Chair: Janice Lough
Malcolm T. McCulloch (1)*, Michael Holcomb (1), James Falter (1), Paolo Montagna (2), Juan Pablo D’Olivo Cordero (1), Marco Taviani (2) and Julie A. Trotter (1)
1 School of Earth and Environment, UWA Oceans Institute and ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, WA, 6009, Australia
2 Institute of Marine Sciences, National Research Council, 40129 Bologna, Italy
Scleractinian corals have been spectacularly successful in building reef edifices that harbour ~1/3 of the oceans biodiversity, as well as occupying many cold-water, deep-sea habitats. This success can be largely attributed to their ability to biologically mediate the composition of their calcifying fluid (cf), and thereby increase aragonite saturation state (cf) to enhance the kinetics of calcification. Manipulation of calcifying fluidcomposition is thought to occur via Ca-ATPase controlled up-regulation of pH and still poorly understood transport mechanisms for DIC. How the biologically mediated process of pHcf up-regulation will respond to the combined pressures of both extremely rapid CO2-driven warming and ocean acidification, is thus critical to the future of scleractinian corals.
We have undertaken a global survey of hermatypic zooxanthellate corals sampled from the tropical Indo-Pacific and Caribbean, as well as azooxanthellate corals from both shallow-water tropical and deep-sea environments. Combined boron isotopic (11B), B/Ca, and Sr/Ca systematics in their carbonate skeletons have been used to infer pHcf, and DICcf and hence the cf required to sustain biomineralisation across these diverse environments.
Regardless of location, we find that the dominant aragonitic zooxanthellate reef-building corals (e.g. Acropora, Favia, Porites, Pocillopora, Galaxea, Turbinaria, Fungia, Montipora, Montastraea, Stylophora, Trachyphyllia, Lobophyllia) have a similar range of pHcf of 8.4 to 8.6, ~0.3 to ~0.5 pH units higher than ambient seawater. Interestingly, we find that the azooxanthellate tropical coral Tubastrea exhibits high pHcf up-regulation (+0.5 to 0.6 pH units), similar to that found in deep-sea cold-water corals (e.g. Desmophyllum). The DICcf characteristics are found to be systematically enriched (x1.5 to x2 relative to seawater) with tropical corals having significantly elevated cf (14 to 20).
Up-regulation of calcifying fluid pHcf and hence cf is a ubiquitous feature of scleratinian corals and crucial to understanding their future in a high CO2 World.