Factors Regulating in situ Filtering Rates of Cladocera

Abstract

Individual filtering rates of 4 species of Daphnia, as well as Holopedium, Diaphanosoma, Ceriodaphnia and Bosmina, were measured in 10 lakes. Carapace length accounted for almost 60% of the total variance in individual filtering rates when data were pooled. Zooplankton in these lakes probably filter-feed in proportion to their volume, since the functional slope of this regression approximated 3. Temperature (12-22oC) had no statistically significant effect on filtering rate. Since the two main determinants of in situ filtering rates were zooplankton carapace length and concentration of edible phytoplankton, both of which are independent of taxonomic affiliation, investigators interested in assessing grazing losses should seriously consider measuring zooplankton in terms of size distribution rather than taxonomic affiliation. -from Authors