Abstract
We report in this work data of two independent studies carried out in the Pertuis Charentais for which a link might exist. A 30-year-local time series study of hydro-climatic variations in water temperature and salinity, which show significant warming of the water masses in the Marennes-Oleron bay (+1.5 °C) associated with a significant drop (≥15%) of freshwater intakes by nearby rivers. In this changing local climate context several major epizootics have appeared, severely affecting farmers and the production of Pacific oysters and mussels, from the first French shellfish-producing department (catching and growing, Agreste 2014). Following the massive mortality event of blue mussels in 2014, a specific study (MORBLEU) is conducted, trying to identify the factors favoring the development of the phenomenon which, furthermore, involves pathogenic bacteria. First analyzes of environmental conditions suggest that there may be a link between (i) the local climate context, (ii) a downward trend in phytoplankton diversity indices, (iii) imbalances in the dynamics of bacterial community composition. These last two points are concomitant with the recent emergence of spring mortalities of mussels. The hypothesis of this link asks the question of evolution in the interactions between the plankton communities of the water column, mussel microbiota and the emergence of pathogenic microbial flora in bivalve mollusks as underlying the recent shellfish mortality events. Such a question requires performing a functional ecology approach with long-term monitoring at different scales, involving particularly NGS technology (metabarcoding) for environmental DNA research. Such a study is underway.