Big blue octopuses, Octopus cyanea, are commonly found in the region of the Indian and Pacific Oceans. They are scattered throughout warm waters, from the Hawaiian Islands to the Red Sea (northeast Africa). There have also been reports of big blue octopuses in the Mediterranean sea and southeast of Africa such as along the coast of Madagascar, Tanzania, Somalia, and Seychelles. ("Hawaiian octopus, Octopus cyanea", 2004; Guard and Mgaya, 2002; Unsworth and Cullen-Unsworth, 2012; Yarnall, 1969)
Big blue octopuses are commonly found in coral reefs at depths of 1 to 100 meters. Big blue octopuses are found living in muddy, sandy, or rocky bottoms, and in seagrass beds. They create lairs or dens in crevices or coral rubbles within coral reefs. These dens aren't used for long term; on average individuals spend up to 35 days in one den. ("Seasonal closures of no-take zones to promote a sustainable fishery for Octopus cyanea (Gray) in south west Madagascar", 2006; Unsworth and Cullen-Unsworth, 2012; Van Heukelem, 1976)
Big blue octopuses are commonly mistaken for the common octopuses, Octopus vulgaris. They both have eight tentacles, an enormous head, same brownish reddish skin tone, and the ability to camouflage. The specific epithet cyanea means dark blue, and big blue octopuses have dark blue circles across their skin. Common octopuses lack this distinct coloration.
Big blue octopus lengths range from 16 cm from head to dorsum, and 80 cm from arm to arm. Males have a longer arm (third right arm) reaching to about 48 cm. Males also have very large suckers when they are 7 to 9 months of age. The suckers are usually the 7th or 8th pair of suckers. Males are sexually mature at 320 g and females reach maturity at or above 600 g. Big blue octopuses reach their full sizes between 13 to 15 months, right before reproduction. Size variation depends on food availability. Adult females range from 600 to 4800 g and males reach 400 to 6600 g; average size across the entire species is 1200 g. ("Seasonal closures of no-take zones to promote a sustainable fishery for Octopus cyanea (Gray) in south west Madagascar", 2006; Guard and Mgaya, 2002; Unsworth and Cullen-Unsworth, 2012; Van Heukelem, 1976)
Big blue octopuses are a fast-growing, highly-fecund, short-lived species. Because big blue octopuses lack larva, they instead have large yolk-filled eggs. Egg development requires about 20 to 30 days and eggs are 3mm long when laid. Their growth rate post-hatching ranges from 5.6 to 5.8% per day. Male big blue octopuses start developing larger suckers on their seventh or eighth pair of suckers when they are 7 to 9 months old.
At 10-12 months males and females become sexually mature. Males are sexually mature at the weight of 320g, and females 600g. Males will start developing a larger arm on their third right arm during this time. These arms will be used during reproduction to be inserted into females’ mantle cavity, where the sperm are unleashed. As for females, their eggs become fertile during this time.
Big blue octopuses reach their full sizes between 13 to 15 months right before reproduction. Size variation depends on food availability. Adult females range from 600g - 4800g and males reach 400g - 6600g. Once the suckers have fully enlarged (at about 15 to 18 months), males start eating less, lose weight, and slowly lose their ability to change color, and die. As for females, they stop eating and lose weight after spawning. They die 60 days after they lay their eggs. This happens because females don’t eat while protecting their eggs from predators. ("Seasonal closures of no-take zones to promote a sustainable fishery for Octopus cyanea (Gray) in south west Madagascar", 2006; Forsythe and Hanlon, 1997; Mather and Mather, 2004; Talbot and Marshall, 2011; Van Heukelem, 1976)
Big blue octopuses reproduce sexually, and they are polygynous. Females die after spawning because they stop eating to protect their eggs. Reproduction in big blue octopuses is not seasonal. It depends on when they reach their sexual maturity which is 10 to 12 months of age. Big blue octopuses make spermatophores. When males grow their third right arm to its full length (43 cm) they are able to insert it into females’ mantle cavity and deliver their sperm internally.
Big blue octopuses usually mate during the day while foraging. Males can spot a female from 8m away. Males will wave their longer tentacle to attract females. There have been some cases where females will take males into their dens to mate, but typically they will mate on solid surfaces. (Forsythe and Hanlon, 1997; Huffard and Hochberg, 2005; Talbot and Marshall, 2011; Unsworth and Cullen-Unsworth, 2012; Van Heukelem, 1976)
Big blue octopuses are gonochoristic. Males have a distinctive longer third right arm. They reproduce sexually and will start mating around 10 to 12 months. There have been some cases where young (older than 10 months) females that mate without mature eggs will store sperm in their glands for about three months. Females are oviparous; on average they will lay up to 700,000 eggs (500,000 to 1,000,000) that weigh up to 0.33g and are 3mm in length. They lay their eggs near the surface of the water. Females are semelparous as they stop eating after spawning and die 60 days after laying their eggs to protect them from predators.This is about the same time it takes for the eggs to hatch. There have been some cases where they live longer due to lower temperatures which slows down their ovary gland enlargement. Females turn very aggressive during mating season and there have been some cases of sexual cannibalism. (Forsythe and Hanlon, 1997; Huffard and Hochberg, 2005; Mather and Mather, 2004; Van Heukelem, 1976)
Only female big blue octopuses exhibit parental investment beyond mating. Females brood their eggs until they hatch, some females will even brood without the presence of their eggs. They protect their eggs day and night, never stopping to eat. Approximately 10 days after the last egg hatches, female big blue octopuses will die. (Goodman-Lowe, et al., 1999; Mather, 2006; Unsworth and Cullen-Unsworth, 2012; Van Heukelem, 1976)
The average lifespan of big blue octopuses is 12 to 15 months in the wild and in captivity. The longest known lifespan is 18 months both in the wild and in captivity. Females die from ovary enlargement after a single spawning and 60 days after laying eggs. There has been a case where a female lived 6 months longer (24 months total) due to exposure of low temperatures and consequently a lower metabolic rate. Males die from enlargement of specialized suckers, about 13 to 15 months of age. ("Hawaiian octopus, Octopus cyanea", 2004; Ambrose, 1982; Forsythe and Hanlon, 1997; Goodman-Lowe, et al., 1999; Grimsditch, 2008; Guard and Mgaya, 2002; Mather, 2006; Van Heukelem, 1976)
Big blue octopuses are unique because they are diurnal hunters. They spend about 30% of the daytime foraging and at night barricade their dens with rocks to avoid predators. They are solitary creatures that only interact with each other for reproduction. They are very aggressive, and larger individuals can cannibalize smaller ones. Specialized pigments in their skin give them the ability to camouflage to their surroundings for hunting and avoiding predation. These octopuses also have the ability to release black ink when threatened. They squirt ink at their predators, which inhibits the predators’ vision and their sense of smell. This helps big blue octopuses to escape without being tracked.
Big blue octopuses are sedentary, they generally stay in a den for 35 days and move about 60 to 80 meters away from their old den. They will forage 81m from their dens. Although big blue octopuses are natatorial, they crawl rather than actively swim, for physiological reasons; when they swim one of their three hearts (systemic heart) stops beating. ("Hawaiian octopus, Octopus cyanea", 2004; "Seasonal closures of no-take zones to promote a sustainable fishery for Octopus cyanea (Gray) in south west Madagascar", 2006; Ambrose, 1982; Forsythe and Hanlon, 1997; Furuya, et al., 2004; Grimsditch, 2008; Guard and Mgaya, 2002; Mather and Mather, 2004; Talbot and Marshall, 2011; Unsworth and Cullen-Unsworth, 2012; Van Heukelem, 1976; Yarnall, 1969)
Home range areas have not been reported, but big blue octopuses typically forage within 81m of their den. The maximum distance from their den was reported as 129m. Although they defend their den, territory size has not been reported. (Goodman-Lowe, et al., 1999; Grimsditch, 2008; Talbot and Marshall, 2011; Unsworth and Cullen-Unsworth, 2012; Van Heukelem, 1976)
Most cephalopods can use camouflage in their surroundings. Mainly a mechanism to avoid predation, color changes can also employ it for communicating with other octopuses. They use specific colors and lighting to communicate with each other. When males are trying to catch the attention of females, they tend to change into dark colors when in an area where there is a lot of light. Their keen eyesight helps them keep guard while mating, they can spot a predator 8 m away. Big blue octopuses can also mimic banded sole (Microchirus wittei) to avoid predation. They can also alarm other octopuses by changing their skin tone rapidly almost like flashing a light.
Their keen eyesight is used for creating foraging paths. They first scan for predators and they visually wait for their prey to get close enough to trap them. Big blue octopuses use tactile senses to morph into surrounding objects. Males also use their tactile senses for mating, locating where to insert the sperm. (Forsythe and Hanlon, 1997; Huffard and Hochberg, 2005; Talbot and Marshall, 2011)
Big blue octopuses are also called day octopuses because they hunt diurnally, an uncommon trait among octopuses. On average, octopuses spend 28 to 30% of the daytime foraging. They will typically forage up to 81 m away (maximum 129 m) from their dens. Big blue octopuses have a very diverse diet and appear to be opportunistic feeders. Their diets get more diverse when there are more smaller prey. Big blue octopus diets consist of sessile molluscs, small fish, and crustaceans. Juvenile octopods have similar diets but because they have smaller masses (ca. 500 g), they will eat smaller prey. ("Hawaiian octopus, Octopus cyanea", 2004; "Seasonal closures of no-take zones to promote a sustainable fishery for Octopus cyanea (Gray) in south west Madagascar", 2006; Ambrose, 1982; Grimsditch, 2008; Mather and Mather, 2004; Unsworth and Cullen-Unsworth, 2012)
The common predators of big blue octopuses are Hawaiian monk seals (Monachus schauinslandi), large fish, sharks, moray eels (Muraenidae), sperm whales (Physeter catodon), and dolphins (Delphinidae). Big blue octopuses are known for their advanced behaviors to avoid predators. One of their famous antipredator adaptation is crypsis, the ability to camouflage. There are five mechanisms in this category: camouflaging into any background, countershading, mimicry (mimicking a venomous fish like the banded sole, Microchirus wittei), changing their appearance into different varieties throughout a short period of time, and controlled ability to change their phenotype.
Big blue octopuses can spot a predator from almost 8 m away. Once spotted, octopuses will either camouflage into their surrounding or hide in their dens. They also developed the ability to squirt out ink when threatened by a predator. Ink may blind predators and inhibit their sense of smell. This allows the octopus to escape. (Goodman-Lowe, et al., 1999; Grimsditch, 2008; Huffard and Hochberg, 2005; Talbot and Marshall, 2011; Van Heukelem, 1976)
Big blue octopuses have no reported parasites. They play no pivotal role in their ecosystem, based on their opportunistic feeding behavior, and few predators relying on them as a food source. (Furuya, et al., 2004)
Big blue octopuses are source of food for humans. In southwest Madagascar big blue octopuses die and are washed up on to shore. They make up 11.8% of marine resources with a catch rate of 17,145 kg/km2/year. This is beneficial for humans because octopods are a source of food and can be sold in the fisheries market, boosting up the economy in local areas. ("Hawaiian octopus, Octopus cyanea", 2004; "Seasonal closures of no-take zones to promote a sustainable fishery for Octopus cyanea (Gray) in south west Madagascar", 2006)
Big blue octopuses have no negative economic impacts on humans.
Big blue octopuses have have not been evaluated on the IUCN red list or for CITES. They have no special status on the US federal list or State of Michigan List.
Due to climate change, coral reef ecosystems in which these octopods live are threatened. This constitutes an indirect threat to octopods. Their capture in commercial fisheries also has an impact on the species. Ching et al. consider them a highly vulnerable species. However, no conservation measures are in place for big blue octopuses. ("Hawaiian octopus, Octopus cyanea", 2004)
heidi chicas (author), Radford University, Alex Atwood (editor), Radford University, Karen Powers (editor), Radford University, Joshua Turner (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
parental care is carried out by females
A substance that provides both nutrients and energy to a living thing.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
having more than one female as a mate at one time
structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.
mainly lives in oceans, seas, or other bodies of salt water.
remains in the same area
offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.
uses touch to communicate
uses sight to communicate
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