Feeding & growth
 

photograph of beak of a giant squid Moroteuthis robusta Octopuses catch prey by reaching out with an arm, or arms, and snagging it with the suckers and curled arm tip(s), or by chasing after it by crawling/jetting and pouncing on it with arms and web expanded. A bite from the beak accompanied by injection of salivary-gland toxin incapacitates the prey. Multiple prey items can be accommodated within the web and eaten one at a time, or transferred en masse back to the den for later consumption.

Squids float or swim about seeking prey fishes. Attack involves rapid extension of a pair of tentacles that may be expanded into a club-shape, and bear extra-large suckers and sometimes hooks. The tentacles are joined together by a temporary suckering arrangement for this manouvre. The prey is drawn back into the 8 arms, subdued, killed by the beak, and often swallowed whole.

Beak of a giant squid Moroteuthis robusta. Dorsal is on the left.
The radula/salivary-gland complex can be seen within the jaws

 
  Prey capture
  The section on feeding & growth is divided into prey capture, considered here, and DIETS, PREY HANDLING & DRILLING, and GROWTH, considered in other sections. 
 
 
photograph of octopus sitting at the side of its aquarium tank taken from a video

CLICK HERE to see a video of an octopus Enteroctopus dolfleini catch a crustacean and tuck it under its web.

NOTE the video replays automatically

 

Research study 1
 

photograph of Octopus rubescensA report on Octopus rubescens attacking crabs Hemigrapsus oregonensis in the laboratory emphasises colour changes.  On detecting the prey and during early attack the predator is light orange-grey.  On rising up and during descent with arms open the octopus is colorless and nearly transparent.  When siezing the crab the octopus becomes spotted or mottled and, afterwards, it adopts various colours.  The authors suggest that the colours may be acting to match the background, or perhaps acting to camouflage the octopus from the prey during its descent (light underbody seen against lighter surface waters).  Warren et al. 1974 Anim Behav 22: 211.


Octopus rubescens in non-attack colours 1X

 
 
photograph of octopus Enteroctopus dofleini carrying prey

CLICK HERE to see a short video of an octopus Enteroctopus dolfleini with a crustacean prey caught up in its web.

NOTE the video replays automatically

 

 
Research study 2
 

graph showing survival of laboratory-cultured squids Doryteuthis opalescensSquids, especially pelagic species such as Doryteuthis opalescens, are difficult to keep graph showing relationship between age and successful attacks by squids Doryteuthis opalescens on living brine shrimpin captivity, let alone rear to juvenile stage.  However, this has been accomplished with D. opalescens at the Scripps Institution of Oceanography, California using cylindrical rearing tanks and brine shrimp Artemia salina as food.  For the first 4wk newly hatched Artemia are provided as prey, while small adults are given during the remainder of the rearing period.  Attack success on Artemia prey is a function of age, as shown in the graph on the Left. Lack of success by young squids is attributed by the author mainly to prey escaping after being initially struck by the tentacles. 

Survival of squids is poor over the first 30d, better over the next 35d, then poor again over the final 35d, and only a handful survive to 100d of age. Oxygen-uptake measurements show that the daily maintenance energy needs of a newly hatched squid could be met with 23 Artemia nauplii, while those of a 2mo-old squid of 7mm mantle length could be met with 225 nauplii.  Actual consumption rates are estimated by the author to be considerably more than this, by a factor in each case of about 6, so perhaps an essential nutrient is missing from the brine-shrimp diet or some other condition of culture is wanting. Hurley 1976 Fish Bull 74: 176.

 
Research study 3
 

photograph of a hatchling octopus Enteroctopus dolfleini courtesy Shawn Robinson, Simon Fraser University, British ColumbiaLaboratory culture of octopuses Enteroctopus dofleini at the Vancouver Aquarium, British Columbia provides a unique opportunity to observe early feeding in the pelagic juvenile stages.  Newly-hatched octopuses will eat live brine shrimp, larval fishes, and pieces of krill Euphausia pacifica.  If the krill is floating at the surface the juvenile octopuses are able to rise up and attach to the surface film upside down, and feed on the pieces.  The behaviour disappears after 28d of age, perhaps when mass-to-surface area ratio becomes unfavourable for surface-film attaching.  The author suggests that young octopuses could use the ability to attach to surface films in order to exploit neustonic food sources, but adds that it has not yet been reported in the field for any octopus species.  Marliave 1981 Veliger 23: 350. Photograph courtesy Shawn Robinson, Simon Fraser University, British Columbia. 

 

Hatchling of Enteroctopus dofleini 2X

 
Research study 4
 

photograph of Octopus bimaculatus courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, CaliforniaMany or most bottom-dwelling octopus species inhabit dens from which they make foraging excursions.  A prey may be eaten where it is caught or, more often, it is brought back to the den to be consumed.  The uneaten parts of carapaces and shells are piled outside the den and may form middens, easily recognisable from a distance.  One species that rarely forms middens, though, is the 2-spotted octopus Octopus bimaculatus in Santa Catalina Island, histogram showing shelters of Octopus bimaculatus with associated numbers of discarded shells and carapaces of preyCalifornia.  This is not for want of discarded material, because the species’ main prey in this area is snails (78% of the diet). 

A study of “discards” (shells of snails, abalone, bivalves, and chitons, and carapaces of crabs) outside of 104 shelters shows that only one shelter has more than 20 discards and only a handful have more than 6 discards (see histogram on Right). What happens to the discards around these dens, especially the many empty snail shells?  Some items are lost to currents and surge, but by far the major loss is to hermit crabs looking for new shells in which to live.  Apparently, the hermits select shells from the rich pickings around a den and drag them off to effect the change in private.  The author is able to correlate the greater loss of snail shells over bivalve shells from these shelters with the greater incidence of hermit crabs in the area.  Ambrose 1983 Mar Behav Physiol 10: 137. Photograph of Octopus bimaculatus courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, California.

NOTE  dietary records for octopuses invariably include only hard-shelled prey, as these comprise the identifiable midden remains. Does this mean that no soft-bodied prey is eaten?

NOTE  most shelters are located at <15m depth

 
Research study 5
 

A short report by a researcher at The Seattle Aquarium suggests that octopuses Enteroctopus dofleini in captivity have little trouble capturing and eating live fishes.  Included as prey are dogfish, ratfish, and even slippery salmon.  Common fishing behaviour for the octopus is to snag a fish with an arm, then draw it in close enough to wrap more arms around it.  The fishes appear to be active and healthy at their time of capture.  When provided live herring during routine feeding sessions, a different method is used for capture, involving raising the arms, expanding the web, and descending over the prey like a “throw-net” or parachute (see Research Study 11 below).  The same method is used by E. dolfleini to capture shrimps.  Anderson 1991 J Cephalopod Biol 2 (1): 75.

 
Research study 6
 

An unusual observation from a ROV-mounted camera at 200m depth in Monterey Bay, California is of Octopus rubescens feeding on pelagic euphausids.  In fact, the authors comment that they occasionally see octopuses with their webs filled with euphausids (the species is not identifiable, but is estimated at about 1cm carapace length).  The observers identify 2 different feeding methods.  The first is when an octopus pounces on a euphausid by rising up on its arms, then descending and encompassing the prey in its web.  The octopus’ colour changes from dark reddish-brown to white or grey during the pounce, then back to dark reddish-brown after the attack.  The second mode of capture involves the predator rising off the bottom to 1m or more, then sinking down with arms spread.  When an arm contacts a prey, the other arms assist with the capture.  The octopus descends to the bottom and eats the euphausid.  This is the first description of an octopus feeding on pelagic euphausids in the field.  Laidig et al. 1995 Calif Fish Game 81: 77.

Octopus rubescens with web spread, being held
by a diver. The octopus has part of one arm missing

 
Research study 7
 

Squids capture prey such as fishes and crustaceans by rapid extension of the 2 tentacles, presumably by hydraulic forces generated through muscular contraction of hemocoelic fluid. These capture tentacles are withdrawn and partially tucked away when not in use. On the tentacles, suckers are present only on the club-shaped pads, known as mani, while the 8 arms have suckers along their complete lengths. A strike is made with the tentacles joined temporarily at their bases and with the club-shaped terminal pads spread out drawing of red snapper fish with wedge-shaped bite on spinal cord caused by a giant squid Moroteuthis robustasideways; this allows better control of tentacle orientation during the strike. The tentacles are joined just below their tips during the strike and during manipulation of the prey by a system of interlocking suckers and knobs located just proximal to the mani. This joining not only coordinates the tentacles during a strike, but also permits the mani to act in concert photograph of a 2.5m giant squid Moroteuthis robusta captured off the coast of Vancouver Island, British Columbiaduring subsequent quelling of the prey during its transfer to the mouth. The stomach of the specimen shown here contained 2 partially digested 36-cm red snappers, each with a wedge-shaped piece removed from behind their heads in exactly the same location. Each wedge precisely severed the spinal column and spinal nerve. The large size of the prey indicates that the beak is capable of considerable disarticulation during swallowing.


A 3.5m (arm tip to mantle-flap tip) giant squid Moroteuthis robusta
captured off the coast of Vancouver Island, British Columbia at a depth
of about 600m. The tentacles are about 3m in length. Note their expanded tips


 
 
Research study 8
  The photo series below feature Humboldt squids Dosidicus gigas stranded on a beach on the west coast of Vancouver Island, British Columbia in August, 2009. Known mostly from the coasts of Baja California and southern California, Humboldt squids are becoming increasingly common in post-reproductive strandings along the entire west coast as far north as southern Alaska. Photos below courtesy Josie Osbourne and the Raincoast Educational Society, Tofino, British Columbia. raincoasteducation.
 
photograph of Humboldt squid Dosidicus gigas stranded at Tofino, British Columbia courtesy Josie Osborne, Tofino
A mass stranding of several hundred Humboldt squid Dosidicus gigas occurred in summer 2009 on a beach near Tofino, British Columbia
photograph of Humboldt squid Dosidicus gigas stranded at Tofino, British Columbia courtesy Josie Osborne, Tofino
Each squid was about 1m in length, not including the tentacles. Other strandings seem to consist mostly or entirely of males, presumably post-copulatory and dying
photograph of beaks of a Humboldt squid Dosidicus gigas stranded at Tofino, British Columbia courtesy Josie Osborne, Tofino
Beak of Dosidicus gigas. Note the muscular surrounds (expanded here because of morbidity) that permit considerable flexibility of the beak during feeding
photograph of tentacle suckers of a Humboldt squid Dosidicus gigas stranded at Tofino, British Columbia courtesy Josie Osborne, TofinoSuckers on the tentacles of Dosidicus. Note their relatively small size as compared with those of octopods, reflecting their use primarily for prey handling rather than for crawling along the bottom
photograph of tentacle suckers of a Humboldt squid Dosidicus gigas stranded at Tofino, British Columbia courtesy Josie Osborne, Tofino
The suckers on Humboldt squids and other large squid species are stalked, presumably for better motility. The suckers on D. gigas on both arms and tentacles are also armoured with a serrated ring of hard tissue
photograph of armoured rings in the tentacle suckers of a Humboldt squid Dosidicus gigas stranded at Tofino, British Columbia courtesy Josie Osborne, Tofino
The armoured rings appear to be made of calcified chitin. Their function is likely to aid in grasping and manipulating the prey (mostly slippery fishes) during transfer to the beak and mouth
 
Research study 9
 

Apart from the observation in Research Study 6 of giant squids Moroteuthis robusta eating red-snapper fishes, the only other record of their diet is a notation of the photograph of 2 siphonophores Velella velella stranded on the shorepresence of heart urchins Brisaster latifrons and surface-floating siphonophores Velella velella in the stomach of a specimen trawled photograph of a heart urchin Brisaster latifronsup in California. Smith 1963 Calif Fish Game 49: 209. Photoraph of Velella courtesy Josie Osborne, Tofino, British Columbia.

 

Two by-the-wind-sailors Velella velella stranded on a beach near Tofino, British Columbia 1X

 

 




Heart urchin Brisaster latifrons dredged from a mud
bottom in Barkley Sound, British Columbia at 80m depth 1X

 
Research study 10
 

schematic showing adult-type prey-capture behaviour in a young squid Doryteuthis opalescensschematic showing adult-type prey-capture behaviour in a young squid Doryteuthis opalescensAfter they hatch, squids Doryteuthis opalescens have an instinctive attack response to small moving prey like copepods.  These early attacks, however, involve simple lunges toward the prey with arms open and are rarely successful. A successful attack begins with orientation to the prey, then a slow approach by the squid with open arms. The squid jets forward, closes its arms on the prey, withdraws, and eats it. Unsuccessful attacks lead to the prey's escape and backwards jetting by the squid (see schematic on Left).

Later, the squid modifies its attack strategy that leads to greater success.  A detailed study of this ontogenetic progression at the Hopkins Marine Station and Montery Bay Aquarium, California shows that by 40d post-hatching, attack behaviour is more adult-like, involving mainly adjustments in position to attack towards the head of the prey, and involving use of tentacles rather than lunges. This is shown in the series of drawings on the Right illustrating use of both tentacles and arms in a more experienced juvenile squid. During this ontogenetic learning, both attack speed and attack distance decreases.  Interestingly, if a hatchling is raised exclusively on brine shrimp, an easily catchable prey, then switched after 40d to copepods, they display only the simple attack behaviour characteristic of young squids. None of these initial attacks is successful and few of these animals survive the transition.  Chen et al. 1996 Biol Bull 190: 69.

NOTE  the schematic takes a bit of time to noodle out. However, it is worth it if you have interest in the subject

NOTE  copepods have extremely fast forward-directed escape responses, among the fastest of any animal

 
Research study 11
 

A researcher at the Royal British Columbia Museum, Victoria, British Columbia provides this report of an in situ observation by SCUBA-divers of what is termed “web-over” hunting by an octopus.  The mode of hunting is also termed “speculative” hunting, as the predator pounces almost photograph of an octopus with outspread tentacles courtesy Kevin Lee, Fullerton, Californiarandomly on an area such as rocks with outspread web, then feels about under the web with its tentacles for food items.  During 10min of observing the octopus in question, a small female Enteroctopus dofleini, it made about 7 such pounces.  During a pounce the web and tentacles blanche white and remain so for 10-20sec during the search, before returning to normal red colour.  No prey was captured by the octopus during these behaviours, but several crabs offered by the SCUBA divers were readily accepted.  Several small crabs and fishes were flushed out of the rocks by the predator but not pursued.  The behaviour has been described for other species of octopuses, but this is one of only a few such records for E. dofleini Cosgrove 2003 Can Field-Naturalist 117 (1): 117. Photograph courtesy Kevin Lee, Fullerton, California DIVERKEVIN.

 

An Octopus sp. makes a pounce 0.5X

 
Research study 12
 

histogram showing effects of upstream food odours on ventilatory rates in Octopus bimaculoidesDistance chemoreception is a topic relating to food location by octopuses that seems all but ignored by west-coast researchers.  It is, however, examined by researchers at the University of Pennsylvania who test responses of Octopus bimaculoides to various food odours (live fiddler crabs, frozen shrimp tails) caged upstream from the test subjects.  The researchers use a clever hands-off, distance-viewing method to assess positive response by an octopus, namely,  change in ventilatory rate.  Each octopus is used as its own control.  Response to plain seawater is used to establish a control level, then this is compared with subsequent responses to one or other of the 2 food types.  No attempt is made to quantify any chemical aspect of the odour plume, nor are experiments done using different concentrations of substances such as amino acids or fatty acids known to be phagostimulatory for other marine invertebrates.  Results show significantly increased ventilation rates to both types of food (see histogram).  Subsequent Y-maze tests with single octopuses using food odour presented in one arm of the maze and seawater in the other, however, show no significant attraction to food odours.   The authors have no explanation for this apparently counter-intuitive result, other than noting that small sample sizes combined with high behavioral variability may have played a role.  Walderon et al. 2011 J Moll Stud 77: 309.

NOTE  also tested are responses to conspecifics, both sexes, and to conspecific eggs.  Only the food-odour results are considered here.  Octopuses are shipped in from southern California and maintained in artificial seawater

NOTE  note that results can be positive or negative, depending on whether there is an increase or decrease in ventilatory rate.  Without having done some preliminary tests the investigators would not know whether a rise in excitation level would be reflected by an  increase or decrease in ventilation.  A differentr study at the Seattle Aquarium, Washington, however, shows that individual humans can be recognized by captive Enteroctopus dolfleini, and that one of the responses to the human selected to irritate the specimens with a brush (as opposed to feeding them) is increased ventilatory rate.  Anderson et al. 2010 J Appl Anim Welfare Sci 13: 261.

 
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