2022 Volume 83 Issue 2 Pages 103-114
In the Shishizukaoike pond, Ibaraki Prefecture, the Nelumbo nucifera community disappeared in 2020. This disappearance is attributed to foraging by the American red swamp crayfish, Procambarus clarkii, whose population dramatically increased after the decline of largemouth bass, Micropterus salmoides. To examine whether there are other animals that prey on the crayfish in the ecosystem, and whether the crayfish eat aquatic plants such as lotus, we analyzed carbon and nitrogen stable isotope ratios that were sampled before the disappearance of the lotus community. It was confirmed that American red swamp crayfish feed on aquatic plants, including lotus. Largemouth bass less than 10 cm in length eat the crayfish and bullfrog (Lithobates catesbeianus) tadpoles. These tadpoles also feed on aquatic plants. Although the crayfish were imported to Japan as food for bullfrogs, it is presumed that the bullfrogs in Shishizukaoike pond did not mainly feed on crayfish. Therefore, without largemouth bass in Shishizukaoike pond, there would be no animals that feed mainly on crayfish and bullfrog tadpoles, which would make it difficult for aquatic plants, including lotus, to grow.
