Role of interference from Daphnia and predation by cyclopoid copepods in zooplankton community structure: Experimental analysis using mesocosms

The reduction of planktivorous fish populations in lakes through biomanipulation often results in increased abundance of the large cladoceran Daphnia and invertebrate predators, such as cyclopoid copepods, and also in decreased numbers of small zooplankters, such as the cladoceran Bosmina longirostris and rotifers. To investigate the factors causing reduced abundance of small zooplankton species in lakes, we performed a mesocosm experiment where the abundance of Daphnia and cyclopoid copepods (Mesocyclops sp.) were controlled. Bosmina populations declined substantially in mesocosms with abundant copepods, implying that predation by cyclopoid copepods is a major factor controlling Bosmina populations in lakes. In contrast, rotifer densities were reduced in the mesocosms with Daphnia, even though excess food (Chlorella vulgaris) was provided. This suggests that rotifer populations are effectively controlled by interference competition with Daphnia.