Effects of a cyclopoid copepod (Diacyclops thomasi) on phytoplankton and the microbial food web

A plankton community unconditioned by Diacyclops thomasi predation was incubated with and without D. thomasi for 10 d to test the hypothesis that a recent manipulation of the food web of Castle Lake, CA; USA, altered phytoplankton biomass and productivity via effects of cyclopoid predation on microconsumers. Microconsumer grazing rates on bacteria and phytoplankton, ciliate abundance, chlorophyll, phytoplankton biovolume, and bacterial abundance were quantified before and after incubation. D. thomasi significantly reduced ciliate abundances relative to controls lacking D. thomasi. D. thomasi treatments also had higher chlorophyll concentration, bacterial abundance and maximum growth capacity of phytoplankton relative to controls. These results are consistent with the hypothesis that increases in D. thomasi in Castle Lake following food web manipulation affected limnological processes by affecting microconsumer abundances with subsequent effects on algae and bacteria.