Macrozoobenthos structure in relation to environmental changes in the Archipelago Sea, northern Baltic Sea

Since the 1960s, the major environmental change affecting the water quality of the Baltic Sea has been eutrophication. Several types of effects were attributed to increasing eutrophication in the benthic communities. In the present study, we describe the soft bottom benthic assemblages based on species number, abundance and biomass in the Airisto Inlet in 1994, and analyse the changes of community structure in relation to major environmental changes in the Archipelago Sea area since the 1950s. Special emphasis was put on alterations of Macoma balthica and Monoporeia affinis proportions. Our results provided evidence of a general increase of benthic macrofauna, especially in the middle and southern parts of the study area. The greatest relative increase seemed to occur to polychaetes and oligochaetes, whereas M. affinis showed the greatest absolute increase. However, the relative proportions of M. balthica and M. affinis generally remained unchanged. We conclude that, in the middle and southern parts, the changes observed in macrozoobenthos were due to general eutrophication in the Archipelago Sea. In the northern parts, the communities have been remarkably influenced by local pollution and dredging.