Experimental effects of large-bodied Daphnia, fish and zebra mussels on cladoceran community and size structure

Abstract

Understanding the factors that regulate the abundance, size structure and community structure of cladocerans is an important goal of aquatic ecologists. While both top-down and bottom-up factors help to structure cladoceran communities, there may be interactions between these factors. We conducted a mesocosm study to determine how alien large-bodied Daphnia, zebra mussels and fish affected cladoceran community and size structure. We found that large-bodied Daphnia reduced algal resources and the fecundity of smaller bodied cladocerans. Fish removed the large-bodied Daphnia magna from the mesocosms and shifted the cladoceran community to a smaller body size. Fish also appeared to promote increases in cladoceran diversity through the coexistence of several smaller bodied taxa. In contrast, zebra mussels increased cyanobacteria and helped to promote the success of the alien Daphnia, but reduced the biomass of small-bodied cladocerans. Zebra mussels reduced the carbon (C):phosphorus (P) ratio of the phytoplankton in the mesocosms which may have favored the relatively P-limited Daphnia. Combined, our results highlight the complex interactions of multiple factors that help to regulate cladoceran community and size structure.