Big blue octopus (Octopus cyanea)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Mollusca · Class: Cephalopoda · Order: Octopoda · Family: Octopodidae · Genus: Octopus.

Accepted name: Octopus cyanea · Authority: J. E. Gray, 1849 · Taxonomic status: accepted · AphiaID: 210788.

Synonyms and superseded combinations recorded for this taxon: Callistoctopus magnocellatus Taki, 1964; Octopus cyanea var. gracilis G. C. Robson, 1929; Octopus glaber Wülker, 1920; Octopus herdmani Hoyle, 1904; Octopus horsti Joubin, 1898; Octopus marmoratus Hoyle, 1885; Sepia barffi Curtiss, 1938.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=210788 (CC BY 4.0). Accessed 2026-09-25.

Biology and life history (SeaLifeBase)

Measured values published by SeaLifeBase for Octopus cyanea. Only fields the database actually holds for this species are shown; these are database values, not aquarium guidance.

Maximum length: 22 cm · Depth range: 0–150 m · Habitat zone: reef-associated · Vulnerability index: 12 of 100 · Fishery importance: commercial.

SeaLifeBase notes: Shallow-water benthic species inhabiting coral reefs and found in a variety of substrata (Ref. 81543). Occupies lairs in coral bedrock, live and dead coral heads and excavations in sand and rubble (Ref. 96968). In naturally-occurring holes on rocks or dens (Ref. 81543). Males and females can occupy adjacent dens (Ref. 96968).

Juveniles rapidly form homes and defend these against conspecifics (Ref. 105171). Opportunistic predator that predominantly uses tactile foraging methods (Ref. 81543). Reported to pounce and capture crabs. Another feeding strategy involves speculative hunting where an individual uses its interbrachial web to cover and explore with the tips of its arms the coral heads, rocks or clumps of algae (Ref. 105172).

Feeds primarily on bivalves, gastropods and xanthid crabs. Employs crypsis in reaction to threat (Ref. 81543). Exhibits diurnal activity (Ref. 105171). Day-active species with higher activity peaks at dusk and dawn (Ref. 96968).

Source: SeaLifeBase species summary (SpecCode 57253) — https://www.sealifebase.se/summary/Octopus-cyanea.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-25.

Distribution and occurrence records (GBIF)

4,354 georeferenced occurrence records for Octopus cyanea are published through GBIF from 60 countries or marine areas. The map above plots 335 distinct locations from a sample of 3,000 records, omitting 45 inland records that carry an institution's coordinates rather than a collection site; it shows where the species has been observed and reported, not a modelled range.

Most records by country or area: United States of America (725); Australia (526); Indonesia (380); New Caledonia (380); Egypt (283).

The full country table, WoRMS marine regions and the sampling notes are on this species' Distribution page.

Source: GBIF Occurrence Search (taxonKey 2289535) — https://www.gbif.org/occurrence/search?taxon_key=2289535&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=210788 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-25.

Conservation status (IUCN Red List)

The IUCN Red List assesses Octopus cyanea Gray, 1849 as Least Concern (code LC). No trend, population estimate or threat analysis is given here, because none is available from this source without the Red List API; follow the source link for the full assessment, including its date.

Source: IUCN Red List of Threatened Species (taxon 163055) — https://www.iucnredlist.org/species/163055/0; GBIF IUCN Red List category endpoint (taxonKey 2289535) — https://api.gbif.org/v1/species/2289535/iucnRedListCategory. Accessed 2026-09-25.

Description and natural history (Wikipedia)

Living as it does on coral reefs, and hunting by day, O. cyanea is adept at camouflage 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.

As it moves across the seabed it makes changes in its colouring and appearance to match the substrate beneath. The colour changes are instantaneous and made by chromatophores under direct control of the brain. 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.

Distribution

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.

Ecology

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.

They sometimes engage in cooperative hunting with the roving coral grouper. 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 67 to 6500 g. Its growth curve is nearly exponential and it converts its prey into new growth with an efficiency greater than 50%, relying on protein for growth, energy production, and energy reserves.

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.

Ethnozoology

In the Hawaiian language, the octopus is called generically as hee, or hee mauli''' to distinguish it from the night octopus (hee pūloa'') species. Of these, only the day octopus was typically eaten by the natives. A traditional method of capture made use of a cowrie shell lure to attract the octopuses.

Source: Wikipedia: Octopus cyanea — https://en.wikipedia.org/wiki/Octopus_cyanea (CC BY-SA 4.0). Accessed 2026-09-25.