Seawater carbonate chemistry and changes in the sources of carbon for calcification of Caribbean Coral@en

It is thought that the active physiological regulation of the chemistry of a parent fluid is an important process in the biomineralization of scleractinian corals. Biological regulation of calcification fluid pH (pHCF) and other carbonate chemistry parameters ([CO32−]CF, DICCF, and ΩCF) may be challenged by CO2 driven acidification and temperature. Here, we examine the combined influence of changing temperature and CO2 on calcifying fluid regulation in four common Caribbean coral species—Porites astreoides, Pseudodiploria strigosa, Undaria tenuifolia, and Siderastrea siderea. We utilize skeletal boron geochemistry (B/Ca and δ11B) to probe the pHCF, [CO32−]CF, and DICCF regulation in these corals, and δ13C to track changes in the sources of carbon for calcification. Temperature was found to not influence pHCF regulation across all pCO2 treatments in these corals, in contrast to recent studies on Indo-Pacific pocilloporid corals. We find that [DIC]CF is significantly lower at higher temperatures in all the corals, and that the higher temperature was associated with depletion of host energy reserves, suggesting [DIC]CF reductions may result from reduced input of respired CO2 to the DIC pool for calcification. In addition, δ13C data suggest that under high temperature and CO2 conditions, algal symbiont photosynthesis continues to influence the calcification pool and is associated with low [DIC]CF in P. strigosa and P. astreoides. In P. astreoides this effect is also associated with an increase in chlorophyll a concentration in coral tissues at higher temperatures. These observations collectively support the assertion that physicochemical control over coral calcifying fluid chemistry is coupled to host and symbiont physiological responses to environmental change, and reveals interspecific differences in the extent and nature of this coupling.人们普遍认为，母体流体化学的主动生理调控是石珊瑚（scleractinian corals）生物矿化过程中的关键环节。钙化液pH（pHCF）及其他碳酸盐化学参数（[CO₃²⁻]CF、DICCF与ΩCF）的生物学调控，可能会受到CO₂驱动的酸化与升温的挑战。本研究针对四种常见加勒比海珊瑚物种——Porites astreoides、Pseudodiploria strigosa、Undaria tenuifolia与Siderastrea siderea——探讨了温度与CO₂分压变化对其钙化液调控的综合影响。我们采用骨骼硼地球化学方法（B/Ca比值与δ¹¹B同位素），探究这些珊瑚的pHCF、[CO₃²⁻]CF与DICCF调控机制，并通过δ¹³C同位素示踪钙化作用的碳来源变化。研究发现，与近期针对印度-太平洋杯形珊瑚科珊瑚的研究结果不同，在所有CO₂分压处理组中，温度并未对这些珊瑚的pHCF调控产生影响。我们观察到，所有珊瑚的[DIC]CF均在高温条件下显著降低，且高温与宿主能量储备耗竭相关，这表明[DIC]CF的降低可能源于用于钙化的DIC库中呼吸释放CO₂的输入量减少。此外，δ¹³C同位素数据表明，在高温与高CO₂环境下，藻类共生体的光合作用仍会对钙化池产生影响，且与P. strigosa和P. astreoides较低的[DIC]CF相关。在P. astreoides中，这一效应还与高温条件下珊瑚组织内叶绿素a浓度升高有关。上述观测结果共同支持了"珊瑚钙化液化学的物理化学调控与宿主及共生体对环境变化的生理响应紧密耦合"这一论断，并揭示了这种耦合的程度与本质存在种间差异。