Divergent desalination effects on alien and native gammarid functional responses

Abstract

Climate change could shift the impacts of biological invasions on aquatic ecosystems. Sea freshening is an often-inconspicuous consequence of climatic change that may modify invasive alien species performance in enclosed seas. Several gammarid crustaceans have been particularly successful aliens across fresh, brackish, and marine waters. Here, we use comparative functional responses (feeding rates across resource densities) to examine the ecological impacts of an invasive alien (Gammarus tigrinus) and native (Gammarus locusta) gammarid, present in the Baltic Sea, under three different salinity regimes (14, 10, 6) toward larval chironomid prey. Feeding rates differed between the two species, but these differences depended on salinity, whereby at the lowest salinities, the invasive alien species showed significantly improved performance compared to the native species. Both gammarids exhibited hyperbolic Type II functional responses, with attack rates similar across salinity regimes. Handling times were significantly shortened, and maximum feeding rates heightened, in the alien under sea freshening scenarios compared to the native. These results have implications for enclosed sea systems, where projected freshening could shift the performance advantage toward invasive alien species over natives, thereby exacerbating their ecological impacts.