Bioerosion of Mediterranean 'coralligene' concretions by boring organisms:assay of quantification of processes

An experimental study of the bioerosion of 'coralligene' concretions of the Provence coasts demonstrates that the first stages of colonisation are cha racterised by a weak presence of microperforating organisms. After 12 month s of exposure, the only species of microborer present at -60 m is a Chlorop hycea (Ostreobium quecketti). At -20 m, the diversity is higher with two Ch lorophycea and two Cyanobacteria. Among macroborers, Spionid annelids repre sent the pioneering stage of colonisation; they appear within the first thr ee months. As from 6 months, the bivalve Hiatella arctica colonises the exp erimental substratum; it becomes the main borer after 12 months. The mass o f CaCO3 eroded by the macroborers changes with depth. After a year, it reac hes a maximum of 5.73 +/- 0.77 CaCO3.m(-2) to -20 m and does not go beyond 1.50 +/- 0.99 g CaCO3.m(-2) to -60 m. ((C) Academie des sciences / Elsevier , Paris.).