Will marine heatwaves help these venomous sea creatures thrive in Europe?
Beachgoers have been warned to stay vigilant after a Portuguese man o’ war washed up Anglesey, an island in north Wales.
Closely related to jellyfish, the alien-like sea creatures are recognisable for their striking blue-violet balloon-like floats, thought to resemble a war ship’s sail.
Usually found floating through tropical and subtropical oceans, the creatures have been increasingly appearing on British beaches - especially at the end of summer, when sea temperatures peak.
On Wednesday, dog walkers came across a Portuguese man o’ war on Porth Dafarch beach.
This week, South Hams District Council also issued a warning on social media following sightings in the south of England. “Portuguese Man O'War spotted on local beaches… Rarely deadly, but give a nasty sting even after dead. Keep away and don't touch,” it read.
Such sightings are expected to become more common if the UK’s oceans continue to heat up.
Though men o’ war are rarely deadly to humans, they are most dangerous when washed up on the shore, as their painful sting remains active for weeks.
What is a Portuguese man o’ war?
Portuguese man o’ war are sometimes referred to as 'false jellyfish'. Only they aren’t singular living organisms like jellyfish. They’re made of a group of individual organisms, zooids, to form a colony called a siphonophore.
Legions of Portuguese man o’ war can travel in groups of up to 1,000. Their 30-metre-long tentacles are deadly to prey like small fish and shrimp. They are easily recognisable for their iridescent bulbous air-filled balloon and blue-violet colour.
Are Portuguese man o’ war thriving due to climate change?
This year, meteorologists measured record-breaking marine heatwaves off the UK and Irish coasts. In June, sea temperatures were up to five degrees Celsius warmer than normal.
It is thought these warmer waters could bring creatures like jellyfish, basking sharks and man o’ war closer to the shore. As their range expands, man o’ war that reach the UK could be larger and more numerous.
Another reason they may be thriving with climate change is that “some siphonophore species are known to be resistant to at least mild hypoxia,” researcher Gillian M. Mapstone says in a study on siphonophores.
Hypoxia is a below-normal level of oxygen in the blood, which means they may not be suffering from the low levels of oxygen in the ocean like other marine creatures are.
Are Portuguese man o’ war dangerous?
Thankfully, these creatures don’t attack humans. Most incidents occur by standing on them once they’ve been washed up on the shore or by not being vigilant while swimming.
They’re carnivorous with a diet of small fish, plankton, worms and crustaceans. Like the Man-of-War sailing warship that they were named after, they are carried slowly through the water by the wind catching their inflated, sail-like bubble.
It’s only the tentacles that can sting you. If a tentacle wraps around any part of your body it can sting you numerous times through its tiny harpoon-like venom darts that are triggered by touch.
Stings can be excruciatingly painful and may require hospital treatment, but are rarely deadly. If you are stung, apply a hot compress of 40C or soak in vinegar for 20 minutes.
Despite being a risk to beachgoers, Portuguese man o’ war are essential for our survival.
As part of the ocean’s delicate ecosystem, the “ancient” creatures have a similar level of “importance as bees in the terrestrial ecosystem,” according to researcher Bruno Ivo Magalhães at the Okeanos Marine Science Research Institute, University of the Azores. “And human beings indirectly depend on them for survival.”
How to avoid being stung by a Portuguese man o’ war
A full-length wetsuit can protect you from stings, but it is advisable not to go in the water if you can see any nearby. Bearing in mind how far their tentacles can stretch, it’s hard to know which areas are safe.
A good rule to go by is never intentionally touch a Portuguese man o’ war - even if it looks dead, it can still pack a punch.
Care should also be taken to keep dogs away from the creatures.