Distribution of the Freshwater Shrimp Palaemon sinensis（Decapoda: Palaemonidae）in the Saga Plain, Kyushu, Japan

The establishment of alien species is one of the major causes of biodiversity loss and can have serious impacts on native ecosystems. The Saga Plain is an important area for biodiversity conservation, where many endangered aquatic organisms are distributed. In recent years, the alien freshwater shrimp Palaemon sinensis（Sollaud）（Decapoda: Palaemonidae）has been reported to have invaded domestic freshwater ecosystems in Japan and is suggested to have displaced a native congener, Palaemon paucidens De Haan, at various localities. In this study, we investigated the distribution of these species in the Saga Plain. As a result, P. sinensis was found widely in the central and southern parts of the Saga Plain. In these areas, P. paucidens was not found at most localities, suggesting that the alien species is replacing the native species. Based on monthly surveys of body size and ovigerous individuals, P. sinensis reproduces once in the spring.