Marine life

Nudibranchs

Nudibranchia

Sea slugs of absurd colour and variety — the reason temperate Australian macro diving has a global reputation.

Nudibranchs are shell-less marine molluscs, and they are the single biggest reason Australian temperate macro sites have an international reputation among photographers.

Nelson Bay's Fly Point, Bare Island in Sydney and Edithburgh in South Australia hold extraordinary diversity — dozens of species on a single dive for anyone prepared to search slowly.

Their colours are honest advertising. Most are toxic or unpalatable, many sequestering defensive chemicals from the sponges and hydroids they eat, and the brightness is a warning rather than camouflage.

Australian macro life, represented by an AI-generated editorial image.

Scientific name	Nudibranchia
Typical size	Mostly 1–5 cm
Peak months	August, September, October
Documented sites	10
States	New South Wales, South Australia, Victoria, Western Australia

When to see them

possible good peak

Present year-round; diversity and abundance often peak in the cooler months and into spring on temperate reefs.

Where they are

Documented sites for Nudibranchs. Hover a marker for the site name.

Identification

no shell in the adult stage
paired rhinophores on the head — the sensory 'horns'
many species carry exposed gills as a plume on the back
extraordinary range of colour and form

Behaviour

Grazes on sponges, hydroids, bryozoans and anemones depending on species.
Many sequester defensive chemicals or stinging cells from their prey.
Hermaphroditic; egg ribbons are often laid beside the food source.

Finding them

Nudibranchs are found by slowing down almost to a stop. Work sponge gardens, hydroid growth and jetty piles systematically rather than covering ground.

Egg ribbons are a useful cue — a spiral ribbon on a sponge usually means the animal that laid it is within a few centimetres.

In-water etiquette

How divers behave around this species affects both the animal and everyone else's encounter.

Do not handle or reposition for photographs.
Excellent buoyancy is essential — these are silty sites and a careless fin ends visibility for everyone.
Limit strobe firing per animal.

Where to see them

Sites where this species is documented as a reliable encounter.

Fly PointA protected sponge garden at Nelson Bay with some of the richest macro life in Australia.Bare IslandSydney's most-dived shore site — weedy seadragons, extraordinary macro life and multiple routes.Edithburgh JettyOne of the world's great muck dives — an unremarkable jetty hiding extraordinary small life.PipelineFly Point's neighbour — sponge gardens and macro life within the same protected reserve.Blairgowrie PierVictoria's most popular pier dive, and the best-known site for giant spider crab aggregations.Gordons BayAn Eastern Suburbs shore dive with a long-established underwater nature trail.KurnellA cluster of Botany Bay shore dives including The Steps and The Leap, with wall terrain.Port Noarlunga ReefA shore-accessible aquatic reserve reef reached via a jetty — South Australia's main training site.Exmouth Navy PierA structure dive with extraordinary fish density, on Defence land with controlled access.Rye PierA shallow, sheltered pier known for seahorses, seadragons and night diving.

Operators servicing those sites

Businesses documented as diving the sites above. Confirm seasonality and requirements directly.

Feet First DiveA Nelson Bay operation serving the Fly Point and Port Stephens shore-diving community alongside training and boat diving.Abyss Scuba DivingA Sydney operation associated with training across recreational and technical levels, boat diving and equipment services.Dive Centre BondiAn Eastern Suburbs operation providing recreational training, local diving and technical pathways.Diving AdelaideAn Adelaide training and guided diving operation serving local sites and organised trips.Exmouth Dive & Whalesharks NingalooAn Exmouth operation running certified scuba diving alongside whale shark and other wildlife tours. The scuba and snorkelling products are distinct and should be booked deliberately.Dive NingalooAn Exmouth operation focused on certified scuba diving, including Navy Pier access.

Often seen on the same dives

Eastern Blue GroperNew South Wales' state fish — large, inquisitive and often the first thing to greet a Sydney shore diver.Giant Australian CuttlefishThe world's largest cuttlefish, gathering in tens of thousands at Whyalla each winter.Giant Spider CrabTens of thousands of crabs piling into the shallows of Port Phillip Bay to moult, in one of Victoria's strangest dives.Grey Nurse SharkAustralia's most recognisable dive shark — ragged teeth, entirely harmless, and critically endangered on the east coast.Leafy SeadragonSouth Australia's emblem and the most elaborately camouflaged fish in the world.Port Jackson SharkA small, harmless, harness-marked shark that gathers in southern NSW winters to breed.

Frequently asked questions

Where is the best nudibranch diving in Australia?

Nelson Bay's Fly Point, Bare Island in Sydney and Edithburgh in South Australia are the standouts, all shore dives.

Are nudibranchs dangerous to touch?

Many are toxic or carry stinging cells sequestered from their prey. They should not be handled, for their sake and yours.

Last researched: September 2026. Dive businesses change frequently — confirm current services, prices and requirements directly with the operator before booking.