Influence of light on the foraging impact of an introduced predatory cladoceran, Bythotrephes longimanus

1. Identifying factors that influence the foraging ability of an introduced predator is essential for assessing its potential impact on the invaded community. We conducted a series of in situ enclosure experiments to determine the effect of light on the foraging ability and community-level effects of the invasive cladoceran Bythotrephes longimanus in lakes. 2. In 1-L enclosures with only Daphnia prey, a strong effect of predation under ambient light conditions was observed. There was no evidence of predation in dark treatments, suggesting that Bythotrephes is unable to feed by mechanoreception alone. 3. A subsequent experiment using larger enclosures exposed an assemblage of prey from an uninvaded lake to Bythotrephes predation across a similar light gradient. Consistent with regional lake surveys, Bythotrephes reduced cladoceran abundance under ambient light conditions. 4. At the community level, predation effects were overall strongest under ambient light; however, the influence of light on predation varied across trials that differed in initial community structure of prey. Also, some predation under dark conditions was possible on Ceriodaphnia and Bosmina, suggesting that Daphnia, in particular, may be less vulnerable under low-light conditions. 5. Our results suggest that light refuges for some prey taxa could play an important role in mediating the impact of Bythotrephes.