The rise of CO 2 has been identified as a major threat to life in the ocean. About one-third of the anthro-pogenic CO 2 produced in the last 200 yr has been taken up by the ocean, leading to ocean acidification. Surface seawater pH is projected to decrease by about 0.4 units between the pre-industrial revolution and 2100. The branching cold-water corals Madrepora oculata and Lophelia pertusa are important, habitat-forming species in the deep Mediter-ranean Sea. Although previous research has investigated the abundance and distribution of these species, little is known regarding their ecophysiology and potential responses to global environmental change. A previous study indicated that the rate of calcification of these two species remained constant up to 1000 µatm CO 2 , a value that is at the upper end of changes projected to occur by 2100. We examined whether the ability to maintain calcification rates in the face of rising pCO 2 affected the energetic requirements of these corals. Over the course of three months, rates of respiration were measured at a pCO 2 ranging between 350 and 1100 µatm to distinguish between short-term response and longer-term acclimation. Respiration rates ranged from 0.074 to 0.266 µmol O 2 (g skeletal dry weight) −1 h −1 and 0.095 to 0.725 µmol O 2 (g skeletal dry weight) −1 h −1 for L. pertusa and M. oculata, respectively, and were independent of pCO 2. Respiration increased with time likely due to regular feeding, which may have provided an increased energy supply to sustain coral metabolism. Future studies are needed to confirm whether the insensitivity of respiration to increasing pCO 2 is a general feature of deep-sea corals in other regions.