Grazing and food size selection by crustacean zooplankton compared to production of bacteria and phytoplankton in a shallow Norwegian mountain lake

Food size selection by suspension-feeding crustaceans in a shallowmountain lake was investigated with radiolabelled algae andbacteria, and with a series of monodisperse fluorescent latexbeads with diameters ranging from 0.25 to 5.18 µm. JuvenileDaphnia longispina was a more efficient grazer on bacteria-sizedparticles than adults. Bosmina longispina and Cyclops scutiferwere both able to ingest bacteria-sized food particles. Thecrustaceans harvested {small tilde} 100% of the primary productionduring the day investigated, but only 20% of the bacterial production.To keep the bacterial biomass in or near steady state, the microzooplanktonmust be harvesting most of the bacterial production.