"This article is a warning about the need to adapt to climate change," Fabrice Pernet, a researcher at Ifremer (French Research Institute for Exploitation of the Sea) and lead author of the study published in the journal Earth's Future, told AFP.

For 14 months, between 2022 and 2023, researchers studied the survival of mussels and oysters placed in a container filled with unfiltered water from the Thau lagoon (southern France), a region with significant mollusc farming activity.

"We are as close as possible to the truth about the future," assured Pernet, specifying that the molluscs were immersed in the salinity, oxygen, phytoplankton, viruses, and bacteria of the lagoon.

To reproduce the expected conditions in 2050, 2075, and 2100, the water was only heated (from +1°C to +3°C) and enriched with CO2 to simulate ocean acidification.

At the end of the experiment, mussel mortality was "almost total under all future temperature and acidification conditions," according to the study, which describes the results as alarming.

"This is an experiment whose results are corroborated by observations in the Eastern Mediterranean, where we are already seeing episodes of mass mortality in mussel farms in Italy and Greece," Pernet reminded.

Oysters

In comparison, oysters have shown greater resistance to current and future climatic conditions.

Although their mortality rate is 1.5 times higher, according to the experiment replicating expected conditions for 2100, these bivalves still have a comfortable survival rate of around 77%.

However, their growth is reduced by 40% in 2100 compared to current conditions, which could lead to increased operational costs and longer exposure to environmental risks (toxic algae, pollutants, pathogens, etc.) to reach a comparable size.

For researchers, it is already urgent to work on adaptation strategies, such as selecting more resistant varieties, co-cultivating molluscs with algae, or transferring mollusc farming activities to the open sea, where water temperature and acidity are lower.

"We are very close to the tipping point," Pernet warned.