Cyanea

• While scuba diving off the south-west coast of England this summer, I was lucky to encounter several different species of jellyfish in just a matter of weeks.
• The good news for fellow jellyfish enthusiasts is that both the abundance and diversity of jellyfish around the UK may be on the rise.
• Meanwhile, there is evidence suggesting that jellyfish blooms (where the jellyfish population rises suddenly) are increasing in certain regions worldwide, including the UK.
• So, here are five common jellyfish species that people may well see more of as the seas around the UK continue to warm.

1. Compass jellyfish

Compass jellyfish are easy to identify by the dark stripes on their pale bells. These jellyfish can grow to 30cm in diameter, boast long tentacles and are a favourite food for turtles. This species is often the most commonly reported jellyfish in UK waters. In 2022, almost one-quarter of the UK jellyfish sightings that were reported to the Marine Conservation Society were compass jellies. Compass jellyfish have a very painful sting.

2. Moon jellyfish

Moon jellies (Aurita aurita) have a distinctive appearance. They have relatively short tentacles and are transparent with four purple rings on the top of their bells. They can grow to 40cm in diameter. These jellyfish can be found almost anywhere in the world, but they are most commonly encountered in coastal waters. Moon jellies have only a mild sting that most people don’t react to.

3. Barrel jellyfish

• Barrel jellyfish (Rhizostoma pulmo) are huge compared to most of the other jellyfish species found in the UK.
• Barrel jellies have a relatively mild sting and are even eaten in some parts of the world, including Asia.

4. Lion’s mane jellyfish

Lion’s mane jellyfish (Cyanea capillata) are usually around 50cm in diameter, though they can grow to around 2 metres. These jellies are reddish brown in colour and have both thin tentacles and thick frilly arms. Due to their size, only young lion’s mane jellies are eaten by fish and turtles. Lion’s mane jellyfish have a painful sting.

5. Mauve stinger

• Mauve stingers (Pelagica noctiluca) are small – less than 10cm in diameter – and a beautiful pink or mauve colour.
• They glow in the dark and can form aggregations, known as a “smack”, that are so large they can clog fishing nets.
• Not only do their tentacles sting; their bells can also sting too, which is uncommon among jellyfish.