Shell formation in cultivated bivalves cannot be part of carbon trading systems: a study case with Mytilus galloprovincialis

Respiration and calcium carbonate (CaCO3) production by the farmed Mediterranean mussel Mytilus galloprovincialis were calculated to assess their importance as carbon dioxide (CO2) sink/source in the Sacca di Scardovari (Po Delta River, Italy). The ratio of CO2 released to CaCO3 precipitated was calculated as a function of the near-bottom temperature. From our estimates, M. galloprovincialis sequestered 136.6 molCO2 m−2 year−1 for shell formation, but the CO2 fluxes due to respiration and calcification resulted 187.8 and 86.8 molCO2 m−2 year−1 respectively. Mussel farming seems therefore to be a significant additional source of CO2 to seawater. For this reason shell formation in cultivated shellfish cannot be part of carbon trading systems.