Coexistence patterns between the invasive amphipod Crangonyx pseudogracilis and native Echinogammarus meridionalis: a laboratory approach

Freshwater ecosystems are known as hotspots of biodiversity. These systems and their resident shredder communities are very sensitive to multiple anthropogenic environmental disturbances. Disturbance in the form of invasion by alien species is a major contributor to the observed declines in biodiversity. In freshwater shredder communities, non-native amphipod species may negatively affect ecosystem function and energy transfers. The aim of this study was to analyze the interactions between two freshwater amphipods: Echinogammarus meridionalis, native in the Iberian Peninsula, and Crangonyx pseudogracilis, a recently introduced invasive species. The objectives were to determine if the survival of Echinogammarus meridionalis is affected by Crangonyx pseudogracilis in the absence of food. Additionally, the influence of coexistence on functional parameters such as food consumption or moulting rates was also assessed. The presence or absence of food and, in addition, the non-native amphipod presence did not affect the survival of the native species for the duration of the experiment. Nonetheless, E. meridionalis presented a much higher overall mortality. Consumption of alder leaves was significantly higher for E. meridionalis. Overall, these results suggest that C. pseudogracilis effects on E. meridionalis may be residual.