The increased frequency and expansion of hypoxic and anoxic deep water has affected the structural and functional diversity of benthic communities. Phytoplankton productivity has increased and there has been a shift from dominance of diatoms to dominance of dinoflagellates in the phytoplankton spring bloom (HELCOM, 2009). Changes have also occurred in the zooplankton community where copepod biomass and the mean size of zooplankton have decreased, with consequences for the weight-at-age in herring stocks, Figure 26 (HELCOM, 2009).