Shellfish farming in a high CO2 world: carbonate chemistry monitoring and long-term mesocosm experiment highlight major risks for French aquaculture by 2050

As part of the CocoriCO₂ project, we established a carbonate chemistry monitoring network across shellfish farming areas along the French coastline. This three-years-old network reveals short but recurrent episodes of extreme acidification at most sites, which are expected to intensify in coming years. In parallel, we developed mesocosms to simulate future warming and acidification scenarios under fluctuating field conditions, allowing us to study the survival, growth, reproduction, and next-generation development of bivalves in the Mediterranean. Pacific oysters and Mediterranean mussels, the primary cultivated species in the region, were exposed to present and projected temperature and pH conditions for 2050, 2075, and 2100, based on the most likely CO₂ emission trajectories. Our results reveal that future warming and acidification conditions significantly reduce oyster and mussel yields as early as 2050, with mussels showing mass mortalities. These findings highlight the urgent need for effective adaptation strategies in the Mediterranean. We will present results and perspectives on co-culturing shellfish with algae as a promising nature-based approach to mitigate acidification impacts and enhance resilience in shellfish farming.