title: pH homeostasis during coral calcification in a free ocean CO2 enrichment (FOCE) experiment, Heron Island reef flat, Great Barrier Reef.
abstract: Geochemical analyses (δ(11)B and Sr/Ca) are reported for the coral Porites cylindrica grown within a free ocean carbon enrichment (FOCE) experiment, conducted on the Heron Island reef flat (Great Barrier Reef) for a 6-mo period from June to early December 2010. The FOCE experiment was designed to simulate the effects of CO2-driven acidification predicted to occur by the end of this century (scenario RCP4.5) while simultaneously maintaining the exposure of corals to natural variations in their environment under in situ conditions. Analyses of skeletal growth (measured from extension rates and skeletal density) showed no systematic differences between low-pH FOCE treatments (ΔpH = ∼-0.05 to -0.25 units below ambient) and present day controls (ΔpH = 0) for calcification rates or the pH of the calcifying fluid (pHcf); the latter was derived from boron isotopic compositions (δ(11)B) of the coral skeleton. Furthermore, individual nubbins exhibited near constant δ(11)B compositions along their primary apical growth axes (±0.02 pHcf units) regardless of the season or treatment. Thus, under the highly dynamic conditions of the Heron Island reef flat, P. cylindrica up-regulated the pH of its calcifying fluid (pHcf ∼8.4-8.6), with each nubbin having near-constant pHcf values independent of the large natural seasonal fluctuations of the reef flat waters (pH ∼7.7 to ∼8.3) or the superimposed FOCE treatments. This newly discovered phenomenon of pH homeostasis during calcification indicates that coral living in highly dynamic environments exert strong physiological controls on the carbonate chemistry of their calcifying fluid, implying a high degree of resilience to ocean acidification within the investigated ranges.
authors.affiliation: School of Earth and Environment, The University of Western Australia, Crawley, WA 6009, Australia; Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, WA 6009, Australia; lucy.georgiou@research.uwa.edu.au.
authors.forename: Lucy
authors.initials: L
authors.lastname: Georgiou
authors.affiliation: School of Earth and Environment, The University of Western Australia, Crawley, WA 6009, Australia; Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, WA 6009, Australia;
authors.forename: James
authors.initials: J
authors.lastname: Falter
authors.affiliation: School of Earth and Environment, The University of Western Australia, Crawley, WA 6009, Australia;
authors.forename: Julie
authors.initials: J
authors.lastname: Trotter
authors.affiliation: School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia;
authors.forename: David I
authors.initials: DI
authors.lastname: Kline
authors.affiliation: School of Earth and Environment, The University of Western Australia, Crawley, WA 6009, Australia; Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, WA 6009, Australia;
authors.forename: Michael
authors.initials: M
authors.lastname: Holcomb
authors.affiliation: School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia; ARC Centre of Excellence in Coral Reef Studies, University of Queensland, St. Lucia, QLD 4072, Australia; Global Change Institute, University of Queensland, St. Lucia, QLD 4072, Australia.
authors.forename: Sophie G
authors.initials: SG
authors.lastname: Dove
authors.affiliation: School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia; ARC Centre of Excellence in Coral Reef Studies, University of Queensland, St. Lucia, QLD 4072, Australia; Global Change Institute, University of Queensland, St. Lucia, QLD 4072, Australia.
authors.forename: Ove
authors.initials: O
authors.lastname: Hoegh-Guldberg
authors.affiliation: School of Earth and Environment, The University of Western Australia, Crawley, WA 6009, Australia; Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, WA 6009, Australia;
authors.forename: Malcolm
authors.initials: M
authors.lastname: McCulloch
mesh_terms: D001895:Boron / Q000032:analysis; D002113:Calcification, Physiologic / Q000502:physiology*; D002245:Carbon Dioxide / Q000737:chemistry; D057894:Coral Reefs; D006706:Homeostasis / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D010140:Pacific Ocean; D011793:Queensland
chemical_list: D002245:Carbon Dioxide; D001895:Boron
keywords: FOCE; Heron Island; coral resilience; ocean acidification; pH up-regulation