**Exotic Sea Life and Safety Concerns as Wales Enter Marine Heatwave**
Beachgoers across Wales are being urged to stay alert as experts warn that the ongoing marine heatwave could usher in new, and in some cases dangerous, sea creatures to local shores. Scientists have noted that waters around the UK and Ireland are now up to four degrees Celsius warmer than the seasonal average, with the effects of this marine heatwave being felt most acutely in the Celtic Sea and along the north and west coasts of Wales.
The UK’s Meteorological Office (Met Office) reported that current surface sea temperatures in some areas match those usually observed in mid-June, and highlighted that April and May readings are the warmest since satellite records began in 1982. Temperatures along the coastlines of Cardigan Bay and North Wales are particularly pronounced, up to 2.5C above normal. While this may tempt more people to visit the seaside, experts caution that warmer waters might bring with them unwelcome surprises beneath the waves.
According to Dr Ségolène Berthou from the Met Office, a convergence of factors has led to these unusual conditions: an extended period of high pressure, abundant spring sunshine, and unusual calm has allowed sea temperatures to rise well ahead of schedule. “We saw the seas start to warm as early as mid-February,” Dr Berthou explained, “almost a month before the seasonal norm. Compounding this, the trend of rising ocean temperatures has persisted for four decades, averaging an increase of 0.3C per decade.”
The broader backdrop is of ongoing global climate change, resulting in more frequent marine heatwaves and warmer waters worldwide. On 19 May, the UK’s average sea surface temperature was documented at nearly 12.7C—well above the May heatwave threshold of 11.3C. These unprecedented temperatures are expected to abate in the coming days, as cooler weather arrives, but the warm spell’s impact could be lasting.
The change in ocean conditions has already affected marine life. There are reports of increased sightings of jellyfish, including the large barrel jellyfish, recently washed ashore in Gwynedd and Ceredigion. Frankie Hobro, director of the Anglesey Sea Zoo, has raised concerns that rising sea temperatures could draw more exotic, and sometimes hazardous, species to Welsh beaches. “With these changes, we risk seeing visitors like pufferfish and Box jellyfish—one of the most venomous animals globally—turn up,” she noted. “Some of these are newcomers, while others may simply be growing larger in the warmer waters.”
Even familiar coastal creatures present increased risks. The weever fish, known for its painful sting, might become a greater hazard as higher-heat tolerances make them more abundant near busy beaches. The notorious Portuguese man o’ war, famed for its powerfully stinging tentacles, could also make more appearances during these hot spells, experts warn.
Beyond the dangers to people, there are further ecological concerns. Warmer and calmer seas often provide ideal conditions for algal blooms, resulting in mats of green algae that can be harmful to other marine species. However, there is a curious upside—as bioluminescence becomes more common, some night-time beachgoers may encounter spectacular glowing displays in the surf.
Still, not all marine residents will thrive. Frankie Hobro noted, “There’s no relief for marine animals during a heatwave; they can’t escape into the shade or turn down the temperature like we can.” Some species risk being pushed away from British coastal waters in search of cooler habitats, possibly altering Wales’s traditional marine biodiversity.
The Met Office’s Dr Berthou described the mechanics of these marine heatwaves: “A layer of warm water forms on the surface, acting like a ‘lid’ and keeping the heat from mixing into deeper, cooler waters. Like a thin film of oil on water, it traps heat, and we have recently observed the surface sea temperature jump by an extra degree in less than two weeks.”
Climate scientists caution that the long-term picture could see such marine heatwave events become more frequent, more intense, and persistent. Dr Jonathan Tinker of the Met Office remarked, “Projections suggest sea temperatures might rise by up to 2.5C by the middle of the century, which can intensify heatwaves on land, alter rainfall patterns, and make these extreme oceanic episodes routine rather than rare.”
As Welsh beaches prepare for a busy summer amid these shifting conditions, both holidaymakers and local authorities must be vigilant for novel safety risks in the surf. While the prospect of new marine life might entice wildlife enthusiasts, most experts agree that public education and awareness around these changes is critical to ensuring everyone enjoys the shoreline safely.