While most species of octopus are nocturnal,
O. cyanea is diurnal, although mostly
crepuscular, 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. It is a
predator 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. Empty
mollusc shells and crab
carapaces are discarded outside the den, forming a
midden. Day octopuses have also been observed participating in group hunts with
blacktip grouper and
goatfish in the
Red Sea. During these hunts, individuals have been seen to punch and strike groupers with their arms, 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. As some occurrences of punching occurred outside of these situations, day octopuses are also speculated to engage in this behaviour out of
spite, as a response to normally-cooperative partners stealing prey from the octopus or other fish in the group.
O. cyanea has a lifespan of 12–15 months after settling from the
planktonic larval state. During this time, it grows from about . In captivity, it breeds at any time of year, probably depending on when the female reaches maturity. Mating may become
cannibalistic. However
Octopus 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. 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. File:Octopus cyaneain Kona.jpg File:Octopus cyanea3.jpg == Ethnozoology ==