Secondary calcification and dissolution respond differently to future ocean conditions@en

Climate change threatens both the accretion and erosion processes that sustain coral reefs. Secondary calcification, bioerosion, and reef dissolution are integral to the structural complexity and long-term persistence of coral reefs, yet these processes have received less research attention than reef accretion by corals. In this study, we use climate scenarios from RCP 8.5 to examine the combined effects of rising ocean acidity and sea surface temperature (SST) on both secondary calcification and dissolution rates of a natural coral rubble community using a flow-through aquarium system. We found that secondary reef calcification and dissolution responded differently to the combined effect of pCO2 and temperature. Calcification had a non-linear response to the combined effect of pCO2 and temperature: the highest calcification rate occurred slightly above ambient conditions and the lowest calcification rate was in the highest temperature-pCO2 condition. In contrast, dissolution increased linearly with temperature-pCO2 . The rubble community switched from net calcification to net dissolution at +271 µatm pCO2 and 0.75 °C above ambient conditions, suggesting that rubble reefs may shift from net calcification to net dissolution before the end of the century. Our results indicate that (i) dissolution may be more sensitive to climate change than calcification and (ii) that calcification and dissolution have different functional responses to climate stressors; this highlights the need to study the effects of climate stressors on both calcification and dissolution to predict future changes in coral reefs.气候变化正对维持珊瑚礁存续的造礁加积与侵蚀过程构成威胁。次级钙化作用（secondary calcification）、生物侵蚀作用（bioerosion）与礁体溶蚀作用（reef dissolution）是维持珊瑚礁结构复杂性与长期存续的核心过程，但相较于珊瑚介导的造礁加积作用，学界对上述过程的研究关注度仍相对不足。本研究采用典型浓度路径8.5（Representative Concentration Pathway 8.5, RCP 8.5）的气候情景，借助流水水族箱系统（flow-through aquarium system），探究海洋酸化加剧与海表温度（Sea Surface Temperature, SST）升高对自然珊瑚碎礁群落次级钙化速率与溶蚀速率的联合影响。研究发现，礁体次级钙化与溶蚀对二氧化碳分压（partial pressure of carbon dioxide, pCO2）与温度的联合响应存在显著差异：钙化作用对二者的联合响应呈非线性特征，最高钙化速率略高于环境基准条件，最低钙化速率则出现在温度与二氧化碳分压均最高的处理组中；与之相反，溶蚀速率则随温度与二氧化碳分压的升高呈线性增长趋势。当二氧化碳分压较基准升高271微大气压、温度较基准升高0.75℃时，珊瑚碎礁群落将从净钙化状态转为净溶蚀状态，这表明碎礁生态系统可能在本世纪末前完成从净钙化到净溶蚀的状态转换。本研究结果表明：其一，溶蚀作用对气候变化的敏感性或高于钙化作用；其二，钙化与溶蚀对气候胁迫因子（climate stressors）的功能响应模式存在显著差异。这一发现凸显了同时探究气候胁迫因子对钙化与溶蚀过程的影响，对精准预测未来珊瑚礁生态系统演变的必要性。