Environmental parameters and carbonate chemistry for the five different treatments during the course of the experiment (mean ± SD).

The partial pressure of CO2 (pCO2), dissolved inorganic carbon concentration (CT) as well as the saturation state of seawater with respect to aragonite and calcite (Ωa and Ωc respectively) were computed from pHT and total alkalinity (AT).*: Ωa and Ωc were increased by addition of calcium (CaCl2-2H2O; ×2.6 in situ Ca2+ concentrations).