Research ArticleOCEANOGRAPHY

Regulation of calcification site pH is a polyphyletic but not always governing response to ocean acidification

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Science Advances  29 Jan 2020:
Vol. 6, no. 5, eaax1314
DOI: 10.1126/sciadv.aax1314
  • Fig. 1 Comparison of net calcification rate, δ11B, pHCF, and ΔpH (pHCF − pHsw) responses to CO2-induced OA for the 10 investigated species of marine calcifiers.

    (A) to (J) net calcification responses of the 10 species to OA. (K) to (T) δ11B values of the 10 species and the boron-inferred pHCF values versus pHsw. (U) to (AD) pH offsets of the 10 species versus pHsw; the pH control envelope, bounded by red dashed lines (see also Fig. 2) is superimposed over each plot. The δ11B compositions of the 10 species ranged from 11 to 41‰, with coralline red algae exhibiting the highest δ11B, followed by shrimp, temperate corals, urchins, serpulid worms, mollusks, and crabs. Values of pHCF estimated from measured δ11B are plotted using the right axes of (K) through (T). In panels (U) to (AD), ΔpH-pHsw trends below, within, and above the envelope indicate weak, moderate, and strong control over pHCF. Significant trends (P > 0.05) with 95% confidence levels are plotted as solid and dashed curve lines, respectively (see tables S1 to S3 for regression statistics). wt %, weight %.

  • Fig. 2 Schematic diagram of the “pH control envelope” to aid interpretation of ∆pH trends as a function of pHsw.

    The upper boundary of the pH control envelope is defined by a 1:1 relationship between ∆pH and pHsw, such that pHCF remains constant regardless of pHsw. The lower boundary is defined by the scenario in which ∆pH remains fixed regardless of pHsw, such that changes in pHCF track changes in pHsw. The envelope therefore describes three categories of pHCF control: weak control at or below the lower bound of the envelope, moderate control within the envelope, and strong control at or above the upper bound of the envelope. The apex of the envelope is translated up or down relative to ∆pH = 0 if pHCF is respectively greater or less than pHsw under control pCO2 conditions.

  • Table 1 Summary of the growth, boron isotope/boron–derived pHCF, and ΔpH patterns as a function of aragonite saturation state or seawater pH and the inferred pHCF regulation ability of the investigated organisms.

    OrganismNet calcification response
    to pCO2*
    δ11B(pHCF) response
    to pCO2
    ΔpH response to pHswAbility to control pHCF in
    response to pCO2 increase§
    Purple urchinParabolicParabolicPositiveStrong
    Pencil urchinThreshold negativeNonlinear negativeNonlinear positiveModerate/Strong
    Temperate coralThreshold negativeNeutralPositiveModerate/Strong
    OysterNegativeNeutralNonlinear positiveModerate/Strong
    Hard clamThreshold negativeNeutralPositiveModerate/Strong
    Blue musselNeutralNeutralNonlinear positiveModerate/Strong
    Coralline red algaParabolicParabolicNeutralModerate
    Serpulid wormNegativeNonlinear negativeNonlinear positiveModerate
    ShrimpPositiveNegativePositiveModerate
    Blue crabPositiveNeutralNeutralWeak

    *The net calcification response to variable pCO2 conditions as reported in Ries et al., (5).

    † and ‡Describes direction and shape of the best-fit regression of the δ11B and ΔpH as a function of seawater pH, respectively, via the least squares method. Detailed analysis is available in tables S2 and S3. The patterns are also shown in Fig. 1.

    §A species’ ability to control pHCF in response to pCO2 increase is classified based on ΔpH versus pHsw trends relative to the theoretical pH control envelope (Fig. 2), not to the absolute offset of pHCF relative to pHsw under a single treatment.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/5/eaax1314/DC1

      Section S1. Species selection

      Section S2. Consideration of the potential for non-pH effects on calcium carbonate δ11B

      Fig. S1. Calcification response patterns of the full sample collection and of the subset of samples used in this study.

      Table S1. Seawater chemistry (pCO2 in μatm, total alkalinity (TA) in umol/kg-SW, pHsw), net calcification rate (% change/60 days), δ11B (‰) of biogenic CaCO3, calcification site pH (pHCF), and ∆pH (pHCF − pHsw).

      Table S2. Linear and quadratic regression analysis of boron isotopic composition (δ11B) of biogenic carbonates as a function of seawater pH via the least squares method.

      Table S3. Linear and quadratic regression analysis of ∆pH as a function of seawater pH via the least squares method.

      References (3341)

    • Supplementary Materials

      This PDF file includes:

      • Section S1. Species selection
      • Section S2. Consideration of the potential for non-pH effects on calcium carbonate δ11B
      • Fig. S1. Calcification response patterns of the full sample collection and of the subset of samples used in this study.
      • Table S1. Seawater chemistry (pCO2 in μatm, total alkalinity (TA) in umol/kg-SW, pHsw), net calcification rate (% change/60 days), δ11B (‰) of biogenic CaCO3, calcification site pH (pHCF), and ∆pH (pHCF − pHsw).
      • Table S2. Linear and quadratic regression analysis of boron isotopic composition (δ11B) of biogenic carbonates as a function of seawater pH via the least squares method.
      • Table S3. Linear and quadratic regression analysis of ∆pH as a function of seawater pH via the least squares method.
      • References (3341)

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