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Dip below the surface to discover the extraordinary plants and animals that call Sydney Harbour home.

The beauty beneath the surface

Image: John Turnbull

Sydney’s Opera House, Harbour Bridge and stunning beaches are recognisable worldwide, but dip beneath the water’s surface and its beauty and diversity are perhaps even more breathtaking.

In Underwater Sydney, authors (and marine ecologists) Inke Falkner and John Turnbull explore this beautiful and biologically diverse region, showcasing the incredible array of animals and plants that thrive there.

The bizarre and the beautiful

In Sydney’s harbour there is no shortage of rare, charismatic, stunningly beautiful and just plain weird inhabitants.

Blue dragons are actually sea slugs covered in finger-like appendages

Image: John Turnbull

Blue dragons (Pteraeolidia ianthina) may not breathe fire, but these gorgeous sea slugs have their own special magic. Their body is covered with finger-like appendages called ‘cerata’ which contain photosynthetic algal cells that convert sunlight to energy. The end of each appendage also hides a nasty surprise: stinging cells similar to those of a jellyfish.

Pineapple fish really do resemble their namesake

Image: John Turnbull

Funnily enough the pineapple fish (Cleidopus gloriamaris) looks like a pineapple! But this uncanny resemblance is just one of many fascinating features. They also possess a light organ on each side of the lower jaw which produce an eerie glow and helps the fish to detect and maybe even attract prey.

Underwater forests and sponge gardens

Masters of deception

Many marine inhabitants are masters of disguise, deception and defence – here are a few favourites.

Mourning cuttlefish displaying their gender specific body patterns. The male is on the left, the female on the right

Image: John Turnbull

Mourning cuttlefish (Sepia plangon) communicate through colour displays, rapidly changing the size and shape of the pigment cells in their skin to camouflage themselves, show anxiety, warn opponents or charm the opposite sex. Male mourning cuttlefish have even been known to use two patterns at once: the side facing an interested female displays the white stripes of a male courtship pattern, while the side facing a rival male displays a female pattern so that the rival male doesn’t attack and disrupt the courtship.

A sea hare feeds on sea lettuce

Image: John Turnbull

Sea hares (Aplysia juliana) live among the seagrass beds in Sydney Harbour. Whilst their common name comes from their pointy ‘rabbit ears’, they are in fact giant sea slugs. Sea hares use chemicals extracted from their algal food to make themselves taste unpleasant to predators. When disturbed, they also secrete a dark purple ink to distract predators and confuse their sense of smell.

The striped anglerfish lurks in the shadows

Image: John Turnbull

Anglerfish are generally known from the deep sea, but the striped anglerfish can be found sitting perfectly still on the shaded, gloomy seafloor below Sydney’s wharfs, occasionally waving a lure attached to the front of its head. It mostly crawls on its feet-like pectoral fins, but this master of disguise can strike within milliseconds when unsuspecting prey ventures too close.

Visitors welcome

Twice yearly, humpback whales pass Sydney on their migration between Antarctic feeding grounds and the tropical breeding grounds off the Queensland coast.

A humpback whale breaches off Sydney

Image: Vanessa Pirotta

The Port Jackson shark features on the front cover of Underwater Sydney

Underwater Sydney celebrates Sydney’s incredible harbour and coast with eclectic stories based on informative science and accompanied by stunning underwater photography. With underwater forests and gardens, hundreds of species of fish and thousands of invertebrates, you’ll discover that Sydney is as colourful and diverse below the water as it is above!

Available now through bookshops or order online through our website.

This post was first published on the CSIRO Publishing blog