The threat represented by ocean acidification (OA) for coral reef has received considerable attention because of the sensitivity of calcifiers to changing water carbonate chemistry. However most studies have focused on the organismic response of calcification to OA, and only a few have addressed community-level effects, or investigated parameters other than calcification, such as photosynthesis. Light (Photosynthetically Active Radiation, PAR) is a driver of biological processes on coral reefs, and the possibility that these processes might be perturbed by OA has important implications for community function. Here we investigate how CO<sub>2</sub> enrichment affects the relationships between PAR and community net O<sub>2</sub> production (<i>P</i><sub>net</sub>), and between PAR and community net calcification (<i>G</i><sub>net</sub>), using experiments on three coral communities constructed to match (i) the back reef of Moorea, French Polynesia, (ii) the fore reef of Moorea, and (iii) the reef flat of Oahu, Hawaii. The results were used to test the hypothesis that OA affects the relationship between <i>P</i><sub>net</sub> and <i>G</i><sub>net</sub>. For the three communities tested, pCO<sub>2</sub> did not affect the <i>P</i><sub>net</sub>-PAR relationship, but it affected the intercept of the hyperbolic tangent curve fitting the <i>G</i><sub>net</sub>-PAR relationship for both reef communities in Moorea (but not in Oahu). For the three communities, the slopes of the linear relationships between <i>P</i><sub>net</sub> and <i>G</i><sub>net</sub> were not affected by OA, although the intercepts were depressed by the inhibitory effect of high pCO<sub>2</sub> on <i>G</i><sub>net</sub>. Our result indicates that OA can modify the balance between net calcification and net photosynthesis of reef communities by depressing community calcification, but without affecting community photosynthesis.