Seawater carbonate chemistry and endosymbiont density, photosynthesis and net calcification rates of reef-building coral Pocillopora damicornis

Ocean acidification is a growing threat to coral growth and the accretion of coral reef ecosystems. Corals inhabiting environments that already endure extreme diel pCO2 fluctuations, however, may represent acidification-resilient populations capable of persisting on future reefs. Here, we examined the impact of pCO2 variability on the reef-building coral Pocillopora damicornis originating from reefs with contrasting environmental histories (variable reef flat versus stable reef slope) following reciprocal exposure to stable (218 ± 9) or variable (911 ± 31) diel pCO2 amplitude (μtam) in aquaria over eight weeks. Endosymbiont density, photosynthesis and net calcification rates differed between origins but not treatment, whereas primary calcification (extension) was affected by both origin and acclimatization to novel pCO2 conditions. At the cellular level, corals from the variable reef flat exhibited less intracellular pH (pHi) acidosis and faster pHi recovery rates in response to experimental acidification stress (pH 7.40) than corals originating from the stable reef slope, suggesting environmental memory gained from lifelong exposure to pCO2 variability led to an improved ability to regulate acid–base homeostasis. These results highlight the role of cellular processes in maintaining acidification resilience and suggest that prior exposure to pCO2 variability may promote more acidification-resilient coral populations in a changing climate.

海洋酸化对珊瑚生长及珊瑚礁生态系统的形成构成日益严峻的威胁。然而，栖息于已长期承受极端昼夜pCO₂波动环境中的珊瑚，或许代表了具有酸化抗性（acidification-resilient）的种群，能够在未来的珊瑚礁中存续。本研究考察了pCO₂变异性对造礁珊瑚鹿角杯形珊瑚（Pocillopora damicornis）的影响——这些珊瑚来自环境历史迥异的珊瑚礁（可变礁坪 vs 稳定礁坡），并在水族箱中交互暴露于稳定（218±9）或可变（911±31）的昼夜pCO₂振幅（μatm）达八周。内共生体密度（endosymbiont density）、光合作用及净钙化速率（net calcification rate）在不同来源种群间存在差异，但不受处理条件影响；而初级钙化（primary calcification，延伸）则同时受来源种群及对新pCO₂条件的适应（acclimatization）影响。在细胞水平上，来自可变礁坪的珊瑚在实验酸化胁迫（pH 7.40）下，细胞内pH（intracellular pH, pHi）酸化程度更低，且pHi恢复速率更快，相比来自稳定礁坡的珊瑚；这表明，长期暴露于pCO₂变异性所获得的环境记忆（environmental memory）提升了其调节酸碱稳态（acid-base homeostasis）的能力。这些结果强调了细胞过程在维持酸化抗性中的核心作用，并提示预先暴露于pCO₂变异性或能在气候变化背景下促进更具酸化抗性的珊瑚种群的形成。