A bioenergetic model to address carbon sequestration potential of shellfish farming: example from Ruditapes philippinarum in the Venice lagoon

Shellfish are increasingly been looked at as sustainable food sources that provide additional ecosystem services. However, their role as CO2 sinks or sources is still debated. To quantify it, shell accretion dynamics should be accounted for. However, the shell component is usually calculated with allometric scaling, in most bivalve models. With this study, shell accretion was added to a bioenergetic model of the Manilla clam (Ruditapes philippinarum), and a parameter linking assimilated energy towards shell growth (KSH) was calibrated for four sites, where clams from the same cohort were monitored during a transplant experiment. The model was then used to calculate CO2 fluxes resulting from respiration and shell calcification, taking into account CaCO3 stocked in the shell and CO2 emission. The findings show that KSH varied slightly among sites and that clams played a role as a moderate sink of CO2 over a whole year. CO2 fluxes were characterized by a seasonal variability: clams were net sources in wintertime and sinks in summer time, suggesting the need of accounting for seasonality and growth should shellfish farming be included in carbon markets.