Southern France's seagrass meadows vanish at an unprecedented pace

The Underwater World of Southern France Suffers Under Climate Change

Yet beneath the waves of southern France, marine ecosystems are struggling in the age of climate change. Heatwaves in the ocean are driving mass extinction, and even seagrass meadows—often called the lungs of the Mediterranean—are under threat.

"The Mediterranean lives and dies with its seagrass," emphasizes Manuel Marinelli, an Austrian marine biologist who founded Project Manaia, an initiative dedicated to protecting and restoring seagrass beds. For eight years, Marinelli and his team have been traversing the Mediterranean, measuring whether seagrass populations are shrinking or expanding, thinning or thickening. "The bottom line is grim: year after year, we're losing roughly 20 percent of our seagrass," the researcher explains.

A devastating loss, because seagrass does far more than sway with the rhythm of the waves. It produces vast amounts of oxygen while sequestering carbon—about 83 million tons annually—making it a critical ally in the fight against climate change.

The ribbon-like blades also trap microplastics before they drift further into the sea. The plants' dense root networks stabilize coastal sediments, reducing erosion. Seagrass meadows can even dampen wave energy by up to 40 percent, mitigating flooding. And unlike many seasonal ecosystems, they thrive year-round in the Mediterranean, providing a vital winter habitat for countless species.

From above, the seagrass sways gently in the clear water, resembling a soft, undulating carpet. But the illusion of untouched nature is deceptive. Even in the protected waters of Port-Cros National Park, seagrass is in decline.

The species found here, known as Neptune grass (Posidonia oceanica), faces multiple threats. "There are many dangers to Posidonia," says Alain Barcelo, the park's scientific director. "We're seeing a steady decline in the bays around Port-Cros, and we can't reverse the trend. There's still a lot we don't understand."

Beyond global warming, careless anchoring by yachts and small boats is damaging seagrass beds. "If we enforce stricter anchoring rules, the situation will improve," Barcelo notes.

But new regulations alone won't solve the problem, warns Manuel Marinelli. "Every law is only as good as the enforcement behind it," the marine biologist says. On Ibiza, Posidonia is even a UNESCO World Heritage site, and other countries have protections in place. "In theory, the species is untouchable. In practice, no one cares," Marinelli laments. With roughly a third of all Mediterranean life directly dependent on Posidonia, he stresses the urgency of educating younger generations about why seagrass must be protected.

Yet awareness alone isn't enough if the climate doesn't cooperate. "Mediterranean seagrass seems to hit a tipping point at 30 or 31 degrees Celsius. We visited a bay in Sardinia with stunning seagrass—days later, we returned to find the entire meadow dead," Marinelli recounts. As temperatures rise, could more resilient seagrass species offer a solution?

In German waters, the SeaStore project is already exploring this question. "Since some marine habitats like lagoons or sandbanks heat up significantly in summer, we can select donor populations that tolerate temperatures 2 to 3 degrees higher than others," explains Thorsten Reusch, a marine biologist at the Helmholtz Centre for Ocean Research in Kiel.

However, planting these adapted populations will be a slow process. Seagrass grows just 2 to 3 centimeters per year, and research from the SeaStore project suggests it takes 12 to 18 years for a new meadow to reach its full carbon-sequestering potential. The race to save the Mediterranean's seagrass is against time—and the clock is ticking.

"Awareness of seagrass protection is growing," says 23-year-old South African Dylan Robinson. He is the captain of the catamaran Vaka Okeanos, operated by the Okeanos Foundation, which advocates for marine conservation education. On his phone, he has the Donia app, which maps all the seagrass meadows along the Mediterranean coast. "When we anchor, we always make sure to drop the anchor over sand—not over a seagrass bed."

Robinson believes that simply witnessing the beauty of the underwater world while diving can deepen one's environmental consciousness. He pulls on his fins and glides into the depths with effortless strokes.