Blue-ringed octopuses, comprising the genus Hapalochlaena, are four extremely venomous species of octopus that are found in tide pools and coral reefs in the Pacific and Indian Oceans, from Japan to Australia. They can be identified by their yellowish skin and characteristic blue and black rings that can change color dramatically when the animals are threatened. They eat small crustaceans, including crabs, hermit crabs, shrimp, and other small sea animals.

They are some of the world’s most venomous marine animals. Despite their small size—12 to 20 cm (5 to 8 in)—and relatively docile nature, they are very dangerous if provoked when handled because their venom contains a powerful neurotoxin called tetrodotoxin.

The species tends to have a lifespan around two to three years, which may vary depending on factors such as nutrition, temperature, and the intensity of light within its environment.

Behavior

Blue-ringed octopuses spend most of their time hiding in crevices while displaying effective camouflage patterns with their dermal chromatophore cells. Like all octopuses, they can change shape easily, which allows them to squeeze into small crevices. This, along with piling up rocks outside the entrance to their lairs, helps safeguard them from predators.

If they are provoked, they quickly change color, becoming bright yellow with each of the 50–60 rings flashing bright iridescent blue within a third of a second, as an aposematic warning display. In the greater blue-ringed octopus (H. lunulata), the rings contain multilayer light reflectors called iridophores. These are arranged to reflect blue–green light in a wide viewing direction. Beneath and around each ring are dark-pigmented chromatophores that can be expanded within one second to enhance the contrast of the rings. No chromatophores are above the ring, which is unusual for cephalopods, as they typically use chromatophores to cover or spectrally modify iridescence. The fast flashes of the blue rings are achieved using muscles that are under neural control. Under normal circumstances, each ring is hidden by contraction of muscles above the iridophores. When these relax and muscles outside the ring contract, the iridescence is exposed, thereby revealing the blue color.

Toxicity

The blue-ringed octopus, despite its small size, carries enough venom to kill 26 adult humans within minutes. Their bites are tiny and often painless, with many victims not realizing they have been envenomated until respiratory depression and paralysis begins. No blue-ringed octopus antivenom is available

The octopus produces venom containing tetrodotoxin, histamine, tryptamine, octopamine, taurine, acetylcholine, and dopamine. The venom can result in nausea, respiratory arrest, heart failure, severe and sometimes total paralysis, and blindness, and can lead to death within minutes if not treated. Death is usually caused by suffocation due to paralysis of the diaphragm.

Direct contact is necessary to be envenomated. Faced with danger, the octopus’s first instinct is to flee. If the threat persists, the octopus goes into a defensive stance, and displays its blue rings. If the octopus is cornered and touched, it may bite and envenomate its attacker.

Conservation

Currently, the blue-ringed octopus population information is listed as least concern according to the International Union for Conservation of Nature. Threats such as bioprospecting, habitat fragmentation, degradation, overfishing, and human disturbance, as well as species collections for aquarium trade, though, may be threats to population numbers. Hapalochlaena possibly contributes to a variety of advantages to marine conservation. This genus of octopus provides stability of habitat biodiversity, as well as expanding the balance of marine food webs.

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