Zooplankton community structure in southwestern Québec lakes: the rÔles of acidity and predation

Abstract

The zooplankton community structure of 22 lakes with varying acidity and fish biomass, located southwest of the mining and smelting region of Rouyn/Noranda, Quebec, was examined in July 1987. Lakes with dominant piscivorous fish communities could be discriminated from non-piscivorous communities using solely pH and Chaoborus abundance, demonstrating that modifications in the zooplankton community occurred concurrently with changes in the fUh communities. Strong discontinuities in zooplankton species distributions were discerned in lakes with pH values <5.3; abundance ranges for several species could be semi-quantitatively related to lake morpho-metry or chemistry. Small shallow kettle lakes with elevated heat budgets had high biomasses of small herbivorous organisms. The presence of >5 mg m −3 of advanced Chaoborus instars (III and IV) was associated with reduced microcrustacean biomass in many lakes, particularly those with low fish biomass. There was little evidence for size-selective predation by fish in these oligotrophic lakes. Fish biomass/effort could be semi-quantitatively related to the biomass of Leptodora kindtii and the ratio of adult Diaptomus nunutus to copepodite stage IV.