Seawater carbonate chemistry and biological processes during experiments with temperate coral Cladocora caespitosa, 2010

Atmospheric CO2 partial pressure (pCO2) is expected to increase to 700 µatm or more by the end of the present century. Anthropogenic CO2 is absorbed by the oceans, leading to decreases in pH and the CaCO3 saturation state of the seawater. Elevated pCO2 was shown to drastically decrease calcification rates in tropical zooxanthellate corals. Here we show, using the Mediterranean zooxanthellate coral Cladocora caespitosa, that an increase in pCO2, in the range predicted for 2100, does not reduce its calcification rate. Therefore, the conventional belief that calcification rates will be affected by ocean acidification may not be widespread in temperate corals. Seasonal change in temperature is the predominant factor controlling photosynthesis, respiration, calcification and symbiont density. An increase in pCO2, alone or in combination with elevated temperature, had no significant effect on photosynthesis, photosynthetic efficiency and calcification. The lack of sensitivity C. caespitosa to elevated pCO2 might be due to its slow growth rates, which seem to be more dependent on temperature than on the saturation state of calcium carbonate in the range projected for the end of the century.

大气二氧化碳分压（pCO2）预计将在本世纪末升至700微大气压（µatm）及以上。人为排放的二氧化碳被海洋吸收后，会导致海水pH值与碳酸钙（CaCO3）饱和状态下降。已有研究证实，高浓度pCO2会显著降低热带虫黄藻共生珊瑚的钙化速率。本研究以地中海虫黄藻共生珊瑚丛生筒星珊瑚（Cladocora caespitosa）为实验材料，结果显示：当pCO2升高至2100年预测的浓度范围时，该珊瑚的钙化速率并未出现下降。因此，"海洋酸化将影响钙化速率"这一传统认知，在温带珊瑚中未必具有普适性。温度的季节变化是调控光合作用、呼吸作用、钙化速率及共生体密度的主导因素。单独升高pCO2，或同时升高温度与pCO2，均对光合作用、光合效率及钙化速率无显著影响。丛生筒星珊瑚（C. caespitosa）对高浓度pCO2缺乏敏感性，这一现象可能源于其缓慢的生长速率：相较于本世纪末预测范围内的碳酸钙饱和状态，其生长速率似乎更依赖于温度变化。