Interacting effects of CO2 partial pressure and temperature on photosynthesis and calcification in a scleractinian coral

We show here that CO2 partial pressure (pCO(2)) and temperature significantly interact on coral physiology. The effects of increased pCO(2) and temperature on photosynthesis, respiration and calcification rates were investigated in the scleractinian coral Stylophora pistillata. Cuttings were exposed to temperatures of 25degreesC or 28degreesC and to pCO(2) values of ca. 460 or 760 muatm for 5 weeks. The contents of chlorophyll c(2) and protein remained constant throughout the experiment, while the chlorophyll a content was significantly affected by temperature, and was higher under the 'high-temperature-high-pCO(2)' condition. The cell-specific density was higher at 'high pCO(2)' than at 'normal pCO(2)' (1.7 vs. 1.4). The net photosynthesis normalized per unit protein was affected by both temperature and pCO(2), whereas respiration was not affected by the treatments. Calcification decreased by 50% when temperature and pCO(2) were both elevated. Calcification under normal temperature did not change in response to an increased pCO(2). This is not in agreement with numerous published papers that describe a negative relationship between marine calcification and CO2. The confounding effect of temperature has the potential to explain a large portion of the variability of the relationship between calcification and pCO(2) reported in the literature, and warrants a re-evaluation of the projected decrease of marine calcification by the year 2100.