The creatures, which are a kind of brightly-coloured sea slug or nudibranch, were pushed down the coast by north-easterly winds, according to marine biology student Lawrence Scheele
Mr Scheele, who is also a photographer, captured images of the blue dragons and posted a video to his Instagram page last month.
“I was really lucky to have caught them all at Long Reef,” he told ABC News, adding that he had been visiting Sydney at the time “escaping the cyclone, crocodile and box jellyfish”.
Blue dragons have the scientific name Glaucus marginatus and are also referred to as blue glaucus or blue angels. They are found in the Atlantic, Pacific and Indian Oceans in temperate and tropical waters.
It is rarer than the feared, jellyfish-like bluebottle – Physalia utriculus, or the Portuguese man o’ war – but blue dragons can actually pack a far more painful sting if touched.
It is a unique nudibranch – a category of marine mollusc – that floats on the water, upside down, showing its brightly coloured underbelly to airborne predators. The bright blue colour acts as a camouflage against the ocean backdrop.
Like most nudibranchs, the blue dragon isn’t venomous by itself and it incorporates toxic chemicals from its prey into its own skin and uses this ability as a defence mechanism against predation.
“Had an unsuspecting visit by hundreds of these beautiful creatures known as Glaucus marginatus, not to be confused with their cousin Glaucus atlanticus. During summer strong winds wash these 1cm nudibranches onto shore (sic),” Mr Scheele wrote on Instagram.
Both the species, Glaucus marginatus and Glaucus atlanticus, are referred to as blue dragons, but the former are smaller, growing to about 1.3 cm, while the latter reaches about 3 cm.
Last year in November, Glaucus atlanticus made headlines after they washed up on a beach near Cape Town in South Africa.
Mr Scheele said you have to be in the right place at the right time to catch the blue fleet and that he loves to post about them on Instagram.
“I think they’re just fascinating, and whenever I post about them fans want to know more,” he said.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies