The colour-changing Cuttlefish is frequently seen on the low use reefs off shore from Port Douglas

Both snorkelers and divers enjoying an exciting day on the Great Barrier Reef aboard our own ABC Scuba Dive vessel where you can have the unique pleasure of observing the well camouflaged and colour-changing cuttlefish.

Are Cuttlefish really fish?

Cuttlefish, despite their name, are not fish, but molluscs that are actually marine invertebrates (animals without a backbone). However, they do possess an internal shell known as a cuttlebone. This is a unique feature used as a buoyancy control device and is composed of porous calcium carbonate. Most people will have seen these on local beaches or displayed in bird cages to provide an excellent source of calcium for the bird’s diet. Individual species have cuttlebones that differ in size, shape and also texture. Amazingly, cuttlefish have an ingenious system for regulating their buoyancy in water by changing the ratio of liquid to gas in this cuttlebone.

Because the small groups on ABC Scuba dives allows for flexibility of programmes, divers can really enjoy the unique experience of the changing colours and behaviour of the cuttlefish.

Other related animals are the squid and octopuses, which all belong to a sub-group called Cephalopoda. Cuttlefish have two tentacles with suckers to latch onto their prey as well as eight arms. They, in turn, are prey to dolphins, sharks, seals, fish and other cuttlefish. Just like octopus, cuttlefish show remarkable intelligence.

They are famous for their ability to change colour instantaneously. They do this to blend into their immediate surroundings as camouflage from predators and also for communication. The rapid skin colour change is produced by special pigment cells called chromatophores, which can be found at densities of up to 200 per square mm. It is so sophisticated it can deliver pulsating and flashing colours in reds, browns, blacks and yellows, and can be used in varying combinations to produce infinite colour variations. Many ABC divers and snorkelers have been totally captivated by this display.

Cuttlefish have incredibly developed eyes that feature big W-shaped pupils. The eyes are amongst the most sophisticated of any in the animal kingdom. It is thought by scientists that their eyes are fully functional even before birth and that they can observe their surroundings and begin following prey before hatching from the egg.

Other unusual physiological features of cuttlefish include their three hearts and green-blue blood. The blood colour phenomenon is due to the oxygen carrying protein hemocyanin, which contains copper. In mammals haemoglobin, which contains iron, is utilised to carry oxygen. This gives our blood and other mammals, the red colour instead.
The taxonomic name for cuttlefish, Sepia, comes from the colour of ink that they dispel when they feel threatened. Their ink was once used by artists, but this has now been replaced by artificial dyes.

Cuttlefish courtship is quite the show. Males tries to impress the female with their display of pulsating colours. Generally males outnumber females two to one, making mating communities quite aggressive as they all vie for her attention. The biggest guy isn’t always the winner. If two bigger cuttlefish are fighting, a smaller male may pose as a female and, because she values brain over brawn, he may become the mating partner.

Once chosen, the male and female line up head to head, whereby the male transfers the sperm into a sac/pouch just below her mouth. The male is able to wash away any sperm from a previous mate if the eggs haven’t yet been fertilised . After the transfer, the female chooses from which mating partner she wishes to fertilise the eggs . She lays her eggs deep within branching and digitate coral structures to protect them from predators which are after an easy meal.

The female lays up to two hundred eggs over a few days and will die not long after, implying they only reproduce once during their life cycle. Pending the water temperature, the eggs will hatch up to 2 months later. When born, hatchlings are 6-9mm. They develop quite rapidly, preying upon small crustaceans,  reaching adulthood within 18-22months and will not live much longer than two years.

We regularly see cuttlefish at ABC Scuba Diving although it can be take skill to notice them due to their inexhaustible range of textures and kaleidoscope of pulsating colours. They are one of the most delightful and fascinating creatures in the ocean.

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