Invasion and Dispersion of the Exotic Species Procambarus clarkii (Decapoda Cambaridae) in Yeongsan River Basin, South Korea

Simple Summary Currently, the dispersion of the exotic species Procambarus clarkii in the Yeongsan River basin is a major issue in South Korea, where the majority of domestic crayfish occur in upstream river sections, while P. clarkii is mainly abundant in the middle and lower river reaches. In 2018, the species was initially observed only in the Jiseok Stream, a tributary stream of the Yeongsan River. Since then, the species has gradually dispersed in the Yeongsan River basin, and by 2021, the species was recorded in most of the main basin and tributary streams. The larvae of P. clarkii were abundant in areas with dense aquatic plants, whereas adults inhabited areas with silt/clay cover. However, P. clarkii appears to cause little impact on the freshwater ecosystem, despite its extensive dispersion. The species did not utilize native biological communities as food sources and is unlikely to be consumed by predators. The introduction of exotic species negatively affects the distribution and interactions within local biological communities in an ecosystem and can threaten ecosystem health. This study aimed to provide the basic data required to manage P. clarkii in the Yeongsan River basin. We identified the dispersion pattern and evaluated the ecosystem risk of this newly introduced species. The distribution survey investigated Procambarus clarkii populations at 25 sites in the Yeongsan River basin over a four-year period. The initial introduction occurred in Jiseok Stream. The larvae of P. clarkii were most abundant in areas with a dense aquatic plant cover, whereas adults preferred silt/clay areas. The alterations in the water flow by the river refurbishment project (carried out in 2012) increased their preferred habitats and contributed to P. clarkii dispersion. However, stable isotope analysis showed that the dispersion has had little effect on the freshwater ecosystem. The interrelationship between P. clarkii (i.e., larvae and adults) and other biological communities has been limited. Although the rapid dispersion by P. clarkii in the Yeongsan River basin has not impacted the freshwater ecosystem, further ecological information is required on how to manage P. clarkii beyond this early stage of invasion.