Seawater carbonate chemistry and calcification rate, net photosynthesis and respiration rate of reef-building corals

Coral reefs are deteriorating under climate change as oceans continue to warm and acidify and thermal anomalies grow in frequency and intensity. In vitro experiments are widely used to forecast reef-building coral health into the future, but often fail to account for the complex ecological and biogeochemical interactions that govern reefs. Consequently, observations from coral communities under naturally occurring extremes have become central for improved predictions of future reef form and function. Here, we present a semi-enclosed lagoon system in New Caledonia characterised by diel fluctuations of hot-deoxygenated water coupled with tidally driven persistently low pH, relative to neighbouring reefs. Coral communities within the lagoon system exhibited high richness (number of species=20) and cover (24-35% across lagoon sites). Calcification rates for key species (Acropora formosa, Acropora pulchra, Coelastrea aspera and Porites lutea) for populations from the lagoon were equivalent to, or reduced by ca. 30-40% compared to those from the reef. Enhanced coral respiration, alongside high particulate organic content of the lagoon sediment, suggests acclimatisation to this trio of temperature, oxygen and pH changes through heterotrophic plasticity. This semi-enclosed lagoon therefore provides a novel system to understand coral acclimatisation to complex climatic scenarios and may serve as a reservoir of coral populations already resistant to extreme environmental conditions.

气候变化背景下，海洋持续增温、酸化，热异常事件的发生频率与强度不断提升，珊瑚礁生态系统正逐步退化。体外实验被广泛用于预测造礁珊瑚的未来健康状况，但这类实验往往无法考量调控珊瑚礁生态的复杂生态学与生物地球化学相互作用过程。因此，针对自然极端环境下珊瑚群落的观测数据，已成为优化未来珊瑚礁形态与功能预测的核心依据。本研究介绍了新喀里多尼亚的一处半封闭泻湖系统：相较于邻近珊瑚礁，该泻湖内存在高温低氧水体的昼夜波动，且受潮汐驱动持续维持低pH环境。该泻湖系统内的珊瑚群落物种丰富度较高（共计20种），各站点的珊瑚覆盖度介于24%至35%之间。针对泻湖种群的关键珊瑚物种（花鹿角珊瑚*Acropora formosa*、美丽鹿角珊瑚*Acropora pulchra*、粗糙棘星珊瑚*Coelastrea aspera*及团块滨珊瑚*Porites lutea*），其钙化速率与邻近礁体种群相当，或最高降低约30%-40%。珊瑚呼吸作用增强，加之泻湖沉积物中颗粒有机物含量较高，表明这些珊瑚通过异养可塑性，对温度、溶氧与pH的三重变化产生了生理驯化。因此，这座半封闭泻湖为研究珊瑚对复杂气候情景的驯化过程提供了全新的实验系统，同时也可作为已适应极端环境的珊瑚种群的庇护库。