Predators & defenses
   
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  Defenses
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Colour change/camouflage
 

Defenses of octopuses and their relatives can be divided into passive and active. Topics relating to passive defenses include colour change/camouflage, considered in this section, and HIDING AWAY, NOCTURNAL BEHAVIOUR and MAKE BODY SEEM LARGER, considered in other sections.  Active defenses include BEAKS & BITING and WITHDRAWAL & INKING. 

Colours in cephalopods result from contraction and expansion of chromatophores, or colour cells, scattered within the skin. In cephalopods the chromatophores are under nervous control; hence, colour changes are virtually instantaneous. In comparison, chromatophores in fishes and crustaceans are under hormonal control and responses are slower - measured in minutes, hours, or days.
 
Research study 1
 

photograph of an octopu model showing arm curling Abrupt colour changes including blanching are common responses to distubance or stress in octopuses.  They may be accompanied by escape by crawling and jetting, and by ink release. photograph of octopus Enteroctopus dolfleini in its denAdditionally, when an octopus is in defensive attitude, the arms may curl around on themselves (see model on Right) while the chromatophores rapidly change colour. Mather 1998 J Comp Psychol 112: 306.


Enteroctopus dolfleini in
partially blanched mod
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photograph of a hunched-up octopus Enteroctopus dolfleini taken from a video

CLICK HERE to see a short video of an octopus Enteroctopus dolfleini exhibiting quick colour change.

NOTE the video replays automatically
 
Research study 2
 

Eyebars, as a strategy for disguising the distinctiveness of eyes in both predator and prey alike, are common in many animals including birds and tropical fishes, but not apparently in west-coast cephalopods. As the photographs below show, of 5 common west-coast species, only Enteroctopus dofleini possesses distinctive eyebars. All photographs are taken in daytime. What the function of the eyebars could be is not known, but consider this: eyebars as "eye-disruptors" would be most effective against daytime predators but, of the octopod species shown, O. rubescens and O. bimaculoides are generally diurnally active, while E. dolfleini is generally nocturnally active. Photograph #2 in the series is courtesy of Roland Anderson & Seattle Aquarium, #4 is courtesy Roger Hanlon, and #5 is courtesy Kevin Lee diverKevin.

NOTE whether eyebars are present or not in octopuses, even in E. dolfleini, depends in large extent to the particular pattern and magnitude of activity of surrounding chromatophores. The photograph selected below for O. dolfleini (#1 in the series) shows off the eyebars particularly well
 
photograph of eye of octopus Enteroctopus dolfleini photograph of eye of octopus Octopus rubescens courtesy Roland Anderson photograph of eye of Humboldt squid Dosidicus gigas photograph of eye of octopus Octopus bimaculoides courtesy Roger Hanlon photograph of eye of squid Doryteuthis opalescens courtesy Kevin Lee
Eye of octopus Enteroctopus dolfleini Eye of O. rubescens within its egg mass. Note the shading on the eye Eye of squid Dosidicus gigas. Body shading is dark above, light below Eye of O. bimaculoides. Note "ocellus" beneath eye Eye of squid Doryteuthis opalesc-ens. Note large tapetum area
 
Research study 3
 

photograph of octopus appearing to mimic worm tubes, courtesy Kevin Lee, Fullerton, CaliforniaCamouflage through mimicking has not been studied in west-coast octopuses, yet their ability to adjust body posture, skin texture, and colouring makes this subject worthy of research consideration.  Photograph courtesy Kevin Lee, Fullerton, California diverKevin.

 

 

 

 

 

An unidentified octopus appears to be mimicking
the worm tubes that it is perched amongst.
Alternatively, it may be attacking one of the
worms pulled down in its parchment tube 1X
 
Research study 4
 

Detailed studies of colours and patterning in Octopus bimaculoides in southern California disclose 8 general colour patterns.  These are:

Photograph of O. bimaculoides courtesy Roger Hanlon, Woods Hole Marine Biological Laboratory, Woods Hole, Massachusetts.1 & 2. UNIFORM LIGHT & GENERAL MOTTLED:  these common or "chronic" patterns are used for concealment and persist for a long time.  In comparison, the next 6 “acute” patterns last only seconds or minutes, and are used for localised encounters involving sex, aggression, and the like.
3. UNIFORM DARK & ACUTE MOTTLED
4. DISRUPTIVE: in hatchlings the body is divided into dark halves separated by a longitudinal whiteish central stripe.  Variations of pattern are used for concealment.
5. DEIMATIC ("god-like" L.): a mottled pattern accompanied by well-defined ocelli.
6. FLAMBOYANT: an uncommon behaviour seen in small swimming individuals; accompanied by raised skin papillae.
7. PASSING CLOUD: waves of chromatophore expansions radiating from arm bases to tips; seen in young animals. Forsythe & Hanlon 1988 Malacologia 29: 41. Photograph of O. bimaculoides above and the 2 Right-hand eyspots below courtesy Roger Hanlon, Woods Hole Marine Biological Laboratory, Woods Hole, Massachusetts.



Rapidly moving O. bimaculoides displaying No. 1 colour pattern
 

Other than general pattern disruption and camouflage, the function of colour patterns in O. bimaculoides and octopuses, in general, are not well understood. In addition, in adult O. bimaculoides there are 2 or more prominent white spots on the mantle, and 2 prominent eyespots or ocelli symmetrically placed on the upper arm web.  The spots are usually brilliant blue on a variable background, but colours vary depending upon age and behaviour. Their function is unknown, but could be defensive,social, or perhaps something else. The subject would certainly make a nice research topic for someone.

NOTE the obvious function, that of mimicking an eye, is hard to reconcile. In tropical fishes, purported defensive eyespots are located towards the tail, thus potentially deflecting attacks of predators to that part of the body and leading to ready escape by fast swimming in a forwards direction. The eyespots in O. bimaculoides are located below and just to the front of the head region
 
photograph showing close view of the eyespot of Octopus bimaculoides photograph showing close view of the eyespot of Octopus bimaculoides <empty>photograph showing close view of the eyespot of Octopus bimaculoides photograph of 4-eye butterflyfish Chaetodon capistratus showing eyespot photograph of juvenile rock beauty Holocanthus tricolor showing eyespot
Eyespot coloration in juvenile O. bimaculoides Eyespot coloration in a dark-coloured adult Eyespot coloration in a light-coloured adult Eyespot location in a 4-eye butterflyfish. Note also the vertical eyebar 0.5X Eyespot location in a juvenile rock beauty Holocanthus tricolor. Note blue eyebar 1X
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photograph of a stranded and moribund Humboldt squid Dosidicus gigas exhibiting chromatophore changes taken from a video

CLICK HERE to see a video of chromatophore activity in a Humboldt squid Dosidicus gigas. This individual has been stranded on the beach for several hours and is nearly dead. What you see is a rapid flickering as chromatophores in the mantle skin expand and contract.

NOTE the video replays automatically
 
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