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Octopus cyanea (Family Octopodidae)

Day Octopus, Reef Octopus

Distribution:

Found on coral reefs throughout the tropical Indian and Pacific Oceans. Occurs across northern Australia, south to Brisbane and Perth (WA, NT, QLD).

Features:

A large muscular octopus with long arms and deep webs. Body to 20 cm long, arms to one metre long. Skin has fine creased texture that can be raised as spikes over the body and upper arms (photo). Colour patterns include a pair of dark false-eye spots and dark red arm tips with rows of small white spots. Males have special enlarged suckers on the second and third arms near the base.

Ecology/Way of Life:

Day Octopuses live in crevices in living coral and amongst coral rubble, from intertidal reef flats to at least 30 metres. Their lairs are recognised by the scatter of empty crab shells around the entrance. These octopuses emerge throughout the day (mainly near dawn and dusk) to feed on crabs, lobsters and fish. They have excellent camouflage and hunt as ambush predators, by stalking their prey or by covering small coral heads in their webs and using the arm tips to scare prey into the suckers. They paralyse their prey using poisonous saliva. The main predators of this octopus are sharks, large groupers and moray eels. Their main defense is camouflage. If seen they escape in a cloud of ink which acts as a smoke screen.

Mating occurs year round. The male inserts his special third arm into the female's gill cavity and transfers sperm into her oviducts. He sits up to one metre away from the female and uses a special groove along the edge of his arm to pass the small sperm packages. He has to be careful as the females sometimes catch and eat the male after mating. Females lay up to 600,000 tiny eggs (2 mm long) deep in crevices amongst live corals. They care for the eggs until they hatch. Then the mother dies. On hatching the transparent young swim up into the water and are carried in ocean currents as part of the plankton until they settle down to become adults.

Interaction with Humans/Threats:

Many cultures harvest this octopus by hand or spear throughout the Indian and Pacific Oceans. It is primarily collected for local consumption but some countries do have small-scale commercial fisheries (particularly Fiji, Tonga and Indonesia). This species is the most commonly seen by divers in tropical Australia due to its large size and habit of sitting in the mouth of its lair. It is also one of the few octopuses active during the day. These inquisitive creatures will quickly become familiar with regular visits by divers and will emerge to interact. They pose little threat to humans. The few reported biting incidents have been spearfishermen or divers trying to capture or kill animals.

Further Reading:

Norman, M.D. 1992. Octopus cyanea Gray, 1849 (Mollusca: Cephalopoda) in Australian waters: description, distribution and taxonomy. Bulletin of Marine Science, 49(1-2): 20-38.

Norman, M.D. and A. Reid. 2000. A guide to the squid, cuttlefishes and octopuses of Australasia. Gould League/CSIRO Publishing, Melbourne. 96 pp.

Norman, M.D. 2000. Cephalopods: A World Guide. Conchbooks, Hackenheim, Germany. 320 pp.

Acknowledgments:

Text, map and phtographs by Mark Norman, Museum Victoria.

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