title: Coralline algae elevate pH at the site of calcification under ocean acidification.
abstract: Coralline algae provide important ecosystem services but are susceptible to the impacts of ocean acidification. However, the mechanisms are uncertain, and the magnitude is species specific. Here, we assess whether species-specific responses to ocean acidification of coralline algae are related to differences in pH at the site of calcification within the calcifying fluid/medium (pHcf) using δ11B as a proxy. Declines in δ11B for all three species are consistent with shifts in δ11B expected if B(OH)4-was incorporated during precipitation. In particular, the δ11B ratio in Amphiroa anceps was too low to allow for reasonable pHcfvalues if B(OH)3rather than B(OH)4-was directly incorporated from the calcifying fluid. This points towards δ11B being a reliable proxy for pHcffor coralline algal calcite and that if B(OH)3is present in detectable proportions, it can be attributed to secondary postincorporation transformation of B(OH)4-. We thus show that pHcfis elevated during calcification and that the extent is species specific. The net calcification of two species of coralline algae (Sporolithon durum, and Amphiroa anceps) declined under elevated CO2, as did their pHcf. Neogoniolithon sp. had the highest pHcf, and most constant calcification rates, with the decrease in pHcfbeing ¼ that of seawater pH in the treatments, demonstrating a control of coralline algae on carbonate chemistry at their site of calcification. The discovery that coralline algae upregulate pHcfunder ocean acidification is physiologically important and should be included in future models involving calcification.
authors.affiliation: School of Earth Sciences and Oceans Institute, The University of Western Australia, Crawley, WA, Australia.|ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, WA, Australia.
authors.forename: Christopher E
authors.identifier: 0000-0002-6154-4082
authors.initials: CE
authors.lastname: Cornwall
authors.affiliation: School of Earth Sciences and Oceans Institute, The University of Western Australia, Crawley, WA, Australia.|ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, WA, Australia.
authors.forename: Steeve
authors.initials: S
authors.lastname: Comeau
authors.affiliation: School of Earth Sciences and Oceans Institute, The University of Western Australia, Crawley, WA, Australia.|ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, WA, Australia.
authors.forename: Malcolm T
authors.initials: MT
authors.lastname: McCulloch
mesh_terms: D002118:Calcium / Q000502:physiology*; D057894:Coral Reefs; D006863:Hydrogen-Ion Concentration; D009792:Oceans and Seas; D000461:Rhodophyta; D012623:Seawater
chemical_list: D002118:Calcium
keywords: boron isotopes; calcification; coralline algae; ocean acidification; pH upregulation