At the beginning of April, it blows like summer air in the harbor of Villefranche-sur-Mer. On the beach, it is over 20 degrees and some are already sunbathing, while a few brave people dip their feet in 12 degree water. Although the water temperature may seem low to humans, it is above average for the season. “Our latest analyzes show that the temperature is increasing by 0.3 degrees per decade, which is really rapid and brutal,” worries Steeve Comeau, marine biologist at the Sea Institute in Villefranche-sur-Mer. During the summer of 2022, here in the harbor, we reached 29.2 degrees, almost one degree more than previous records. So there we really had significant stress for marine organisms. »
The organisms concerned are mainly calcareous algae, vast meadows of posidonia, sea grasses, and especially gorgonians, large colorful corals, essential to the marine world. “It’s really all the organisms that will structure the ecosystem, which we tend to lose,” says Steeve Comeau. Those that have long life cycles, that form large three-dimensional structures and that are home to fish and molluscs. We have entire regions where we are losing them and we have mortalities approaching 100%. It’s a bit like losing the trees in a forest. »
These observations are all the more worrying given that the Mediterranean basin is warming 20% faster than the global average. As the sea is almost closed, the mercury rises more quickly and the body of water takes longer to cool down.
A worm resistant to warming
Unlike gorgonians, certain species are resistant to this brutal warming, such as the marine worm, platynereis dumerilii, which hides in algae and which is of great interest to scientists. The small animal, less than a centimeter long, is collected throughout Europe as part of the TREC expedition.
The platynereis dumerilii worm, caught in the Mediterranean Sea. (GUILLAUME FARRIOL / RADIOFRANCE)
The platynereis dumerilii worm, caught in the Mediterranean Sea. (GUILLAUME FARRIOL / RADIOFRANCE)
It is considered a “model organism” and, despite its small size, it has a lot to teach us. “It’s supposed to be a very good approximation of the ancestor of all human beings,” explains Cyril Cros, researcher at the European Molecular Biology Laboratory. It is present throughout Europe and by taking samples from all European coasts, we can try to see how it adapts to colder or warmer waters. One of our ideas is to see the genetic differences between its different worm populations and to see how they adapt to human activity and global warming. »
Researcher Cyril Cros, studying the platynereis dumerilii worm. (GUILLAUME FARRIOL / RADIOFRANCE)
Researcher Cyril Cros, studying the platynereis dumerilii worm. (GUILLAUME FARRIOL / RADIOFRANCE)
Cyril Cros’ research is only just beginning, but ultimately, it could shed light on the adaptation mechanisms of this worm, and even other species. “In general, all of his scientific approaches adapt to multiple species,” says the researcher. There is a target species, but our idea is to always try to identify broad principles, to try to understand how other species can adapt to these changes. »
Understanding the effects of warming on biodiversity
These upheavals beneath the surface directly affect our societies. “We talk a lot about the impact of human activities on the sea, but the Mediterranean Sea also has a lot of impact on our human activities,” explains Nathalie Himi, environmental economist at the Monaco scientific center.
Fishing is on the front line of warming, as fish flee the southern Mediterranean in search of a little freshness. “It disrupts an entire industry, because fishermen in North Africa will lose species, as the fish go north and end up in the nets of French, Italian and Spanish fishermen,” says Nathalie Himi. It’s the same for sardines since they move around in search of better temperatures and they find themselves stuck on the northern coasts and after a while, they reproduce less well, which means that we are in the process of to lose cash. »
To reverse the trend, there are few short-term solutions, other than reducing human pressure, with less fishing, less urbanization and less polluting discharges. Scientists agree that a healthier ecosystem will always better resist warming waters.
