Mysid predation on amphipods and Daphnia in a shallow coastal lake:: prey selection and effects of macrophytes

Interactions between mysids and invertebrates other than pelagic zooplankton have not been well studied. We tested the hypothesis that the mysid Tenagomysis chiltoni preys on the co-occurring amphipod Paracalliope fluviatilis in laboratory experiments. In prey size preference experiments with single prey species, male and female T chiltoni consumed more. small than large amphipods in the absence of the macrophyte Elodea canadensis, but were not selective when macrophytes were present. When offered small and large Daphnia, T chiltoni males consumed more small than large Daphnia, whereas female T chiltoni did not show any preference. When amphipods and Daphnia of similar size were presented together, male T chiltoni strongly selected Daphnia in the presence and absence of E. canadensis, whereas female mysids did so only in the presence of macrophytes. The total number of prey consumed by each sex did not differ between macrophyte treatments. However, female T chiltoni, which are larger than males, consumed more prey than males. These data suggest that mysids may be an important source of mortality to the amphipod P. fluviatilis. Mysids may also prey on amphipods in other aquatic systems where they co-occur.