The day octopus is an expert at living in coral reefs. It can change colors with ease, often shifting well over a hundred times over the course of a few hours — an important skill when you need to blend into such a colorful environment!
This species is a keystone species for coral reefs, meaning that lots of other reef species depend on them for their own survival!
This octopus uses spatial reasoning to navigate reefs. Even if it wanders randomly, it can always zip back home!
A study demonstrated that this species is not a member of the genus Octopus (i.e., O. vulgaris group). This species shows stronger similarities with the genus Abdopus. Its generic placement remains unresolved.
Besides the Giant Pacific Octopuses, this is one of the largest octopus species. Its mantle length is to 160 mm (6 in) and its total length to greater than 1 m (over 3 ft!). The body weight of this species can be at least 6 kg (13 lbs). In larger animals, there are around 450-500 suckers on each arm!
Their lifespan is 12-15 months.
The day octopus lives throughout the tropical Indo-West Pacific Oceans from the east coast of Africa to Hawaii, and southern Japan to northern Australia.
This octopus inhabits shallow coral reefs from intertidal flats to at least 22 m (72 ft) deep. It occupies large dens in coral bedrock, in live and dead coral heads, and can excavate a den in sand and rubble.
Shellfish is on the menu for this species! This octopus hunts during the day-time searching for mussels, clams, shrimps, and crabs hiding among the corals and crevices. Stomach contents of 49 Octopus cyanea from Hawaiian waters contained 89% crab, 41% stomatopods, 27% shrimps, and 10% bony fish. One individual had remains of a moray eel!
Its color patterns range from uniform white to various mottle patterns to uniform dark brown and it can have short dark bars along all arms. Most distinguishing body pattern features include 3 to 7 rows of small white spots on the arm tips that are distinct against a dark brown body color.
The day octopus has false eye spots (ocelli) present at the base of its arms that are dark oval patches with no iridescent rings. This species has a transverse pair of white spots on its dorsal mantle and four large primary papillae in a diamond arrangement on its dorsal mantle and single large papilla over each eye.
Its camouflage is outstanding since it lives in a complex habitat: coral reefs with high diversity of corals, sponges, and algae and many predators searching for a rich protein meal. This species could be dubbed the King of Camouflage. During a 4-hour forage, the day octopus may change its skin patterning more than 150 times to accomplish camouflage among the coral reef.
Spatial memory and navigational skills are also very important in a complex environment with many predators. Individual octopuses were observed foraging twice a day, covering an average of 100 m (330 ft) per day, then finding their way back to their den. Octopuses have also been observed to terminate their foraging and swim in a “bee line” back to their den, indicating an advanced visual map.
During foraging, the day octopus commonly uses “parachute attacks” where it pounces over a feeding spot and simultaneously spreads the arms and web. Foraging is commonly accompanied by 1-4 fishes. Small groupers follow day octopuses and will feed on small shrimps and fishes that escape the octopus. The octopus is grazing on bivalves and shrimps and helping out (indirectly) small groupers.
On coral reefs, the day octopus (and many other octopuses) is important prey for larger predators such as snappers and barracuda. This illustrates the octopus plays an important role as a keystone reef species- a species on which other species in an ecosystem largely depend.
Van Heukelem WF (1983a), Norman MD (1992a), Young RE and Harman RF (1997), Goodman-Lowe GD et al. (1999), Hanlon RT and Forsythe JW (2008), Sauer WHH et al. (2011) IN Jereb, P.; Roper, C.F.E.; Norman, M.D.; Julian K Finn (eds)
Cephalopods of the world. An annotated and illustrated catalogue of cephalopod species known to date. Volume 3. Octopods and Vampire Squids. FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 3. Rome, FAO. 2014. 370 p
Hanlon and Messenger. Cephalopod Behavior 2018. 2nd edition
Forsythe JW, Hanlon RT (1997) Foraging and associated behavior by Octopus cyanea Gray, 1849 on a coral atoll, French Polynesia. Journal of Experimental Marine Biology and Ecology 209:15-31. doi: 10.1016/s0022-0981(96)00057-3
Hanlon R, Vecchione M, Allock L. Octopus, squid, and cuttlefish. A visual, scientific guide to the oceans’ most advanced invertebrates.
Guzik MT, Norman, MD, Crozier R (2005) Molecular phylogeny of the benthic shallow-water octopuses (Cephalopoda: Octopodinae). Molecular Phylogenetics and Evolution 37: 235-248