Thousands of jellyfish washed up on the beaches. This is what walkers on the Breton and Mediterranean coasts have observed in recent days. A common phenomenon at this time of year, when large quantities of plankton attract these gelatinous animals. Jellyfish are creatures that are still poorly understood. Appeared on Earth about 650 million years agothey have evolved very little since then and have survived all the mass extinctions. Devoid of skeleton, heart and brain, they are however equipped with an effective defense system: their stinging tentacles, feared by swimmers. But while jellyfish get a bad rap, sometimes rightly so, they are no less useful for humans and the environment.
The main disadvantage of jellyfish is their proliferation. A phenomenon accentuated by climate change and warming of waters, which is leading to a significant multiplication, particularly in the Mediterranean. But also by overfishing. “Jellyfish, with the disappearance of their predators like tuna, proliferate all the more quickly as their food, plankton and micro-organisms, is more abundant”, explains to Ouest-France Dominique Barthélémy, curator in charge of the living environment at Océanopolis , in Brest.
“The straw that broke the camel’s back”
Combined with overfishing, the proliferation of jellyfish can have a detrimental impact on marine biodiversity. According to a report from the Food and Agriculture Organization of the United Nations (FAO), they could “be the straw that breaks the camel’s back”, particularly because they feed fish larvae and juvenileswhich “further reduces the resilience of fish populations already hit by overfishing”.
More anecdotally, the proliferation of these animals can also lead to an increase in bites when swimming. Most jellyfish are safe for humansalthough their stings can be very painful. However, some are much less harmless. This is particularly the case of the Australian box jellyfish, also called “sea wasp” or “hand of death”. As Geo reports, “its venom can kill a human in just a few minutes.”
Jellyfish, however, play an important role in the marine ecosystem. For a long time, scientists thought that only a limited number of marine animals consumed them because they were too unnutritious. But researchers from the Center for Ecology at Deakin University in Australia and the University of Cork in Ireland demonstrated in a study published in 2018 that they had a real place in the food chain. Because they are nevertheless provided with certain nutritional elements, such as collagen or lipids and, above all, they are easy to catch and digest. As Sciences et Avenir indicates, “the low nutrient content would thus be compensated by a lower energy expenditure devoted to hunting and the speed of elimination”.
“An iodized flavor, a bit like oysters”
They also present many benefits for humans. Some collect them on the coasts, with the aim of “sending them to a laboratory which extracts the collagen from their umbrellas to use it in cosmetics or to repair burned skin”, Clément Larrouy explains to Reporterre. Others use them as fertilizer, like the class of high school students of Anne-Charlotte Carsalade d’Ornano, who developed a product based on dried jellyfish to keep the soil moist. Still others cook them. This is the case of Manuel Marchioretti, doctor of biology, who tried several recipes, including donuts. “It has an iodized flavor, a bit like oysters, with a glass of rosé it goes very well,” he explains, still to Reporterre. But while they are common in Asia, jellyfish-based foods are currently banned in Europe.
The notion of harmful and useful species is generally obsolete because it is a very anthropocentric vision of living things, harmful and useful being defined in relation to the human species. Touching a jellyfish can be very stinging indeed, but jellyfish are otherwise quite harmless. They have their place in the ecosystem.”
And jellyfish mucus could even constitute a natural filter which would rid water of nanoparticles resulting from human discharge of sunscreen, cosmetics, electronic components or medicines. This is what researchers from Inserm, the National Institute of Health and Medical Research, discovered. “This mucus is composed of a very dense network of molecules such as oligosaccharides and peptins, which traps the nanoparticles and retains them. They aggregate there, precipitate and it is then possible to recover them,” explains Philippe Barthélémy, the responsible for this work, in a press release.
However, we must not forget that jellyfish are part of lifejust like all other organizations. And their existence should not be reduced to their harmfulness for humans, or to the usefulness they can derive from it, as Dominique Pelletier, research director at Ifremer, the French Research Institute, explains to ID. for the exploitation of the sea. “The notion of harmful and useful species is generally obsolete because it is a very anthropocentric vision of living things, harmful and useful being then defined in relation to the human species. Touch a jellyfish can be very stinging indeed, but jellyfish are otherwise quite harmless. They have their place in the ecosystem.
