Combined geochemical tracer (δ11B, B/Ca, δ18O, Δ47) constraints on the environment of biocalcification in common Caribbean shallow water corals grown under varying pCO2 and temperature

• Main Author: DeCorte, Ilian Antoine
• Other Authors: Eagle, Robert A
• Format: Thesis
• Language: English
• Published: eScholarship, University of California 2020
• Subjects: Biogeochemistry; Climate change; Biological oceanography; Aragonite; Boron isotope; Calcification; Clumped isotope; Coral; Ocean acidification
• Online Access: https://escholarship.org/uc/item/26k286g2; https://escholarship.org/content/qt26k286g2/qt26k286g2.pdf

The mechanisms by which tropical hermatypic corals biomineralize to build aragonite skeletal material has received increased attention in recent years, but uncertainties remain regarding the relative importance of different biomineralization processes. In particular, the biological modification of a semi-isolated calcification fluid pH (pHCF) and other carbonate chemistry parameters ([CO32-]CF, DICCF, and ΩAR-CF) within an extra-cellular calcifying space may be critical to facilitate biomineralization, and thus, a determining factor for coral growth responses to anthropogenic carbon dioxide induced reductions in seawater pH and aragonite saturation state (ΩAR). The extent to which a coral’s inability to compensate for external seawater carbonate chemistry changes govern coral calcification responses to ocean acidification and temperature stress remains debated. This work builds on a prior study by Bove et al. (2019) that tested the calcification responses of four common Caribbean coral species - Porites astreoides, Psuedodiploria strigosa, Undaria tenuifolia, and Siderastrea siderea - under a range of experimental pCO2 and temperature culture conditions. We utilize skeletal boron geochemistry (B/Ca and δ11B) to probe the pHCF, [DIC]CF, and ΩAR-CF regulation in these corals, finding evidence for modest declines in pHCF but stable or increasing [DIC]CF across increasing seawater pCO2 treatments, with subtle variations in responses between species as well as subtle differences between temperature treatments. Combining our results with boron-isotope, pH-microprobe and pH-sensitive dye data from the literature on scleractinian corals reveals that almost all studied species show evidence of pHCF buffering against changes in external seawater pH (pHSW) but that, in many cases, this compensation is imperfect (i.e. pHCF is not maintained at a constant level across all pHSW conditions). In total, these data suggest that corals do invest additional energy into actively regulating pHCF in high CO2 conditions but that ...