Everything you need to know about the jellyfish on our beaches

Jellyfish are commonplace in Irish waters all year round, but the number will continue to increase over the next few months according to CEO of Irish Water Safety John Leech.

“Each summer, we are seeing more and more jellyfish. Global warming and overfishing are the two main reasons for this. When the jellyfish are small, fish will feed on them. But if we don’t have those fish to eat those smaller jellyfish, because they have been fished, these jellyfish will continue to breed in very large numbers and that’s what we’re seeing,” he says.  

In cooler months, jellyfish will typically live near the bottom of the seabed but as the temperatures rise, so will they rise to the surface. According to Leech, the number of sightings of the lion’s mane jellyfish – Ireland’s most dangerous species of jellyfish – have been prevalent in areas where they wouldn’t normally be seen.

“A lion’s mane jellyfish went up the Shannon estuary as far as Glin Pier in Co Limerick – that is unheard of. Nobody has ever seen a lion’s mane in Limerick before but that gives you an idea of the large number of them,” he says. 

Whether you go for a sea swim or a walk on the beach this summer, here is a handy guide to help you identify the different species to be seen in Ireland.

Moon Jellyfish 

Moon jellyfish. Picture: TheBeanieBox76/Instagram

About the size of a plate, moon jellyfish are recognisable by the four purple circles visible through its pinkish, translucent dome. They deliver mild stings and can be typically seen washed up on the shore or floating just below the surface of the water. Ireland’s most common type of jellyfish, moon jellyfish typically appear from May to September – recently thousands were spotted in Cobh and it is advisable to move away from the area where spotted.

Lion’s Mane Jellyfish 

Lion's mane jellyfish on Portmarnock beach recently. Picture: @Portmarnocktri1

Lion’s mane jellyfish on Portmarnock beach recently. Picture: @Portmarnocktri1

The lion’s mane jellyfish is the most dangerous species of jellyfish in Ireland. A sting from one can cause nausea, sweating and cramping. Their tentacles can reach up to two metres in length and can sting even if detached from the jellyfish. Typically seen from May to October, they prefer the cooler waters of the Irish Sea, but recent sightings have been reported in Galway and Limerick. In 2019, a beach in Donegal had to be closed following several sightings of lion’s manes and the public are warned to take care if swimming near an area where sightings have been reported.

Barrel Jellyfish

Barrel jellyfish can cause a severe allergic reaction

Barrel jellyfish can cause a severe allergic reaction

Barrel jellyfish have been described as white, large and meaty and the largest of the jellyfish typically seen in Ireland. Commonly seen between June and October, barrel jellyfish are identified by their opaque colour and purple edges. Although they do not have a particularly strong sting, prolonged exposure to this jellyfish can cause a severe allergic reaction including swelling and white bumps on the skin. Where there is one barrel jellyfish, there will be many. They travel in large groups and have been spotted mainly around Rosslare and Wexford harbours.

Compass Jellyfish

Compass jellyfish can deliver a painful sting. Picture: Damien Enright

Compass jellyfish can deliver a painful sting. Picture: Damien Enright

Compass jellyfish are yellowish-white in colour and can be found around the coasts from July to September. Easily identified by their reddish-brown V-shaped markings, compass jellyfish are very common around the South and West coasts in the summer months. They can deliver a painful sting on par with lion’s manes and should be treated with salt water immediately. It is advised not to approach them if washed ashore. If a sting does occur, immediate treatment with seawater is advised to keep swelling to a minimum.

Portuguese man o’war

A Portuguese man o’war on Long Beach near Clonakilty, Co Cork. Picture Dan Linehan

A Portuguese man o’war on Long Beach near Clonakilty, Co Cork. Picture Dan Linehan

While technically not a jellyfish, the Portuguese man o’war is a close relative that appears in Irish waters during bouts of good weather, when south-westerly breezes carry them from their tropical habitats. Travelling in large groups, they are also referred to as “floating terrors” due to the severity of their sting. They can be blue, pink or purple in colour and if washed ashore, it is advised to stay well away as their tentacles can sting even if detached. In the event of being stung, you must wash the affected area with hot water for at least 20 minutes to reduce swelling.

Jellyfish stings 

Watch your step!

Watch your step!

Jellyfish stings in Ireland are not usually life threatening but require basic first aid and pain relief. The sting comes from their tentacles and brushing against them can cause the release of venom that causes a numbing sensation.

What to do if you get stung 

If you, or someone you know, gets stung by a jellyfish this summer, here are a few tips:

  • Rinse the affected area with seawater. Do not use fresh water, vinegar, alcohol or urine, the salt in the seawater will act as an antiseptic
  • If any tentacles are still attached to the skin remove them with a stick or a towel 
  • Do not rub the affected area as this may result in further venom release 
  • Seek medical attention if there is anything other than minor discomfort 
  • Signs of a severe allergic reaction include swelling, breathing difficulties, heart palpitations or chest tightness – the patient should be taken to the nearest emergency department urgently in this case. 

 For more information on identifying jellyfish visit the Irish Water Safety website.

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