There was also a significant difference between exposed and sheltered sites for these species (LMM, p < 0.001 and p < 0.01 respectively). In addition, there was an increase over time of G. zaddachi and juvenile gammarids at the exposed sites, measured as the significant difference between the first and last sampling (LMM, p < 0.01 and p < 0.0001 respectively, Appendix). In a similar way

to algae, the biomass GSK2656157 mouse of invertebrates increased significantly over time (LMM, p < 0.01, Appendix, Figure 5). The biomass of G. zaddachi peaked in early May at the wave-exposed sites, while the biomass was low and constant at the sheltered sites ( Table 1b, Figure 4). The biomass was significantly higher at the wave-exposed sites than at the wave-sheltered sites (LMM, p < 0.001, Appendix). In contrast, the biomass of Cardiidae and Hydrobiidae were significantly higher at the wave-sheltered sites (LMM, p < 0.001, p < 0.01, Appendix) ( Figure 4). The increase in biomass of all these species (except Cardiidae) was delayed compared to the algal biomass ( Figure 4, Table 1a,b). Hydrobiidae only increased in abundance at the wave-sheltered sites (p < 0.01, Appendix),

while the biomass of Cardiidae showed no significant changes over time ( Figure 4). Red filamentous algae, in this case 99% C. tenuicorne, were positively correlated with the abundance of M. edulis (LMM, p < 0.001). The isopods Idotea spp. were less abundant, this website but showed Rolziracetam a positive correlation with the non-filamentous algae (LMM, p < 0.05). No specific correlations were found for brown filamentous algae or green filamentous algae with the abundance of any of the invertebrates.

After the sea ice broke up in the middle of March, a community dominated by filamentous macroalgae rapidly established itself in the rocky hydrolittoral zone. As expected, because of increased temperature and light and from the life cycles of the organisms, the biomass increased from the first sample collection in March to the last sample collection in May at three of the sheltered sites and at four of the exposed sites. During the same period, the number of taxa increased only slightly. Three species were mainly responsible for the significant changes in algal biomass over time: Pylaiella littoralis, Ceramium tenuicorne and Fucus vesiculosus ( Figure 5). The peak of P. littoralis and C. tenuicorne occurred in early May, coinciding with the development of increased faunal biomass. In contrast to previous findings in the northern Baltic Sea (e.g. Hällfors et al., 1975 and Rönnberg, 1975), we found a higher macroalgal biomass at the exposed sites than at the sheltered sites on the last two sampling occasions. This difference could be explained by the fact that the present study was performed during spring and because we focused on the hydrolittoral zone (0–0.5 m under MWD). Other comparable investigations (see Hällfors et al.