Biogeography of the Giant Pacific Octopus

Kingdom: Animalia
Phylum: Mollusca

Class: Cephalopoda
Order: Octopoda
Family: Octopodidae
Genus: Octopus
Species: (Octopus dofleini)

Description of Species:
(Right: Octopus dofleini, the giant pacific octopus, in the Sea of Japan at about 5-10m. Source: Nesis p.67.)

The giant pacific octopus, (Octopus dofleini, recently reclassified as Enteroctopus dofleini), is a bilateral symmetrical mollusk that is one of the few cephalopods that is entirely lacks a shell. The head is very large and well distinguished from the rest of the body. It has a mantle, which is a muscular sac used for locomotion and encloses the organism’s main organs including the respiratory, digestive, circulatory, genital, excretory systems. Below the head and mantle are eight arms, each with up to 280 suckers that in large individuals can span 23 feet from arm tip to arm tip, (Scheel. 2001a).

On average, the giant octopus can grow to over 100 lbs and there have been rare cases of individuals observed reaching 300-400 pounds. This is the world’s largest species of octopus. In the Pacific Ocean it is easily distinguishable by it’s large size and is only mistaken at young ages with the red octopus. If the young invertebrate lacks eye lashes, has flat, paddle-like body papillae, one centrally located white spot on the head in front of the eyes, a white streak from each eye to base of the second arm, almost black longitudinal grooves down the mantle, and a series of large, dark blotches down the arms, it is a giant octopus, (Scheel, 2001b).

The digestive system begins with a very parrot-like beak. Inside the beak is the radula, which is a tongue like structure covered with rows of teeth for digging, drilling and scraping food from substrates. O. dofleini has two salivary glands that aid in digestion and secrete toxins known a alpha and beta cephalotoxins that are fatal for many crustaceans. Food enters the esophagus and is then stored in the crop until it is ready for digestion. Inside the stomach there is constant mixing of digestive juices from the salivary glands, liver, pancreas, and food to insure complete digestion, which is important because of the animals soft, vulnerable body. Absorption occurs in the liver, pancreas and cecum. The intestine fundamentally serves as a mucous supplier to the stomach and path to the anus. Waste, after passing through the excretory system, is finally released through the funnel in the form of urine, (ammonium), and formless masses (Wells 1978).

The brain, sense organs, and central nervous system are among the most highly developed of the invertebrates. The brain continues to grow throughout the life of the animal and consists of over 170 million nerve cells, 130 million of which are optical (Wells 1978).

Over 350 million nerve cells of the central nervous system are located in the arms of the animal alone. The octopus can distinguish between objects as readily by touch as it can by sight. The highly developed eyes have monocular vision but are so big that the field of view for both eyes reaches almost 360 degrees. They do not have the ability to see in color but are capable of distinguishing different wavelengths of light. Also contributing to the nervous system are olfactory papillae capable of smell, stratocysts for balance and orientation, and chemo and mechano receptors in the mouth (Wells 1978).

Sex determination is genetically predetermined before the creature is born. Females have an ovary, oviduct, oviducal, nidamental, and accessory nidimental glands. Males have testis, the seminal duct, a spermatophoric organ, accessory gland, spermatophoric sac and penis (Wells 1978).

Some other interesting facets about the anatomy and morphology of O. dofleini include the animal’s thin epidermis covered in mucous cell that lubricate the animal for locomotory aid, ocellar spots on the arms that mimic large fish eyes to deter predation, photophores that make luminescence possible, and chromotophores which allow color change. Under favorable conditions, the animal can regenerate body parts, such as arms very rapidly and even voluntarily break them off themselves (Wells 1978).

Octopus inhabit naturally occurring dens on the ocean floor which are in crevices and under rocks for several weeks before they will find a new one. They are nocturnal, solitary creatures that hunt for several hours at night collecting food that is brought back to the den and devoured (Sheel 2001c).

They are active members of the marine food web, which supports all life in the sea. As plankton, they consume other plankton and are also an energy source for other types of primary consumers. Adult diet includes mostly crustaceans, mollusks, and fish including small crabs, bivalves, snails and other octopus (Sheel 2001c). When eating shelled prey they may use arms to pull it apart, bite it with its beak or use the radula to actually drill through the shell. The mouth is able to secrete enzymes that soften the shell and toxins to paralyze prey and dissolve tissue.

When quick moving food approaches it is carefully observed by the octopus, which changes color to a deep reddish brown upon the sighting. If it is not too intimidated, (octopus are timid creatures), it leaps out of it’s home and smoothly stalks the prey until it attacks, covering it’s victim with it’s interbranchial web and gathered by the arms to the mouth. When these animals thrive on slow moving organisms, hunting is most successful by touch. The octopus scurries about rocks in search of food that lives in the crevices of rocks and under stones.

Octopuses are a source of nutrition for many marine species. Other octopus, various fishes, sea otters, and seal lions are the main threat of predation. Humans are also interested in octopus as a commodity and fisheries pursue them. Predation is a major source of mortality for small to medium benthic animals, but much less for the extremely large ones. Fortunate for the octopus, it has evolved several mechanisms to deter predation. Ink may be ejected through the funnel to temporarily blind and agitate predators. Color change allows camouflage among substrates and apparent disappearance into the currents. Photophores emit light to produce counter shading that hides the organism from predators above and below them in the water column and extremely rapid movement by jet propulsion may allow escape (Wells 1978).

Natural History:

Newly hatched from the egg, larvae spend their first 28-90 days drifting as plankton through the ocean currents. At 4-12 weeks the small octopus, weighing approximately five grams, settle to the bottom where growth is very rapid. At this stage, as well as the larval stage, babies are very similar looking to the adults. Adults live for 3-5 years. Maximum life expectancy of five years is in the absence of reproduction. Females tend to die soon after the eggs hatching and males a few months after mating (Scheel 2001c).

In October, large numbers of males and females have been recorded to converge upon their breeding grounds in Hokkaido. Mating occurs at the end of November and in December (Akimushkin 1965).

Upon mating, a male will approach a female and expose the underside of his arms to show enlarged suckers that identify his sex. Chemical sensors also recognize sex. If a male has found that he has unknowingly approached another male, they will fight and the smaller one will be killed and eaten. If it is a female the male will approach her with his third hecotylized arm, (a modified arm for reproduction), spread his arms to appear larger because females tend to favor larger males, and produce dynamic coloration. The female usually submits and is then stroked on her head and abdomen with the hetycotylus until it is inserted into her mantle cavity. Copulation occurs for about an hour and eventually spermatophores are passed into her reproductive system where fertilization takes place (Wells 1978).

Females care for their eggs throughout the 4-6 weeks before they hatch. Eggs are laid in strings attached to the rocks in their homes. She rarely leaves the eggs or feeds and becomes very weak. Death usually occurs at two years, which is the average age for the reproductive stage to occur in the lifetime.

Members of the family Octipodidae are distributed worldwide throughout temperate and tropical seas from the intertidal to abyssal (2000-6000m) zones. They are bottom dwelling or benthic creatures. Pelagic, (located throughout the water column), relatives do exist such as the species Amphitretidae pelagicus but are not classified within the same family or genus.

The genus Octopus includes about 90 species located in all oceans except the Arctic and Antarctic. Northern range extends through Long Island Sound, in the southern part of the Northern Sea, and near Bering Strait. Southern range extends to near Cape Horn, Falkland Islands, Crozet, Kerguelen, Auckland and the Campbell Islands (Neisis 1982).

Octopus dofleini, however, is endemic to the northwest and northeast Pacific Ocean from Bering Strait to Korea, Central Honshu and Baja California. They are commercially important in Northern Japan, North and South Korea, in the far East of the Soviet Union, on the Aleutian Islands, off British Columbia, Washington and Oregon, (Nesis 1982). They are very common off the shores of Japan and Korea, but rare off the shores of the former U.S.S.R (Akimushkin 1965).

The oceanic environment inhabited by the genus Octopus, including O.dofleini,is characterized by oceanographers as the bathyl-sublittoral zone, which is the benthic zone extending from the low tide mark to the outer edge of the continental shelf at depths of 200-2000m depending on location, (Lalli and Parsons 1997).

Due to their elusive nature, lack of study, and limitations encountered when attempting to survey these animals, surprisingly little is known about the ecology and reasons for distribution of this species, (Lalli and Parsons. 1997). Therefore I can only speculate upon their behavior responsible for distribution.

Although O. dofleini is capable of rapid jet propulsion, energy is conserved from not constantly having to travel through the water column against currents while remaining in suspension. Large animals without swim bladders that aid in buoyancy must expend much energy to avoid sinking. Instead they reside in the benthos, which is an adequate source of nutrition and shelter from predators.

As for global distribution, they must have originated in the northern boreal waters under ideal biotic, (adequate food source, appropriate ecosystem), and abiotic, (temperature, salinity, pressure, nutrients), conditions for their species to survive. The southern temperate waters and coastal areas are probably too cold for habitation while subtropical and tropical waters are too warm. Changes in ocean temperature with latitude and depth of ocean may serve as barriers of further global species dispersal.

Because they are benthic organisms, and open oceanic depths may reach 11,000 meters, they must reside relatively near the shore and continental shelf where depths do not usually exceed 2,000m. At extremely deep areas of the oceans life exists only near vents, which are substitute energy sources for solar radiation. Ecology of deep-sea vents along with intense pressures apparently is not sufficient to support O.dofleini populations.

Map of Distribution:

Above left: Global distribution of O. dofleini. Above right: Vertical oceanic distribution of O. dofleini occurs between 200-2000m.
(Source: NOAA. 2001).

Early Life

Most modern biologists believe that life began more than 3.5 million years ago from non-living materials that became ordered into molecular aggregates that were eventually capable of self replication and metabolism (Campbell 1999). It was from this chemo-biological revolution that spawned the first single celled, non-nucleated organisms, the prokaryotes, most commonly known as bacteria.

Eukaryotes, organisms with a nucleus, evolved about 2 billion years ago from prokaryotes and gave rise to multicellular organisms. In the five-kingdom system, eukaryotes include the kingdoms Protista, Plantae, Fungi, and Animalia. It is from the diversity of Protists, single celled eukaryotes, that we get the amazing biodiversity of life, as we know it today on Earth. Autotrophic Protists capable of photosynthesis became plants. Heterotrophic Protists that absorbed organic materials became fungi, and from heterotrophic protists capable of ingestion evolved the animals.

An animal is a multicellular, heterotrophic, eukaryote that lacks cell walls. Only animals have nervous and muscle tissue. All animals have a common ancestral protist that lived over 700 million years ago (Campbell 1999). The first animals had no true tissues, were immobile and are known as sponges. Radially symmetrical motile animals with true tissues such as jellyfish, corals and sea anemones came next. Later bilaterally symmetrical flatworms without any body cavities evolved. Partial body cavities appeared in organisms such as roundworms and complete body cavities in organisms such as ribbon worms, locophores and mollusks (Campbell 1999). By following the evolution of the invertebrates thus far, we can see that animal complexity seems to increase with the evolution of body cavities and the sophistication of the digestive system.

Evolution of the Phylum Mollusca

The phylum Mollusca is a group of over 150,000 known soft bodied animal species that have a muscular foot, (usually used for movement), a visceral mass containing most of the internal organs, and a mantle, (a fold of tissue above the visceral mass which in many mollusks secretes a shell made of calcium carbonate (Campbell 1999.)

Mollusks shared a recent common ancestor with the Lophophorate phyla which are suspension feeding animals that have ciliated tentacles surrounding their mouth that draw in water despite their sessile existence. All lophophorates, such as tube worms and lamp shells, secrete some type of hardy substance which creates the animals tube or shell (Campbell 1999).

It seems that mollusks evolved most directly from the lamp shells which greatly resemble clams but have tentacles surrounding their mouth. The class Bivalvia, including clams, oysters, mussels and scallops, are the mollusks that most closely resemble these animals. It is my guess that gastropods, sea and land snails, eventually evolved from bivalves as modifications of the shell and foot caused the evolution of two very distinct classes of organisms. The muscular foot becomes substantially more adapted for locomotion in Gastropods, a distinct head appears, suspension feeding is lost to grazing and the development of the radula, and tentacles appear much more profound and provide advanced sensory ability when compared with Bivalves.

Evolution of the Octopus

Octopus belong to the class Cephlaopoda, meaning “head foot,” which is a group of carnivorous animals with a closed circulatory system, advanced nervous system, well developed sensory organs, and a complex brain. Most cephalopods have a mouth with a beaklike jaw that is located at the center of several long tentacles and are capable of injecting poison into their victims. All but the chambered nautiluses have a reduced, internal or missing shell (Campbell 1999).

The shell in octopuses and squid has been lost as these animals became advanced predatory carnivorous invertebrates, while other structures characteristic of cephalopods became more pronounced. “The ancestors of octopuses and squids were probably shelled mollusks that took up a predaceous lifestyle, the loss of the shell occurring in later evolution. Shelled cephalopods called ammonites, many of them very large, were the dominant invertebrate predators of the seas for hundreds of millions of years until their disappearance during the mass extinctions at the end of the Cretaceous period (Campbell 1999).

From such an ancestral creature, evolved the various families, genus and species of Octopoda, which are characterized by their eight arms that may be fused together by a web, are nocturnal, solitary creatures with a high growth rate and usually die after spawning, including O.dofleini. O. dofleini, as well as the other species that belong to this order have acquired their unique characteristics through an evolutionary process known as adaptive radiation. Adaptive radiation is defined as the emergence of numerous species from a common ancestor introduced into an environment, presenting a diversity of new opportunities and problems (Campbell 1999). During adaptive radiation various traits of various individuals depending on the environment become favored by natural selection and successfully dominate the next generation while unfavorable traits are eliminated. After numerous generations traits, such as arm length or number of spots, become so different for the entire population of Octopoda that new species develop.

The giant octopus is not listed or endangered under the endangered species act and you can even own one as a pet. That is if you are willing to purchase the animal for $125-500 dollars. Owning a giant octopus is a major commitment and only advanced aquarists should attempt to create a hobby out of these creatures. They require maintenance of water that is 10°C and can only be achieved by installing a $700-1000 water chiller in their system. Also, these animals can grow to be huge and require tanks larger than 300 gallons, (and even larger if the specimen gets extremely big).

Safety of the animal and surrounding humans must be taken into consideration as well. The giant octopus can easily escape from it's tank if a proper lid is not installed. These animals are capable of extreme strength and are actually able to pull a small child into it's tank. Giant octopuses are not known to do such things, but they are very strong and should not be handled alone or by one that is not experienced with octopuses.

It may be best to leave this hobby to the experts. If you would like to see a live giant octopus and are in the Seattle, Washington area, the Seattle Aquarium has a great giant octopus exhibit that shows the anatomy, reproduction, life history and current research being done on the animal. .

Giant octopuses can eat 2-4% their body weight and grow by 1-2% of their total body weight every day! It is the aquarium's goal to grow it's octopus, "Dudley," to be the largest octopus in captivity. For more information check out http://www.seattleaquarium.org/.

Akimushkin, I.I. Cephalopods of the Seas of the U.S.S.R. U.S Department of Commerce Clearinghous for Federal Scientific and Technical Information, VA.1965.

Campbell. Reece. Mitchel. Biology, Fifth Edition. Addison Wesley Longman Inc, CA. 1999.

Lalli. Parsons. Biological Oceanography An Introduction, Second Edition. Butterworth-Heinemann, Oxford. 1997.

Nesis, Kir N. Cephalopods of the World. V.A.A.P. Copyright Agency of the USSR for Light and Food Industry Publishing House, Moscow. 1982.