Hordes of 'Blue Dragons' are Washing Up on Australian Beaches

These rare, venomous creatures usually show up after a full Moon—but rising sea temperatures might be contributing to their sudden arrival.
Gavin Butler
Melbourne, AU
blue dragon nudibranch
Glaucus atlanticus, a close and almost identical cousin of Glaucus marginatus. Photo via Getty, S.Rohrlach

Sydney’s beaches are currently awash with hordes of blue dragons: hundreds of rare, alien-like sea creatures that have swept in from the north-east.

The animals are called nudibranchs, which are a type of shell-less, soft-bodied mollusc well-noted for their intense blue colour. These tiny, venomous sea slugs—otherwise known as sea swallows, blue angels or, if you want to be scientifically accurate, Glaucus marginatus—are typically found in the open ocean, floating face up, where their ultramarine hues camouflage them against predatory birds in a method known as countershading. 


But during the southern hemisphere's summer months, oceanic winds buffet the so-called “blue fleet” towards the shoreline. In Sydney’s northern beaches, they’re turning up in droves.

Marine biology student Lawrence Scheele has been tracking the fleet—which also consists of blue bottles, blue buttons, by-the-wind sailors and violet snails—over the past few months, photographing the otherworldly creatures that have washed into the inlets and rock pools of Australia’s southeastern coast.

“Been looking forward to the return of these Blue Dragon Nudibranchs (Glaucus spp.),” Scheele wrote on Instagram last October. “Fingers crossed they hit Australia's shores later this summer.”

Then, in January, another post:

Befitting their name, blue dragons are ocean predators, eating their brethren bluebottles and absorbing the latter’s stinging cells—making them potentially dangerous to humans. The dragons store their prey’s venom in the extremities of their finger-like cerata, and can inflict a painful sting to anyone who comes in contact with them, producing potential symptoms of nausea, vomiting, acute dermatitis and hyperpigmentation.

And their numbers are on the rise.

"I notice that in the past few years we're having a lot more of those nudibranchs than we have before," marine scientist Sarah-Jo Lobwein, of the Australian Environmental Educators Association, told the ABC. "I think it is the combination of warming or changing seas … possibly leading to a 'trigger' in the explosion of the animals at certain times but reliant on that perfect mix of the effect of the Moon on tides, wind direction, water temperature and the currents.

“They seem to arrive a few days after a full Moon.”

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