The environment recording unit in coral skeletons: structural and chemical evidences of a biochemically driven stepping-growth process in coral fibres

International audienceTo improve our understanding of the environment recording by scleractinian corals, a detailed study of the skeleton microstructure has been carried out. A series of physico-chemical in situ characterizations was made, an approach that provides us with structural and biochemical information at the micrometric and nanometric scales. Gathering of these data results in a significant change in our concept of the growth of coral skeletons. In contrast to the usual view of an aggregate of purely mineral units (the coral fibres) independently growing by a simple chemical precipitation, coral skeletons appear to be biochemically controlled structures. Both structural and biochemical data reveal the micron-scaled stepping growth-mode of fibres, and its global coordination. In this process, sulfated acidic proteoglycans probably play a major role, due to their ability to create polymeric frameworks. Atomic force microscopy confirms the close relationship of organic and mineral phases at the nanometric scale. A new microstructural model of coral skeleton formation is proposed, that places coral skeletons among the typical "matrix mediated structures". From a practical standpoint, these results may contribute to develop a new high resolution approach in the study of paleoenvironments