PELAGIA NOCTILUCA – THE PURPLE ONE
Its charming appearance hides a formidable animal. This violet jellyfish, about 10 cm in diameter, offers a nocturnal spectacle as it becomes luminescent when waves strike. Very common in the Mediterranean, the Red Sea, and the Atlantic, it forms impressive swarms in southern France.
Beaches are regularly closed to prevent painful stings from the Pelagia, which is venomous in its entirety: stinging cells are spread across its eight long tentacles, its bell, and its four oral arms.
PHYSALIA PHYSALIS – BIG “GALERES” AHEAD
Physalias are not true jellyfish but distant relatives, far more venomous. These marine siphonophores, made up of a bluish float that gives them the nickname “Portuguese man o’ war,” are increasingly present on the Atlantic coast and off Corsica.
Originating from the tropical Atlantic, Portuguese man o’ wars sometimes wash up on beaches, pushed by southern winds. Their filaments, which can reach 50 meters, remain venomous after death and can burn swimmers, even causing discomfort and a rapid heartbeat.
RHIZOSTOMA OCTOPUS
Its massive presence caused the shutdown of the Gravelines nuclear power plant (North of France) on the North Sea coast. The barrel jellyfish (Rhizostoma octopus), very common in the Atlantic from August to November, arrives in swarms carried by currents.
Rhizostoma octopus is smaller than its Mediterranean cousin, Rhizostoma pulmo, nicknamed the “sea lung,” which can reach 1 meter. Its bell, edged with blue, has no tentacles on the sides, making it almost harmless.
NEMOPILEMA NOMURAI – THE MULTIFACETED GIANT
Far from harmless to humans (its stings can cause fever, nausea, and respiratory distress), the Nomura’s jellyfish can reach 2 meters in diameter and weigh 200 kg. It proliferates mainly in the Sea of Japan, damaging fishermen’s nets, capsizing boats, and reducing fish catches.
It is also valued for its green fluorescent protein and collagen.
NO HEART, NO BRAIN
Jellyfish have been making headlines all summer, invading the Mediterranean and the Atlantic. They can clog the filtration systems of nuclear plants, like Gravelines, and appear in large numbers on beaches.
Although jellyfish are not humans’ best friend, they adapt to polluted and eutrophicated environments and seem little affected by ocean acidification caused by CO₂.
They have an exceptional ability to adapt, having survived mass extinctions, ice ages, warming periods, and predators.
IMMORTAL JELLYFISH AND CUBOZOA
TURRITOPSIS DOHRNII – IMMORTAL MOTHER, IMMORTAL DAUGHTER
Found in the Mediterranean, Atlantic, and Pacific, this 3 mm species has a unique power: it does not die of old age. After reproduction, it returns to its juvenile form and can generate a polyp that will give rise to new jellyfish.
CUBOZOA – THE HANDS OF DEATH
Box jellyfish (Cubomedusae) have cube-shaped bells and are among the most venomous in the world. Their venom can kill within minutes. The most well-known, Chironex fleckeri, lives in the Indo-Pacific region.
THE JELLYFISH BLOCKADE AT GRAVELINES
On 28 October, a massive swarm of jellyfish paralyzed the Gravelines nuclear plant, preventing reactor cooling. Production units were shut down, and teams had to clean jellyfish-clogged drums.
EDF emphasized that reactor safety was not compromised, but the situation highlights the ecological impact of jellyfish on human infrastructure.
Source : Libération
