Effects of variations in carbonate chemistry on the calcification rates of Madracis mirabilis (Duchassaing 1861): Bicarbonate concentrations best predict calcification rates

Physiological data and models of coral calcification indicate that corals utilize a combination of seawater bicarbonate and (mainly) respiratory CO2 for calcification, not seawater carbonate. However a number of investigators are attributing observed negative effects of experimental seawater acidification by CO2 or hydrochloric acid additions to a reduction in seawater carbonate ion concentration and thus aragonite saturation state. Thus there is a discrepancy between the physiological and geochemical views of coral biomineralization. Furthermore, not all calcifying organisms respond negatively to decreased pH or saturation state. Together, these discrepancies suggest that other physiological mechanisms, such as a direct effect of reduced pH on calcium or bicarbonate ion transport and/or variable ability to regulate internal pH, are responsible for the variability in reported experimental effects of acidification on calcification. To distinguish the effects of pH, carbonate concentration and bicarbonate concentration on coral calcification, incubations were performed with the coral Madracis mirabilis (Duchassaing 1861) in modified seawater chemistries. Carbonate parameters were manipulated to isolate the effects of each parameter more effectively than in previous studies, with a total of six different chemistries. Among treatment differences were highly significant. The corals responded strongly to variation in bicarbonate concentration, but not consistently to carbonate concentration, aragonite saturation state or pH. Corals calcified at normal or elevated rates under low pH (7.6 to 7.8) when the seawater bicarbonate concentrations were above 1800 μM. Conversely, corals incubated at normal pH had low calcification rates if the bicarbonate concentration was lowered. These results demonstrate that coral responses to ocean acidification are more diverse than currently thought, and question the reliability of using carbonate concentration or aragonite saturation state as the sole predictor of the effects of ocean acidification on coral calcification.



Jury, C. P., Whitehead, R. F. & Szmant, A. M., 2009. Effects of variations in carbonate chemistry on the calcification rates of Madracis mirabilis (Duchassaing 1861): Bicarbonate concentrations best predict calcification rates. Global Change Biology in press doi: 10.1111/j.1365-2486.2009.02057.x . Article (subscription required).

2 Responses to “Effects of variations in carbonate chemistry on the calcification rates of Madracis mirabilis (Duchassaing 1861): Bicarbonate concentrations best predict calcification rates”


  1. 1 João Francisco 19 October 2009 at 18:24

    I would be greatful in receiving this article.
    Thanks


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