The effects of food quantity, light, and temperature on clearance rates in freshwater bivalves (Cyrenidae and Unionidae)

Assessing the environmental variables that influence freshwater bivalve filtration activity is key to better understand the functioning of stream ecosystems. In the present study, the effects of light (0 ± 0 µmol m⁻² s⁻¹ and 19 ± 2 µmol m⁻² s⁻¹) and temperature (10, 15, 20 and 25°C) on the clearance rates of two bivalve species: the Asian clam Corbicula fluminea (Cyrenidae) and pocketbook Lampsilis ovata (Unionidae) were assessed under controlled laboratory conditions at two different concentrations of algal food (i.e., 10,000 cells ml⁻¹ and 100,000 cells ml⁻¹). Clearance rates for C. fluminea varied from 0 to 491 ml g⁻¹ h⁻¹, while the observed range for L. ovata was 0 to 905 ml g⁻¹ h⁻¹. We found that the relative contribution of the tested variables was species-dependent. While temperature plays a major role in the clearance rates of C. fluminea, food concentration was the most significant variable in the clearance rate of L. ovata. Our results confirm the complex interactions between abiotic and biotic factors in freshwater bivalve filtration activity. Overall, clearance rates are highly variable especially in C. fluminea and presumably regulated by other untested factors suggesting high plasticity in filtration.