Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation: Boron Isotopes: The Fifth Element

Malcolm T. McCulloch, Juan Pablo D’Olivo, James Falter, Lucy Georgiou, Michael Holcomb, Paolo Montagna, Julie A. Trotter

Research output: Chapter in Book/Conference paperChapter

Abstract

The boron isotopic composition (δ11B) of scleractinian corals has been used to track changes in seawater pH and more recently as a probe into the processes controlling bio-calcification. For corals that precipitate aragonite skeletons, up-regulation of pH appears to be a general characteristic, typically being ~0.3 to ~0.6 pH units higher than ambient seawater. The relationship between the pH of the corals calcifying-fluid (pHcf) and seawater pHT (total scale) is shown to be dependent on both physiological as well environmental factors. In laboratory experiments conducted on symbiont-bearing (zooxanthellate) corals under conditions of constant temperature and seawater pH, changes in the δ11B derived calcifying fluid pHcf is typically 1/3 to 1/2 of that of ambient seawater. Similar linear relationships are found for cold water corals that live in relatively stable, cold, deep-water environments but at significantly elevated levels of pHcf (~0.5–1 pH units above seawater), a likely response to the lower pH of their deep-sea environments. In contrast, zooxanthellae-bearing corals living in shallow-water reef environments that experience significant natural variations in temperature, light, nutrients and seawater pH, show different types of responses. For example, over seasonal time-scales Porites corals from the Great Barrier Reef (GBR) have a large range in pHcf of ~8.3 to ~8.5, significantly greater (~×2 to ~×3) than that of reef-water (pHT ~8.01 to ~8.08), and an order of magnitude greater than that expected from ‘static’ laboratory experiments. Strong physiological controls, but of a different character, are found in corals grown in a Free Ocean Carbon Enrichment Experiment (FOCE) conducted in situ within the Heron Island lagoon (GBR). These corals exhibit near constant pHcf values regardless of external changes in temperature and seawater pH. This pattern of strong physiologically controlled ‘pH-homeostasis’, with elevated but constant pHcf has been found despite large natural seasonal variations in the pH (±0.15 pH units) of the lagoon waters, as well as the even larger super-imposed decreases in seawater pH (~0.25 pH units) designed to simulate year 2100 conditions. In natural reef environments we thus find that the processes influencing the up-regulation of pHcf in symbiont-bearing corals are subject to strong physiological controls, behaviour that is not well simulated in the current generation of aquaria-based experiments with fixed seawater pH and temperature. Conversely, cold-water corals that lack symbionts and inhabit the relatively stable deep-sea environments hold the best prospects for providing reliable reconstructions of seawater pH. Clearly, further studies utilising the δ11B-pHcf proxy combined with other DIC/carbonate-ion proxies (e.g. B/Ca), but conducted under realistic ‘natural’ conditions, are required to elucidate the processes controlling coral bio-calcification and to better understand the vulnerability of scleractinian corals to anthropogenic driven warming and ocean acidification.
Original languageEnglish
Title of host publicationBoron Isotopes: The Fifth Element
EditorsHorst Marschall, Gavin Foster
Place of PublicationCham
PublisherSpringer International Publishing AG
Pages145-162
Number of pages18
ISBN (Print)9783319646664
DOIs
Publication statusPublished - 2018

Publication series

NameAdvances in Isotope Geochemistry

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boron isotope
boron
coral
seawater
fluid
symbiont
regulation
reef
calcification
barrier reef
cold water
deep sea
lagoon
temperature

Cite this

McCulloch, M. T., D’Olivo, J. P., Falter, J., Georgiou, L., Holcomb, M., Montagna, P., & Trotter, J. A. (2018). Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation: Boron Isotopes: The Fifth Element. In H. Marschall, & G. Foster (Eds.), Boron Isotopes: The Fifth Element (pp. 145-162). (Advances in Isotope Geochemistry). Cham: Springer International Publishing AG. https://doi.org/10.1007/978-3-319-64666-4_6
McCulloch, Malcolm T. ; D’Olivo, Juan Pablo ; Falter, James ; Georgiou, Lucy ; Holcomb, Michael ; Montagna, Paolo ; Trotter, Julie A. / Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation : Boron Isotopes: The Fifth Element. Boron Isotopes: The Fifth Element. editor / Horst Marschall ; Gavin Foster. Cham : Springer International Publishing AG, 2018. pp. 145-162 (Advances in Isotope Geochemistry).
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abstract = "The boron isotopic composition (δ11B) of scleractinian corals has been used to track changes in seawater pH and more recently as a probe into the processes controlling bio-calcification. For corals that precipitate aragonite skeletons, up-regulation of pH appears to be a general characteristic, typically being ~0.3 to ~0.6 pH units higher than ambient seawater. The relationship between the pH of the corals calcifying-fluid (pHcf) and seawater pHT (total scale) is shown to be dependent on both physiological as well environmental factors. In laboratory experiments conducted on symbiont-bearing (zooxanthellate) corals under conditions of constant temperature and seawater pH, changes in the δ11B derived calcifying fluid pHcf is typically 1/3 to 1/2 of that of ambient seawater. Similar linear relationships are found for cold water corals that live in relatively stable, cold, deep-water environments but at significantly elevated levels of pHcf (~0.5–1 pH units above seawater), a likely response to the lower pH of their deep-sea environments. In contrast, zooxanthellae-bearing corals living in shallow-water reef environments that experience significant natural variations in temperature, light, nutrients and seawater pH, show different types of responses. For example, over seasonal time-scales Porites corals from the Great Barrier Reef (GBR) have a large range in pHcf of ~8.3 to ~8.5, significantly greater (~×2 to ~×3) than that of reef-water (pHT ~8.01 to ~8.08), and an order of magnitude greater than that expected from ‘static’ laboratory experiments. Strong physiological controls, but of a different character, are found in corals grown in a Free Ocean Carbon Enrichment Experiment (FOCE) conducted in situ within the Heron Island lagoon (GBR). These corals exhibit near constant pHcf values regardless of external changes in temperature and seawater pH. This pattern of strong physiologically controlled ‘pH-homeostasis’, with elevated but constant pHcf has been found despite large natural seasonal variations in the pH (±0.15 pH units) of the lagoon waters, as well as the even larger super-imposed decreases in seawater pH (~0.25 pH units) designed to simulate year 2100 conditions. In natural reef environments we thus find that the processes influencing the up-regulation of pHcf in symbiont-bearing corals are subject to strong physiological controls, behaviour that is not well simulated in the current generation of aquaria-based experiments with fixed seawater pH and temperature. Conversely, cold-water corals that lack symbionts and inhabit the relatively stable deep-sea environments hold the best prospects for providing reliable reconstructions of seawater pH. Clearly, further studies utilising the δ11B-pHcf proxy combined with other DIC/carbonate-ion proxies (e.g. B/Ca), but conducted under realistic ‘natural’ conditions, are required to elucidate the processes controlling coral bio-calcification and to better understand the vulnerability of scleractinian corals to anthropogenic driven warming and ocean acidification.",
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McCulloch, MT, D’Olivo, JP, Falter, J, Georgiou, L, Holcomb, M, Montagna, P & Trotter, JA 2018, Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation: Boron Isotopes: The Fifth Element. in H Marschall & G Foster (eds), Boron Isotopes: The Fifth Element. Advances in Isotope Geochemistry, Springer International Publishing AG, Cham, pp. 145-162. https://doi.org/10.1007/978-3-319-64666-4_6

Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation : Boron Isotopes: The Fifth Element. / McCulloch, Malcolm T.; D’Olivo, Juan Pablo; Falter, James; Georgiou, Lucy; Holcomb, Michael; Montagna, Paolo; Trotter, Julie A.

Boron Isotopes: The Fifth Element. ed. / Horst Marschall; Gavin Foster. Cham : Springer International Publishing AG, 2018. p. 145-162 (Advances in Isotope Geochemistry).

Research output: Chapter in Book/Conference paperChapter

TY - CHAP

T1 - Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation

T2 - Boron Isotopes: The Fifth Element

AU - McCulloch, Malcolm T.

AU - D’Olivo, Juan Pablo

AU - Falter, James

AU - Georgiou, Lucy

AU - Holcomb, Michael

AU - Montagna, Paolo

AU - Trotter, Julie A.

PY - 2018

Y1 - 2018

N2 - The boron isotopic composition (δ11B) of scleractinian corals has been used to track changes in seawater pH and more recently as a probe into the processes controlling bio-calcification. For corals that precipitate aragonite skeletons, up-regulation of pH appears to be a general characteristic, typically being ~0.3 to ~0.6 pH units higher than ambient seawater. The relationship between the pH of the corals calcifying-fluid (pHcf) and seawater pHT (total scale) is shown to be dependent on both physiological as well environmental factors. In laboratory experiments conducted on symbiont-bearing (zooxanthellate) corals under conditions of constant temperature and seawater pH, changes in the δ11B derived calcifying fluid pHcf is typically 1/3 to 1/2 of that of ambient seawater. Similar linear relationships are found for cold water corals that live in relatively stable, cold, deep-water environments but at significantly elevated levels of pHcf (~0.5–1 pH units above seawater), a likely response to the lower pH of their deep-sea environments. In contrast, zooxanthellae-bearing corals living in shallow-water reef environments that experience significant natural variations in temperature, light, nutrients and seawater pH, show different types of responses. For example, over seasonal time-scales Porites corals from the Great Barrier Reef (GBR) have a large range in pHcf of ~8.3 to ~8.5, significantly greater (~×2 to ~×3) than that of reef-water (pHT ~8.01 to ~8.08), and an order of magnitude greater than that expected from ‘static’ laboratory experiments. Strong physiological controls, but of a different character, are found in corals grown in a Free Ocean Carbon Enrichment Experiment (FOCE) conducted in situ within the Heron Island lagoon (GBR). These corals exhibit near constant pHcf values regardless of external changes in temperature and seawater pH. This pattern of strong physiologically controlled ‘pH-homeostasis’, with elevated but constant pHcf has been found despite large natural seasonal variations in the pH (±0.15 pH units) of the lagoon waters, as well as the even larger super-imposed decreases in seawater pH (~0.25 pH units) designed to simulate year 2100 conditions. In natural reef environments we thus find that the processes influencing the up-regulation of pHcf in symbiont-bearing corals are subject to strong physiological controls, behaviour that is not well simulated in the current generation of aquaria-based experiments with fixed seawater pH and temperature. Conversely, cold-water corals that lack symbionts and inhabit the relatively stable deep-sea environments hold the best prospects for providing reliable reconstructions of seawater pH. Clearly, further studies utilising the δ11B-pHcf proxy combined with other DIC/carbonate-ion proxies (e.g. B/Ca), but conducted under realistic ‘natural’ conditions, are required to elucidate the processes controlling coral bio-calcification and to better understand the vulnerability of scleractinian corals to anthropogenic driven warming and ocean acidification.

AB - The boron isotopic composition (δ11B) of scleractinian corals has been used to track changes in seawater pH and more recently as a probe into the processes controlling bio-calcification. For corals that precipitate aragonite skeletons, up-regulation of pH appears to be a general characteristic, typically being ~0.3 to ~0.6 pH units higher than ambient seawater. The relationship between the pH of the corals calcifying-fluid (pHcf) and seawater pHT (total scale) is shown to be dependent on both physiological as well environmental factors. In laboratory experiments conducted on symbiont-bearing (zooxanthellate) corals under conditions of constant temperature and seawater pH, changes in the δ11B derived calcifying fluid pHcf is typically 1/3 to 1/2 of that of ambient seawater. Similar linear relationships are found for cold water corals that live in relatively stable, cold, deep-water environments but at significantly elevated levels of pHcf (~0.5–1 pH units above seawater), a likely response to the lower pH of their deep-sea environments. In contrast, zooxanthellae-bearing corals living in shallow-water reef environments that experience significant natural variations in temperature, light, nutrients and seawater pH, show different types of responses. For example, over seasonal time-scales Porites corals from the Great Barrier Reef (GBR) have a large range in pHcf of ~8.3 to ~8.5, significantly greater (~×2 to ~×3) than that of reef-water (pHT ~8.01 to ~8.08), and an order of magnitude greater than that expected from ‘static’ laboratory experiments. Strong physiological controls, but of a different character, are found in corals grown in a Free Ocean Carbon Enrichment Experiment (FOCE) conducted in situ within the Heron Island lagoon (GBR). These corals exhibit near constant pHcf values regardless of external changes in temperature and seawater pH. This pattern of strong physiologically controlled ‘pH-homeostasis’, with elevated but constant pHcf has been found despite large natural seasonal variations in the pH (±0.15 pH units) of the lagoon waters, as well as the even larger super-imposed decreases in seawater pH (~0.25 pH units) designed to simulate year 2100 conditions. In natural reef environments we thus find that the processes influencing the up-regulation of pHcf in symbiont-bearing corals are subject to strong physiological controls, behaviour that is not well simulated in the current generation of aquaria-based experiments with fixed seawater pH and temperature. Conversely, cold-water corals that lack symbionts and inhabit the relatively stable deep-sea environments hold the best prospects for providing reliable reconstructions of seawater pH. Clearly, further studies utilising the δ11B-pHcf proxy combined with other DIC/carbonate-ion proxies (e.g. B/Ca), but conducted under realistic ‘natural’ conditions, are required to elucidate the processes controlling coral bio-calcification and to better understand the vulnerability of scleractinian corals to anthropogenic driven warming and ocean acidification.

U2 - 10.1007/978-3-319-64666-4_6

DO - 10.1007/978-3-319-64666-4_6

M3 - Chapter

SN - 9783319646664

T3 - Advances in Isotope Geochemistry

SP - 145

EP - 162

BT - Boron Isotopes: The Fifth Element

A2 - Marschall, Horst

A2 - Foster, Gavin

PB - Springer International Publishing AG

CY - Cham

ER -

McCulloch MT, D’Olivo JP, Falter J, Georgiou L, Holcomb M, Montagna P et al. Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation: Boron Isotopes: The Fifth Element. In Marschall H, Foster G, editors, Boron Isotopes: The Fifth Element. Cham: Springer International Publishing AG. 2018. p. 145-162. (Advances in Isotope Geochemistry). https://doi.org/10.1007/978-3-319-64666-4_6