Impacts of invasive alien fish species— Micropterus salmoides and Lepomis macrochirus (Actinopterygii, Centrarchiformes, Centrarchidae)—on freshwater fish communities in lakes and reservoirs of Korea: A five-year monitoring study

Invasive alien fish species, such as the largemouth bass, Micropterus salmoides (Lacepède, 1802), and bluegill, Lepomis macrochirus Rafinesque, 1819, have rapidly spread across freshwater ecosystems in Korea, raising serious ecological threats. This study investigated the impact of these invasive alien species on fish communities in large lakes and small reservoirs over a 5-year monitoring period (2019–2023). Eight sites, including four lakes and four reservoirs, were surveyed twice a year. Fish were collected using cast nets, kick nets, and gillnets (for lakes). Species diversity indices (Shannon’s H ʹ, Pielou’s J ʹ, and Margalef richness) and dominance indices were calculated. Poisson-based analysis of variance models was applied to examine the relationship between the densities of invasive alien species and the diversity of fish communities. Sites with higher densities of largemouth bass and bluegill had significantly lower diversity indices. Non-metric multidimensional scaling analyses indicated distinct community groupings according to the type of waterbody and the presence of invasive alien species. These results emphasize the need for continued monitoring and management strategies tailored to different habitat scales.