July 2023

Jellyfish of North Wales

Why are our waters filled with them?

One of this marine conservationist’s favourite times of the year is here once again – no, not Christmas – jellyfish season! The North Wales coastline seems to be filled to the brim with the brainless creatures, and while they tend to have a bad reputation with most beachgoers, their colourful patterns and slow, peaceful movements are rather endearing. In fact, most of our jellyfish species don’t pack a sting any worse than a nettle sting, with two species (barrel and moon) rarely strong enough to effect humans at all. The ones you need to watch out for are the lion’s manes, dark reddish-brown and up to 50cm in diameter. They pack a severely painful sting that could potentially wind you up in A&E, or at least in the lifeguard’s hut, and being more common in the Irish sea than the rest of the UK, this is one species we’re likely to encounter in North Wales. The lion’s mane is actually the largest jellyfish species in the world, growing up to two metres in diameter in warmer waters, and the longest recorded lion’s mane jelly had tentacles that were thirty-six metres long – longer than a blue whale! However, they don’t get that big in our temperate waters, so although they’re the biggest in the world, they’re not the biggest in the UK. Confusing, right? The barrel jelly wins the trophy for largest jellyfish in the UK, growing up to one metre in diameter, and earning them their other name – dustbin lid jellyfish. You may have seen the famous photo taken by underwater cinematographer, Dan Abbott, of biologist, Lizzie Daly, diving with a massive barrel jellyfish off the coast of Cornwall.

Well, it’s unlikely that you’ll come across one that big, but your chances of seeing a barrel jelly on any beach in North Wales are high. There’s no need to panic though. Like I said earlier, barrel jellyfish possess an extremely mild sting that can’t be felt by most people at all.

If you’ve grown up in North Wales, you might feel like year after year, you’re seeing more jellyfish than you ever have before. Well, you’re not wrong. I’ve seen some arguing recently about whether jellyfish numbers are really growing or not. The reality is most jellyfish species feed on plankton which includes algae. Rising sea temperatures are causing more algal blooms, and these algal blooms trigger baby jellyfish (or ephyras) to be born during an abundance of food. So, in fact, jellyfish seem to be one of the only species that are actually thriving due to global warming. Since jellyfish aren’t very strong swimmers, they tend to get transported around by the tides and currents and winds, which means they all normally end up in the same place, especially the juveniles. So, it’s completely normal to see many of the same species in the shoreline or washed up on the beach, like this compass jelly bloom in Criccieth photographed by Alex McGregor.

Additionally, jellyfish tend to prefer warmer waters, which is probably why we’re seeing higher jellyfish numbers and new species such as the Portuguese man-o-war. Although it gets bundled in with the jellyfish, man-o-wars are actually a floating colony of hydrozoans – organisms that each have different jobs to do and rely on each other to survive. Fun fact – while man-o-wars can’t actually swim like jellyfish can because they don’t have a muscle band, they can quickly deflate their air sac and sink to avoid surface attacks – kind of like a BCD! Portuguese man-o-war come from the Mediterranean and have always been an occasional visitor to the UK, but since around 2020, sightings have been increasing every year. Is it possible that their distribution could be used as an indicator for tracking the effects of climate change? Portuguese man-o-war have a slightly worse sting than a lion’s mane jellyfish, one that could be potentially fatal for dogs, small children, or those with heart conditions, so they are definitely best avoided, and if a bloom of man-o-war are spotted washed up on a beach, they should be reported to the local council so that they can be safely removed.

All in all, the presence of jellyfish shouldn’t spoil your day at the beach. Just wear a wetsuit or rash guard, gloves, and boots, and if you do happen to be stung, follow NHS guidance on how to treat a jellyfish sting, and don’t urinate on it… that’s a myth!

Written by Kathryn Brass

Education and public engagement lead and marine conservationist