| Big blue octopus | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Order: | Octopoda |
| Family: | Octopodidae |
| Genus: | Octopus |
| Species: | O. cyanea |
| Binomial name | |
| Octopus cyanea | |
| Synonyms[2] | |
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Octopus cyanea, also known as thebig blue octopus[3] orday octopus,[4] is anoctopus in thefamilyOctopodidae. It occurs in both the Pacific andIndian Oceans, fromHawaii to the eastern coast of Africa.[5]O. cyanea grows to 16 cm inmantle length with arms to at least 80 cm.[5] This octopus wasdescribed initially by the British zoologistJohn Edward Gray in 1849; thetype specimen was collected off Australia and is at theNatural History Museum inLondon.[6]
Living as it does on coral reefs, and hunting by day,O. cyanea is adept atcamouflage and not only can change colour frequently, but also can change the patterns on and texture of its skin. One researcher observed it change its appearance 1000 times in seven hours.[3][4] As it moves across the seabed it makes changes in its colouring and appearance to match the substrate beneath.[7] The colour changes are instantaneous and made bychromatophores under direct control of the brain.[8] This octopus sometimes produces a "passing clouds" display when stationary near prey such as a crab; this mimics a dark shadow passing across its surface and may encourage the crab to move incautiously.[9]
O. cyanea is found on reefs and in shallow waters in the Indo-Pacific. Its range extends from the Red Sea, the East African coast, and Madagascar, to southeastern Asia, Oceania, and as far as Hawaii.[7]
While most species of octopus are nocturnal,O. cyanea is diurnal,[4][10] although mostlycrepuscular, being active at dawn and dusk. It maintains a den to which it returns after foraging; a rock crevice, a hidden place under an overhang, a hiding place among coral heads, or a hole excavated in rubble or sand.[11]
It is apredator and searches the reef for fish, crabs, shrimp, and molluscs. Small items may be eaten where they are caught, while larger items are carried back to the den for consumption. Crabs may be killed by a bite and given an injection of toxic saliva, then chewed up in the beak of the octopus, while molluscs may have their shells drilled and the animal inside being predigested to ease extraction. Emptymollusc shells and crabcarapaces are discarded outside the den, forming amidden.[4][7]
They sometimes engage incooperative hunting with theroving coral grouper.[12] Day octopuses have also been observed participating in group hunts withblacktip grouper andgoatfish in theRed Sea. During these hunts, individuals have been seen to punch and strike groupers with their arms,[13] theorised to be a 'discipline' response towards fish exploiting the hunt rather than actively participating, and as a means to prevent fish from crowding around the octopus.[14] As some occurrences of punching occurred outside of these situations, day octopuses are also speculated to engage in this behaviour out ofspite, as a response to normally-cooperative partners stealing prey from the octopus or other fish in the group.[15]
O. cyanea has a lifespan of 12–15 months after settling from theplanktonic larval state. During this time, it grows from about 67 to 6,500 g (0.1 to 14.3 lb).[16] Its growth curve is nearlyexponential and it converts its prey into new growth with an efficiency greater than 50%, relying on protein for growth, energy production, and energy reserves.[17]
In captivity, it breeds at any time of year, probably depending on when the female reaches maturity. Mating may becomecannibalistic.[18] HoweverOctopus cyanea will socially tolerate other individuals by sharing tanks and dens and with typically no loss to cannibalism or escape. They also exhibit significant levels of social repulsion, and individuals often chose a solitary den when given the option.[19] The male may mate with several different females, but after this, the suckers on the edge of his webbing expand in size. During the next two to three months, they continue enlarging while the octopus goes into a decline and dies. Meanwhile, the female remains beside her eggs that are deposited in a den, and dies soon after they hatch.[16]
In the Hawaiian language, the octopus is called generically asheʻe', orheʻe mauli to distinguish it from thenight octopus (heʻe pūloa) species.[20][a] Of these, only the day octopus was typically eaten by the natives.[22][b] A traditional method of capture made use of acowrie shell lure to attract the octopuses.[20]
