10 facts about jellyfish – plus what to do if you are stung

Jellyfish swarm in the UK's seas in the summer – so get to know these mysterious creatures better. And if you're unlucky enough to be stung by one – here is how to treat the jellyfish sting

22nd June 2017
Compass jelly fish Getty

1. Jellyfish are an ancient design. Fossilised imprints of prehistoric jellyfish recently unearthed in Utah from about 540 million years ago  tell us their design has barely changed.

2. Jellyfish have no brain, no blood, and no heart. They are 95 per cent water.

3. The opening to a jellyfish’s stomach serves as both mouth and anus.

4. Jellyfish tentacles are lined with thousands of stinging cells known as nematocysts. Each cell contains a spring-loaded, toxic harpoon designed to paralyse and secure prey – plankton and small fish.

5. In UK waters jellyfish blooms, or ‘smacks’, peak at the height of our summer, and this is when the adult males release their sperm into the sea. The nearby females in the smack suck the sperm up through their mouth into their stomachs where fertilization occurs.

A beached jellyfish
Beached jellyfish in Pembrokeshire. Getty Images

6. Leatherback turtles feed almost exclusively on jellyfish. Each year they perfectly time their epic migrations to UK seas to coincide with peak jellyfish numbers in July and August.

7. Jellyfish numbers are rising. Studies show that overfishing of plankton-eating fish, such as herring, which predate on the early life stages of jellyfish and compete with the adults, can tip the ecological scales in favour of jellyfish. Collapsing fish stocks have been quickly followed by increasing jellyfish numbers in in the Irish Sea, the South Atlantic and the Mediterranean. Global increases in jellyfish numbers have also been linked to warming sea temperatures through climate change.

8. The stretch of the Bristol Channel between the Gower Peninsula and the North Devon is the UK’s hottest spot for huge jellyfish blooms.

Barrel jellyfish
Barrel jellyfish can reach the size of a dustbin lid and occur in huge blooms. Getty Images

9. Jellyfish blooms can be a problem to businesses. In 2007, mauve stingers inundated Northern Ireland’s only fish farm at the time, wiping out about £1 million’s worth of stock. In the summer of 2011, the Torness nuclear power station near Dunbar was forced to shut down its reactors for a couple of days after large blooms of moon jellyfish clogged the filters in the station’s intake pipes.

Moon jellyfish.
Close up of a moon jellyfish. Getty Images

10. At up to 2 metres in diameter, the lion’s mane is Britains largest jellyfish. Its longer tentacles reach tens of metres in length.

Lion's mane jellyfish
Lion's mane jellyfish. Getty Images

Stung by a jellyfish? Here's what you should do.

1. Do not panic.

2. If you are in the water get out, and thoroughly rinse the affected area with sea water immediately.

3. Do not use urine.

4. So long as the stinging tentacles are on you they will continue to inject you with the toxin, and worsen the effect. If you can see them, remove them with a stick or tweezers.

5. Apply an ice pack if available.

6. For the best advice see www.nhs.uk/Conditions/Stings-marine-creatures/Pages/Treatment.aspx or visit a medical specialist.

 

Main image: Getty

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