, Volume 63, Issue 1, pp 89-101

Effects of Eutrophication on Young-of-the-year Freshwater Fish Communities in Coastal Areas of the Baltic

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Abstract

Abundance, growth, habitat and food choice of young-of-the-year (Y-O-Y) freshwater fishes were investigated in a gradient of eutrophication in a Baltic inlet. Secchi-disc depth decreased from 3 to 0.5 m along the gradient with an accompanying reduction in submerged vegetation coverage. There were positive trends in Y-O-Y abundance with increasing turbidity for cyprinids, pikeperch, ruffe and smelt, and a negative trend for perch, leading to a shift from a perch dominated community in the reference area to a cyprinid dominated in the eutrophic area. The species composition of adult fishes resembled the Y-O-Y species community, indicating that community structure was determined already during early juvenile interval. Perch and cyprinid Y-O-Y preferred areas with submerged macrophytes while pikeperch and smelt were found more frequently in open waters. Perch Y-O-Y growth was reduced in eutrophic areas compared to references, especially in the size range where they change from foraging on zooplankton to benthic organisms. The deterioration of visual conditions caused by high turbidity is suggested to be negative for feeding of perch especially in deeper water. There was no evident growth reduction for pikeperch, which may be explained by a visual physiology well adapted to turbid conditions. The combined effects of turbidity and competition for food resources on growth and survival in eutrophic waters are discussed.