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.

到本世纪末，大气二氧化碳分压（pCO2，partial pressure of CO2）预计将升至700微大气压（µatm）及以上。人为源二氧化碳被海洋吸收，导致海水pH值与碳酸钙（CaCO3）饱和态下降。已有研究表明，升高的pCO2会显著降低虫黄藻共生热带珊瑚的钙化速率。本研究以地中海虫黄藻共生珊瑚——团块枝管珊瑚（Cladocora caespitosa）为实验材料，结果显示：在2100年预测的pCO2升高范围内，该珊瑚的钙化速率并未出现下降。因此，"钙化速率将受海洋酸化影响"这一传统认知，并非普遍适用于温带珊瑚。温度的季节性波动是调控光合作用、呼吸作用、钙化过程以及共生体密度的主导因素。单独升高pCO2，或其与升温联合作用，均未对光合作用、光合效率及钙化过程产生显著影响。团块枝管珊瑚对升高的pCO2缺乏敏感性，这可能与其缓慢的生长速率有关：相较于本世纪末预估的碳酸钙饱和态变化范围，其生长速率似乎更依赖于温度，而非碳酸钙饱和态。