The Impacts of Crustacean Zooplankton on a Natural Ciliate Community: a Short-term Incubation Experiment

Direct and indirect effects of crustacean zooplankton (cladocerans and copepods) are important regulators of ciliate communities, especially in eutrophic systems. However, it is not clear whether pseudodiaptomids (e.g., Schmackeria), one of the dominant calanoid copepods in Chinese lakes, effectively impacts natural ciliate communities. The impacts of small-bodied cladocerans (e.g., Bosmina) on ciliates are also controversial. We performed an incubation experiment using winter lake water from Lake Chaohu to assess the structuring effects that crustacean zooplankton have on natural ciliate populations. The presence and absence of cladocerans (Bosmina sp.) and copepods (Schmackeria inopinus) were alternated in four treatments. Both Bosmina sp. and Schmackeria inopinus had substantial impacts on ciliate abundance, biomass, and community structure. The response of ciliates was different in the presence of Bosmina sp. compared with Schmackeria inopinus and varied among categories such as the ciliate population, relative body size and functional feeding group. Our results also highlight the importance of interference and exploitative competition among metazooplankton groups.