Deadly Fascination - Blue-ringed Octopus

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by Sheree Marris (with photographs by Steven Walsh)

Do you ever find yourself questioning the form, function and design of nature? I do, and it never ceases to amaze me, especially those found sliming, swimming and jetting around in our blue backyard. When it comes to Blue-ringed octopuses it is as though a crazy scientist was let loose to design a creature of their wildest dreams.

The result: a jet powered, blue-blooded, contortionist that digests food through their donut-shaped brain.

They pack all of this awesomeness into their heads, which is impressive for an animal  no more than 20 centimetres big. Oh, and the real kicker? They are some of the most venomous animals on the planet. Forget claws and jaws, their weapon of choice is saliva.

Blue-rings can be found throughout the Pacific and Indian Oceans, from Japan to Australia around coral reefs and rocky shores. Their name is a reference to trademark vibrant blue rings and or lines decorating their bodies. It is broadly applied to the genus of octopus which includes 3 scientifically accepted species. Researchers are confident that more of these delicate little jewels are waiting to be discovered.

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So, what creates the signature blue? Iridophores. Little balls of reflective pigments that give the blue-rings their razzle dazzle. They are arranged to reflect blue–green light, appearing when muscles above the iridophores relax, exposing their bright blue colour. Hundreds of these iridophores form rings or lines. Beneath and around them are dark pigmented chromatophores (bags of coloured pigment) that when activated, make the blue pop, signalling predators that they should think twice before eating it.

To secure their own meals, the Blue-ringed octopus inject victims with a saliva laced with the deadly neurotoxin, tetrodotoxin or TTX. It is more potent that cyanide, and blue-ring octopuses are the only known octopuses to store TTX in their venom glands, tissues, gills and organs.

So how do they make the TTX? They do not. Researchers like PhD candidate, Brooke Whitelaw, hypothesise that the TTX may be produced from bacteria. “Our research has revealed a diverse array of bacterial species present in the venom gland of blue-ringed octopus, some of which may produce TTX. Identifying, which species are capable of producing tetrodotoxin and the possible relationship between the octopus and its bacteria is an area that we will be exploring in the future to answer this question”.

How does this super saliva work? Blue-rings are mostly nocturnal, emerging at night to feed, using camouflage their launch themselves onto prey such as crabs, fish and molluscs. They wrap their eight arms around their victim, engulfing it like a cape. A bird-like beak then bites through the flesh or shell of its victim, releasing the venomous saliva.

TTX is a strong, toxin that quickly paralyses prey by blocking the transmission of nerve impulses to muscles. While it does not stop the heart from beating, it stops the diaphragm from working and starves the body of oxygen. It allows the beak of the octopus to get busy, pulling their victims apart.

Although they have this fearsome reputation, they are actually quite shy and will usually jet away at any given opportunity. Reproduction also reveals a gentler side. The male will lightly caress the female with his penis-like arm, called the hectocotylus. He then grabs her and inserts the hectocotylus into her head (mantle cavity), transferring sperm bundles.

When ready, the female will lay a single clutch of 50-150 eggs depending on the species, caring for them until they hatch. Some species lay them on rocks, others carry them around in their arms. During this time the females do not eat, and die after their eggs hatch. Although there is no parental care, they pass on their potent TTX. The young are venomous as soon as they begin their life in the sea. They also carry the trademark blue-rings and lines.

Scientists are still unsure how the TTX finds its way into the eggs, however given there is a high concentration of it in the ovaries, that is the most likely source. There are so many fascinating aspects to Blue-ring octopus biology which have yet to be explained and is one of the many motivators for scientists like Brooke to continue their work.

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