Selective Consumption of Pelagic Cladocerans by Bluegill Sunfish (Lepomis macrochirus Rafinesque) Contributes to Dominance of Epiphytic Cladocerans

Abstract

Fish predation is restricted in areas with high aquatic macrophyte coverage; however, bluegill sunfish (Lepomis macrochirus), an exotic fish species, can consume prey even in such spaces. Here, we hypothesized that the cladoceran community structures in three wetlands (Upo, Jangcheok, and Beongae) with abundant macrophytes within the Nakdong River basin, South Korea, were influenced by high abundance and foraging activities of L. macrochirus. The study areas were dominated by L. macrochirus with body sizes < 10 cm, and their cladoceran consumption was higher than that of larger size classes. Most of the cladoceran species that were highly consumed by L. macrochirus were pelagic (i.e., Daphnia obtusa and Daphnia pulex); epiphytic species were consumed less (i.e., Chydorus shpaericus, Alona retangula, and Pleroxus laevis). We hypothesize that epiphytic cladoceran species are not easily explored by L. macrochirus. Selective consumption of pelagic species by L. macrochirus was reflected in the seasonal cladoceran distribution. Epiphytic species were the most abundant, whereas pelagic species abundance was relatively low. The low density of pelagic cladoceran species further increased the epiphytic species abundance. We conclude that the dominance of L. macrochirus introduced into Korean wetlands has been sufficient to change the cladoceran community structure; therefore, the abundance of epiphytes cladocerans in other countries or regions needs to be provided priority to the dominance and consumption pattern of L. macrochirus.