Coming to a beach near you: a guide to the jellyfish you'll find off the UK coast

The Guardian

11 hours ago

Moon jellyfish are the most common species in UK seas, easily identified by its markings of four purple circles within its translucent white bell. The bell has a layer of mucus over it, which the moon jellyfish uses to catch plankton, which it inserts into its mouth using special tentacles.
Nasa launched more than 2,478 young moon jellyfish in a container into space in 1991 to study the effects of microgravity on the gravity-sensitive organs of the species. Although they did not reach the moon, scientists discovered that the space-born jellyfish had difficulty swimming in Earth's gravity, as their nervous system had adapted too well to microgravity.
The largest species of jellyfish in the world is the lion's mane, which gets its name from its up to 3-metre-long, hair-like tentacles that look like, yes, a lion's mane. These reddish-brown tentacles are packed with stinging cells and are used to prey upon fish and smaller jellyfish. The largest recorded lion's mane specimen was found off the coast of Massachusetts, US, in 1865. It had a bell diameter of 210cm and tentacles measuring about 36.6 metres long.
Although not fatal, the sting of a lion's mane jellyfish can cause serious discomfort to a person, from localised redness and pain to vomiting and chest pain. A 34-year-old woman was taken to hospital in 2016 after suffering an allergic reaction from the sting of six lion's mane jellyfish.
Another large species to look out for is the barrel jellyfish, with a bell diameter of as much as 90cm and which weigh as much as 35kg. They have eight frilly tentacles and, due to their enormous size, are often found washed up on beaches after searching for prey in shallow waters. Fish and small crabs are known to seek shelter within the tentacles of the barrel specimen, as a safe space from predators.
The sting of a barrel jellyfish is typically mild and does not cause real harm to people. Countries across the world and particularly in south-east Asia have eaten barrel jellyfish for more than 1,700 years.
The mauve stinger is a small and beautiful jellyfish, typically coloured pink, purple or a bluey purple, and packs a punch with its 3-metre long tentacles full of stinging cells. The mauve stinger has one of the worst stings of all the species and can glow brightly at night when disturbed, giving it the scientific name Pelagia noctiluca, which translates to 'night-light of the sea'.
A common summer visitor to the UK is the compass jellyfish, named for its brown lined markings running down the centre of its yellowish-white bell that resemble a compass. When the compass jellyfish stings something, it often detaches a tentacle and leaves it behind, which can still sting despite not being connected to a body.
The species, frequently encountered in Cornish coastal waters, can inflict a lot of pain from its sting, which should be rinsed with warm water for 30 minutes to reduce the pain.
The nearly transparent and bioluminescent crystal jellyfish can emit light and exhibit a bright green light when exposed to light ranging from blue to ultraviolet. With up to 150 tentacles, this unique jelly is often used in scientific experiments for its bioluminescent properties and proteins, which have revolutionised fields such as cell biology, neuroscience and disease research.
Their sting is considered not strong enough to penetrate through human skin and cause harm, but is strong enough to harm and paralyse their prey in the water.
The blue jellyfish, similar in shape to the lion's mane species, can be colourless when young and develop its blue-purple bell once mature. This species can have up to 800 fine tentacles that resemble a head of hair; the jellyfish uses these tentacles to direct food – including other jellyfish – towards its mouth.
The venom from a blue jellyfish sting can cause serious pain, which can last for hours or even days. Although the sting is nonlethal, it can be potentially dangerous for young children, elderly people, and those with allergies such as anaphylaxis.