Compositional diversity of soluble mineralizing matrices in some resent coral skeletons compared to fine-scale growth structures of fibres: discussion of consequences for biomineralization and diagenesis

In contrast to the purely crystalline model of the coral fibre, a transvers al zonation is made visible within fibres by specific preparations (enzymat ic or light acidic etchings). This growth zonation that corresponds to the successive positions of the secretory ectoderm during septal development sh ows that crystallization of coral fibre is controlled not only by an extern al organic coating of fibres, but also includes intra-fibrous organic compo nents. This results in a micron-scaled internal structure of fibres, with a noticeable diversity depending on species. In parallel, soluble matrices a lso exhibit significant differences, although the global high content in ac idic amino acids is always observed. Gathering these two sets of data allow s the current ideas concerning structures and growth modalities of coral se pta to be discussed. Basically, the respective role of centres of calcifica tion and fibres during septal development appears clearly different from th e current ideas, resulting in significant change in interpretation of coral structures, with concerns in both skeleton formation and understanding of diagenetic processes.