The effects of fish assemblage composition on lake water quality

Abstract

Current trophic cascade theories predict that changes in the piscivore to planktivore biomass ratio will cascade down the food web, and will cause both chlorophyll and water clarity to deviate from nutrient – predicted values in individual lakes. An extensive survey of mid summer observations for nutrients, phytoplankton, zooplankton, and fish in Argentinean lakes and reservoirs, were used to study the effects of planktivorous and piscivorous fishes on chlorophyll concentrations and Secchi disk transparency. Regression analysis for different subsets of the data was used in this study. Regressions of chlorophyll on total phosphorus and Secchi disk on total phosphorus differed significantly among lakes with different fish assemblages. At comparable total phosphorus concentrations, lakes with planktivores but without piscivores had the highest phytoplankton biomass and the lowest water clarity. In conclusion, the results show that the fish assemblage composition has a dramatic effect on chlorophyll concentrations and water transparency when nutrient effects have been accounted for. © 1995 Taylor & Francis Group, LLC.