Invasion of the bryozoan Membranipora membranacea to the Gulf of Maine provided an additional prey resource to the dorid nudibranch Onchidoris muricata (Müller, 1776). We examined prey choice based on past diet history and compared growth and reproductive output among laboratory-reared O. muricata on exclusive bryozoan diets of M. membranacea and the native, historically preferred prey, Electra pilosa. Adult nudibranchs were collected from Cape Neddick, York, Maine for the prey choice experiment and post-metamorphic juveniles were collected from Jaffery Point, Newcastle, New Hampshire for the growth and reproduction experiments. Nudibranchs were laboratory reared under controlled conditions for up to 10 months until completion of spawning. Growth was monitored biweekly, and reproductive performance was assessed with a weight-adjusted dimensionless reproductive index (ΣRI) of each individual's spawn summed over the reproductive period. Prey choice experiments showed nudibranchs tended to select prey based on prior feeding history. Diet influenced reproductive output: nudibranchs fed E. pilosa had larger first spawn, more total spawn, and larger average spawn, as well as higher reproductive effort. Diet did not influence weight-specific growth rate, maximum body size, or pre-spawn body size. Since the temporal abundances of these bryozoan prey differ, the predator benefits by consuming the novel prey when the native prey is rare. With the increased awareness of invasive species in communities, we suggest studies need to consider predator-prey paradigms that include the seasonality of non-native prey to gain an understanding of the influence these organisms have on native predator population dynamics.
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Vol. 34 • No. 1