Comparison of control pCO2 treatments of M. edulis growth trials conducted in our laboratory.

The summer and autumn experiments lasted 8 weeks [10], [15], the present winter experiment 7 weeks. Filtration rates were calculated for a standard 18 mm mussel (see methods) to illustrate the impact of temperature dependent changes in seawater viscosity. As M. edulis has a retention rate of ca. 100% for particles with a diameter >4 µm, reduced filtration rates at low temperatures directly translate into reduced energy uptake, even if aquarium algae concentrations are similar. See Methods for calculation of filtration rates in response to seawater viscosity. Means and standard deviations (in brackets). Shell length growth corresponds to growth during the entire experimental period of the respective experiments. Cell density refers to the average Rhodomonas cell density in the experimental aquaria. Ωarag refers to the aragonite saturation states in the experimental aquaria.