Bacterivorous flagellates as food resources for the freshwater crustacean zooplankter Daphnia ambigua

The cladoceran Daphnia ambigua was able to grow and produce viable young on a diet of heterotrophic flagellates. Clearance rates of D. ambigua fed either heterotrophic (Spumella = Monas sp., Chilomonas sp.) or autotrophic (Chlamydomonas reinhardi) flagellates were similar, ranging from 1.2 to 1.5 ml cladoceran−1 h−1, but were lower (0.7–0.9 ml cladoceran−1 h−1) on single loricae of the larger mixotrophic alga Dinobryon. Size of the flagellate was a major factor determining ingestion rate. Age of first reproduction for D. ambigua fed Chilomonas (7.4 d) was similar to that found in previous studies with algae as a food source (6.1–7.6 d). Ingestion of heterotrophic and mixotrophic flagellates by cladocerans, which are a common food for many fish, may serve as a relatively efficient shunt of microbial carbon and energy to higher trophic levels.