Cascading effects of generalist fish introduction in oligotrophic lakes

Abstract

Introduction of strictly planktivorous fish to lakes can alter plankton communities via cascading interactions in food webs. Less is known about the large-scale and long-term effects resulting from the introduction of fish with more generalist feeding habits, and the extent to which these effects depend on lake trophic status. Paleolimnological records of three oligotrophic lakes in Maine, USA were used to analyze the response of plankton communities to the introduction of white perch (Morone americana), a fish that often numerically dominates fish assemblages and switches from strict planktivory to a more generalist diet during ontogeny. After white perch introduction, cladoceran ephippia size increased up to 50 %, suggesting that the most important role of this generalist fish, with respect to water quality, is as a piscivorous trophic link. Algal standing crop declined by a quarter to over a half of pre-introduction levels, suggesting that top-down effects of white perch reduced phytoplankton biomass. In comparing these oligotrophic lakes to prior work in a eutrophic system, white perch introduction had similar effects on zooplankton body size; however, cascading effects to phytoplankton were only observed in low productivity lakes.