Blue mussels from the Baltic Sea grew less when raised for seven weeks under ocean acidification conditions and with limited food algae. Corrosion of the internal shell surface occurred at a range of ocean acidification levels when food supply was low. When food supply was high, corrosion occurred only in the two highest levels of ocean acidification. Both factors—food and acidification—significantly influenced the amount of shell corrosion. It is likely that when food is limited, mussels allocate their energy to more vital processes, such as reproduction, instead of shell growth or maintenance. (Laboratory study)