Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia.

The processes that occur at the micro-scale site of calcification are fundamental to understanding the response of coral growth in a changing world. However, our mechanistic understanding of chemical processes driving calcification is still evolving. Here, we report the results of a long-term in situ study of coral calcification rates, photo-physiology, and calcifying fluid (cf) carbonate chemistry (using boron isotopes, elemental systematics, and Raman spectroscopy) for seven species (four genera) of symbiotic corals growing in their natural environments at tropical, subtropical, and temperate locations in Western Australia (latitudinal range of ~11°). We find that changes in net coral calcification rates are primarily driven by pHcf and carbonate ion concentration [ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mtext>CO</mml:mtext> <mml:mrow><mml:msub><mml:mrow/> <mml:mi>3</mml:mi></mml:msub> </mml:mrow> <mml:mrow><mml:mi>2</mml:mi> <mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> </mml:math> ]cf in conjunction with temperature and DICcf . Coral pHcf varies with latitudinal and seasonal changes in temperature and works together with the seasonally varying DICcf to optimize [ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mtext>CO</mml:mtext> <mml:mrow><mml:msub><mml:mrow/> <mml:mi>3</mml:mi></mml:msub> </mml:mrow> <mml:mrow><mml:mi>2</mml:mi> <mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> </mml:math> ]cf at species-dependent levels. Our results indicate that corals shift their pHcf to adapt and/or acclimatize to their localized thermal regimes. This biological response is likely to have critical implications for predicting the future of coral reefs under CO2 -driven warming and acidification.