The pioneering reconstruction of coral fluid chemistry has allowed researchers at the University of St Andrews to discover that corals concentrate carbon in order to produce their skeletons.
The new research, published this month in Nature Communications, found high levels of carbon and pH within coral fluid which facilitate the production of aragonite, from which coral reefs are built.
We know reef-building corals are under increasing physiological stress from a changing climate and ocean acidification. Studies have shown that coral calcification decreases with declining seawater pH. However what this new research reveals is that corals are able to modify the chemistry of the fluid used to produce their skeletons.
Coral calcification is vital to the health of reef ecosystems, because tens of thousands of species associated with reefs depend on the structural complexity provided by the calcareous coral skeletons. These biologically diverse ecosystems and are also of substantial economic importance; in terms of fisheries, tourism and coastal protection.
Despite the importance of coral reefs, the processes whereby the corals produce calcium carbonate skeletons are poorly understood.
Corals are marine invertebrates which secrete external calcium carbonate skeletons to support and protect the coral animal. It is these skeletons which combine together to form the framework of coral reefs. To produce the skeleton, calcium reacts with carbonate (a soluble form of carbon in seawater) creating a crystalline form of calcium carbonate called aragonite. This process takes place in a small volume of fluid which is contained between the skeleton and the overlying coral animal.
Lead author Dr Nicola Allison, of the University of St Andrews’ Department of Earth and Environmental Sciences, said:
“In our research we have pioneered an approach to reconstruct the carbon chemistry of the coral fluid used for calcification. We have found that corals concentrate carbon in the fluid well above values observed in natural seawater. Corals also increase the pH of the fluid and these combined effects generate a high aragonite saturation state in the fluid, a measure of the ease with which the skeleton forms.”
This new technique provides a window to understand how environmental changes affect calcification in reef building corals and other organisms. Researchers are poised to apply to the technique to explore how ocean acidification affects the calcification fluid chemistry and to understand why some coral species are sensitive to decreasing ocean pH while other species are more tolerant.
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