Blooming Octopus!
- Eloise
- Oct 17
- 9 min read
This year Cornwall’s shores (and front-pages) have been awash with tentacles. Divers have delighted in surprise encounters, while fishers report mixed fortunes - some landing record catches, whilst others face empty pots. With World Octopus Day having just passed (8th Oct), what better time to discuss our eight-armed neighbours and why they’ve been making such a splash.
Cornwall’s Octopuses
Found in temperate, sub-tropical, and tropical waters, the European octopus (Octopus vulgaris) can be found pretty much everywhere besides the poles, including Cornwall. One of two species seen year-round, their tentacles are lined with double rows of suction cups, and stretch a whopping 2-3x their body length. Usually a rare sight in Cornwall, European octopus population growth is favoured by warming sea temperatures.
The curled octopus (Eledone cirrhosa) is smaller and a more common sighting here. With single-rowed suckers and curly-tipped tentacles, they also possess small horn-like protrusions on their heads. This blog will hone in on the European octopus as they’re the star of the moment here in Cornwall.
Taxonomy
Strange as it sounds the plural is octopuses - not octopi! Octopuses are bottom-dwelling Cephalopods, meaning “head-foot” in Greek. This Class includes Vampyromorphida (vampire squid) and Sepiida (cuttlefish) amongst others. Cephalopods all have eyes, tentacles, and a mantle to enclose their important organs.
Ecology & Importance
A valuable asset to the Cornish fishing industry, the European octopus is worth more than crab - providing a lucrative catch. But their value doesn’t stop there. Skilled mid-level predators, they keep crab, shrimp and other mollusc populations in check whilst feeding dolphins, sharks and seabirds.
Octopuses are habitat engineers. If you’ve seen the clip of an octopus covered in shells from Blue Planet II, you’ll know just how good they are at manipulating objects (if not, watch it here). Octopus dens, constructed using discarded shells and rock, serve as an oasis of hiding spots for marine life. Subtly changing the seabed, they attract grazers, scavengers and fishes.
Octopus encounters are sought after by tourists. Filmmakers, pleasure divers and snorkellers alike revel in even the most fleeting of experiences. Remember that documentary, My Octopus Teacher? Despite their elusive habits, octopuses can be extremely characterful and have been known to befriend divers - exploring arms, legs and fins. It’s best to keep a distance from marine wildlife but when a curious octopus grabs on, you’ll just have to wait it out.
Anatomy
Like all invertebrates, octopuses have no backbone. This doesn’t mean they’re cowardly, but rather their body is held together by a hydrostatic skeleton instead of bones. Having a fluid-filled system enables strong muscular movements and allows an octopus to squeeze into keyhole-sized crevasses other creatures cannot. Scientists have discovered that hydrostatic skeletons take less time to heal than bones, as the fluid quickly regenerates.
Using a combination of jet propulsion and muscular arms, octopuses possess immense speed and agility. Siphons, side-facing openings below their eyes, direct jets of water away from the mantle much like a squid. Each of their eight arms are packed with dense muscle that is buoyant thanks to the lack of bone. All this together results in a very nimble predator indeed.
It takes three hearts to power an octopus. Such speed requires an additional supply of oxygen to the muscles, achieved by two branchial hearts which pump blood to the gills. The third systemic heart supplies oxygenated blood to the body, and actually stops when an octopus is swimming! So if you spot an octopus, try to avoid scaring them into a dash for safety - you’ll literally stop their heart.
Octopus blood carries oxygen via Hemocyanin, a copper-based compound which appears blue. Hemocyanin is less efficient than our iron-based hemoglobin, further explaining why three hearts might be necessary. With such incredible anatomy, it’s no surprise octopuses are also masters of perception and cunning…
Brains for Days
Octopus brains have confused scientists A LOT. Firstly, they’re folded and lobed. These are traits usually shared with highly evolved vertebrate brains like mammals, not invertebrates! Recent studies also suggest that the level of folding (gyrification) is dependent on habitat. Reef-dwelling octopuses may require a greater brain surface-area to account for camouflaging, compared to nocturnal deep-sea species who rely less on visual disguises.
Octopuses have the largest brain-to-body ratio of any invertebrate. Cephalopods all have donut-shaped brains which stretch out when the animal consumes food, giving a whole new meaning to the phrase “food on the brain”! But octopuses don’t stop there - their central, ‘donut’ brain oversees a separate mini-brain found in each tentacle. Yep, nine brains.
This decentralised nervous system allows acute control over each tentacle, meaning octopus arms can move more or less independently of one another. Four might be swimming, whilst two crack open a crab, and the other two navigate tasty morsels into its mouth.
Experts of Deception
When you imagine an octopus, what colours do you see? If I put out a poll with this question, I’d get a few different answers. That’s because octopuses are known for their colour-changing skin, used to blend into their surroundings or stand-out with eye-dazzling patterns.
Colour-shifting skin is especially helpful for communicating messages like “don’t touch me, I’m dangerous!” or “please, will you go out with me?”. But how do they do it? Chromatophores. Tiny cells filled with an elastic sac of pigment, chromatophores are controlled by nerves in the skin. When they expand, the colour becomes more intense like a paint-filled balloon being blown up.
Blending into your background isn’t enough to flounder most marine life - to truly disappear, you must BECOME the reef. Octopuses do this by changing their skin texture with papillae - small projections that get raised to mimic surrounding features like coral, seaweed, or even other wildlife.
Colour Vision
To the human eye, life under the ocean is an explosion of colours. Despite their colour-changing abilities, life for an octopus is mostly black and white. They experience the world through fine-sensitivity to light, using acute detection of shadows to navigate and hunt.
The human eye uses photoreceptive cells called ‘cones’ to detect colour, which cover a very specific part of our retina. But the octopus’s retina is covered by photoreceptors in all sorts of horizontal and vertical patterns. This allows them to detect polarised light from different angles, a type of light our eyes aren’t evolved for.
Being colour-blind may seem like an evolutionary flaw, but is actually helpful underwater. Certain colours get filtered out with depth, starting with red (as divers will know). Polarised light is unaffected by depth so the octopus can continue its stealthy lifestyle.
Poked, Prodded… and Protected?
Octopus intelligence is revered by scientists worldwide. However, as invertebrates they’ve been subject to decades of invasive and cruel research techniques. I’m talking about arm-amputations and live brain dissections, in the name of wound-tending behaviour and neuroscience studies. Through this horror, we’ve learned that their intelligence outweighs that of all other invertebrates.
Proven sentience, ability to feel pain, and excellent problem-solving skills have earned octopuses a degree of protection from invasive studies in the UK. In 1993, the Animals Scientific Procedures Act of 1986 was amended to include octopuses as a “protected animal” species based on evidence of their advanced nervous systems. In 2022, they gained further protection from the new Animal Welfare Sentience Act - which recognised octopuses amongst other invertebrates as sentient beings.
Whilst change is happening, it’s slow. These legislations don’t ban invasive octopus studies - they simply restrict them. Sadly not all countries recognise octopuses as sentient, so the number being experimented on worldwide keeps growing.
Live Fast, Die Young
Octopuses have a short lifespan - 1-2 years. As “semelparous” breeders, they reproduce only once in a lifetime. Investing all their energy into producing thousands of eggs, males die soon after mating. The females use their last few months to guard the eggs, starving as they do so. Baby octopuses (fry) enter the world already orphaned.
Drifting as “paralarvae” the size of a grain of rice, fry are at the mercy of the ocean. Dodging currents and predators, they seize every opportunity to hide and feed, often attaching to drifting debris or rubbish. After a few weeks, they settle in a crevice which serves as their den.
We don’t tend to encounter octopuses until early adulthood, when they move out of the shadows and start to hunt. From the thousands of eggs, only 1 or 2 will survive to become mature and start the semelparous cycle all over again.
Octopus Overload
This year on the South West coast, we experienced the biggest European octopus bloom in living memory. The bloom ramped up in March/April, when sea temperatures surged to 2-4 degrees above average spring temperatures. Cornwall has been subject to an 18-month long marine heatwave, lending juvenile octopuses a greater chance to survive to adulthood.
Scientists have described “boom-and-bust” strategies in many marine species, and the European octopus is no exception. Owing to their short life-cycle and immense investment into egg production, a few previous blooms have been observed across history - in 1899, 1933, and 1950. Aligning with unusually warm sea surface temperatures, other factors explaining these blooms include changes to fishing pressure, shifting prey stocks, and improved habitat quality.
This bloom has had contrasting impacts across Cornwall. Providing some fishers with a much needed boost, in June, Newlyn trawler “Enterprise” landed a record-breaking catch worth £158,000. 90% of this was European octopus. However, the very same octopuses have been gorging themselves silly on shellfish - leaving crab, lobster and scallop fishers out of pocket.
It is thought that octopuses are entering pots through IFCA-introduced “escape gaps” - a conservation measure intended to protect undersized shellfish. Now there is talk of sealing the gaps, to prevent entry from unwanted, hungry, eight-armed guests.
Concerns about the long-term depletion of crustacean stocks still circulate Cornwall’s fishing communities. However, history suggests this current bloom will fade within a season or two. Previous events died down with colder weather, and the octopus’ naturally short lifespan should curb numbers.
What’s next?
Local councils, the Department for Environment, Food & Rural Affairs (DEFRA) and the fishing industry have joined forces to understand the bloom. Using baited remote underwater vehicles (BRUVs) and time-lapse cameras, they’re capturing octopus behaviour to try and understand the bloom’s drivers. Data will hopefully be used to pioneer an early-warning system for fishers in the future.
This summer, Dr Bryce Stuart (Marine Biological Association) confirmed this bloom is a combination of unusually warm sea temperatures and shifting ocean currents driven by climate change. But the best insights often come from those closest to the water. Divers, snorkellers, and beach-combers are invaluable sources of information when it comes to understanding our marine life.
Locals this year have described abnormally large gatherings of European octopuses and vast amounts of washed-up egg cases. If you witness any unusual octopus behaviour, please let your local marine group know. At Falmouth Marine Conservation, we’d love to hear about your sightings as this strangely-tentacled season unfolds.
Octopuses are sources of inspiration and mythology - intelligent, shape-shifting, short-lived, and vital to our seas. This year’s bloom highlighted their ecological importance, and the challenges of sharing waters with them. As climate change reshapes our coasts, it is vital we consider the intersection of marine conservation and the longevity of our fishing communities. Keeping watch on our eight-armed neighbours will help us understand, adapt, and look after both.
Shout-outs go to our generous and talented photo contributors:
● Lewis Jefferies is a passionate conservationist, self-shooting filmmaker, cameraman & award winning underwater photographer based in Falmouth, Cornwall. He’s worked with clients like Cornwall Wildlife Trust, RSPB and Natural England to help communicate environmental issues and celebrate progress within nature conservation. Check out his awesome work:
○ Website - Lewis Michael Jefferies | Filmmaker | Underwater Photographer | Drone operator | Camera Operator
○ Instagram - @lewismjefferies.camera
● You can find the works of David Nicholson and George Rundle, both talented marine photographers, on the MarLIN website - an esteemed online repository showcasing thousands of marine species for researchers and the public.
● Ryan Hunnisett is a local scuba instructor and marine biologist based in Helston, where he operates a dive shop and assists conservation organisations like the National Lobster Hatchery. To see what he’s been up to, and for info on Cornwall’s best dive sites:
○ Website - Scuba Ry Divers
○ Instagram - @scuba.ry.divers
● Paul Newland is a widely traveled diver and member of the Totnes Subaqua Club, with a keen interest in marine life. His work has also contributed to the growth of the MarLIN website.
Want to dive deeper? Click the link below to read the Marine Management Organisation’s official Octopus Bloom Stakeholder Update (PDF). 2025-08-06_Octopus_Bloom_Stakeholder_Update_Minutes_EXTERNAL.pdf
References
● ‘The seabed is full of them’: English fishers enjoy surprise octopus boom | Fishing | The Guardian
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