How did you go? You probably guessed correctly that it was an octopus but did you know the species?
This is a Southern Blue-ringed octopus, one of ten species of octopus that have these tell-tale blue rings. This species is found across Southern Australia while other species can be found on shallow reefs of the eastern Pacific Ocean all the way to Japan.
This octopus has a body around 4-6 cm long and arms 10 cm long and despite its small size, it is the largest of the ten blue-ringed octopus species. Its body is tan or dark yellow with dark brown bands on the legs and its 50-60 iridescent blue circles are only displayed when the octopus is threatened. It relies on camouflage to avoid predators and hides during the day and hunts for food at night. Unlike other octopus, the southern blue-ringed octopus has lost the ability to produce ink, so it relies on its rings to ward off possible threats.
The Southern Blue-ringed octopus lives from the intertidal zone to a depth of around 50 metres on reefs, rubble areas and seagrass beds. Food is primarily crabs and shrimp that are hunted using its arms to feel in the gaps between rocks to locate prey. Once the prey is caught, the octopus uses its beak to bite through the exoskeleton and releases a toxin, killing the prey. The toxin is not injected like a bee sting instead it is in the saliva of the octopus.
The Southern Blue-ringed octopus does not make the toxin, it uses bacteria that live in the salivary glands to make the powerful neurotoxin called tetrodotoxin. The toxin works by interrupting the nerve signals and therefore movement, breathing and other vital functions needed for life. The same toxin is found in a wide range of animals including newts, fish, frogs, crabs and worms.
Like all cephalopods, the Southern Blue-ringed octopus can change the colour and texture of their skin to camouflage themselves. Muscles in the skin contract to create the desired texture and colours are made using sacs of pigment called chromatophores. The chromatophores can expand or contract to reveal or hide the colour they contain and by using combinations of these across the body the octopus creates the desired colour pattern.
The blue rings are not created by chromatophores, instead, they are special ring-shaped reflectors in the skin that reflect blue/green light in a wide viewing area. Muscles above the rings contract to hide the rings from view and relax to reveal them. The rapid contraction and relaxation of these muscles create the flashing of the rings. Around and underneath these rings are darkly pigmented chromatophores that expand rapidly to increase the contrast around the rings.
Like many other octopus, the Southern Blue-ringed octopus reproduces at the end of its life. The male dies after mating and the female carries her 50-100 eggs around with her until they hatch. She is unable to feed during this time and dies soon after the eggs hatch.
Watch as a Blue-ringed octopus camouflages itself, catches a meal and of course, flashes its blue rings: https://www.youtube.com/watch?v=bFGMPsb0YV0
