Calcification by Hermatypic Corals: Regulation of the Calcium Pathway

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9415936 Mueller Reef-building corals display two modes of calcification, that which occurs in the light and that taking place in the dark. Calcium carbonate deposition is greater in the light, a phenomenon attributed to the photosynthetic activity of algal endosymbionts (zooxanthellae). There is evidence that the two modes may differ in mechanism as well as quantitatively. In spite of numerous studies, the link between coral calcification and zooxanthellae photosynthesis remains unresolved. The significance of this link can be succinctly stated: the partnership of corals and their zooxanthellae is essentially responsible for the existence of the world's living (and most fossil) coral reefs. A major question is whether either of the calcium carbonate substrates, calcium and dissolved inorganic carbon dioxide, are limiting to calcification and, if so, under what conditions. The importance of calcium to living systems has led to a variety of well-conserved calcium regulatory mechanisms, however, very little coral research has examined such regulation. This strategy has a large base of information from research on other biomineralizing organisms and in many areas of cellular physiology. Such an approach, coupled with recent advances in coral culture, promises substantial progress in a research area that has made little during the past decade. This research project will focus on whether coral calcification is limited by calcium availability at the site of skeletogenesis (not in seawater) and how availability may be affected by symbiont photosynthetic activity. Using a combination of pharmacologic and kinetic approaches, the calcium pathway from seawater to skeleton will be compartmentally characterized. Calcium movement and regulation between compartments by membrane transport systems and messenger systems (i.e. cAMP, calmodulin ) will be of central interest. While this basic research question may be sufficient justification for this projec t, there are benefits of more practical value as well. Optimization of coral culture could have far reaching implications for coral reef conservation. Directly, it offers a means for propagation of corals to repair damaged reefs. Use of coral culture in the aquarium trade could indirectly help natural reefs by reducing the rapidly increasing wild harvest. Understanding the light-enhancement of coral calcification would allow manipulation of culture conditions to produce skeletons with consistent physical properties. Such skeletons would be of value for use in bone reconstruction where natural coral has been successfully employed. ***