A Model System for Studying the Effects of Invasive Predatory Cladocerans on Zooplankton Behavior
The Great Lakes have experienced a new wave of species invasions dominated by exotic invertebrates. Two of these species include the predatory cladocerans Bythotrephes cederstroemi and Cercopagis pengoi. Currently, they are suspected to be disrupting the Great Lake food webs at the lower trophic levels with possible effects permeating bottom-up into the higher trophic levels that directly influence fish recruitment. One way these invasive predators may be causing significant changes in the Great lakes could be through their effects on the diel vertical migration (DVM) behavior patterns of zooplankton prey. The long-term aim of this study is to research the effects of the invasive predatory cladocerans (IPC), B. cederstroemi and C. pengoi, on the behavior of a variety of zooplankton species and to better understand how these changes are affecting overall food web dynamics in the Great Lakes. To begin this research, it is important to develop a model system. For two months, I worked on developing a successful experimental design as well as the best methods for accomplishing the overall project goals. In this preliminary stage, we substituted the IPC with the predator Mysis relicta and used the well-studied zooplankton species Daphnia galeata mendotae as prey. Experiments were conducted with control and predator treatments (Mysis scent), two clones of prey (Daphnia clones A and B), and varying food levels. In the presence of Mysis scent, the Daphnia did exhibit differences in their average vertical positions. Although not all results were statistically significant, the discovery of differences suggests that this is a research direction worth exploring. If we continue to develop this model system so that it can be applied to the study of the IPC, it might provide some very important answers to critical questions currently being asked. The research presented in this paper is aimed at providing a foundation upon which further work can be built. There is much more to be explored and studied in this direction and the findings could provide greatly needed insight into future steps needed to best maintain the food web balance in the Great Lakes.
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