The jellyfish population in Saundersfoot

The jellyfish population around Pembrokeshire made it into the news when in summer and autumn 2017 thousands of giant jellyfish washed up on beaches in Tenby, Saundersfoot and Newport. However, these bizarre creatures have drifted through our oceans for over 500 million years. Despite lacking a brain, heart or blood, their soft bodies are over 90 per cent water, and they move in a mesmerising pulsing motion operated by a simple net of nerves. Let’s have a closer look at the different types of jellyfish that are predominant in the bay of Saundersfoot and what to do if you get stung.

Every summer more and more jellyfish are being washed up onto the shorelines around Wales. Little is known about jellyfish off the coast of Wales but rising sea temperatures are definitely having an effect on their numbers and migratory patterns, which in turn effects the turtle population which feeds on them. Another factor for their rise is the near-removal of herring from the Irish Sea through overfishing (oily fish such as herring like to eat plankton, a good part of which contains baby jellyfish).

The waters around the Pembrokeshire coast are stirred by strong tidal currents which circulate nutrients, and make the waters rich in sea life, perfect feeding for dolphins and whales. During the summer, weather and sea conditions combine to draw into the Irish Sea plankton, fish and squid in large numbers.

Leather back turtles follow the Jellyfish population but they are shy creatures and you will be very lucky if you see one. A big danger to turtles are plastic bags closer to land as they look similar to their pray; Jellyfish. Some giant leatherback sea turtles have been spotted in Pembrokeshire and their population is expected to increase. Gitan leatherback turtles are up to three metres long, which is why they are also called ‘Turtlezilla’, and sightings normally are extremely rare. If you want to be lucky, then August is the month to watch for them.

As the water warms up from May onwards the Jellyfish arrive. Moon, compass and lions mane are the most common. Don’t touch or hold the jellyfish, they are capable of stinging even hours after being washed up on a beach and dying. Some people will tell you that not all Jellyfish sting but all, including the moon jellyfish, are capable of at least a mild sting. Below, we listed the main species of jellyfish that you’re likely to encounter on Welsh beaches: the lion’s mane, compass, barrel or root mouth, blue, and moon Jellyfish.

Lions Mane

Lion’s Mane Jellyfish, Cyanea capillata. This is the largest species of jellyfish.

The Lion’s Mane Jellyfish is fairly common and large – often growing to ‘dustbin lid’ sized proportions and reaching up to 2m in diameter.

They are umbrella shaped and reddish brown in colour with long thin tentacles which can reach up to 30ft in length and produce a sting if touched.

Compass Jellyfish

The Compass Jellyfish are smaller and roughly have a diameter of a ruler – 30cm or smaller and are very distinct in colour.

The bell shaped body is covered with brownish ‘v’ shaped markings which radiate out, from a brown spot located in the centre of the body.

They have a variety of tentacles underneath – 32 marginal lobes, 24 long thin tentacles and 4 long thick frilled arms hanging down, all of which give a very painful sting to humans.

This gigantic jellyfish was filmed off coast of West Wales – but be careful because the two metre creature can pack a ‘very painful’ sting.

Barrel Jellyfish

Barrel jellyfish are one of the largest in UK waters with a diameter of up to 90cm and weight reaching up to 35kg.

Luckily, they feed entirely on tiny plankton, so their sting is too weak to hurt humans.

Blue Jellyfish

These are similar in size to the compass jellyfish and also bell shaped but have a purplish/blue tinge to them.

If you look closely, you’ll be able to see through the body and notice darker radial lines inside. Like other jellyfish, they will sting but it is very mild.

If you find a jellyfish washed up on the beach then it is probably dead but be warned, they can still give you a sting if handled, so leave well alone.

Moon Jellyfish

These are very easy to spot and wash up regularly on most beaches in Wales. They’re umbrella shaped and around 40 cm in diameter.

The main body is translucent in colour with four pinky/purple spots on the top which are actually the creatures gonad rings.

Their stings are like minute harpoons fired by springs and are not powerful enough to pierce our thick skin.

Why do Jellyfish sting?

Jellyfish stings are relatively common problems for people swimming, wading or diving in seawaters. Jellyfish tentacles contain microscopic barbed stingers. Each stinger has a tiny bulb that holds venom and a coiled, sharp-tipped tube. The jellyfish uses the venom to protect itself and kill prey. When you brush against a tentacle, tiny triggers on its surface release the stingers. The tube penetrates the skin and releases the venom. It affects the immediate area of contact and may enter the bloodstream.

Jellyfish stings vary greatly in severity. Most often they result in immediate pain and red, irritated marks on the skin. Some jellyfish stings may cause more whole-body (systemic) illness. And in rare cases jellyfish stings are life-threatening. Jellyfish that have washed up on a beach may still release venomous stingers if touched. Most jellyfish stings get better with home treatment. Severe reactions require emergency medical care.

What to do if you get stung by a jellyfish

If you are stung, the best thing to do initially is to rinse the wound in salt water. Rinse with vinegar (if you have some) as the acid will neutralise the toxin in the sting. Urinating on a sting is unlikely to help. Gently scraping the affected area with a credit card or razor will remove any remaining nematocysts (the tiny poisonous sacs released by the jellyfish tentacles).

What to do in the water

Jellyfish – although some can provide their own momentum – generally follow the current, which is why they often get washed up. Swimmers should be vigilant, especially in warm shallow waters. If you do spot a jellyfish floating along, don’t try and move it or wave it away, just move out of its path and alert others to its presence.

What to do on land

Look out for flags announcing whether large numbers of jellyfish have been spotted, and watch your feet in the shallows and along the tide line.

The barrel jellyfish can grow up to three feet in diameter and even though they are relatively harmless, beach-goers have been warned not to move the creatures as they can sting.


The following tips can help you avoid jellyfish stings:

  • Wear a protective suit. When swimming or diving in areas where jellyfish stings are possible, wear a wet suit or other protective clothing. Diving stores sell protective “skin suits” or “stinger suits” made of thin, high-tech fabric. Consider protective footwear as stings can also occur while wading in shallow water.
  • Get information about conditions. Talk to lifeguards, local residents or officials with a local health department before swimming or diving in coastal waters, especially in areas where jellyfish are common.
  • Avoid water during jellyfish season. Stay out of the water when jellyfish numbers are high.

Note: we recommend that you always wear at least a shorty wetsuit to protect from Jellyfish sting. If you get stung, seek advice from RNLI, the Harbor of Saundersfoot or come to our paddleboard school in Saundersfoot.

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