Predation on eggs and larvae of the Japanese brown frog <i>Rana japonica</i> Boulenger, 1879 by the invasive crayfish <i>Procambarus clarkii</i> (Girard, 1852) (Decapoda: Astacidea: Cambaridae) under laboratory conditions

Abstract We hypothesized that the North American invasive crayfish Procambarus clarkii (Girard, 1852) can negatively affect the populations of native frog species through predation. We conducted three laboratory experiments to examine whether P. clarkii can prey on eggs or larvae of the Japanese native frog Rana japonicaBoulenger, 1879: Experiment I crayfish + frog egg in an aquarium without a substrate or aquatic plants, Experiment II crayfish + frog larva in an aquarium without a substrate or aquatic plants, and Experiment III crayfish + frog larva in an aquarium with a substrate and aquatic plants as shelter for the larva. We used three experimental groups of crayfish individuals (small, intermediate, and large size), each of 10 individuals, and simultaneously placed one crayfish individual and one egg or frog larva in the same aquarium for 24 h and checked for predation by the crayfish. We found that 88.9% and 86.7% of eggs and larvae used in Experiments I and II were preyed upon, respectively. Predation rate of frog larvae was still high (77.8%) in Experiment III, suggesting that crayfish can potentially find and prey on frog larvae in nature. Predation on frog eggs or larvae was high regardless of the crayfish body size. Our results indicate that P. clarkii can potentially have a marked effect on the population of R. japonica by preying on eggs and larvae.