Seawater carbonate chemistry and coral calcification media pH@en

Ocean acidification typically reduces the calcification rates of massive Porites spp. corals, but increasing seawater temperatures (below the stress and bleaching threshold) can offset this effect. Here, we use delta 11B to reconstruct the pH of the calcification media (pHECM) used to precipitate the skeleton in poritid corals cultured over a range of seawater pCO2 and at 25 °C and 28 °C. Increasing temperature had no significant effect on pHECM at high pCO2 although corals increased their calcification rates. pHECM was reduced at 28 °C compared to 25 °C at low seawater pCO2, although calcification rates remained constant. Increasing calcification rates could reflect the positive influence of temperature on aragonite precipitation rate, an increase in calcification media saturation state or a change in the concentration/behaviour of the skeletal organic matrix. The two temperatures utilized in this study were within the seasonal range at the coral collection site and do not represent a heat stress scenario. Increasing seawater temperatures may promote calcification in some corals in the future but are unlikely to benefit the majority of corals, which are already living close to their maximum thermal tolerance limits.海洋酸化通常会降低团块滨珊瑚（Porites spp.）的钙化速率，但在未达到胁迫与白化阈值的前提下，海水温度升高可抵消这一效应。本研究利用硼同位素δ¹¹B（delta 11B），对在一系列海水二氧化碳分压（pCO₂）条件下、分别于25℃与28℃环境中养殖的滨珊瑚科珊瑚（poritid corals）中用于骨骼沉积的钙化介质pH（pHECM）进行了重建。在高pCO₂条件下，尽管珊瑚钙化速率有所提升，但温度升高对pHECM无显著影响。在低海水pCO₂条件下，相较于25℃，28℃环境中的pHECM有所降低，但钙化速率保持稳定。钙化速率的提升，可能反映了温度对文石沉积速率的正向作用、钙化介质饱和状态的提升，或是骨骼有机基质浓度与行为的改变。本研究采用的两个温度均处于珊瑚采集地的季节温度区间内，并未构成热胁迫情境。未来海水升温或可促进部分珊瑚的钙化过程，但对于多数已处于最大热耐受极限附近的珊瑚而言，升温难以使其获益。