Changes in zoobenthic community structure after pollution abatement from fish farms in the Archipelago Sea (N. Baltic Sea)

Long-term changes in sediment macrofauna communities at two sites affected by fish farming in the Archipelago Sea, south-west Finland have been invest igated. Sampling stations in the Sarkansalmi Strait and Kaukolanlahti Bay, previously investigated 1982-1991, were revisited in 1994, 1995 and 1998 to detect signs of recovery following a decrease in organic load since 1990 a nd 1991, respectively. The results indicate a partial recovery in Sarkansal mi during post-pollution years, whereas no improvement has taken place in K aukolanlahti. The improvement in Sarkansalmi is shown by a significant incr ease in the number of species and total abundance, and by the community str uctures becoming more similar over time. On the other hand, a significantly decreased number of species, abundance and biomass values over time as wel l as the occurrence of defaunated anoxic sediments, are clear signs of cont inued deterioration in Kaukolanlahti. Differences in the recovery potential of the two water areas are interpreted as consequences of topography and w ater exchange patterns causing differences in oxygen saturation. (C) 2001 E lsevier Science Ltd. All rights reserved.