Lion's mane jellyfish size and structure
The lion's mane jellyfish, or Cyanea capillata, can stretch over 30 meters in length but remains less than 2 meters wide. Its massive size is not due to the size of its umbrella or age, but rather its unique hunting strategy, which involves extending its tentacles to cover a large area for capturing prey.Tentacle length and hunting method
The tentacles of the lion's mane jellyfish can reach up to 36.6 meters, longer than an adult blue whale. These tentacles, covered with stinging cells called cnidocytes, release venom to paralyze plankton and small fish. The jellyfish uses this method to remain stationary while sweeping a wide area with its long, trailing tentacles.Weight and comparison to blue whales
In extreme cases, the lion's mane jellyfish can weigh over 1,000 kilograms, including its long tentacles. This weight, spread across a stretched-out body, has led to comparisons with blue whales in terms of length, even though the two species are biologically very different.Impact on human infrastructure
In August 2026, a large number of lion's mane jellyfish near the Gravelines nuclear power plant in France caused the shutdown of several reactors. The jellyfish clogged water pumping stations used for cooling, forcing EDF to temporarily halt production. A similar event occurred in 2025, and these incidents are linked to the warming of coastal waters.Ecological and scientific significance
While the lion's mane jellyfish prefers cold waters of the North Atlantic and Arctic, it highlights how unusual marine life can both intrigue scientists and disrupt human activities. More common jellyfish species along coasts can also cause significant disruptions to energy infrastructure.
