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Ten fascinating facts about jellyfish

Donna Coutts, November 20, 2019 7:05PM Kids News

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Jellyfish numbers are booming.

There are frequent news and scientific reports of massive jellyfish blooms all around the world, including an incredible population explosion along the coast of Queensland in January this year that forced authorities* to close beaches.

Swimmers reported thousands of stings at Queensland beaches in the first week of January alone.

The reported global population explosion is in contrast with prospects for many other species.

Up to one million of Earth’s estimated eight million plant, insect and animal species are at risk of extinction — many within decades, according to the United Nations Global Assessment released in May.

Many scientists believe the good times for jellyfish could be because they are taking advantage of warming ocean water and are filling the gap in ecosystems* left by declining populations of other marine species due in part to pollution and overfishing.

Some, but certainly not all, jellyfish species can be dangerous. So, as many of us look forward to a trip to the beach over the holidays, it’s a good time to learn more about these fascinating creatures.

Moon jellyfish. Picture: Sea Life media_cameraMoon jellyfish. Picture: Sea Life
Blue blubber jellyfish. Picture: Sea Life media_cameraBlue blubber jellyfish. Picture: Sea Life
Pacific sea nettles. Picture: Sea Life media_cameraPacific sea nettles. Picture: Sea Life

Jellyfish expert Jarvis Aland from Sea Life Melbourne Aquarium in Victoria is preparing for the opening of a special exhibition about jellyfish, called Ocean Invaders.

He has put together the 10 things he finds most fascinating about jellyfish so we all know what we’re looking at ahead of a trip to the beach or an aquarium.

VIDEO: Jarvis Aland talks about the exhibition Ocean Invaders he is helping prepare for at Sea Life Melbourne Aquarium. 

Jarvis talks about jellyfish


1. Jellyfish have been living in our oceans for at least 500 million years, which means they have been around roughly twice as long as the earliest bony fish and insects.

2. Jellyfish are made up of 95-98 per cent water.

3. One word for a group of jellyfish is a bloom.

4. The name jellyfish isn’t actually correct. They are not technically fish but Cnidarians, which is the same family as corals and sea anemones.

5. A jellyfish is made of two simple parts: the bell (main body which contains the digestive and reproductive systems) and stinging tentacles.

Sea nettles, a type of jellyfish. Picture: Sea Life media_cameraSea nettles, a type of jellyfish. You can clearly see the bell at the top and the tentacles trailing from the bell. Picture: Sea Life

6. The diameter* of a jellyfish’s bell can range in size from around 1mm to nearly 2m!

7. The lion’s mane jellyfish is the largest jellyfish that’s ever been found, with tentacles reaching over 36m in length. We have lion’s mane jellyfish in our Ocean Invaders exhibit at the Sea Life Melbourne Aquarium but they certainly won’t get that big.

Lion's mane jellyfish. Picture: Sea Life media_cameraLion’s mane jellyfish. Picture: Sea Life

8. To catch their prey jellyfish use tentacles armed with special stinging cells called nematocysts. When a jellyfish’s tentacle comes into contact with its prey, it triggers millions of nematocysts to fire out little harpoon-like structures that pierce the skin and inject venom.

9. There are hundreds of species of jellyfish but only 70 can actually sting humans. There are some species, such as the box jellyfish and Irukandji jellyfish, that can kill a human.

10. Jellyfish populations in the ocean have been increasing over recent years and many scientists believe this is due to rising water temperatures and human impacts due to overfishing. It could be that jellyfish are filling ecological niches left open by species being overfished.

VIDEO: Jellyfish look incredible when you can see them swimming

Watch the jellyfish


  • authorities: such as lifesavers, police, ambulance, firefighters and government officials
  • ecosystems: community of plants, animals and fungi living in a habitat
  • diameter: distance across


Incredible fluther of human-sized jellyfish

Kids find giant jellyfish

Beware tiny creatures hiding in seashells

Extinction alert for one million species

Colourful dreams of a sleeping octopus


  1. What is one collective noun or word for a group of jellyfish?
  2. What kinds of creatures are in the Cnidarian family?
  3. What is one fact you now know about lion’s mane jellyfish?
  4. Is a box jellyfish dangerous?
  5. How many species of jellyfish can sting humans?


1. Ask the expert
If you could ask Jarvis Aland two questions about jellyfish not covered in his 10 fascinating facts, what would you ask him?

Write at least two questions for him.

Time: allow 10 minutes to complete this activity
Curriculum Links: English, Science

2. Extension
Do you think the government should try to reduce jellyfish numbers? Write arguments or reasons for and against.

Time: allow 15 minutes to complete this activity.
Curriculum Links: English, Geography, Science, Civics and Citizenship

With a partner see if you can identify all the doing words/verbs in this text. Highlight them in yellow and then make a list of them all down your page. Now see if you and your partner can come up with a synonym for the chosen verb. Make sure it still makes sense in the context it was taken from.

Try to replace some of the original verbs with your synonyms and discuss if any are better and why.

HAVE YOUR SAY: What is your favourite kind of jellyfish to look at?
No one-word answers. Use full sentences to explain your thinking. No comments will be published until approved by editors.

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