| Summary: | International audience Biogenic dissolution of carbonates by microborers (or microbioerosion) is one of the main destructive forces in coral reefs. This process seems to be enhanced by eutrophication and ocean acidification and the chlorophyte Ostreobium sp., the main agent of this process, appears as the most responsive microboring species to those environmental factors. Ostreobium sp. recruitment period, its development along community successions, the impact of its dynamics on rates of biogenic dissolution and how it is affected by environmental factors remain however, poorly known. An experiment was thus carried out on a reef in New Caledonia to study with a monthly resolution, Ostreobium’s ecology, microboring community successions and biogenic dissolution dynamics over time. Blocks of dead coral were used and exposed to colonization by microborers over six periods of one year, 3 starting in summer and 3 starting in winter, allowing the determination of the seasonal and interannual variability of the biogenic dissolution process. In parallel, environmental parameters (T°C, pH, chla, etc…) and biotic factors (grazing pressure and epilithic cover) were recorded every month and/or continuously. Results showed that (a) microboring communities at their early developmental stage (1-3 months) were dominated by large chlorophytes and induced low rates of biogenic dissolution whatever the studied year, (b) between 3 and 6 months, the chlorophyte Ostreobium sp. started dominating communities which consequently increased rates of carbonate dissolution more or less exponentially depending on the studied year, and (c) after 6 months of exposure, Ostreobium was finally well settled and biogenic dissolution rates slowed down to reach a ‘plateau’ with some variations probably correlated to biotic factors. At a larger temporal scale, biogenic dissolution dynamics and rates varied greatly among studied years and seasons. Multivariate analyses were carried out to determine the main factors (biotic and abiotic) which could ...
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