FILTERING RATES OF DIAPTOMUS-MINUTUS, BOSMINA SPP, DIAPHANOSOMA SP, HOLOPEDIUM-GIBBERUM (CRUSTACEA), AND ZOOPLANKTON COMMUNITY GRAZING RATES IN SOME ACIDIC AND CIRCUMNEUTRAL ONTARIO LAKES

Filtering rates of several zooplankters and grazing rates of the zooplankton community were investigated in 7 Ontario lakes ranging in mean pH from 4.6-7.1. Filtering rates of Diaptomus minutus, Diaphanosoma sp., and Holopedium gibberum were negatively correlated with lake pH and alkalinity; rates for these species averaged 89, 171, and 514 μL.ind-1.h-1, respectively in the circumneutral lakes, and 200, 374, and 1853 μL.ind-1.h-1 in acidic lakes. The filtering rate of Bosmina spp. was not correlated with lake pH; its average rates were 35 and 44 μL.ind-1.h-1 in circumneutral and acidic lakes, respectively. Other environmental parameters examined (temperature, light intensity, plankton biomass, chlorophyll a concentration) did not appear to influence the filtering rate of most species tested. Zooplankton community grazing rates were not correlated with lake pH; rates averaged 1.1%.h-1 in circumneutral lakes, and 1.5%.h-1 in acidic lakes. This result does not support a previous hypothesis that the efficiency of energy transfer from primary to secondary trophic levels is reduced by acidification. There was no indication that grazing pressure on small versus large cells changed at low pH, based on comparisons of community grazing rates on the small alga Chlorella and the larger Cosmarium. -Authors