Jellyfish In Cornwall

Jellyfish can be found all over our UK coastlines as well as in all of the global oceans, but how much do you actually know about the magnificent jellyfish?

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Jellyfish are often misunderstood, frequently receiving bad press due to their unforgettable sting. However, they’re actually really fascinating creatures, so here at Padstow Sealife Safaris, we thought we’d give you the low down on all you need to know about these interesting invertebrates.


Made of water - They have no brain, no heart and no blood


Jellyfish as a species has been around for at least 600 million years. That's even before dinosaurs!


People a year are stung by jellyfish - but most of them are completely harmless

7 more unusual Jellyfish facts:


Some Jellyfish glow in the dark

The light helps them warn off or distract predators or help them to attract their prey.

Jellyfish can clone themselves

If a jellyfish gets cut in two, it can regenerate itself and create new jellyfish! In one research project, a group of marine biologists from Australia left an injured jellyfish in a tank and came back to find 200 young jellyfish which were exact clones of the original injured one.

Collective noun

A group of jellyfish are called a bloom, a swarm or a smack.

They swim by pulsating their bodies through the ocean

So how far they travel depends on the currents and the tides of the sea they’re swimming in.

They live in every ocean on the planet

Yep... every one!

Although you might think of a jellyfish as being translucent, actually jellyfish come in many colours

This includes orange, red, yellow, pink, white, blue and green

Jellyfish can reproduce twice in their life

As polyps (juveniles) and medusa (adult jellyfish). For more reproductive facts, read on.
Jellyfish in Cornwall deep ocean

Jellyfish reproduction

Jellyfish have an unusual way to reproduce. Male jellyfish release their sperm into the water, which then swims into the mouth of the female jellyfish, or in some jellyfish a specially developed brood pouch under their arms or orifices. This allows the egg to develop.

The jellyfish embryo created by this breeding routine is called a planula, and the planula leaves and swims off to find somewhere to develop into a polyp.

Surprisingly a polyp can also reproduce new polyps asexually. Jellyfish can produce in two different forms! As an adult and as a polyp. Sometimes the polyp can live for several years before it moves onto the next stage.

The second stage of the polyp’s growth sees a number of grooves appear on the polyp which becomes deeper over time until a number of discs that resemble a pile of coins is produced.

Each ‘coin’ is a baby jellyfish of the adult ‘medusa’ type which will break off, float away and begin its own life. The medusa form is the type of jellyfish we usually see.

Sexing Jellyfish

There are both male and female jellyfish. A jellyfish’s reproductive organ can be found in the lining of its gut and it’s easy to distinguish the male as their reproductive organs are brightly coloured.

How long do Jellyfish live for?

There are over 2000 jellyfish species, each species lives for a vastly different period. Some jellyfish only live for a few hours. Moon jellyfish which are one of the most well-known species usually live for about 18 months but have also been known to live up to 20 years.

One species of jellyfish, Turritopsis dohrnii is also known as the immortal jellyfish. When the immortal jellyfish has reproduced they transform back to the polyp stage. They shrink in size, their tentacles withdraw and they drop to the bottom of the ocean to become a juvenile polyp.

They never die from old age – although they could still be eaten by a predator or die from a disease.

Large jellyfish

What is the largest Jellyfish?

The prize for the largest jellyfish goes to the Lions Mane. The Lions Mane is also known as the giant jellyfish. It lives in harsh climates in the cold waters of the northern seas and oceans. The largest ever recorded jellyfish washed up in Massachusetts Bay in 1870 and it was a whopping 2.3 metres in diameter. It had tentacles that were 37 metres long which is over four times the size of a London bus. You wouldn’t want to meet that in the sea!

Tiny Irukandji jellyfish in test tube

What is the smallest Jellyfish?

The Irukandji jellyfish is the size of a thumbnail at about one cubic centimetre and is the smallest jellyfish in the ocean. Interestingly despite being small, it’s also one of the deadliest and most venomous of jellyfish.

How dangerous are Jellyfish?

The jellyfish sting comes from their tentacles and is faster than a bullet. Their sting is their defence mechanism and they use it to protect themselves from predators. Jellyfish are likely to think we as humans are predators, and that’s why they sting us.

Though infamous for their stinging tentacles, most species are harmless to humans. Some can be dangerous though… These include the box jellyfish, the Portuguese Man o’ War and the tiny but deadly Irukandji Jellyfish.

The most important thing to do if you’re stung by a jellyfish is to seek medical attention immediately. If someone can take a photo or description of the jellyfish this can also help with identification.

Large Jellyfish in sunlight

Jellyfish and the modern environment

With the modern impacts of climate change and environmental damage, what’s the future for these amazing creatures?…With the changes in the ocean, including the seas warming and pollution, you’d think like other species they’d be on the brink of extinction. Far from it, jellyfish are thriving. In fact, jellyfish are growing so fast that scientists believe one day they may starve whales to extinction.

This creature without a brain, a heart or any blood has a remarkable capability to survive in any ocean, with the threat of man, environmental changes and predators. They are truly an unusual looking but pretty mighty species.

With all this jellyfish information, you’re likely to want to come and see one of these miraculous creatures in the flesh. Contact us now to book a Padstow Sealife Safari.

Jellyfish in the modern environment aquarium

Types of Jellyfish

Although fascinating jellyfish can be found in seas all over the world, they’re a familiar sight to the coasts of Cornwall. In fact, we have a variety of different species that are native to our seas, as well as a number of jellies who visit us from abroad. Read on and find out the most common jellyfish that you’ll find in Cornwall.

Barrel Jellyfish

The barrel jellyfish tend to be a pale, milky colour and have a trademark smooth, rounded bell and eight thick, root-like tentacles.

They are some of the largest jellyfish in Britain, can weigh up to 35 pounds and can grow up to a size of 90cm!

These jellyfish tend to be common to Cornwall, often seen floating in the sea in large groups and sometimes found washed up on the shore. They’re gentle giants with a sting that is next-to-none. In most cases, it can’t be felt at all. However, if you have broken skin or particularly sensitive skin, it may have a little sting and cause a rash.

People swimming with Barrel Jellyfish in cornwall

Moon Jellyfish

Moon jellyfish are found all over British coasts, often being sighted in harbours and brackish water. They have an almost clear body, that will take up the colour of whatever it has just eaten (usually tiny animals or plankton). The moon jellyfish’s tentacles surround the bell and are thin and short.

Thanks to its plankton heavy diet, this jellyfish sting is mild to non-existent. There have been reports of it causing a rash, itching and sometimes reddening of the skin.

They’re easily identified by the four horseshoe markings (gonads) that are at the centre of the bell. They tend to be 25–40 cm in size and you’ll usually see them floating just below the surface of the water. They can often be mistaken for plastic bags.

Moon jellyfish

Lion’s Mane Jellyfish

The Lion’s Mane Jellyfish is the largest in the world – perhaps something you wouldn’t expect in the UK! They often grow to around 50cm across in the UK, but have been recorded to grow over 2 metres across and have tentacles over 40 metres long! Thankfully, they’re a rarer sighting and tend to be on the smaller side here.

They’re more likely to be seen in the Northern Sea and off the west coast of Scotland. However, they have been known to sporadically turn up in Cornwall, with a huge swarm appearing in 2010, thought to have been attracted by plankton blooms in the area.

They pack a powerful sting that can be dangerous to some people and will definitely hurt. It’s mostly compared to a wasp sting, but it can be more severe and causes blistering, redness and a rash. In rare cases, they can cause health complications such as muscle spasms and even heart attacks.

Recognisable by their cloudy jelly, thick oral arms and extremely long and thin, string-like tentacles, you should never touch a Lion’s Mane Jellyfish, even if you think it is dead.

Lions Mane Jellyfish

Portuguese Man-o’War

The Portuguese Man-o’War isn’t actually a jellyfish. In fact, it is termed as a siphonophore, which is a colonial organism that’s made up of same-species individual animals called zooids or polyps. It’s rather interesting looking and can be described as looking like a deflating purple balloon or plastic bag, with blue ribbons attached and a pink outline.

They are native to the warmer seas of tropical and subtropical regions but will move to where the wind, current or tide takes them. In recent years, they have caused alarm by being spotted off the west coast of Britain and in Cornwall, although they have been recorded to make appearances in the country since 1999.

Their sting is fierce and can cause serious harm to those who are stung. It often leaves painful weals and can blister and cause severe redness. Two deaths caused by the Portuguese Man-o’War have been recorded in the UK. If you do happen to see one of these creatures, you should stay away and it’s recommended that you alert any beach authorities.

Portuguese man o war jellyfish

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