Cladoceran filtration rate-body length relations: model improvements developed for a Microcystis-dominated hypertrophic reservoir

Abstract

Filtering rates were measured for zooplankton species in Situ on single-celled Chlorella and on four Microcystis colony size fractions (5–20, 20–40, 40–60 and 60–100 μm) in a hypertrophic reservoir. Natural-log-transformed filtration rates of five cladoceran species, one copepod and one rotifer were included in an all-food-particle, all-species multiple regression model which explained 43% of the variance in filtration rate as a function of animal body length. An additional 14% and 7.6% of the variance was attributable to food type and zooplankton species respectively, with temperature accounting for <4% of the variance. Restricting the filtration rate model to cladocerans alone explained 51% of the variance as a function of animal length, 16% as a function of food type, 7.5% as a function of species and only 0.2% as a function of temperature. In linear filtration rate models for each food type, cladoceran body length explained 70% of the variance when feeding on Chlorella and between 57 and 67% of the variance on the four Microcystis colony fractions. Models describing cladoceran filtration rates on Chlorella and the 5–20 μm Microcystis colony fraction were significantly different from the three models on larger colonies due to cladoceran responses to increasing food particle size. Accordingly, a combined model for Microcystis colonies >20 μm was developed. Inclusion of food quality factors such as cyanophyte colony size seems justified in models aimed at estimating clearance rates, resource utilization and phytoplankton grazing losses in plankton or ecosystem studies when applied to eutrophic or hypertrophic lakes where large cyanophyte particles are abundant.