Seawater carbonate chemistry and net calcification during experiments with coral communities, 2009@en

Acidification of seawater owing to oceanic uptake of atmospheric CO2 originating from human activities such as burning of fossil fuels and land-use changes has raised serious concerns regarding its adverse effects on corals and calcifying communities. Here we demonstrate a net loss of calcium carbonate (CaCO3) material as a result of decreased calcification and increased carbonate dissolution from replicated subtropical coral reef communities (n=3) incubated in continuous-flow mesocosms subject to future seawater conditions. The calcifying community was dominated by the coral Montipora capitata. Daily average community calcification or Net Ecosystem Calcification (NEC=CaCO3 production - dissolution) was positive at 3.3 mmol CaCO3 m-2 h-1 under ambient seawater pCO2 conditions as opposed to negative at -0.04 mmol CaCO3 m-2 h-1 under seawater conditions of double the ambient pCO2. These experimental results provide support for the conclusion that some net calcifying communities could become subject to net dissolution in response to anthropogenic ocean acidification within this century. Nevertheless, individual corals remained healthy, actively calcified (albeit slower than at present rates), and deposited significant amounts of CaCO3 under the prevailing experimental seawater conditions of elevated pCO2.由化石燃料燃烧、土地利用变化等人类活动产生的大气二氧化碳被海洋吸收后引发的海水酸化，已引发学界对其危害珊瑚与钙化群落的严重关切。本研究通过在模拟未来海水环境的连续流中型围隔实验系统（mesocosms）中培育三组重复亚热带珊瑚礁群落（n=3），观测到因钙化作用减弱、碳酸盐溶蚀加剧所导致的碳酸钙（calcium carbonate, CaCO₃）净流失现象。该钙化群落以头状微孔珊瑚（Montipora capitata）为优势物种。在环境海水二氧化碳分压（pCO₂）条件下，群落日均钙化速率即净生态系统钙化速率（Net Ecosystem Calcification, NEC，计算公式为NEC=CaCO₃生成量-溶蚀量）为正值，达3.3 mmol CaCO₃ m⁻² h⁻¹；而在两倍环境pCO₂的海水条件下，该速率为负值，为-0.04 mmol CaCO₃ m⁻² h⁻¹。本实验结果佐证了如下结论：本世纪内，部分净钙化群落可能因人为海洋酸化而转变为净溶蚀状态。尽管如此，在实验所用的高pCO₂海水环境中，单个珊瑚仍保持健康状态，仍能主动进行钙化作用（尽管速率较当前水平有所下降），并沉积了大量碳酸钙。