Vertical Distribution and Seasonal Abundance of Zooplankton in Two Shallow Lakes of the Experimental Lakes Area, Northwestern Ontario

Abstract

Seasonal variations in the abundance of zooplankton were studied in lakes 122 and 132 for a period of 10 months beginning in mid-May 1968. Seasonal dynamics of various species are discussed in relation to their patterns in the Canadian Shield and in other localities.Day and night vertical distributions for each lake were sampled on two dates in summer. Three species of rotifers migrated diurnally in lake 122, but no evidence of diurnal movement was found in lake 132. All crustaceans studied in both lakes migrated vertically to some degree, except for nauplius larvae and Leptodora kindtii. There was little difference in vertical distribution patterns on the two dates studied.Average zooplankton biomass in the two lakes was calculated and compared with that found in other studies. Average zooplankton biomass during the ice-free season was 72 and 156 mg/m3 dry weight for lakes 122 and 132, respectively. Dominant species in both lakes were Diaptomus minutus, Cyclops bicuspidatus thomasi, Holopedium gibberum, and Bosmina longirostris. Ecological tolerances for rotifer species agreed well with those found for Swedish waters.