I tested the hypothesis that high pCO2 (76.6 Pa and 87.2 Pa vs. 42.9 Pa) has no effect on the metabolism of juvenile massive Porites spp. after 11 days at 28 °C and 545 μmol quanta m−2 s−1. The response was assessed as aerobic dark respiration, skeletal weight (i.e., calcification), biomass, and chlorophyll fluorescence. Corals were collected from the shallow (3–4 m) back reef of Moorea, French Polynesia (17°28.614′S, 149°48.917′W), and experiments conducted during April and May 2011. An increase in pCO2 to 76.6 Pa had no effect on any dependent variable, but 87.2 Pa pCO2 reduced area-normalized (but not biomass-normalized) respiration 36 %, as well as maximum photochemical efficiency (F v/F m) of open RCIIs and effective photochemical efficiency of RCIIs in actinic light (∆F/ $$ F_{\text{m}}^{\prime } $$ ); neither biomass, calcification, nor the energy expenditure coincident with calcification (J g−1) was effected. These results do not support the hypothesis that high pCO2 reduces coral calcification through increased metabolic costs and, instead, suggest that high pCO2 causes metabolic depression and photochemical impairment similar to that associated with bleaching. Evidence of a pCO2 threshold between 76.6 and 87.2 Pa for inhibitory effects on respiration and photochemistry deserves further attention as it might signal the presence of unpredictable effects of rising pCO2.