Habitat ecology
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  Octopus
  Studies on habitat ecology of octopuses and their relatives are arranged by taxon. Studies on genus Octopus is presented here, while those on ENTEROCTOPUS and SQUIDS can be found in other sections.
 
Research study 1
 

graph showing proportion of population of Octopus bimaculatus individuals in a population in Santa Catalina Island, California inhabiting shelters for various lengths of timephotograph of O. bimaculatus courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, CaliforniaWhile Enteroctopus dofleini is a mostly "stay-at-home" kind of octopus, other west-coast species are more restless.  Studies on 2-spotted otopuses Octopus bimaculatus in Santa Catalina Island, California, for example, show that on average 25% of the population spends less than a week in den shelters (see graph on Right).  Note that less than half the population stays longer than 3wk in a shelter. Interestingly, during the 6-mo period of study, shelters suitable for habitation by O. bimaculatus are always in excess, suggesting that shelter availability does not limit population size in this species.  Ambrose 1982 Mar Ecol Progr Ser 7: 67. Photograph of O. bimaculatus courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, California.

NOTE  these are spaces under rocks and crevices.  Potential shelters in sand-filled crevices are excavated quickly by a combination of jets of water, and movement of sand by suckers, arms, and web

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Research study 2
 

graph showing the relationship of number of octopuses to abundances of various prey in Santa Catalina Island, CaliforniaFew studies have been done on community ecology of octopuses, undoubtedly owing to the difficulty of data-collection using SCUBA, low densities of subjects, and the logistical difficulty of experimental manipulations.  A 5-yr study done on the 2-spotted Octopus bimaculatus in Santa Catalina Island, California, however, shows that in areas of high abundance of octopuses, species diversity (notably snails and hermit crabs) markedly decreases.  When octopuses are in low abundance, they fail to disrupt the basic patterns of prey abundance that result from other processes. About 75% of the diet of O. bimaculatus is made up of snails, with chitons, bivalves, crabs, and hermit crabs making up most of the remainder.  The author uses the presence of identifiable octopus drill-holes to determine the proportion of prey drilled.  Estimated mortality of several species of gastropods (Chlorostoma, Astraea, and Norrisia) in the overall study area is 57-99%.  In one 100m2 study area, 4-7 octopuses comsume almost 25% of available snails in 24d.  The reason for the decline in octopus numbers over the study period is not known. Ambrose 1986 Mar Ecol Progr Ser 30: 261.

NOTE  this species occurs from Santa Barbara, California to the southern tip of Baja California

 
Research study 3
 

Octopuses are basically solitary animals that do not form social aggregations and prefer to occupy individual dens.  Laboratory studies on Octopus bimaculoides collected at Long Beach, California show that, rather than being a sanctuary, however, a den may be only a  temporary lodging until its occupant is displaced.  If 3 octopuses are allowed to compete for 2 artificial dens in a laboratory situation, it takes only about 2h for a dominance heirarchy to emerge, and the heirarchy is maintained for several days.  The dominance appears to be size-based.  An individual can quickly recognise whether another is dominant or recessive to it, and this is remembered.  Once the relationship is established, a dominant octopus can evict subordinates just by entering a den.  In 12 such trials in the California study, for example, the so-called alpha-male ends up inhabiting the most preferred den 92% of the time.  On first meeting a pair typically squares off, engages in leaping and chasing mostly without contact, and then the recessive individual withdraws.  Sometimes they fight, but the result is the same, with one individual withdrawing and fixing itself with a subordinate “stamp” that governs future behaviour with the same and other dominant individuals.  Cigliano 1993 Anim Behav 46: 677. Photograph of O. bimaculoides courtesy Roger Hanlon, Woods Hole Marine Biological Laboratory, Massachusetts.

NOTE  in this experiment there are 4 experimental dens representing combinations of small and large size, and small and large entrance.  The most favoured is the smallest den with the smallest entrance

 
Research study 4
 

photograph of juvenile Octopus sp.Research at Portland State University, Oregon on behaviour of juvenile Octopus bimaculoides shows that individuals are active more at night than during the day, but the difference is not great (means of 20 vs. 14%, respectively, over 3wk observation).  The author could find no evidence of enhanced crepuscular acitivity.  The observations represent a useful contribution to a subject needful of research.  Sinn 2008 Am Malacol Bull 24 (1): 65. Photograph courtesy John Gosline, University of British Columbia.

NOTE  juveniles are hatched from eggs and used in experiments when they are 2wk in age.  The octopuses are fed ad libitum on littorinid snails, mysid shrimps, and small shore crabs



 

Octopus sp. of about 1wk in age 0.1X

 
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