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A huge common octopus strikes a great pose as it walks along the UK substrate
 

If you know any divers on the south coast of the United Kingdom, you’re probably already well aware of the phenomenon I’m here to talk about: the incredible boom in population of the “common” octopus, Octopus vulgaris, that has occurred over the last 18 months and which has changed the balance of our south coast UK waters, at least for a while.

This species is called “common” because it’s relatively widespread internationally, and our neighbors in the Mediterranean are very familiar with it—including on the dinner table. But in the UK, we are at the northernmost point of its wide range, and a sighting would be a rare moment to be celebrated. In thousands of local dives, prior to 2025, I’d perhaps seen a dozen individuals ever; I’d far more likely see Eledone cirrhosa, the smaller curled octopus, which can be found throughout the UK. 
 

A close-up look at the intelligent eyes of a common octopus
 

Foreplay? Combat? The two look very, very similar in the world of the common octopus!
 

All that changed in 2025 when, in the late spring, we started seeing individuals and then multitudes of large common octopuses on offshore reefs and inshore waters. At my local shore site, I would regularly see over a dozen fully grown adults. This species can reach 20 pounds (9 kilograms) in weight, a hefty predator! I watched, fascinated, as they fed, interacted, competed for dominance, mated, settled into dens, raised their young, and then died. In one local spot alone, I monitored the progress of seven females, each with tens of thousands of eggs, throughout late last year.

This wave of octopuses wasn’t totally unheralded; at Porthkerris Divers on the Lizard Peninsula in Cornwall, a popular dive spot, there had been a handful of octopuses over the last couple of years, including a female with eggs. But this was the only reliable location for a while. And then, of course, there is the mystery of the historical record. Over time, approximately every 60 years, the Wildlife Trusts record several isolated “major octopus plagues” that have lasted for one year only, such as in 1899 and 1948.
 

Female octopuses are wonderful mothers. Each one gives her life, starving to protect her offspring until they set forth into the world on their own
 

A small common octopus sheltered down in the protection of some bryozoans
 

An odd sight until just recently—a common octopus moving through a kelp forest
 

Divers have been utterly fascinated by this change, but it isn’t good news for everyone; these newcomers have to eat, and they have been tucking into all kinds of shellfish with gusto. In 2025, fisherman reported that catches of crab and shellfish were 50% down on average, as the octopuses ate their way through the target species and even raided the pots directly. Some fishermen had diversified, targeting the invaders, and at summer’s peak, 450 tonnes of octopus were being brought in per month.

We can only speculate as to the reasons for the sudden change. Waters have been warming; a mild few months with easterly winds allowing young to cross the Channel at the right time; a dearth of predators on these vulnerable young during critical development time; or perhaps the UK has more crustacean food at present than their previous haunts. More study is needed.   

Last year, we speculated as to whether this too was to be a one-year wonder, our eight-armed friends gone as quickly as they appeared. After all, their lifespan is a fleeting year or two. That has not been the case. We are still seeing many on our rocky reefs, and over the last few weeks, I have seen fantastic mating displays and males guarding the females they’ve attracted. Last week alone, I lost count at 20 individuals on a dive. It seems they are here to stay, and I for one can’t wait to see what will happen next.
 

A large male common octopus protects a female, invisible beneath his cloak of tentacles
 

To see more of Kirsty’s award-winning underwater work, please give her a follow on Instagram and visit her website, www.kirstyjandrews.co.uk.