The Blue-Ringed Octopus on Mabul
A guest once bolted three metres up the water column because a scrap of rubble turned blue. He thought the animal was going to launch at his mask and end his holiday. That is the blue-ringed octopus in the popular imagination. People expect an aggressive assassin hunting divers across the reef. The reality is a creature the size of a golf ball that just wants you to go away. The bottom of the Celebes Sea is a minefield of bad chemistry and this animal is its undisputed king. We dive these sites every day to find them. The secret is knowing how to look at the sand.
Table of Contents
- The size of the reputation versus the animal
- Where the neon rings come from
- The reality of the toxin and the risk
- The heavy neighbours in the muck
- The night shift beneath the rig
- How we photograph a flashing warning
- The no-gloves rule and your buoyancy
- The size of the reputation versus the animal
- Where the neon rings come from
- The reality of the toxin and the risk
- The heavy neighbours in the muck
- The night shift beneath the rig
- How we photograph a flashing warning
- The no-gloves rule and your buoyancy
The size of the reputation versus the animal
The first time I point one out on the sand at Froggy Lair, divers usually stare right past my finger. They expect a monster. What they get is Hapalochlaena lunulata. This is a beige blob no longer than 10 to 12 centimetres. Science calls it the greater blue-ringed octopus. The name is a joke on the observer. It refers only to the large diameter of the rings because the animal itself is smaller than its southern cousins. I look for them among the rubbish. They sit in the shallow silt and the discarded old tyres at 5 to 10 metres deep. They look just like discarded beige sponges until they move. If you swim fast, you will miss them.
We drop down to the sand at Awas Reef and we wait. The dive becomes a slow crawl over broken shells and old wood. Muck diving requires you to look at the ocean through a microscope. You ignore the water column. You stare at the mud until the mud stares back. The octopus hunts at night or hides in the shallow rubble zones. The terrain here is a loose mess of volcanic silt and dead coral. The octopus uses this debris to hide. It folds itself into a crevice and waits for the current to bring dinner.
Where the neon rings come from
The famous neon display is a biological magic trick. The octopus does not generate light. It wears a suit of tiny reflectors beneath its skin that bounce blue-green light back at you. When the animal is relaxed on the rubble at Paradise 1, it flexes a layer of muscle over those reflectors to hide them. It becomes invisible against the dull background. The flash happens when the octopus gets stressed and relaxes those covering muscles. The blue rings snap into view in a third of a second. It is a brilliant neon billboard on a drab sandy slope.
That flash is not a threat display. It is a panic button. Take the flash as your cue to back off. The muscles outside the ring contract to push the bright tissue forward. The contrast against the dark pigment beneath the skin is stark. You are looking at a living warning sign engineered by millions of years of evolution. These displays only show up when the primary camouflage fails and the octopus feels cornered. If you see the rings, you have already annoyed the local.
The reality of the toxin and the risk
The fear comes from the chemistry. The bite carries tetrodotoxin. This potent nerve poison comes from bacteria living in the glands that produce saliva. The toxin blocks the pathways that let your nerves send signals. It paralyses the victim while leaving them completely awake. The medical protocol is brutal. There is no antivenom. A bitten diver requires immediate rescue breathing to stay alive until the body clears the chemical. First responders also apply a pressure immobilisation bandage to slow the venom down. Without help, a complete shutdown of the respiratory system can occur within three minutes.
But here is the perspective you need before you cancel your dive. Bites are exceptionally rare. The bite itself is often so small you would not feel it. I have logged thousands of hours on these muck sites and I do not know anyone who has been bitten. Treat the octopus with respect and give it zero reason to defend itself. Grabbing it or trapping it against the reef risks a bite. Look at the animal and leave it alone.
The heavy neighbours in the muck
Mabul is famous for its small killers. The blue-ringed octopus shares the sand with a heavy cast of toxic residents that use the same camouflage strategies. The flamboyant cuttlefish prowls the mud on its lower arms at Awas Reef. It carries a small, odd-shaped cuttlebone that ruins its buoyancy and forces it to walk across the bottom. It flashes purple and yellow to warn you about its highly lethal muscle tissue. This is one of only three known poisonous cephalopods, the group that includes octopuses, squid and cuttlefish.
The peacock mantis shrimp lives in holes nearby. It swings a club at 23 metres per second to smash shells. The impact vaporises the water and creates a bubble that collapses with the heat of a star. Then you have the ambush predators. Stonefish mimic the coral blocks so well you could rest a knee on one before you see it. They pack venom in the spines along their backs that can pierce thick neoprene. If a diver gets spiked, we have to immerse the affected area in non-scalding hot water to break down the venom proteins. The sand is alive with animals that defend themselves violently.
The night shift beneath the rig
The blue-ringed octopus is active after dark. Mabul changes completely when the sun drops. The sand changes staff and the daytime predators hand the reef over to the night shift. We dive the Seaventures Platform at night to see this transition. The site sits right beneath a towering decommissioned oil rig. The underwater environment is a surreal mess of heavy steel pylons and sunken metal structures resting on the sand at 12 to 18 metres.
This debris field is prime hunting ground. A sweep of the torch sometimes catches eyes looking back from the rubble. Giant moray eels leave their holes to hunt. Frogfish the size of a human fingernail sit perfectly still on the metal. And sometimes a blue-ringed octopus is spotted navigating the rubble. They leave the safety of the crevices to hunt small crabs in the dark. Finding one by torchlight is completely different to seeing one during the day. The beam cuts through the gloom and hits a moving patch of beige. You signal the group and everyone circles up in the dark. We hover in the black water and watch a predator go to work. The metal pylons vanish towards the surface above us. It is the most atmospheric dive on the island.
How we photograph a flashing warning
We spend half our bottom time getting cameras in front of these animals. Isolating a small subject against a pitch-black background is the obsession of Mabul. The technique requires a snoot. This funnel narrows the beam from your underwater flash into a tight spotlight. It acts as a sniper rifle for your lighting. You kill the ambient light with a shutter speed around 1/200s, an aperture of f/16 and an ISO of 100. When the strobe fires, only the octopus is illuminated. The background vanishes into deep black.
The ethical line here is thick and bright. A flashing octopus is a stressed octopus. Harassing an animal with a barrage of flashes until it turns blue is poor form. A good photographer waits in the silt and shoots the animal as it behaves naturally. A bad photographer chases it into a corner to force a reaction. We watch you in the water and we judge you on this. You do not touch the wildlife to get the shot. If you push the animal too hard, the guide will pull you off the site.
The no-gloves rule and your buoyancy
The single best piece of safety equipment you have on Mabul is your buoyancy. Sabah Parks bans recreational dive gloves across these islands to stop divers touching the fragile reef. The logic is brilliant. If your hands are bare, you are far less likely to grab a piece of the bottom to steady yourself. You want your hands folded away anyway. A loose hand on the sand at Eel Garden might find a hiding cone snail. These snails fire a hollow harpoon loaded with venom that stops nerves sending signals. The sting causes total paralysis within hours.
The rule is straightforward. Hover above the muck and use a gentle frog kick to keep the silt down. A flutter kick will kick up a cloud of volcanic dust that blinds the site instantly. You will ruin the visibility for every photographer behind you and bury the hiding spots of the bottom-dwellers. Move slowly and watch the rubble. The ocean rewards the patient diver here. The reef hides its artillery in plain sight.
Short boat rides to every one of these muck sites are a good reason to sleep on Mabul. Review our Mabul muck diving guide or check the underwater photography setups you need and we will build the itinerary around it. Send us an enquiry form and we can put you on the sand.