Since mid-June, on many Corsican and Riviera beaches, Pelagia noctiluca, small purple jellyfish present everywhere in the Mediterranean, have been tossed about by the dozens by the surf of the sea. But hoping to get rid of them is illusory.

Because jellyfish, which appeared 600 million years ago, are among the first inhabitants of the planet.

Made up of 95 to 98% water, brainless, able to float and swim but not resist ocean currents, they are part of zooplankton. And “they are present all year round, in a current that goes around the Mediterranean and tends to stay offshore”, explained to AFP Fabien Lombard, teacher-researcher at the Villefranche-sur oceanography center. -Sea (Alpes-Maritimes). “It was the southerly flow that brought them back to the coasts”.

In Ajaccio, they have been seen by the thousands. On the Saint-François beach, in the heart of the city, Simone Martini, an Italian bather, was one of the many to make their painful encounter: covered with stinging cells, the cnidocytes, the tentacles of jellyfish touched his forehead, releasing tiny harpoons that inject a cocktail of venom.

– Bite to eat –

“Fifteen days later, I still have a burn that hurts me at times,” he told AFP.

“These blind animals bite everything they touch to try to eat. They inject neurotoxins to immobilize their prey, and digestive enzymes”, explains Fabien Lombard.

Websites make it possible to track their presence, such as or And everyone has their own method of soothing post-injection pain. “Peeing on it is useless”, laughs Fabien Lombard, who advises not to “rub, rinse with sea water and remove stinging cells with wet sand”.

At the environmental level, their proliferation would be such that it would cause a “gelling” of the oceans, according to a September 2019 report by the Intergovernmental Panel on Climate Change (IPCC).

An assertion that divides the scientific community: “We have no reliable measurements to say that there are more”, specifies Fabien Lombard. While recognizing that if “in the 80s-90s, in Villefranche-sur-Mer, there were 5 to 6 years with jellyfish and the following 5-6 years without, it is the 25th non-stop year with jellyfish”.

For Lovina Fullgrabe, scientist at the underwater and oceanographic research station (Stareso) in Calvi (Haute-Corse), “overfishing, which eliminates their predators such as tuna or turtles, is one of the” preferred hypotheses to explain this greater frequency.

And if the United Nations Food Organization (FAO) recommended in 2013 to eat them, to fight against their proliferation, Fabien Lombard warns against the idea of ​​​​treating “this symptom of an imbalance in the sea” rather than the original disease, which is the depletion of fish due to overfishing.

– Two Nobel Prizes –

But if these animals are worrying, they have also enabled significant scientific advances.

In 1913, the Nobel Prize for Medicine rewarded work on the functioning of the venom of cousins ​​of jellyfish which made it possible to understand “anaphylactic shock”: the venom decreases instead of strengthening the immunity of people who have already been stung.

“It was a bit of a revolution, until then everyone was more in the idea that the more you expose yourself to something, the less you are sensitive to it”, explains Fabien Lombard.

In 2008, a second Nobel Prize, this time in chemistry, was awarded to work on the ability of certain jellyfish to glow in the dark, via a protein. This fluorescence has been used by many biochemists, biologists and medical researchers in their research, particularly on tumors or Alzheimer’s disease, the Nobel committee pointed out in 2008.

“It has revolutionized cell biology by literally allowing cells to be turned on when they are activated, to see how they work”, summed up Fabien Lombard.

Nasa has embarked jellyfish on board space flights to study their reproduction in weightlessness, and the European Union launched a call for projects in 2017, “GoJelly”, to study how to benefit from them in the food sectors. , fertilization, cosmetics or depollution.

Because “jellyfish are full of potential”, assures the teacher-researcher: they are used as food for aquaculture fish, fertilizer or soil moisture stabilizer for crops such as vines in the Landes, rice in China or basil in Mexico. Their collagen is used in cosmetics, diapers or sanitary tampons, in Israel, and to soften concrete in anti-seismic installations in Russia, lists the scientist.

For him, the most promising use is that of “jellyfish mucus”, composed of a molecule which “seems to promote the regrowth of human cartilage”.

To meditate during the next swim.