Coral and mollusc resistance to ocean acidification adversely affected by warming, 2011

Increasing atmospheric carbon dioxide (CO2) concentrations are expectedto decrease surface ocean pH by 0.3-0.5 units by 2100, lowering the carbonate ion concentration of surfacewaters. This rapid acidification is predicted to dramatically decrease calcification in many marine organisms. Reduced skeletal growth under increased CO2 levels has already been shown for corals, molluscs and many other marine organisms. The impact of acidification on the ability of individual species to calcify has remained elusive, however, as measuring net calcification fails to disentangle the relative contributions of gross calcification and dissolution rates on growth. Here, we show that corals and molluscs transplanted along gradients of carbonate saturation state at Mediterranean CO2 vents are able to calcify and grow at even faster than normal rates when exposed to the high CO2 levels projected for the next 300 years. Calcifiers remain at risk, however, owing to the dissolution of exposed shells and skeletons that occurs as pH levels fall. Our results show that tissues and external organic layers play a major role in protecting shells and skeletons from corrosive sea water, limiting dissolution and allowing organisms to calcify. Our combined field and laboratory results demonstrate that the adverse effects of global warming are exacerbated when high temperatures coincide with acidification.

预计到2100年，大气二氧化碳（CO₂）浓度升高将使表层海水pH值下降0.3~0.5个单位，进而降低表层海水的碳酸根离子浓度。这种快速的海洋酸化被预测会显著抑制多数海洋生物的钙化作用。已有研究证实，在CO₂浓度升高的环境中，珊瑚、软体动物及诸多其他海洋生物的骨骼生长已出现减缓。然而，由于净钙化量的测定无法区分总钙化速率与溶解速率对生物生长的相对贡献，酸化对单个物种钙化能力的影响迄今仍不明确。本研究通过在地中海CO₂喷口区沿碳酸根饱和度梯度开展移植实验，发现当暴露于未来300年预估的高CO₂浓度环境时，珊瑚与软体动物的钙化及生长速率甚至高于正常水平。但由于pH值下降会导致暴露在外的贝壳与骨骼发生溶解，钙化生物仍面临生存风险。本研究结果表明，生物组织与外部有机层在保护贝壳及骨骼免受腐蚀性海水侵蚀、抑制溶解并保障生物正常钙化方面发挥着关键作用。结合野外与实验室的综合实验结果证实，当高温与酸化同时发生时，全球变暖的负面影响会进一步加剧。