Fish Species Composition and Lake Abiotic Variables in Relation to the Abundance and Size Structure of Cladoceran Zooplankton

Abstract

Redundancy analysis and a multiple regression approach to analysis of variance and analysis of covariance were used to evaluate the influence of fish species composition and abiotic variables on the numerical density, biomass, and mean length of individual cladoceran taxa from 43 Laurentian Shield lakes. Cladoceran assemblage structure was still associated with fish species composition when potentially confounding effects of abiotic variables were accounted for by partial redundancy analysis. Cladoceran abundances were strongly related to the occurrence of white sucker (Catostomus commersoni) and lake maximum depth; mean lengths were influenced most by white sucker, water transparency, lake volume, and sampling date. The abundance of bosminids and length of Holopedium were strongly related to the occurrence of white sucker even when the influence of abiotic factors was removed by regression. In lakes with white sucker and brook trout (Salvelinus fontinalis), Holopedium mean length decreased and bosminid abundance increased fourfold relative to lakes with brook trout only; large (>1.2 mm) Holopedium abundance was reduced by 76–81%, suggesting that size-selective predation occurred. The increase in bosminid abundance in the presence of white sucker may have been a response to diminished competition by large Holopedium, but density compensation was not observed.