A new reality for coastal zoobenthos: long-term changes (1958-2005) in a shallow sheltered bay

The zoobenthos in the narrow and shallow brackish-water bay Kuristenlahti in Airisto (SW Finnish archipelago) was studied in 2005, and the results were compared to unpublished data from 1958–1965 from the same area in order to analyse the long-term and spatial variability of the fauna. Observations were made at seven different stations. The length-frequency distribution was recorded for the bivalve Macoma balthica to study recruitment and survival in this specific environment. Significant changes in species composition, diversity, abundance and biomass, corresponding to changes in the environment, had occurred over time. After 1965 a smaller port for leisure boats had been built in the bay, and a fish farmwas active for some years at the seaside of the entrance to the bay. These events, combined with severe eutrophication due to the nutrient load from the agriculture close to the bay have affected the zoobenthos negatively, and the zoobenthic assemblages of today are significantly different from and poorer than those found in the bay 40–45 years ago. This study highlights the importance and value of available referencedata for the evaluation of the present-day environmental status.