The Copernicus report on climate for the year 2025 warns about ocean temperatures and the consequences on biodiversity. Especially on posidonia herbaries, but our region has its specificities that can be beneficial.
The Copernicus Institute’s report on climate in 2025, published this week, is alarming for the planet in general and the Mediterranean Sea in particular. Its editors indicate that last year it had its second hottest year on record, with an average surface water temperature of 21.35 °C. This figure is higher than normal by 1.03 °C, and slightly below the 2024 record (21.5 °C).
Already, on our coast, at the very beginning of May, the temperature shows 17° or 18° towards Paca, above normal, which makes bathers happy but raises concerns for the next few weeks among scientists.
One of the consequences of the recent marine heat waves that have affected the sea: « recurring episodes of mass mortality in coastal ecosystems, » note the authors of Copernicus.
Particularly concerned, the endemic species of the Mediterranean, the precious posidonia herbariums found in Occitanie on the Agathoise (Hérault) and Vermeille (P-O) coasts. Because they suffer from temperature differentials and a third of their surface would have already disappeared for 50 years.
« Weeds play a crucial role in storing carbon »
And this, while their benefits are plural. Not only do they serve as a habitat and nurse for many fish species, but « herbariums play a crucial role in storing carbon, » recalls Renaud Dupuy of Grandrive, director of the marine environment in Agde. An essential function for the planet to breathe, to which is added a third role again essential: « grasshoges are natural swell attenuators, » continues the specialist.
Translation: these marine meadows slow down the erosion of the coastline linked to the rise of the sea, itself correlated with global warming… However, to have a precise photograph, it is necessary to locate the problem. And the coasts of Occitanie offer reasons for hope.
« First, there are temperature differences in the Mediterranean, our Gulf of Lion is one of the coldest places, » recalls Renaud Dupuy of the Grandrive. Then, thermal stress affects posidonia herbariums differently whether in Corsica, the Côte d’Azur or Languedoc-Roussillon.
« With us, it is almost sometimes the opposite, we were able to observe, for example, in warmer water, herb trees develop by attending flowering, » says the specialist. He finally recalls it to nuance the Copernicus report: other factors also undermine these sea meadows essential to the protection of the marine ecosystem. Namely the pressure of pollution but also poorly controlled boat anchors, stricter regulations now limiting this risk on the coast between Nice and Perpignan.
« The Mediterranean is warming twice as fast as the other seas, the major problem is climate change, we must set the bar high to combat greenhouse gas emissions, » concludes the director of the marine environment of Agde.
