass of F. vesiculosus never exceeded 12% of the total algal biomass, which contrasts with previous studies ( Kiirikki, 1996 and Bäck and Ruuskanen, 2000). We found a higher biomass of F. vesiculosus at sheltered
sites compared to wave-exposed sites. The juvenile specimens of F. vesiculosus increased in biomass from March to late May, especially at the sheltered
sites, and this NVP-BEZ235 mw could be an effect of the more severe ice scraping at the exposed sites, resulting in fewer surviving specimens. Disturbance in the form of ice scraping is often found at natural field sites on cold temperate coasts ( Kiirikki & Ruuskanen 1996). Since the settlement TGFbeta inhibitor of F. vesiculosus normally occurs in June ( Berger et al. 2003), the small surviving propagules were able to start growing in March, even though the hydrolittoral zone was still covered by ice. Our findings show that F. vesiculosus specimens were able to grow in spite of competition with P. littoralis: growth was variable, but the maximum biomass was the same as that recorded by Berger et al. (2003). The abundance of Cardiidae, Hydrobiidae and Theodoxus fluviatilis L. was high at the sheltered next sites, where F. vesiculosus was frequently found; these gastropods may favour Fucus growth by selective grazing of the filamentous annual algae ( Worm et al. 2001). Furthermore, the high number of filtering species like Cardiidae may reduce suspended matter in the column, which has been shown to be important for the survival of young Fucus specimens ( Berger et al. 2003). We found endofaunal species like Mya arenaria in the hydrolittoral. This species
and also Macoma balthica, for instance, belong in the sediment but can sometimes be found in other environments. This may be due to active transport of the organism from the sediment ( Sorlin, 1988 and Cummings et al., 1993). The dominance of Mythilus edulis in the abundance was one of the main reasons for rejecting our hypothesis regarding higher diversity at the wave-exposed sites. Koivisto et al. (2011) have shown that the successional stage of the mussels is a strong determinant of faunal abundance: mussel size was positively correlated to faunal abundance and species richness. In the present study young mussels dominated the samples and no positive effect of the presence of mussels on faunal abundance could be observed.