Dietary Change during Development in the Freshwater Calanoid Copepod Epischura lacustris Forbes

The diet of the freshwater calanoid copepod Epischura lacustris from C2 to adult stage was examined with predation experiments, grazing experiments, and stomach content analyses. There was a transition from an exclusively herbivorous diet in early copepodid stages to an omnivorous diet in adults. Laboratory predation experiments revealed that C2 and C3 were incapable of ingesting Bosmina (0.25–0.35 mm), but from C4 to C6, ingestion rate of Bosmina increased with developmental stage. The order or prey selection for adult Epischura was Bosmina over Diaptomus and Cyclops. Grazing rate on small algae (<10 μm) increased with developmental stage. Zooplankton remains were only found in the guts of stages older than C2; cladocerans and crustacean eggs were the most common zooplankton food. Algae with longest linear dimensions greater than 10 μm (e.g. Sphaerocystis, Dinobryon, and diatoms) were common in the guts of all developmental stages of Epischura. The occurrence of small unicells (<10 μm) in the guts decreased with developmental stage.