Identification of bacterial populations associated with the Pacific oyster, Crassostrea gigas from larvae to seed in hatchery. successive microbiota of Pacific oyster, Crassostrea gigas from larvae to seed

The microbiota of larvae and postlarvae of oyster reared in recycling system was monitored during 44 day. As soon as day 2, it appeared diversified and specific, as compared to the bacterial assemblages in seawater. Major shifts occurred during larval development, notably during metamorphosis, likely due to the modifications of oyster anatomy and physiology. On day 44 the seed microbiota diverged with only 44.2% of similarity in average between the different batches. In oyster seed, the core microbiota was composed of Burkholderiales (20 OTUs), Xanthomonales (13 OTUs), α-Proteobacteria (13 OTUs) and candidate phylum TM6 (1 OTU). A noticeable part of the microbiota in seed comprised OTUs already present on day 2 and several dominant taxa were identified two years earlier. This revealed a certain containment of bacterial populations in hatchery that could lead their impoverishment. Nonetheless its diversity remained high, even when bacterial populations of seawater were dominated by two OTUs belonging to Bacteriovoracaceae and Cryomorphaceae. Furthermore none bacterial opportunist or pathogen was detected. Finally since the microbiota, established in hatchery reared seed appeared diverse and may deeply change, it should not weaken them in front of the diseases which have recently emerged.