419 Dive Log Australasia AUGUST 2026

The Secrets of the Blue Rings The Southern Blue-ringed Octopus of Port Phillip Bay P ort Phillip Bay is full of animals that reward slow, observant divers. Some are quite easy to spot: rays gliding over the sand, seahorses clinging to pylons, seadragons drifting through the weed, stingarees half-buried on the bottom, and even the occasional nudibranch out in the open. Others remain almost invisible until they decide to reveal themselves. The Southern Blue-ringed Octopus, Hapalochlaena maculosa , belongs firmly in that second group. Text & Images by Vadim Belakhov

A Southern Blue-ringed Octopus (Hapalochlaena maculosa) moves across the sand with its warning colours lit, searching for its next meal.

Found across southern Australian waters, including Victoria, Tasmania, South Australia and Western Australia, this small octopus inhabits rocky reef, rubble, seagrass beds and other sheltered coastal habitats in Port Phillip Bay, from very shallow water down to deeper subtidal areas. It is secretive, beautifully patterned and highly venomous, but reducing it to “tiny and deadly” misses most of the story. This is not an aggressive animal waiting to attack. It poses no threat to divers unless it is touched, cornered, stepped on or otherwise provoked. Most of the time, it is a shy, highly adapted hunter that spends much of its short life out of sight. Many people will swim straight past one without ever knowing it was there.

Despite its famous blue rings, this octopus does not usually move around glowing like a warning sign. At rest, it is often brown, grey, cream or greenish, mottled enough to blend into its surroundings. The rings may be faint or almost completely hidden. That changes when the animal is stressed, defensive, hunting or highly alert. Then the brilliant iridescent blue rings can flare across the body, head, arms and webbing. It is one of the most striking warning displays in the marine world: beautiful, unmistakable and very clear in meaning. Do not touch. The Southern Blue-ringed Octopus is small, often only a few centimetres across the body, with a total arm

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Dive Log Australasia #419 August‘26

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