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Stealthy Slinker of the Deep

Text and photography by Andrea & Antonella Ferrari


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day octopus picture
close-up detail of eye and siphon of day octopus, Octopus cyanea, Lankayan, Sulu Sea, Sabah, Borneo, Malaysia, Pacific Ocean Image #: 126153

Closely related to cuttlefish and belonging to the same class of Cephalopoda (meaning “Footed head” in Latin), octopi – or octopuses, both forms are correct – are some of the reef’s stealthiest and most cunning predators. Fired by an almost human intelligence and only slightly hindered in their evolutionary course (if compared to humans) by a less energy-efficient copper-based (rather than iron-based) blood, octopi silently slink and slither among the corals’ nooks and crannies, being able to disappear at lightning speed in impossibly tight crevices and sporting amazingly effective camouflage. Being boneless and mostly made of muscle, octopi are easily capable of stretching and bending their sac-like body and eight long suckered limbs to great extremes, and their capability of controlling at will the pixel-like color cells imbedded in their skin (called “chromatophores” or color-carriers in scientific parlance) enables to change the texture of their skin and most of all their color and pattern at an equally surprising speed. Their intelligence and dexterity has to be seen to be believed – an octopus will readily understand it has to uncork a glass bottle to get at the juicy crab contained within, and resident reef ones will rapidly learn to recognize visiting divers, even accepting crabs or shrimp directly from their hands. Their tentacles are unbelievably flexible and strong, offering them an almost human capability of manipulation and extraordinary sensitivity – just look at the way they can clean the inside of a lobster shell entering it from the smallest of cracks! Mostly feeding on hard bivalves and crustaceans – and occasionally fish – which they grab with their incredibly flexible suckered tentacles and rapidly subdue with a crunching venomous bite administered from their robust parrot-like horny beak, octopi are also able to squirt a jet of dense black ink when threatened, temporarily creating a phantom image of themselves which hopefully would confuse a predator. Despite being very clever, octopi are however mercilessly hunted down by many other coral reef species in tropical waters, falling prey on a daily basis to marauding moray eels, groupers and whitetip or zebra sharks. Octopi are distributed all over the world from cold to temperate and tropical seas (the largest species haunts the icy waters off Canada and North America), but the most colorful and often puzzling ones are certainly those encountered in warm Indo-Pacific waters, where divers and photographers routinely meet undescribed or even completely unknown new species.

The most commonly observed species in hard coral reef environments is the so-called Day Octopus Octopus cyanea – this is also one of the larges species, being able to reach a total length of about three feet, and also being one of the less flamboyant ones. Keen divers and photographers will often see one attentively peeking at the surroundings from the safety of its lair, usually a hole or crack among the corals, easily recognized by the collection of discarded empty bivalves lying at its entrance. This species is usually a pale grey or a whitish blue, but it can rapidly become purple, bright red or even strongly banded in black and white, depending on its surroundings, its intentions and most often its emotional mood. A very similar but much smaller species is the Veined or Margined Octopus Octopus marginatus, usually smaller than a spread hand and easily identified by the bright white-blue edge to its purplish tentacles. This species is commonly found – often in very large numbers – on silty, sandy or mucky shallow bottoms, often comically peeking out of broken bottles, halved coconut husks or empty bivalve shells. For obvious reasons it is a great favourite of underwater photographers, being a delightful subject and often tip-toeing away on the substrate carrying along with its tentacles the little fragments of rubble it used to hide itself. Sadly, it is netted in immense numbers, being marketed fresh or dried by the name of “sand bird” in Chinese markets. Even smaller – and apparently represented by at least five or six different species, of which only one is at the moment officially described – is the much-sought after (and occasionally much feared) Blue-ring Octopus Hapalochlaena lunulata, which can vary in size from a small coin to a spread-out child’s hand. This strikingly beautiful species features a pale yellow or mustard background dotted with a large number of electric blue or turquoise rings (of variable size depending on the species) which it can flash at will, advertising its extremely venomous and dangerous bite, which in fact can easily paralyze and kill a full-grown human being. Blue-ring Octopi seem to favor shallow rubble bottoms, but we’ve also seen and photographed them among healthy hard coral colonies and on mucky, silty bottoms, so it’s quite difficult generalizing. In fact we’ve also found one of the most beautiful ones we have ever seen inside a discarded plastic wallet! Blue-rings introduce the real “aristocracy” of the Octopus realm, which features the three rarest species – namely the Mimic Octopus Thaumoctopus mimicus, the Wonder Octopus or Wonderpus (Wunderpus photogenicus – no, it’s not a joke...sadly that’s its real scientific name ) and the so-called Hairy Octopus (for the time being still undescribed). Mimics are the largest of the three, boldly striped in dark purplish brown and white, often observed on mucky, silty bottoms with only their stalked eyes emerging from the substrate: they certainly are the ones which display the best “mimicking”, often looking like different animals (mantis shrimps and flounders especially). Wonderpus are smaller, with a tiny pointed head-sac and a smoother skin texture, and are much more brightly colored, dressed in pale brown, bright orange and bright white: they are more often found out in the open, frequently observed on coral rubble or sand, and much less liable to “mimic” other marine species. A similar species – the so-called “White-V” or Comet Octopus – is much less colorful (being a more or less uniform pale sandy tan) and often observed at night or dusk on silty bottoms, but in fact several observations of this puzzling species might in fact be of male Mimics, which – as we have recently demonstrated with our photographs of mating Mimics in Bali – normally look quite different and much more plain than the females of the species. Last of the group, the mysterious and seldom observed Hairy Octopus is a small, exceptionally cryptic species which features in varying amounts weird “tufts” of fleshy tissue resembling hair, probably depending on its environment. It is rarely observed by eagle-eyed divers and photographers on coral rubble bottoms, especially where colonies of soft corals are present. But let’s be honest – when we are talking about octopi, we are grouping under the convenient umbrella of scientific and common names an exceptionally broad group of animals of which in fact we know very little, and which probably numbers a much larger number of still-to-be described, observed and photographed species. So next time you see that familiar eight-legged shape stealthily slinking among the corals pause for a moment and give it a good hard look – it might be a new species, still unknown to science, of this fascinating and mysterious group of animals!


Large Day, Mimic and Wonder Octopi request a medium lens, and wonderfully creative results can be obtained getting really close with a wide angle, while a good macro lens will be perfect for smaller species like Blue-rings, Hairy or Veined. A close-up of the bright, golden, intelligent eyes of the octopus looking out of its lair will almost always guarantee colorful and quite delightful results, while “action” shots of the animal prowling around are invariably more difficult, more often than not resulting in the speedy departure and disappearance of the critter. Octopi are quite capable of delivering painful, dangerously venomous bites – often deadly in the case of Blue-rings – and should obviously never be grasped or restrained.


Day Octopi are occasionally observed – but one has to look hard! – on healthy, hard coral reefs in shallow, sunlit areas. They’re quite common everywhere in the Indo-Pacific. Margined, Mimic and White-V are encountered on silty substrates, while Wonder and Hairy are relatively more frequent on coral rubble. Best dive destinations to see them fairly regularly and reliably are Lankayan (Wonderpus and Blue-ring), Kapalai (Wonderpus, Blue-ring and White-V), Mabul (White-V, Blue-ring), Lembeh (Mimic, Wonderpus, Blue-ring, Hairy), Bunaken (Mimic, Wonderpus, Hairy, Blue-ring), Bali (Mimic, Blue-ring). Despite being more active at dusk like most other reef predators, most tropical octopi can be regularly observed during daytime.