[LUM#18] Thau, a Glimpse into the Future
With its 6,900 hectares of saltwater, the Thau Basin is the largest coastal lagoon in Occitanie and a major center for shellfish farming. This industry is now under close scrutiny due to the effects of climate change, which have already disrupted the fragile balance of this small inland sea.
The summer of 2018 will long remain etched in the memory of shellfish farmers in the Thau Lagoon. That year, unusually heavy rainfall in the winter and spring, followed by scorching temperatures and a lack of wind, caused what is known as a “malaïgue”—meaning “bad water” in Occitan. Deprived of oxygen for several days, the lagoon suffocated, and the shellfish along with it. “100% of the mussels farmed in the basin died, and 30% to 40% of the oysters—a net loss of 6 million euros,” explains Franck Lagarde.
A phenomenon of exceptional intensity, highlighting the fragility of this unique ecosystem.“The Thau Lagoon, this small inland sea, is a veritable open-air laboratory where we can glimpse the future,” explains the researcher from the Marbec* laboratory. For in the lagoon, the annual average water temperature has already risen by 1.6 degrees over the course of 20 years.
A delicate balance
With rising water temperatures coupled with more intense rainfall in the Mediterranean basin, the entire fragile balance of the lagoon is under threat, and an entire economic sector is being called into question. Because there will be more events like this one. “The risk of anoxia triples for every degree the lagoon water warms, as shown by the research of my colleague Valérie Derolez,” explains Franck Lagarde. Faced with these prospects, professionals, researchers, and policymakers are joining forces to protect the lagoon and its uses.“The good news is that all stakeholders in the basin are working together to adapt new farming practices and mitigate the effects of climate change.”
According to the expert, the pond’s resilience also depends on continuing efforts to ecologically restore the ecosystem and biodiversity. This starts with eelgrass beds—these marine meadows that supply oxygen and thus reduce the risk of water blooms.“We must also encourage the return of engineer species historically present in the lagoon but which have since disappeared, such as the flat oyster or the European clam, which oxygenate the sediments and promote water flow and biodiversity ,” adds Franck Lagarde. These approaches to ecosystem restoration are nature-based solutions that will help strengthen the ecosystem in the face of the more intense stresses we will encounter in the future.
“Will there be a limit?”
These efforts are also essential for professionals in the shellfish industry, who can likewise contribute to this restoration,“for example, by further improving cleanliness beneath the tables to limit the presence of plastic waste, pieces of netting, or piles of oyster bags and polyethylene ropes. “Every plot must be clean to allow this precious biodiversity to return.”These individual and collective efforts promote the lagoon’s resilience,“as evidenced by the absence of malaïgue in 2022 despite hydroclimatic conditions deemed particularly sensitive.”
Don't miss:
- A presentation by Valérie Dérolez illustrating the restoration process of the Thau Lagoon, titled “50 Years of Observation to Understand the Restoration Dynamics and Resilience of the Thau Lagoon.”
Check out:
- In "Science at IFREMER," Caroline Montagnani, a researcher at IFREMER and director of the IHPE** unit, talks to us about vaccinating oysters against oyster herpesvirus.
*Marbec (UM, IRD, CNRS, Ifremer)
**IHPE (CNRS, Ifremer, UPVD, UM)
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