Coral calcification responds to seawater acidification: a working hypothesis towards a physiological mechanism |
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Authors: | F Marubini Christine Ferrier-Pagès P Furla D Allemand |
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Institution: | (1) Centre Scientifique de Monaco, Avenue Saint-Martin, 98000 Monaco, Principality of Monaco;(2) Present address: Joint Nature Conservation Committee, Dunnet House, 7 Thistle Place, Aberdeen, AB10 1UZ, UK;(3) Present address: University of Nice Sophia-Antipolis, EA ECOMERS, BP 71, 06108 Nice Cedex 02, France |
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Abstract: | The decrease in the saturation state of seawater, Ω, following seawater acidification, is believed to be the main factor leading
to a decrease in the calcification of marine organisms. To provide a physiological explanation for this phenomenon, the effect
of seawater acidification was studied on the calcification and photosynthesis of the scleractinian tropical coral Stylophora pistillata. Coral nubbins were incubated for 8 days at three different pH (7.6, 8.0, and 8.2). To differentiate between the effects
of the various components of the carbonate chemistry (pH, CO32−, HCO3−, CO2, Ω), tanks were also maintained under similar pH, but with 2-mM HCO3− added to the seawater. The addition of 2-mM bicarbonate significantly increased the photosynthesis in S. pistillata, suggesting carbon-limited conditions. Conversely, photosynthesis was insensitive to changes in pH and pCO2. Seawater acidification decreased coral calcification by ca. 0.1-mg CaCO3 g−1 d−1 for a decrease of 0.1 pH units. This correlation suggested that seawater acidification affected coral calcification by decreasing
the availability of the CO32− substrate for calcification. However, the decrease in coral calcification could also be attributed either to a decrease in
extra- or intracellular pH or to a change in the buffering capacity of the medium, impairing supply of CO32− from HCO3−. |
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Keywords: | Calcification Biomineralization Carbon supply Calicoblastic cells Buffering capacity Saturation state of aragonite |
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