Examination of the effects of largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) on the ecosystem attributes of lake Kawahara-oike, Nagasaki, Japan

a r t i c l e i n f o Keywords: Invasive fish species Largemouth bass Bluegill Food web modeling Ecosystem attributes Lake Kawahara-oike The introduction of largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) into the freshwater ecosystems of Japan has resulted in the suppression and/or replacement of native species, generating considerable concerns among resource managers. The impacts of largemouth bass and bluegill on native fauna have been examined in aquaria and isolated farm ponds, but there is limited work examining the likelihood to fundamentally modifying Japan's lakes. The objective of the present study is to examine the direct and synergistic ecological effects of largemouth bass and bluegill on the biotic communities of Lake Kawahara-oike, Nagasaki, Japan, using an ecosystem (Ecopath) modeling approach. Specifically, we examine whether the two fish species have played a critical role in shaping the trophodynamics of the lake. We attempt to shed light on the trophic interactions between largemouth bass and bluegill and subsequently evaluate to what extent these interactions facilitate their establishment at the expense of native species. We also examine how these changes propagate through the Lake Kawahara-oike food web. Our study suggests that the introduction of bluegill has induced a range of changes at multiple trophic levels. The present analysis also provides evidence that largemouth bass was unable to exert significant top-down control on the growth rates of the bluegill population. Largemouth bass and bluegill appear to prevail over the native fish species populations and can apparently coexist in large numbers in invaded lakes. Future management strategies controlling invasive species are urgently required, if the integrity of native Japanese fish communities is to be protected. Exotic species are organisms introduced to foreign habitats, and become invasive if they are able to outcompete native species for resources. The number of species transported across biogeochemical borders is expansive, but only a small fraction becomes established, and even fewer become pests (Mooney and Cleland, 2001). Successful invasions can fundamentally alter competitive interactions and reduce native populations within a community, and lead to extinction. Early conceptual models describing species invasions were built upon the premise that species-rich communities were more resistant to invasion than species-poor communities, due to more efficient use of limiting resources as well as the presence of competitors/predators to ward off potential invaders (Elton, 1958). This framework is labeled the Biotic Resistance model, and postulates that successive invasion attempts yield …