Ocean acidification and associated changes in seawater carbonate chemistry negatively influence calcification processes and depress metabolism in many calcifying marine invertebrates. We present data on the cephalopod mollusc Sepia officinalis, an invertebrate that is capable of not only maintaining calcification, but also growth rates and metabolism when exposed to elevated par- tial pressures of carbon dioxide (pCO2). During a 6 wk period, juvenile S. officinalis maintained cal- cification under ~4000 and ~6000 ppm CO2, and grew at the same rate with the same gross growth efficiency as did control animals. They gained approximately 4% body mass daily and increased the mass of their calcified cuttlebone by over 500%. We conclude that active cephalopods possess a cer- tain level of pre-adaptation to long-term increments in carbon dioxide levels. Our general under- standing of the mechanistic processes that limit calcification must improve before we can begin to predict what effects future ocean acidification will have on calcifying marine invertebrates.