Implications of an invertebrate predator's (Bythotrephes cederstroemi) atypical effects on a pelagic zooplankton community

The traditional view of predaceous zooplankton is that they prefer small-bodied prey, are hindered by morphological anti-predator defenses, and have a minor influence on zooplankton communities when fish are present. We performed a series of experiments with the large-bodied onychopod (cladoceran) Bythotrephes cederstroemi, in which we incubated this predator with known prey to determine prey preference and predation rates. We also performed an allozyme analysis of prey tissue in the gut of B. cederstroemi collected from several stations around Lake Michigan to determine what prey types are chosen in the field. We found that B. cederstroemi does not fit the standard invertebrate predator mold: adult B. cederstroemi prefer large (>2.0 mm) Daphnia pulicaria over smaller individuals; the elongated tailspine and helmet of Daphnia galeata mendotae are not effective deterrents to B. cederstroemi predation; and B. cederstroemi is a generalist predator with the potential to consume a significant portion of cladoceran production in Lake Michigan.