Octopus rubescens

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The Pacific Red Octopus (Octopus rubescens) is a marine invertibrate belonging to the class Cephelapoda found in the nearshore intertidal zone along the Pacific coast of North America. Their known range is from the Gulf of Alaska to Northern Mexico.

Octopus rubescens
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Octopoda
Family: Octopodidae
Genus: Octopus
Subgenus: Octopus
Species: O. rubescens

Contents

Phylogeny

The Octopus rubescens species belongs to the family Octopodidae (octopods, octopuses and devilfishes), sister taxa to Argonautidae which contains the paper nautilus and many genera of extinct shelled octopoda. These families belong to the suborder Incirrata (common octopods, octopuses, devilfishes), which evolved during the Halocene era and are characterized by having contractile arms, finless, compound and round to succular bodies. Along with sister taxa Cirromorpha, Incirratas belong to the order Octopoda. Octopoda are characterized as having short, compact forms and eight legs. They evolved from the subclass Coleoidea (octopods, squids, cuttlefishes and their relatives). Coleoids are animals with internal and reduced shells, and most have complicated and enlarged brains (compared to teleost fishes occupying the same environment). Along with the subclasses Ammonoidea (extinct shelled invertebrates) and Nautiloidea (Nautiluses), the Coleoidea evolved from the Cephalopoda class. Cephalopods evolved from Mullosks (phylum Molluska) along with many marine organisms including clams, mussels, snails and chitons. The first mollusks crawled on the ocean floor until they evolved a gas-filled chamber which provided buoyancy, thus allowing controlled movement throughout the water column. [1][2][3]

Biology

Phenotype

Octopus rubescens is among the smallest of the three octopus species found near the coasts of the Pacific Northwest United States [4], growing to a diameter of 15-20 centimeters (6-8 inches), an arm spread of around 50 centimeters (20 inches), and a total weight of 0.4 kilograms (1 pound)[5]. This species has a globular body with very rough, bumpy skin with a muddy-red coloration and three tiny cirri (eye flaps) or "eyelashes" below both eyes, which are characteristics commonly used to distinguish it from small Giant Pacific Octopus specimens. Like other species of Octopoda, the Pacific red octopus has the ability to change its skin texture and coloration, ranging from orange to yellow to white and have even been observed with transparent skin during laboratory experiments. [6][7]

Anatomy

O. rubescens has a mantle comprised of skin and muscle that is less than 10 centimeters in length. Water is drawn in to the mantle cavity as the mantle dilates and enters the gills. The water is then ejected from the cavity through a siphon as the mantle contracts and the opening is closed. This intake and expulsion happens more rapidly as the octopus moves faster through the water, moving it by jet propulsion.[8] The mantle covers its body (or "visceral mass") and contains the systemic and branchial hearts, kidney, gonad, stomach, pancreas, liver, brain, nerves, poison gland and ink sack. [9] Like nearly all extant chephalopods, O. rubescens has two gills, two kidneys and three hearts; one pumps oxygenated blood throughout the entire body and the other two pump deoxygenated blood to the gills. When oxygenated, the blood of these animals is a dark blue color, but when deoxygenated it is pale blue, colored in this way because it contains a copper compound.[10] The ink sack, a pear-shaped organ containing dark reddish brown ink, is situated between the gills. The ink is discharged from a funnel which is connected to the ink sack by a long tube. The sack is comprised of two main parts: the gland which produces the ink and a larger cavity which serves as a reservoir for the ink.[11] Its beak protrudes from its arms which is mostly used for handling prey, such as cracking crab, rather than for defense; it is only seen when the octopus is feeding.[12] It also contains chromatophores, pigment-filled cells on the surface of the body which expand and contract, changing the appearance of the octopus [13][14].

Octopus rubescens has eight boneless, fleshy arms with two rows of sucker disks. Each arm is 3-5 times longer than the body length, which are connected to its globular body by a membranous web. They are often wrongly referred to as tentacles, which only decapods possess. The suckers consist of a muscular membrane, which is strengthened and ticker at the edges. The suckers form a partial vacuum as the center is raised by muscular contraction. It can just as easily release its grip using the same muscle. The sixth pair of suckers on each arm has enlarged sucker disks, with the exception of the ventral arm of males. The male's third arm is a conspicuous hectocotylus, a specialized spermatophore-transfer organ with a cup-like depression, which is used to transfer sperm in to the female's mantle cavity. The hectocotylus is 1/10th of the size of its opposing third arm.[15][16]

Life History

Octopus rubescens have an overall maximum age of two years. They produce 2,000-3,000 small, white eggs resembling grains of rice. To mate, the male transfers his spermatophores (packets of sperm) to a cavity in the female, using his hectocotylus, a modified third arm that only males have. The hectocotylus is about 1/10th of the length of its other arms, and at the end is a ligula, a spoon-shaped groove absent of suckers and used to transport the spermatophores into the female's oviduct. A bulb of spermatophores called a spermatangia form within the oviduct, and fertilization occurs when the eggs are passed through the oviduct. There is a high energy investment on the mother's behalf in ensuring the survival of her young. The larvae exhibit direct, or nonpelagic, development which is usually seen in organisms which produce few offspring. In the case of O. rubescens between 2,000-3,000 small, white eggs are laid, which resemble grains of rice. The female cares for her eggs through early spring to late fall intertidally or in the shallow subtidal region in rocky areas. She broods, staying with the eggs until they hatch, jetting water on to them to keep them clean. She stays in her den for the duration of larval maturation, not even leaving to feed, until she eventually dies when the last embryos hatch (around 120 to 180 days, depending on the water temperature). The larvae are planktonic and spend 60 days in their larval stage. They have two rows of chromatophores on each arm. Juveniles settle in to the kelp beds or sandy mud bottoms where they continue to mature in to their adult form. Adults mate in deep water in late spring. [17][18][19]

Locomotion

Octopus rubescens relies on both "walking" and jet propulsion as means of movement. To move around on the ocean floor or through rocky intertidal zones at low tide, it uses only its eight arms to "crawl" across the ground. To propel the octopus throughout the water, the mantle dilates as water is drawn in to the mantle cavity and enters the gills. The same water is then ejected from the cavity through a siphon as the mantle contracts and the opening closes. This intake and expulsion happens more rapidly as the octopus moves faster through the water, moving it by jet propulsion.[20] Additionally, it can powerfully contract the web-like membrane at the base of the arms to propel itself through the water.[21]

Senses

Octopus rubescens has great eyesight[22], yet relies mainly on touch and smell in order to locate prey on the bottom using its suckers. The suckers on each arm possess thousands of chemical receptors and millions of texture receptors.[23] They do, however, rely on their eyesight to locate prey in the water column, such as the euphausiids described in Ladig et al. (2005).[24] Octopuses are thought to have evolutionarily lost their sense of hearing as a response to the extremely loud vocalizations that their cetacean predators produce to stun prey.<Moynihan, Martin. Communication and Noncommunication by Cephalopods. Bloomington, Indiana: Indiana University Press, 1985.</ref>

The Pacific red octopus relies on three sensory organs: mechanoreceptors, chemoreceptors and photoreceptors. Statocysts, a type of mechanoreceptor, are paired organs below the brain that sense gravity and acceleration which are necessary for staying oriented, as well as vibrations. There are about 10,000 chemoreceptor in each sucker disk on the arm of the octopus, and use them to detect prey from a distance. Photoreceptors allow for the octopus to have great eyesight.[25]

Intelligence

Octopuses are thought to be the most intelligent of all the invertebrates [26]. They are able to distinguish between shapes and patterns [27], solve simple mazes [28], use tools [29], use landmarks to navigate while foraging [30], show play behavior [31] and individuals even exhibit distinctive personalities (O. rubescens was the first Octopoda species to be recognized as having personalities) [32]. Some popular studies demonstrate this intelligence. One showed that it took the octopus an average of five minutes to open a childproof pill bottle containing herring[33], and another in which a jar with a cork stopper containing a lobster was brought to the bottom and the octopus was documented as investigating the glass sides, discovering the stopper, getting an arm between the cork and side of the jar, removing the stopper and consuming the lobster[34].


Behavior

Defense

The Pacific red octopus has a reddish brown ink that it expells from its ink sac when provoked or is at risk of being eaten by a predator[35]. The ink, or sepia, is the main defense mechanism of nearly all cephalopods and its main function is to confuse the enemy by creating an under-water smoke screen, yet some have suggested that it is used to make the predator percieve the octopus as a much larger individual since the ink tends to stay in a definite shape in the water. This ink is a dark, thick liquid comprised mostly of melanin (the same substance which accounts for the pigmentation of human hair and skin). It is so durable that fossilized ink from over a hundred million years ago can still be used by humans today for writing, after dillution[36]. Territoriality is unproven among Octopada species. The Octopus rubescens is typically a docile creature, yet has been known to deliver a venomous bite when sufficiently provoked (which is very rare)[37].

Predator Avoidance

Burrowing behavior has been observed of the Octopus rubescens, where the organism partially buries itself in sand plains and lies there dormant for extended periods of time, typically at night.[38]

Social Interactions

Although octopuses are typically thought to be among the most asocial of the cephalopods, this species has been observed living in clumped dens in Californian waters, with individuals spaced about 1 meter apart from each other. Young Octopus rubescens exhibit schooling behavior, forming large schoals that move collectively throughout the water column. The purpose of this unusual behavior is unknown, and is seen most commonly in Monterey Bay, California[39].


Ecology

Habitat & Range

Octopus rubescens is found along the Pacific Coast of North America, with a range extending as far North as Central Alaska and as far South as Northern Mexico [40].

The Pacific red octopuses are found in the intertidal zone along the coasts of its range. It is found between the water's surface and a depth of 200 meters. It's habitat consist of kelp beds, sandy mud bottoms, rocky areas, and under stones at low tide in the rocky intertidal zone[41]. The abundance of this species is unknown, yet a study at Monterey Bay, California (1991-1997) suggests that population sizes of O. rubescens are decreasing, which could possibly be linked to the steadily increasing population of common seals in the area, which are known to prey upon the Pacific red octopus [42].

Trophic Level & Foraging Behavior

Prey

Octopus rubescens forages at night. It is somewhat of a generalist, feeding on a variety of gastropods, crabs, bivalves, crustaceans, fish and other mollusks. From the little information known on the feeding habits of the Pacific red octopus in the wild, it is known that they prefer small crabs and hermit crabs, and feed mainly on crustaceans, mollusks and fishes. It captures its prey using the sessile suckers lining its arms or by using the membranous web at the base of its arms.It gathers several prey items (mostly crab, clams and snails) before returning to its den. It then secretes venom to kill the prey. The sharp beak is used to crack the crab shells, and its radula is used to drill a hole in snail and clam shells in which venom is secreted, causing the body to seperate from its protective layer. The prey is the consumed in the den, and the empty shells are placed in a pile outside, termed as an "octopus's garden".[43][44][45]

A study done by Berry (1953) revealed that the Pacific red octopus show specific localized drilling behavior when preying on bivalves. Of the 171 shells examined from the clam species Venerupis philippinarum, 64.3% showed localized drilling by Octopus rubescens in the adductor muscle scar areas, either anterior or posterior, and the holes drilled only comprise 6% of the total shell area. [46]

Another study conducted by the California Department of Fish and Game (1995) studied the feeding habits of the Octopus rubescens on an unknown euphausiid species, which is a unique prey item for O. rubescens and was previously undocumented (see the "Scientific Studies" section for more details). It also revealed that juveile O. rubescens feed on pelagic mysids, ostracods and large copepods. [47]

Predators

Predators of the Pacific red octopus include eels, lingcod, dolphins, sharks, common seal and the California sea lion (Zalophus californicus).[48][49] The stomach contents of some common seabirds found along the Pacific Coast, including that of the Northern Fulmar (Fulmarus glacialis), have revealed them to be common predators of the Pacific red octopus [50]. Stomach contents of the Northern fur seal (Callorhinus ursinus) also show a diet partially consisting of the Pacific red octopus [51].

Unique Behavior

Octopus rubescens has a remarkably distinctive body pattern change during and after its attack on prey, and there have been two differing accounts of this published. A field study done by Ladig et al. (1995) describes a reddish-brown pattern before any attack posture, and a remarkable change to white or gray the instant before attack. After capture the octopus returned to a reddish-brown coloration, yet it is noted that these colors are much darker than before attack[52]. This study focused solely on behavior surrounding the capture of euphausiid prey off the coast of lower California, which may account for discrepancies in observations.

Warren et al. (1974) describes a more detailed account of the various stages of change in coloration and body pattern during attack and prey capture by O. rubescens in a controlled laboratory setting. Various stimuli were used to instigate skin color change, including free swimming crabs and crabs of various sizes impaled on sticks. Seven distinct phases of attack were recognized: resting, detection, attack, landing, capture, withdrawl, and after capture. The authors found that before attack the octopuses were of various colors ranging from red to brown. Upon detection of the prey their skin color changed to a light orange or gray. They were colorless or nearly transparent when pursuing the prey; they were transparent enough to see the internal organs at the moment that the octopus landed on the prey. They became mottled or spotted when seizing the crab and returned to their normal coloration after consuming the prey. The authors speculate that the changes in color reflect postural adjustments and locomotive activity during the attack. There was no evidence to suggest that these phenotypic changes can be learned or controlled independent of attack behavior, but little is known about this to date. [53]

Scientific Studies

Anderson et al. (1999) examined the prey of Octopus rubescens by collecting them in their beer bottle dens, taken out of the bottle for measurement and released. The bottles were extracted of their contents and the shells were sieved. The composition of shell types indicating species preyed upon were compared to the contents of beer bottles which were not occupied by O. rubescens. Those which had octopuses living in them contained a far greater diversity and significantly greater density of shells than the unoccupied bottles did. They were found in the areas of mud and sand, and the main prey item was the gastropod Olivella baetica, a small sea snail.[54]

Mather & Anderson (1993) studied personalities of the Octopus rubescens. He tested 44 Pacific red octopuses in three different situations (alerting, threat and feeding) in order to quantify the variation between individuals in response to the stimuli. This was repeated seven times, over a two week period for each situation. The researchers found that the octopuses displayed 19 distinct reactions, which were then categorized in to 3 bins: activity, avoidance and reactivity (which acounted for 45% of the variance). For example, an individual who stayed inside its den in all situations would be rated as having low activity, high avoidance and low on reactivity.[55]

Warren et al. (1974) describes a detailed account of the various stages of change in coloration and body pattern during attack and prey capture by O. rubescens in a controlled laboratory setting. Various stimuli were used to instigate skin color change, including free swimming crabs and crabs of various sizes impaled on sticks. The authors found that before attack the octopuses were of various colors ranging from red to brown. Upon detection of the prey their skin color changed to a light orange or gray. They were colorless or nearly transparent when pursuing the prey; they were transparent enough to see the internal organs at the moment that the octopus landed on the prey. They became mottled or spotted when seizing the crab and returned to their normal coloration after consuming the prey. The authors speculate that the changes in color reflect postural adjustments and locomotive activity during the attack.[56]

Another study conducted by the California Department of Fish and Game (1995) examined the feeding habits of the Octopus rubescens on an unknown euphausiid species. Since this is a unique prey item for O. rubescens and this behavior had not previously been recorded, capture methods and octopus population densities in areas with and without euphausiid swarms were recorded. Video transects were conducted on mud-sand bottoms 200 meters offshore from Santa Cruz, California. Different capture methods were seen in O. rubescens, the most common being an ambush method where the octopus would rest on the ocean floor and ambush a swarm of euphausiids from below. The researchers also observed the octopus slowly crawling toward its prey once visually sighted, extending one or two of its arms once it was close enough, and raise its entire body over the euphausiids, encircling its prey. Distinctive changes in body pattern were observed in O. rubescens during attack. Beforehand, the octopus had a dark reddish brown coloration, yet changed its body pattern to a white or gray color the moment before attack. Once the octopus landed it returned to a darker, more intense version of its original reddish brown coloration. In another capture method, O. rubescens was suspended at least 1 meter off the ocean floor, with the body upright and arms spread radially in each direction. The octopus would then sink slowly toward the bottom until one of its arms encountered a euphausiid. It would then encompass the prey with multiple arms, return to the bottom and feed. Densities of the Pacific red octopus did not show a strong correlation with areas where euphausiids were most dense, however 94 octopuses were observed feeding in swarms of euphausiids and only 15 were seen feeding in areas ithout swarms. This tells us that euphausiids are not sought-after prey item for O. rubescens, yet occur in patches as a sporadic resource near the bottom. [57]

References

  1. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Appendix II, Page 234.
  2. ↑ http://tolweb.org (The Tree of Life Web Project, Accessed February 22 2011).
  3. ↑ Moynihan, Martin. Communication and Noncommunication by Cephalopods. Bloomington, Indiana: Indiana University Press, 1985.
  4. ↑ McLachlan, Dan H. Fieldbook of Pacific Northwest Sea Creatures. Happy Camp, CA: Naturegraph Publishers, Inc., 1979. Page 132.
  5. ↑ McLachlan, Dan H., and Bernard Hanby. Marine Life of the Pacific Northwest: A Photographic Encyclopedia of Invertebrates, Seaweeds and Selected Fishes. Harbour Publishing, 2005. Page 273.
  6. ↑ McLachlan, Dan H., and Bernard Hanby. Marine Life of the Pacific Northwest: A Photographic Encyclopedia of Invertebrates, Seaweeds and Selected Fishes. Harbour Publishing, 2005. Page 273.
  7. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 6.
  8. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 3-4.
  9. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Appendix I, Page 230.
  10. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 3.
  11. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 44
  12. ↑ McLachlan, Dan H. Fieldbook of Pacific Northwest Sea Creatures. Happy Camp, CA: Naturegraph Publishers, Inc., 1979. Page 133.
  13. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960.
  14. ↑ McLachlan, Dan H. Fieldbook of Pacific Northwest Sea Creatures. Happy Camp, CA: Naturegraph Publishers, Inc., 1979. Page 133
  15. ↑ Cowles, Dave. Key to Invertebrates Found At or Near The Rosario Beach Marine Laboratory, Fidalgo Island, Anacortes, WA May 2009.
  16. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960.
  17. ↑ Marine Species with Aquaculture Potential: Octopus. http://hmsc.oregonstate.edu/projects/msap/PS/masterlist/inverts/octopus.html. (Accessed January 16 2011).
  18. ↑ Walla Walla University Biology Department: Octopus Rubescens < http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Mollusca/Cephalopoda/Octopus_rubescens.html> (Accessed January 14, 2011).
  19. ↑ The Tree of Life Web Project. tolweb.org (Accessed February 20, 2011).
  20. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 3-4.
  21. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 69
  22. ↑ Moynihan, Martin. Communication and Noncommunication by Cephalopods. Bloomington, Indiana: Indiana University Press, 1985.
  23. ↑ Virtual Zoo: Octopus rubescens. < http://pioneerunion.ca.schoolwebpages.com> (Accessed February 26, 2011)
  24. ↑ Ladig, Thomas, Peter Adams, Charles Baxter, and John Butler. "Feeding on Euphasiids by Octopus rubescens." California Fish and Game. 81.2 (1995): 77-79.
  25. ↑ Hanlon, Roger. Cephalopod Behaviour. Great Britain: Cambridge University Press, 1996. pp. 12-21.
  26. ↑ Linden, E. 2002. The octopus and the orangutan. Dutton (NY). 242 pp.
  27. ↑ Boal, J. 1991. Complex learning in Octopus bimaculoides. American Malacological Bulletin. 9(1):75-80.
  28. ↑ Wells, M.J. 1978. Octopus - Physiology and Behaviour of an Advanced Invertebrate. Chapman Hall (London). 417 pp.
  29. ↑ Mather, J.A. 1994. “Home” choice and modification by juvenile Octopus vulgaris (Mollusca: Cephalopoda): specialized intelligence and tool use? J. Zool. Lond. 233:359-368.
  30. ↑ Mather, J.A. 1991. Navigation by spatial memory and use of visual landmarks in octopuses. Journal of Comparative Physiology. 168(491-497).
  31. ↑ Mather, J.A. and R.C. Anderson. 1999. Exploration, play and habituation in octopuses (Octopus dofleini). Journal of Comparative Psychology. 113(3):333-338.
  32. ↑ Mather, J.A. and R.C. Anderson. 1993. Personalities of octopuses (Octopus rubescens). Journal of Comparative Psychology. 107(3):336-340.
  33. ↑ inn, D.L., Perrin, N.A., Mather, J.A., & Anderson, R.C. 2001. Early temperamental traits in an octopus (Octopus bimaculoides). Journal of Comparative Psychology, 115(4):351-364
  34. ↑ Cousteau, Jacques. Octopus and Squid: The Soft Intelligence. Garden City, New York: Doubleday & Company Inc., 1973.
  35. ↑ Cowles, Dave. Key to Invertebrates Found At or Near The Rosario Beach Marine Laboratory, Fidalgo Island, Anacortes, WA May 2009
  36. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 44
  37. ↑ McLachlan, Dan H., and Bernard Hanby. Marine Life of the Pacific Northwest: A Photographic Encyclopedia of Invertebrates, Seaweeds and Selected Fishes. Harbour Publishing, 2005. Page 273.
  38. ↑ Hanlon, Roger. Cephalopod Behaviour. Great Britain: Cambridge University Press, 1996. page 78. Print.
  39. ↑ Hanlon, Roger. Cephalopod Behaviour. Great Britain: Cambridge University Press, 1996. Page 151. Print.
  40. ↑ McLachlan, Dan H., and Bernard Hanby. Marine Life of the Pacific Northwest: A Photographic Encyclopedia of Invertebrates, Seaweeds and Selected Fishes. Harbour Publishing, 2005. Page 273.
  41. ↑ Cowles, Dave. Key to Invertebrates Found At or Near The Rosario Beach Marine Laboratory, Fidalgo Island, Anacortes, WA May 2009.
  42. ↑ Virtual Zoo: Octopus rubescens. < http://pioneerunion.ca.schoolwebpages.com> (Accessed February 26, 2011)
  43. ↑ "Red octopus, Kelp Forest, Octopus & Kin" http://www.montereybayaquarium.org (Accessed Februaury 23 2011)
  44. ↑ Ladig, Thomas, Peter Adams, Charles Baxter, and John Butler. "Feeding on Euphasiids by Octopus rubescens." California Fish and Game. 81.2 (1995): 77-79.
  45. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 20-42.
  46. ↑ Anderson, Roland C., David L. Sinn, and Jennifer A. Mather. "Drilling Localization on Bivalve Prey by Octopus rubescens Berry, 1953 (Cephalopoda: Octopodidae)." Veliger 50.4 (2008): 326-328. Biological Abstracts 1969 - Present.
  47. ↑ Ladig, Thomas, Peter Adams, Charles Baxter, and John Butler. "Feeding on Euphausiids by Octopus rubescens." California Fish and Game. 81.2 (1995): 77-79.
  48. ↑ Lane, Frank. Kingdom of the Octopus. New York, New York: Sheridan House, 1960. Page 44
  49. ↑ McLachlan, Dan H. Fieldbook of Pacific Northwest Sea Creatures. Happy Camp, CA: Naturegraph Publishers, Inc., 1979. Page 132.
  50. ↑ Susan Hills and Clifford H. Fiscus (1988). Cephalopod Beaks from the Stomachs of Northern Fulmars (Fulmarus glacialis) Found Dead on the Washington Coast. The Murrelet. Vol. 69, No. 1, pp. 15-20.
  51. ↑ Norbert T. W. Klages. 1996. Cephalopods as Prey. II. Seals. Philosophical Transactions: Biological Sciences. Vol. 351, No. 1343, The Role of Cephalopods in the World's Oceans, pp. 1045-1052
  52. ↑ Ladig, Thomas, Peter Adams, Charles Baxter, and John Butler. "Feeding on Euphasiids by Octopus rubescens." California Fish and Game. 81.2 (1995): 77-79.
  53. ↑ Warren, L. R., M.F. Scheier, and D.A. Riley. 1974. Colour changes of Octopus rubescens during attacks on unconditioned and conditioned stimuli. Animal Behavior 22:211-219.
  54. ↑ Determination of the diet of Octopus rubescens through examination of its beer bottle dens in Puget sound." Malacologia. 41.2 (1999): 455-460
  55. ↑ "Personalities of octopuses (Octopus rubescence)." Journal of Comparative Psychology. 107.3 (1993): 336-340.
  56. ↑ Warren, L. R., M.F. Scheier, and D.A. Riley. 1974. Colour changes of Octopus rubescens during attacks on unconditioned and conditioned stimuli. Animal Behavior 22:211-219.
  57. ↑ Ladig, Thomas, Peter Adams, Charles Baxter, and John Butler. "Feeding on Euphasiids by Octopus rubescens." California Fish and Game. 81.2 (1995): 77-79.
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