Distribution of soft-bottom macrofauna in the deep open Baltic Sea in relation to environmental variability

To analyse the large-scale distribution of soft-bottom macrofauna in the open Baltic Sea, samples for species abundance and biomass were collected in 1996–1997. Benthic community structure was used to classify and describe different assemblages and the observed distribution of communities was related to environmental factors. Distinct benthic assemblages were found that were dominated by only a few species (Harmothoe sarsi, Saduria entomon, Monoporeia affinis, Pontoporeia femorata and Macoma balthica). These assemblages were related to different subareas and/or depth zones of the Baltic Sea. Salinity or the combined effects of salinity, dissolved oxygen and sediment organic matter content best explained the patterns in community distribution, indicating the importance of hydrography and sediment quality as structuring factors of the macrozoobenthos communities. When compared to long-term studies on Baltic macrozoobenthos it is evident that the results represent only a momentary state in the succession of the open-sea communities, which have been affected by past changes in hydrography, and will be subject to future changes in accordance with the variable environment, affected by climate.