The benthic fauna and hydrography in the outer archipelago zone of Åland Islands in the summer of 2006

The benthic fauna was investigated in the archipelago of the Åland Islands during the summer of 2006. In total, 27 stations were sampled for both zoobenthos and hydrography. The stations are located in the depth interval 17-35 m, and have previously been studied in 1994 and 2000. The aim of this study was to get an update on the situation in the benthic community and to continue the longterm studies in the outer archipelago zone to serve as a base for coming assessments of the European water frame directive. The zoobenthic community has increased its total abundance since 2000. The biomass has decreased, but the species richness is unchanged. The largest difference in the benthic community is the increase of the polychaete Marenzelleria sp., which now is the dominating species on 19 stations. The increase of the sensitive amphipod Monoporeia affinis indicates elevated conditions in the benthic environment. The decrease in abundance of the Baltic clam Macoma balthica explains the decrease in the total biomass of zoobenthos. Despite the decrease in abundance, M. balthica shows a healthy length distribution. A preliminary assessment of the environmental status indicates that the largest parts of the exposed, outer archipelago has high or good status, while the more sheltered areas of the archipelago has a moderate or even poor environmental status