Creature Feature: Giant Pacific Octopus

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The Giant Pacific Octopus (Enteroctopus Dofleini)

  • Phylum: Mollusca Class: Cephalopoda
  • Family: Octopodidae

There are approx. 300 recognized species of octopus worldwide, and nine have been identified in our local waters, but the Giant Pacific Octopus is by far the most common and also the largest. Size is the most obvious difference between Giant Pacific Octopuses and the other soft-bodied, eight-armed molluscs of their family. Males typically weigh about 12 kg/25 lb and span 4.5 m/15 ft from the tip of one extended tentacle to another, while females commonly reach 20 kg/45 lb and 6 m/20 ft. But the largest specimen on record was a whopping 272 kg/ 600 lb and 9 m/30 ft!

They can also be recognized by their reddish-pink to reddish-brown default coloration— sometimes. They are mind-bogglingly masterful in the art of camouflage. They can blend seamlessly into the intricate patterns of rocky reefs, sandy seabeds, and foliage formations in their environment, thanks to specialized muscles that can change skin texture, and smart pigment cells, called chromatophores, just below the surface of their skin.

Unlike most other molluscs, octopuses’ shells consist of two small plates, located inside their heads. The head also contains the black, birdlike “beak” or mouth and the primary brain, the “command center” which regulates and coordinates the eight remote, auxiliary brains out in the arms. Their large eyes can detect the polarization of light, and are located at the top of the head. Behind the head is attached the bulbous and hollow mantle, whose muscular walls contain most of the vital organs, including the three hearts, digestive system, gills, and a siphon, sometimes called a funnel.

Where Do They Live?

They are distributed in rocky areas of the Pacific coast, throughout the intertidal zone to depths of about 100 m. Occasionally they can be found as deep as 450 m/1500 ft. They establish dens in caves or crevices, or dig them in sand-shell substrates.

Giant Pacific Octopus On Ocean Floor

What Kills Them, and What Do They Eat?

The most frequent and dangerous natural predator of the octopus is the human being. And while it is illegal to use jigs, gaffs, spears, rakes, or any other sharp-pointed instrument to take octopus, traps are a most effective—and even accidental—method of capturing them, as many anglers have discovered. Aside from Homo sapiens, the Pacific Octopus lives in mortal fear of wolf eels and lingcod. But otters and pinnipeds, orcas, dolphins, sharks, and many other types of large fish, eels, and birds relish a meal of octopus, as well.

All octopuses are carnivores, but they are not picky about the type of meat. They like to bring captured prey back to their dens to eat at their leisure, and their dens often will be flanked by a food storage pile and a trash pile. Sometimes their den will be shared by prey that has eluded its captor or scavengers hoping to benefit from octopodal largesse. Typically, they hunt nocturnally, preferring to feast on crustaceans such as shrimp, prawns, and crabs; and molluscs such as snails, clams, scallops, mussels, and other cephalopods. But they are proficient fishermen as well, and have been known to eat all kinds of fish, including sharks. They will even attack birds, using their sharp beaks to tear the flesh. In times of extreme hunger, they may resort to cannibalism. Some have even started eating their own limbs, and then dying, but we don’t know what causes this bizarre behavior. It could be boredom, stress, or more likely a disease of the nervous system.

How Do They Survive?

Octopuses do have, in their prodigious self-defense arsenal, the capacity for autotomy; similar to lizards and skinks, they can break off an appendage to abandon and regrow it later. The severed limb remains sensitive to stimuli, and will move about and writhe—and even pursue prey or retreat from a predator—for some time after being detached, thanks to its complex independent neurological system.

Their favorite self-defense move is simply to stay hidden in their den, spending as much as 40% of their time there. When suspicious activity is detected outside, an octopus will extend an arm to investigate, preferring to sacrifice one scout in protection of the battalion, so to speak.

Camouflage

As mentioned previously, octopuses are camouflage and mimicry geniuses. When they do venture out, they will disappear into their surroundings or pretend to be more dangerous creatures. They also perform a “moving rock” trick, in which they will inch imperceptibly across an open space, in plain view of a less-savvy predator, by matching their speed to the movement of waves and light in the surrounding water.

Occasionally these opportunistic fighters will brandish physical weapons, such as sticks, or even stinging tentacles ripped off of a Portuguese man-o’-war.

Octopus Ink

But perhaps the most famous defensive tactic of the octopus is its sudden secretion of ink. The ink sac is located under the digestive gland, and close enough to the siphon for the octopus to shoot out ink with a water jet, getting mixed with mucus from yet another gland on its way out. The result is a murky melanin-dense blob of confusion, which not only destroys visibility for predators, but also inhibits their olfactory organs. This is particularly effective in thwarting sharks and other creatures who hunt by their sense of smell.

What Moves Them?

Giant Pacific Octopus Moving

Like most octopuses, the giant Pacific variety is solitary when it isn’t mating, and can be pretty standoffish even when it is. While they are not territorial, they like to hang out on familiar “home turf” near their dens. They have special gravity- and acceleration-sensing statocysts attached to their brains, so that if they sally forth into unknown waters in search of food, they can navigate a return journey, without having to retrace their outbound path. Despite this sophisticated adaptation, they are not known to be migratory.

Propulsion

They have the capacity for jet propulsion, by means of forcibly expelling water through their siphon, but they prefer to swim slowly, backwards and headfirst, or to creep cautiously on their eight iconic arms. In actuality, octopuses could be said to have six arms and two legs. The two rearmost of their extensible appendages are used primarily for “walking” or crawling on the seafloor, and infrequently on land, while the other three pairs are used more like hands, for hunting and exploration. They often use their suckers to haul themselves from one place to another, reaching with one set of arms, while a previous set anchors them, until the foremost set is firmly suctioned to the new location. Even such minor exercise causes the heart rate nearly to double, however, demanding that they rest for 10 or 15 minutes between intervals of activity.

Shapeshifting

Octopuses are also famous shapeshifters. Being made up mostly of soft tissue and lacking a skeleton, they can fit through any hole that will admit their hard beak, which, in mature adults, is about an inch (or 2.5 cm) in diameter, the size of the average cherry tomato. In the absence of bones, arms are articulated by muscular hydrostats—similar in function to a human tongue. Thus, they can extend, contract, twist in either direction, bend at any angle, or be held rigid as required by the situation.

How Do They Grow and Reproduce?

These introverted invertebrates wrote the book on social distancing. While they will occasionally make an exception, and cling to one another during mating, they don’t have to. They often prefer to get on with the process through a simple handshake. Well, maybe it’s not exactly a simple handshake, but the male reproductive organ, containing his gelatinous pencil- shaped spermatophore packets, does reside in one of his arms—the third right one—called the hectocotylus. So if his den is close enough to that of a willing female, he doesn’t even have to leave the comfort and safety of his living room. This scenario also renders him a lot less likely to get eaten alive by his partner. Nevertheless, octopus courtship is usually more similar to the human style, in that it is accompanied by special displays to attract the attention of potential partner, including change in skin texture and color, and demonstration of skill. Once granted access by a female, a male may use his special arm to remove anybody else’s spermatophore, and deposit his own, into her mantle cavity. All this amorous effort exhausts him, and he dies within a few weeks or months of breeding, whether or not his mate is particularly ravenous or irritable.

About 40 days after being impregnated, the female hangs her two litres of delicate, rice-sized eggs (between 10- and 70,000 of them) from the ceiling of her den, like lacy white curtains or strings of party lights. Then she cares for them, cleaning, aerating, and literally guarding them with her life, for about the next five months. In colder subarctic waters, eggs may take up to 10 months to develop. If left unattended, a majority of her eggs will not hatch. So during this brooding period, she subsists solely on the fats and proteins of her own body, fully consuming herself over the course of gestation. Shortly after her eggs hatch, she dies.

Baby Giant Pacific Octopuses are planktonic and drift around in the water until they are about 50 mm/2 in long. Then they descend to the bottom, and continue to mature for two to three years, living up to about five years.

Everything comes back to complex optics with octopuses, and the optic gland is thought to also secrete hormones that cause them to mature, age, and stimulate procreative capacity. Thus environmental factors such as temperature, light, and available nutrition can greatly affect octopus reproduction and lifespan.

Trivia: What Makes Them Special?

Octopus in Barkley Sound recovered from a prawns trap
Photo from Blair Mitchell, April 2020

Octopuses have three hearts: a systemic heart for pumping blood throughout most of its body, and two branchial hearts for circulating it through the gills. The systemic heart is inactive while the octopus swims, which causes it to tire quickly. In addition, octopus blood contains a copper-rich protein called haemocyanin, which carries oxygen more efficiently than haemoglobin in cold environments, and gives it a bluish colour. It also makes it viscous, requiring considerable pressure to pump. This may be the reason it is such a lackadaisical homebody.

Octopus’s Garden

Octopuses are drawn to shiny objects, and have often been observed collecting and arranging these and other curiosities in and around their dens. There’s no known reason for these little “octopus gardens” other than a possible penchant for home decorating. But they can alert a keen observer to the presence of an octopus lair, and they inspired the Beatles’ Ringo Starr to write a catchy tune.

Octopus Intelligence

Octopuses can make strategic decisions, recognize individual humans, navigate mazes, and solve certain types of puzzles. They have been known to board fishing boats and open holds to munch on crabs. In aquariums, they have even been observed playing with LEGOs, and releasing objects—such as rubber duckies—into a circulating current, and later catching them. Not surprisingly, they also have had success in breaking out of aquariums, and in exploring other tanks and nearby labs, where they have opened doors and lids, and disassembled equipment. Jaques Cousteau wrote of an octopus who escaped into a friend’s library, where it removed books from the shelves and turned the pages.

Octopus Brain

Widely considered the most intelligent of all the invertebrates—and smarter than most vertebrates, as well, octopuses have nine brains… sort of. Protected within a donut-shaped cartilaginous capsule, the central brain of an octopus—which some contend is its only “true” brain—controls and coordinates the nervous systems, while a smaller, auxiliary “brain” in each limb controls the movement and sensory perception of that limb. But as we discussed earlier, each of these limbs can operate independent of the octopus’s head and mantle, even after being disconnected. In reality, the arm-brains are more analogous to the brain stems of humans and other vertebrates, being responsible mostly for reflexive action as opposed to conscious decision. In similar fashion to how we can walk, digest food, and feel a breeze without really thinking, any of an octopus’s limbs can sense prey and try to capture and taste it without input from the command center. Of course, they can also function in a coordinated manner, when required. In any case, the arms contain two-thirds of octopuses’ neurons.

The brain capsule encircles the animal’s esophagus, so when octopuses bite off more than they can chew—or more accurately swallow something too large—it can actually give them brain damage.

Octopus Tentacles

The suckers on octopus tentacles can taste whatever they touch, and will stick to just about everything, except octopus skin—presumably because it tastes like octopus skin. So they never get physically tangled up in or stuck on themselves, though they are otherwise pretty solitary and self-absorbed.

Venom

All octopuses, including the Giant Pacific, are venomous, but only one is known to be deadly to humans. And it isn’t this one; if you’re interested, it’s the blue-ringed octopus, which inhabits parts of the Indian and Pacific oceans, ranging from Japan to Australia.

Historical/Cultural References and Uses

Octopus has long been eaten as a delicacy by Asian and Mediterranean cultures, and used as effective halibut bait here in our western fisheries.

But aside from these practical considerations, this clever and mysterious creature has given rise to a multitude of myths and legends, predating the dawn of recorded history. Norway’s Kraken, Japan’s Akkorokamui, and probably ancient Greece’s Gorgon and Scylla owe their inspiration to the Giant Pacific Octopus, or perhaps one of its extinct ancestors. British pop stars have sung about them. Literary greats, like Victor Hugo and Jules Verne, have required their protagonists to battle them. And the silver screen has often been entangled in their spell. Octopuses have caught our imaginations for as long as there have been fish stories, and they will probably continue to captivate us, as long as there are fishermen around to tell of them.

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