Coral Calcification, Cells to Reefs

In spite of more than one century and half of studies, mechanisms of coral biomineralization, leading to coral growth and reef formation, still remain poorly known, although major global threats to coral reefs, such as ocean acidification, primarily affect this process. Coral skeletons are used as environmental archives but the vital processes that govern incorporation of trace elements and stable isotope are still unknown. Our knowledge on coral physiology is restricted to the organismal level due to the lack of appropriate cell model, however the advent of new approaches, such as coral genomic, is changing drastically our knowledge on these animals even if only a few data are available concerning the field of biomineralization. This chapter reviews our present knowledge and discusses the different theories on coral calcification, from the molecular to the reef level. Conclusion is presented in a list of key issues to be resolved in order to understand the intimate mechanisms of calcification of corals, essential to determine the origin of the sensitivity of corals to ocean acidification, to improve paleoceanographic reconstructions or coral reef management, or “just” to understand how genes of a soft organism control the formation of an extracellular 3D-skeleton.