Turf algal assemblages are ubiquitous primary producers on coral reefs, but little is known about the response of this diverse group to ocean acidification (OA) across different temperatures. We tested the hypothesis that CO 2 influences the functional response of epilithic and endolithic turf assemblages to increasing temperature. Replicate carbonate plugs covered by turf were collected from the reef and exposed to ambient and high p CO 2 (1000 µatm) conditions for 3 weeks. Each p CO 2 treatment was replicated across six temperatures (24.0–31.5 °C) that spanned the full seasonal temperature range on a fringing reef in Moorea, French Polynesia, and included one warming treatment (3 °C above daily average temperatures). Temperature and CO 2 enrichment had complex, and sometimes interactive, effects on turf metabolism and growth. Photosynthetic and respiration rates were enhanced by increasing temperature, with an interactive effect of CO 2 enrichment. Photosynthetic rates were amplified by high CO 2 in the warmest temperatures, while the increase in respiration rates with temperature were enhanced under ambient CO 2 . Epilithic turf growth rates were not affected by temperature, but increased in response to CO 2 enrichment. We found that CO 2 and temperature interactively affected the endolithic assemblage, with the highest growth rates under CO 2 enrichment, but only at the warmest temperatures. These results demonstrate how OA may influence algal physiology and growth across a range of ecologically relevant temperatures, and indicate that the effects of CO 2 enrichment on coral-reef turf assemblages can be temperature dependent. The complex effects of CO 2 enrichment and temperature across a suite of algal responses illustrates the importance of incorporating multiple stressors into global change experiments.