A NIGHT DIVE IN EGYPT: sweeping over the sand at the edge of the shallow reef often brings treasures. My torch-beam catches
a reddish chunk of weed half the size of my hand. But it gives itself away – it softens to almost white to match the sand, the tufts flattening, then soft ripples of pinkish-brown flow across its skin. It’s a hooded cuttlefish.
As I move in closer I see the lidded pupils watching me, seeming almost asleep to my human perception but in fact alert and focused.
The skin of this little predator is a superb special effect from a science-fiction movie, spikes and lumps rising and smoothing as ripples of colour flow through the skin. In fractions of a second the little animal goes from red to white to various browns, from stripes to ripples to disruptive camouflage.
One second smooth, with arms tucked in straight in front of the eyes, then spread as rippling ribbons, the central arms raised over its head and curled to look like huge eyes on stalks.
It’s trying to startle me, confuse me and scare me – I’m potentially a predator, and I am hundreds of times its size.
I remember that when I first saw larger cuttlefish under water 20 years ago I was startled, confused and perhaps a little scared – it was so alien, so disorienting even for my relatively sophisticated human brain to grasp.
Its incredible ability to change the colour, pattern and texture of its skin makes an underwater encounter with a cuttlefish or its cousins the octopuses and squids a mesmerising experience, and a highlight for many divers. Waves of colour flow through the skin literally at the speed of nerve transmission.
The colour changes are made possible by hundreds of large coloured cells, called chromatophores, embedded in the white skin. These individual “pixels” give the skin a grainy look.
Most cuttlefish have brown, orange and brick-red chromatophores. Each cell can be squeezed to a pinprick by muscles in the white skin, or opened out and enlarged to a big vivid spot.
From zebra stripes to expanding waves rippling out along their bodies, different arrays of these cells give most cephalopods a repertoire of seven to 10 colour patterns. The European cuttlefish, with 16 skin-pattern combinations, has the most of any animal studied.
These colour patterns combine with postures of arms and changes in the texture of the skin to form a complex range of signals – a simple visual language. Males flash threat patterns at each other with one side of the body while sending courtship patterns from the side of their body facing the female.
Occasionally they fight but, as with most males competing over a female, challenges are mostly settled with displays.
As well as courtship and threats, the patterns can confuse predators or prey, either by startling them or via camouflage and breaking up shape and outline.
As many divers will attest, cuttlefish can also blend into the background, even “turning green” to blend with algae.
They do not have green pigments, but a second layer of skin manages to produce them via iridophores – basically tiny mirrors embedded in the skin that can be angled to either flash or mute reflected light from the cuttlefish’s surroundings.
Flash photography lights the cuttlefish from the “wrong” angle in relation to the iridophores, which is why a cuttlefish that was superbly camouflaged under the ambient light stands out and looks rather orange when lit with flash.
It’s easy to see why divers find cuttlefish such compelling viewing. They are so bizarre, and they are often approachable. The large, lidded, alien pupils of cuttlefish are often easier to get close to than the normally shy octopuses.
Cephalopods’ nerves are the largest and fastest on the planet, and they have extremely well-developed vision, although in most cases no colour vision. Those amazing skin patterns speak of complex communication and hint at intelligence.
The range of behaviour cuttlefish and octopuses show is far more complex than that of any other invertebrate.
Cuttlefish also are clearly looking straight back at us, and more than almost anything else under the sea seem to be thinking about what these strange, noisy, bubble-blowing monsters are (they don’t hear in the way we do, but they do feel vibrations with incredible sensitivity, so effectively “hear” low-frequency sound with their skin and balance organs).
Recent research suggests that cuttlefish can string together short sequences of displays, but nothing more complex – effectively they seem to be able to use short “pattern phrases”, but can’t get to grips with “sentences”, nor really string concepts together.
Their intelligence is at the level of being slightly smarter than everything else on the reef, and having acute senses, rather than having problem-solving intelligence.
Our summer visitors
Many cuttlefish spend much of the year in deeper water offshore, moving seasonally with over-wintering plankton and near-bottom fish. The European cuttlefish comes inshore to breed and, like almost all cephalopods, it will die shortly afterwards.
In the UK this happens in spring and summer, and British divers have found some cuttlefish breeding bays like Babbacombe surrounded by baited traps.
When I most recently dived Babbacombe the only cuttlefish I could find were trapped – displaying, mating and laying – inside fishing traps.
Breeding cuttlefish are close to death anyway, and there’s no reason why fishermen shouldn’t use this superb, efficiently produced protein after the cuttlefish have laid their eggs.
Unfortunately they are not getting the chance to lay their eggs outside the pots before they are caught – I found a single egg attached to some weed, and hundreds upon hundreds laid inside the traps.
There are about 120 species of cuttlefish globally, 100 of them the virtually indistinguishable Sepia cuttlefishes, found in all non-polar seas. They range from smaller-than-your hand to the Australian giant cuttlefish, which can reach the size of a Labrador.
The similarity of many species, combined with the mind-bending colour and texture changes of which they are capable, can make identification of these species difficult where several occur in the same place.
British seas are visited by three Sepia cuttlefishes, as well as two of 70 of the species of the closely related bobtail squids, which are smaller, with rounded bodies, “ear-like” fins and without the cuttlebone.
All cephalopods are pure predators, remarkable in the briefness, intensity and sheer efficiency of their short lives. Most live only a year, but grow faster than any other complex animal.
The secret is an incredible ecological conversion efficiency; the proportion of the food that is converted to body mass rather than being used for energy. Cephalopods digest efficiently and convert a huge proportion of their prey into protein for muscle growth – perhaps half in the case of slow-moving cuttlefish.
Cuttlefish’s internal bone, beloved of budgies everywhere, sets them apart from squid and octopuses. The bone is filled with tiny gas-pockets, allowing them to hover effortlessly and become the most low-energy of all the cephalopods, taking full advantage of their ultra-efficient metabolism.
Watching cuttlefish hunt is a reminder that the slow glide and lethargic-looking eyes belie bodies made up almost entirely of elastic muscle and lightning-fast reflexes. They are extremely effective predators.
One of my finest moments in diving came a couple of years ago, when I finally saw the enigmatic flamboyant cuttlefish Metasepia pfefferi in Indonesia’s Lembeh Strait. These squat, lumpy little cuttlefish don’t so much glide as waddle along on their “elbows” – thickened lower arms.
Their tissues are extremely toxic, and like their cousins the blue-ringed octopuses and the more distantly related nudibranchs, they advertise their toxicity with colour – they have rich dark browns and purples, reds and yellows contrasting with patches of white and stripes along the arms – the greatest range of colours of any shallow-water cephalopod.
One of these cuttlefish was hunting. Its posture became alert, and the lidded eyes became very focused on small crustaceans that we could barely see on the sand.
The arms spread and curled, suddenly painted a pale yellow-brown and standing out against the dark sand. This looked to be a flushing-out mechanism, and the body alternated rapidly between a gritty, grainy camouflage and a vivid dark and deep reddish pattern.
Our guide was almost pleading me to be ready with the camera, as from within the arms a pair of rather phallic white tentacles started extending, then flashed out faster than sight to grab a shrimp.
Instantly the cuttlefish was ready again with outspread arms, and in quick succession several more tiny crustaceans disappeared. After plenty of gasping in delight at this stumpy little killer, laughing and filling my mask with water, I nailed my snapshot on the last frame.