Distribution of introduced freshwater shrimp Neocaridina sp. and native shrimp Paratya improvisa in the Tsurimi River in eastern Japan.

Abstract

Occurrence of Neocaridina sp. has recently been reported in several places in eastern part of Japan. In order to know the impact of this introduced species on a native freshwater shrimp, Paratya improvisa, which occurs in similar habitats, we examined the distribution of N. sp. and P. improvisa in the Tsurumi River in 2014 and from 2016 to 2017. In riverine habitats, N. sp. occurred at almost all sites of examination. P. improvisa co-occurred at only two sites in 2014, and disappeared by 2016. In small ponds, N. sp. and P. improvisa co-occurred at one site and P. improvisa occurred at three sites in 2014. By 2017, N. sp. replaced P. improvisa at two sites and P. improvisa occurred only at two sites. We found that where two species co-occurred in almost the same number, N. sp. replaced P. improvisa within two to three years. It is thus important to prevent introduction of N. sp. into pond habitats where P. improvisa occurs by raising public awareness of the risky consequence of releasing non-native shrimps.