Calcification is not the Achilles' heel of cold-water corals in an acidifying ocean

Ocean acidification is thought to be a major threat to coral reefs: laboratory evidence and CO<inf>2</inf> seep research has shown adverse effects on many coral species, although a few are resilient. There are concerns that cold-water corals are even more vulnerable as they live in areas where aragonite saturation (?<inf>ara</inf>) is lower than in the tropics and is falling rapidly due to CO<inf>2</inf> emissions. Here, we provide laboratory evidence that net (gross calcification minus dissolution) and gross calcification rates of three common cold-water corals, Caryophyllia smithii, Dendrophyllia cornigera, and Desmophyllum dianthus, are not affected by pCO<inf>2</inf> levels expected for 2100 (pCO<inf>2 </inf>1058 ?atm, ?<inf>ara</inf> 1.29), and nor are the rates of skeletal dissolution in D. dianthus. We transplanted D. dianthus to 350 m depth (pH<inf>T</inf> 8.02; pCO<inf>2 </inf>448 ?atm, ?<inf>ara</inf> 2.58) and to a 3 m depth CO<inf>2</inf> seep in oligotrophic waters (pH<inf>T</inf> 7.35; pCO<inf>2 </inf>2879 ?atm, ?<inf>ara</inf> 0.76) and found that the transplants calcified at the same rates regardless of the pCO<inf>2</inf> confirming their resilience to acidification, but at significantly lower rates than corals that were fed in aquaria. Our combination of field and laboratory evidence suggests that ocean acidification will not disrupt cold-water coral calcification although falling aragonite levels may affect other organismal physiological and/or reef community processes.