Seawater carbonate chemistry, photosynthesis, respiration and calcification during experiments with scleractinian coral Stylophora pistillata, 2003

We show here that CO2 partial pressure (pCO2) and temperature significantly interact on coral physiology. The effects of increased pCO2 and temperature on photosynthesis, respiration and calcification rates were investigated in the scleractinian coral Stylophora pistillata. Cuttings were exposed to temperatures of 25°C or 28°C and to pCO2 values of ca. 460 or 760 muatm for 5 weeks. The contents of chlorophyll c2 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-pCO2' condition. The cell-specific density was higher at 'high pCO2' than at 'normal pCO2' (1.7 vs. 1.4). The net photosynthesis normalized per unit protein was affected by both temperature and pCO2, whereas respiration was not affected by the treatments. Calcification decreased by 50% when temperature and pCO2 were both elevated. Calcification under normal temperature did not change in response to an increased pCO2. 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 pCO2 reported in the literature, and warrants a re-evaluation of the projected decrease of marine calcification by the year 2100.

本研究证实，二氧化碳分压（pCO2）与温度对珊瑚生理过程存在显著交互作用。以造礁石珊瑚鹿角杯形珊瑚（Stylophora pistillata）为实验材料，本研究探究了升高的pCO2与温度对其光合速率、呼吸速率及钙化速率的影响。将珊瑚断枝分别置于25℃、28℃两个温度梯度，以及约460 μatm、760 μatm两个pCO2梯度下培养5周。实验全程中，叶绿素c2与蛋白质含量均保持稳定；而叶绿素a（chlorophyll a）含量显著受温度调控，在"高温高pCO2"组合条件下含量更高。珊瑚细胞密度在高pCO2条件下显著高于正常pCO2条件（分别为1.7与1.4）。以单位蛋白质归一化的净光合速率同时受温度与pCO2的调控，而呼吸速率则不受实验处理的影响。当温度与pCO2同时升高时，珊瑚钙化速率下降50%；而在正常温度条件下，pCO2升高并未对钙化速率产生显著影响。该结果与诸多已发表文献中提出的"海洋钙化与CO2呈负相关"的结论并不一致。温度的混杂效应或可解释文献中报道的钙化速率与pCO2之间关联的大量变异性，因此有必要重新评估到2100年海洋钙化速率的预测下降幅度。