The interactive effects of temperature, trophic status, and the presence of an exotic clam on the performance of a native freshwater mussel

Global environmental changes constitute major threats to biodiversity in all ecosystems worldwide. Here we experimentally examined how temperature and trophic condition can influence the interaction between a highly invasive species and a native naiad species. We exposed the native freshwater mussel Unio delphinus to the presence/absence of the invasive Corbicula fluminea under three temperature levels and three trophic conditions. We used linear mixed models and hierarchical partitioning to model and test the independent effects of each variable in explaining U. delphinus feces production, which was used as a proxy for nutrient enrichment. Unio delphinus responded to high temperatures with higher clearance and respiration rates, showing an increase in energy expenditure. Feces production varied significantly with each factor and there was an interactive effect between the factors; increasing with temperature and trophic condition, and declining in the presence of the invasive clam. The hierarchical partitioning model showed that the system trophic condition and C. fluminea were the most important factors explaining feces production and to a lesser extent water temperature. Depletion of energetic reserves to cope with increasing temperatures could compromise the tolerance to additional stressors such as competition with invasive species or food reduction.