Zooplankton Communities in Two Inshore Areas of Great Bear Lake, N.W.T., Canada

Abstract

The composition, structure, and seasonal development of zooplankton communities in Great Bear Lake were determined from monthly collections made between April and October 1978. Samples were taken 2 km off shore near Echo Bay and Conjuror Bay in the upper 40 m of the water column. There were 20 species found in the plankton, of which 10 were crustaceans, 7 were rotifers, and 3 were protozoans. The most common crustaceans in both areas were Diaptomus sicilis, Cyclops scutifer, and Holopedium gibberum; dominant rotifers included Keratella cochlearis, Kellicottia longispina, and Asplanchna priodonta; and the prevalent protozoan was Codonella cratera. Crustaceans reached a total maximum density of 3.1 × 10³ animals m^-3 in August whereas the combined totals for rotifers and protozoans were 10.5 × 10³ and 13.2 × 10³ animals m^-3, respectively. These densities and the total number of species are among the lowest recorded for freshwaters and are probably related to low (<6°C) water temperatures and phytoplankton availability (<90 mg m^-3). The slight temporal and spatial variation in these factors and in water chemistry during the study also possibly accounted for (1) the similarity in the species composition of the plankton between the two widely separated sampling areas, (2) the small vernal and autumnal fluctuations in abundance of the common rotifers and protozoans, and (3) the homogeneous vertical distribution of several species in the upper 30 m of the water column.