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

Abstract

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 pH_cf and carbonate ion concentration [ ${\text{CO}}_{{}_3}^{2-}$ ]_cf in conjunction with temperature and DIC_cf . Coral pH_cf varies with latitudinal and seasonal changes in temperature and works together with the seasonally varying DIC_cf to optimize [ ${\text{CO}}_{{}_3}^{2-}$ ]_cf at species-dependent levels. Our results indicate that corals shift their pH_cf 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.

Keywords: Western Australia; calcifying fluid; carbonate chemistry; climate change; coral calcification.