Laboratory experiments estimated the impact of different Daphnia pulex densities on chlorophyll a and phaeopigment concentrations, and primary productivity. Chlorophyll a declined with increasing Daphnia density, while phaeopigment concentrations increased linearly with increasing zooplankton density. These results are consistent with theoretical predictions regarding the importance of predator-prey interactions in aquatic food webs. Additional studies employed Carbon-14 labelling techniques to determine feeding preferences of Daphnia on cultures of various combinations of Chlamydomonas and Chlorella. In these studies a negative relationship occurred between grazing pressure and primary productivity, whereas food web theory predicts a unimodal relationship. Labelling experiments showed a lack of preferential feeding in Daphnia for either phytoplankton species. The implications of these results to theories of optimal foraging and cascading food web interactions are examined.
Title
Impacts of prey preference by Daphnia pulex on algal productivity
Keough, W. L., N. M. McCreary, C. M. DeLucchi. (1992) "Impacts of prey preference by Daphnia pulex on algal productivity." Journal of the Pennsylvania Academy of Science 66 (1): 9-14