The French mussel industry has faced a severe decline in production this summer, with experts estimating a loss of up to 25% of usual output. This decline is attributed to extreme heat and prolonged drought, which have disrupted the delicate conditions mussels need to thrive. In the bay of Pont-Mahé, near the mouth of the Vilaine river in Loire-Atlantique, mussel farmers like Gilles Foucher are working under challenging conditions. Using cranes to lift mussels from wooden stakes, Foucher reports that only about two-thirds of the mussels he harvests meet the size requirements for sale. He estimates that this summer's yield will be 20 to 25% lower than normal, a direct result of the harsh weather conditions. According to Fabrice Pernet, a researcher at the French Institute for Research for Exploitation of the Sea (Ifremer), mussels require specific environmental conditions to grow. Higher temperatures increase their metabolic rate, forcing them to use more energy, while reduced rainfall limits the availability of nutrients in the water. This leads to a decrease in phytoplankton, the primary food source for mussels, ultimately affecting their growth and survival. Philippe Le Gal, president of the National Oyster Farming Committee, confirms that the overall loss across the industry is estimated at a quarter of the usual production. In northern Brittany, the situation is even more dire. Guillaume Hurtaud, a mussel farmer in the bay of Saint-Brieuc, describes the year as "catastrophic," with losses ranging between 60 and 75% of his usual production. This is due to a combination of factors, including attacks by sea spiders, climate change, and ocean acidification. Ocean acidification, caused by the absorption of CO2 from human activities, makes seawater more acidic and corrosive, which hinders the growth of calcareous organisms like mussels and oysters. Hurtaud notes that mussels have been getting smaller over the past few years and that the current situation is not economically sustainable. Researchers like Fabrice Pernet are working to understand the long-term effects of climate change on shellfish farming. In laboratories near Brest and in the Thau lagoon, they simulate ocean warming and acidification expected by 2100. Last year, a study predicted a "total collapse" of mussel production in the Mediterranean by 2050 due to these conditions. However, this summer saw a similar collapse in the Thau lagoon, with 100% mortality of mussels under current conditions, without the added stress of simulated future changes. While the northern parts of France have not yet experienced the same level of impact, Foucher, a mussel farmer in Morbihan, notes that the increased temperatures this summer did not kill his mussels, which he sees as a positive sign. However, he warns that the current summer may become the new norm by 2050 and questions what the future of mussel farming will look like in the coming decades.