Mesmerised in an octopus garden
MY BUDDY WAS POINTING towards a spot less than a metre in front of my face.
I was looking straight at it – but I couldn’t see it.
A few exasperated seconds later, I realised why I couldn’t make out the shape, as the obliging octopus flushed dark red before moving off.
I had been looking for an octopus shape among a large patch of reef, but the octopus was the entire patch of reef.
Watching an octopus forage around a reef or put on a show to evade a diver are among the most delightfully disorienting sensations diving can offer.
The octopus might freeze, raise lumps on its skin and mottle its colour to blend in with the reef, waves of colour literally flowing through the skin at the speed of nerve transmission.
Then it could turn a vivid white or deep burgundy, while pouncing and spreading over a coral head or rock like an elastic parachute.
Then it might go into evasion mode, flashing colour changes while walking over the floor on the tips of two tentacles, or rolling as if on caterpillar tracks, then jet away a few feet before freezing and “disappearing”, becoming indistinguishable from the reef.
These changing colour patterns are used to confuse and startle (via dramatic “flamboyant” displays of colour and posture) both predators and prey.
The most impressive flamboyant display I’ve seen was in a large maori octopus in New Zealand’s Milford Sound. Maori octopuses have fairly fixed colour patterns compared to most others, so most of their displaying is done with shape changes.
The spread of the web between this large octopus’s arms was the width of a large umbrella – making an already large animal look intimidating to the potential predator (that is, me).
The colour changes produced by most reef-dwelling octopuses are produced by thousands of brownish to reddish cells, called chromatophores, embedded in the white skin.
They are the individual pixels, giving the skin of octopuses a grainy look.
Each cell can be squeezed to a pinprick by muscles in the white skin, or opened out to a large vivid spot. Blocks of cells are stimulated by nerves, and patterns can be changed at the speed of thought.
Reef octopuses might deter predators by spreading their tentacle umbrella wide and change rapidly from pale to an angry red in an impressive flamboyant display known as a deimatic display.
Deep red or pale areas around the eyes are sometimes flashed, contrasting startlingly with the rest of the body.
Beloved of photographers at Lembeh in Indonesia and elsewhere, the coconut or veined octopus displays the whole spectrum, from angry deep red blushes to orange-brown to snowy white.
COCONUT OCTOPUSES really like their shells. Whether they are coconut halves or bivalve shells, they use them as armour and a home, rather as hermit crabs use snail shells.
We watched a couple of coconut octopuses squabble and wrestle over shells in Lembeh. At one point one of them won a third shell after a tug-of- war that involved much deep red blushing on both sides.
Once won, the victor had a bit of an issue – three big shells that he simply couldnt handle. So he simply dropped one. His opponent (sulkily, I think) hiked up his remaining shell under his armpits, turned a grainy cryptic colour and tiptoed off on the ends of his arms.
Smaller sand-dwelling octopuses seem to prefer more “shape-shifting” or camouflage displays – aiming to confuse rather than scare.
The mimic octopus in the image taken in Lembeh Strait had just shown some of the range of vivid striped disguises for which it is so well known, first pretending to be a lionfish, then a sea-snake.
Then, shifting tactics as the photographers continued to approach, within the couple of seconds this and other photos were taken it faded its stripes and changed to grainy camouflage as it melted into the sand.
A pygmy octopus tried the same tactic, going from patterned to cryptic in a fraction of a second.
The delightfully named Wunderpus photogenicus seems to favour keeping similar bold stripes to the mimic, but flashing them darker and paler to startle, rather than mimicking a poisonous animal.
As well as the red and brown displays, octopuses can also match greens with their background, and some can flash vivid blues. They do not have pigments in these colours, yet the second layer of skin still manages to produce them.
This layer is made up of iridophores – pearlescent mirrors that can be angled to reflect local light. The Caribbean long-armed octopus shown is reflecting both the pale sand and some of the green of the seagrass.
As well as fine-tuning the camouflage, this reflective layer opens other startling possibilities. The highly venomous blue-ringed octopuses do not have any blue pigment in their skin, and when they are at rest the blue rings and streaks are fine and fairly inconspicuous.
If you wave your hand above a blue-ring, however, the markings thicken and flash iridescent blue, seeming to glow as well as grow. This is a “leave me alone, I’m dangerous” threat – and it’s all done with mirrors.
BIZARRELY, OCTOPUSES THEMSELVES don’t see colours. They are almost blind to red light, and see most clearly at the blue and turquoise area of the spectrum.
Survival as a concentrated packet of soft protein on shallow reefs is not without challenges. Without the speed or raw power of their cousins the squid, octopuses rely on flexibility – of behaviour as well as of their almost-liquid bodies.
Octopuses have larger brains and more complex behaviour than any other invertebrate.
A cautious demeanour and a good mental map of a small territory is key for reef octopuses. Most divers only ever glimpse a pair of eyes peering out from
a crevice in the coral or a burrow on thee sand, then usually a retreat as you approach.
Octopus foraging trips usually go out and back in varying directions to and from a central den. If an octopus sees a potential threat while away from shelter, it tends to head in a straight line back to the protection of its den, pausing along the way to change colour and try to lose the threat.
Sarah OGorman at Red Sea Diving Safari looks out for blackspot grouper rather than trying to spot the far more elusive octopus – the grouper follow the octopus, looking for prey the cephalopod flushes out.
Octopuses can learn, and lab tests suggest that they are probably smarter than fish and reptiles. But opening screw-top jars to get at food inside and finding their way around mazes seems to be their limit, and their abilities owe as much to trial and error and an acute sense of taste as anything else.
It seems that octopuses are less intelligent and more instinctual than some have suspected. With a one-year lifespan, excessive intelligence is probably not that important – being the smartest animals on the reef is enough.
Humans, once used to watching octopuses, can appreciate that the rapid change in colour or shape does not mean that the octopus is no longer there.
For other predators and prey, however, this is not necessarily the case. Few have the ability to understand the rapid changes in colour or texture of which an octopus is capable. They simply cannot maintain any meaningful awareness of such a shape-shifter.
OCTOPUSES HAVE A SENSE OF TASTE many times more acute than ours. They taste as much as feel with their sensitive suckers as they forage, reaching into crevices and under overhangs with the tips of their arms.
This is probably how the largely solitary octopuses find mates, and possibly how they avoid them when necessary – females of some species are larger than males, and cannibalism after mating may be a good last meal and energy boost for her.
Most of their lives are solitary, and octopuses do not have complex courtship displays, as cuttlefish and squid do. They simply find a mate (by taste), approach and either pounce or tentatively send out an exploratory arm.
The third right arm of the males is the mating arm, and reaches inside the females mantle (the muscular bag that makes up the body and holds the organs) to deposit a sperm sac.
Snorkelling off the Cook Islands, a group of us watched a large male day octopus approach a similar-sized female.
He took refuge behind a giant clam shell and reached around very carefully. She flushed several colour changes but finally accepted his outstretched arm.
Some species den next to each other before mating, the male staying nearby and aggressively chasing off other males while tentatively wooing the female. With other species there may occasionally be several males mating with one female at once. Apparently they dont mind sharing, and she gets her choice of sperm sacs.
The males may then go off and seek other mates, but not the females. Unlike cuttlefish and squid, a female octopus is a dedicated parent.
Once fertilised she will stop eating, lay and care for the eggs in a protective space until they hatch, at which point she will die from exhaustion.
Most cephalopods live only a year or so, but in that time they become supreme predators, and grow far faster than any other complex animal.
At 20 days old the greater octopus commonly seen around the UK may be thumbnail-sized. Three months later it will be 100 times larger, and in another three months it may weigh a kilogram.
A handful of large octopuses may live up to three years, and in that time become giants. With most animals very little of their food is incorporated into growth, but octopuses digest efficiently and convert up to a half of their prey into body mass.
Octopuses are soft-bodied, yet they like to eat crabs and bivalves – fleshy and delicious, but about as heavily armoured as food can be.
The solution is to drill a hole in the shell with the tongue, next to the muscle attachment, then to dribble heavily with digestive saliva to break down the muscle enough to loosen the prey up and get at the meat.
It can take some time to subdue struggling, armoured prey like this.
Large octopuses like the greater octopus use muscle power, wrestling then biting. My brother’s mother-in-law Sal tells of being a young teenager in the Med and earning money from the fishermen by diving down and enticing greater octopus to latch on to her, then being pulled to the surface with the octopus attached.
Apparently the “livebait” technique works well for large octopuses!
IN THE PACIFIC NORTH-WEST the largest octopus of all, the Pacific giant octopus Enteroctopus dofleini, even has a strange “octopus-wrestling” tradition associated with it.
A maori octopus in New Zealand reached out and pounced on me and my camera, trying to anchor onto the reef and pull my camera from me. This was only perhaps a 2kg animal but its all muscle – it took all my strength to peel myself and my camera from his grip.
With that kind of strength I’d be very polite to the Pacific giants, which can weigh 70kg – and certainly not take one on at wrestling.
The armspan of the biggest Enteroctopus is probably 6-7m – longer than the arms of the giant squid.
Some of the smaller octopuses subdue their prey with more potent venom, rather than muscle.
The lesser octopus Eledone cirrhosa found around the UK and elsewhere has strong cephalotoxin venom in its saliva. Bites from lesser octopus are reported to be rather unpleasant, if probably not dangerous to humans. It takes several minutes to effectively paralyse a crab. We don’t really know much about which octopuses produce strong venom and which don’t.
The tiny blue-ringed octopuses from the Indo-Pacific are the only ones known to have greatly expanded venom glands, and much more potent toxin.
I was amazed when I saw my first blue-rings off Indonesia, not only at how tiny they were, but also that they foraged unconcerned over a relatively open sand slope at 30m off the Lembeh Strait.
Their toxin, tetrodotoxin, probably explains their nonchalance. It is the same paralytic poison found in pufferfish and a range of other marine animals, and is 10,000 times more poisonous than cyanide, 10 times stronger than cobra venom.
The venom subdues prey instantly – and has the same effect on would-be predators. They’re not only small and soft-bodied but they’re also somewhat small-limbed and “flabby” – not exactly built for wrestling with prey – or with predators. Yet here they were, wandering in the open among the coral rubble, predators all around.
Deco and air beckoned. We left the tiny blue-rings ambling over the slope.
From the big wrestlers to the tiny but deadly blue-rings, octos just never get old. I get more of a buzz each time I see those slit pupils raised out of a hole looking at me, that lumpy, liquid skin shifting and changing.
You never know quite what game these smart little aliens plan to play.
David Hall’s book Beneath Cold Seas (Saraband, ISBN 978-0295991160) contains many images of giant octopuses and other creatures of the Pacific North-West. £20