Our guide to jellyfish on the Isles of Scilly

If you’re kayaking, paddleboarding or snorkelling in the Isles of Scilly, you will encounter some wonderful marine life. Peering down into the crystal-clear waters you can marvel at fish, anemones, crabs, seaweeds and seagrass.

One of the many creatures you may also be fortunate to see around the coast of our archipelago are jellyfish. As the waters warm up with the summer sunshine, the jellyfish arrive. In this blog we’ll tell you about the most common types of jellyfish on the Isles of Scilly. Whether you need to be worried about being in the water with them. And bust the myths about what you should do should you be unlucky enough to get stung.

To start with a little bit of science, jellyfish are marine invertebrates from a family of animals called cnidarian. They are gelatinous creatures. They have stinging cells called cnidocytes which are used to capture their prey. A group of jellyfish is called a bloom. It’s best to avoid touching any jellyfish as they sting. The severity of the sting varies between different species.

Blue jellyfish 

The blue jellyfish is the species you are most likely to see around Scilly. Frequently the first jellyfish of the summer and a sure sign that the waters are warming up after the winter. You’ll often see them stranded on the tideline of beaches. They can grow up to 30cm across. The dome shaped bell is blue. They feed on plankton. To humans, they have a mild sting. Scientific name Cyanea lamarckii.

Compass jellyfish 

The compass jellyfish is so called because its markings look similar to those of a compass rose. Usually seen in deeper waters, the colour of these jellyfish can vary. They have an umbrella shaped bell with brownish v shaped markings, similar to the spokes of a wheel. These jellyfish are carnivores, feeding on small fish and other jellyfish. A sting from these can be painful. Scientific name Chrysaora hysoscella.

Moon jellyfish

Moon jellyfish have a transparent umbrella shaped bell with short hair-like tentacles. They have four distinctive bright, purple horseshoe-shaped circles which are their reproductive organs. They are filter feeders, consuming plankton and other small organisms. These jellyfish have a very mild sting. Scientific name Aurelia aurita.

Mauve stinger

Last summer there was a huge bloom of mauve stinger jellyfish in August and September. Their numbers were so large that they impacted the Swim Scilly Challenge events. These jellyfish will give a nasty sting. The pain can last one to two weeks, so it’s best not to go in the water if you see them.

Mauve stingers are a distinctive shape and easy to recognise. They are a small jellyfish, growing up to just 10cm long. They have a deep bell with mauve or pink warts and eight hairlike tentacles. Their prey are other small jellyfish and oceanic sea squirts. Scientific name Pelagia noctiluca. 

Portuguese Man O’War

This interesting creature isn’t actually a jellyfish but we’ve included them in this blog. They are a floating colony of hydrozoans, related to jellyfish and coral. Portuguese Man O’War have a distinctive gas filled float with a crest, which looks like a floating plastic bag full of air. It is blue-purple in colour and has many hanging “fishing polyps” that can be many metres long.  

This is another species with a powerful sting that can be dangerous to humans. It’s best not to go in the water if they are present. While you’ll occasionally find them on Scilly, it’s generally in late September and October. Scientific name Physalia physalis.

What to do if you get stung by a jellyfish on the Isles of Scilly

If you are unfortunate enough to be stung by a jellyfish:

●       Leave the water

●       Don’t rub the area but remove any stingers. You can scrape the affected area with a credit card

●       Rinse the sting with salt water

●       Then soak the area in very warm (as hot as you can manage) freshwater for 30 minutes

●       Take painkillers and antihistamine to relieve the pain and reduce the swelling

If the pain is very severe, or you have difficulty breathing, seek medical advice. You’ll be pleased to know that urinating on a jellyfish sting is a myth and can make things worse.

When you’re out on the water, you may be lucky enough to see several different species of jellyfish on the Isles of Scilly. They’re a great indicator that the sea is warming up as the summer progresses. As some species have painful stings, it’s best not to touch any jellyfish, even when found washed up on the shore.

Don’t get into the water if mauve stingers or Portuguese Man O’War are present. But remember, most of the jellyfish you’ll encounter on Scilly are benign. It’s fascinating to see these otherworldly creatures serenely floating through the ocean.

We’d like to thank our talented friend Malcolm Nimmo for allowing us to use his stunning images of jellyfish.

St Martin’s Watersports hire kayaks, paddleboards and snorkel sets from Par Beach on St Martin’s. We love helping our customers have an adventure out on the water. The best moments happen at sea!