Effects of temperature and food availability on the filtration and excretion rates of Diplodon parallelopipedon (Hyriidae)

Bivalves can consume detritus, bacteria, phytoplankton, and zooplankton by filtering the water column. Ecological attributes like filtration rate (FR) and excretion rate (ER) are particularly important to better understand the role of bivalves in ecosystem. Here, we aimed to elucidate the FR/ER of Diplodon parallelopipedon in a five-times replicated laboratory experiment under five levels of temperature (10°C, 15°C, 20°C, 25°C, and 30°C) and three levels of phytoplankton biomass (low, middle, and high). Temperature was the main factor regulating FR and ER in our experimental conditions, as we hypothesized the experimental results showed a nonlinear relationship between FR and water temperature. D. parallelopipedon exerted top-down control over phytoplankton biomass throughout the temperature gradient tested. Contrarily to our expectation, FR and ER did not vary within the phytoplankton biomass range offered. The experimental evidence suggests D. parallelopipedon might control phytoplankton biomass in different temperature scenarios. Moreover, the excretion of nutrients by D. parallelopipedon, together with a capacity to avoid grazing shown by several phytoplankton species (i.e., buoyance regulation) reveal relevant challenges to our understanding of bivalve-phytoplankton dynamics, and consequently to the whole ecosystem response, particularly in the presence of more diverse natural phytoplankton communities.