Measuring the effects of food availability on Lake Superior Diporeia consumption rates using radiolabeled algae

Within the Lake Superior benthic macroinvertebrate community, Diporeia spp. are the most abundant organisms and account for the largest proportion of biomass. As detritivores that feed on organic material in surficial sediments, Diporeia play a major role in transferring energy and nutrients to higher trophic level consumers and are favored prey for Lake Whitefish and other benthivorous fish species. The objective of this study is to quantify and model the response of the Diporeia consumption rate to changes in food availability. Diporeia were introduced to microcosms containing various concentrations of 14C-labeled green algae (Selenastrum capricornutum) and incubated for 24 hours. Consumption was calculated as the radioisotope content of each animal divided by the specific activity of the labeled algae. A hyperbolic (Michaelis-Menten) function was fit to the data, yielding a maximum consumption rate of 1.76 ± 0.4 SE mg C/g DW/d. The predicted consumption rate corresponding to average Lake Superior algal carbon fluxes was 0.08 ± 0.15 mg C/g DW/d. For the observed range of carbon fluxes to benthic habitats in the Great Lakes, the relationship between consumption and food supply is well described by a linear function, with consumption rates ranging from 0.08-0.38 mg C/g DW/d. The parameter estimates presented here may act as inputs for a bioenergetics model used to predict Diporeia growth and production in Lake Superior.