The Australian giant cuttlefish (Sepia apama) is the world’s largest cuttlefish. Specimens can measure up to 50 centimeters in length and weigh up to 10 kilograms (23 pounds). Like other cuttlefish, the giant cuttlefish are masters of color transformation and can use the chromatophores (special transformative muscle cells) in their skin to instantly change the hue, reflectivity, polarization, and even the shape of their skin. They use this ability for hunting, hiding from predators, and for spectacular mating displays. Indeed, the giant cuttlefish is a remarkable animal in many ways, but, above all, it is notable for its operatic sex life!
Sepia apama ranges in all coastal habitats from Brisbane on the Pacific to Shark Bay on the Indian Ocean (effectively the entire southern coast of the continent). Thanks to jet propelled speed, color-transforming ability, sharp eyesight, high intelligence, and lightning fast grab jaws (which are located on two extendable arms), these cuttlefish are terrifyingly effective hunters of fish and crustaceans. Australian giant cuttlefish from different regions of the coast do not interbreed, even though they are genetically the same species. Like humans, the giant cuttlefish seem to form different sorts of societies with different mating customs: for example the giant cuttlefish of the Spenser Gulf region are unique (apparently among all cuttlefish) in that they join together for a spawning aggregation in the waters immediately around Point Lowly.
Unlike humans, there are eleven male cuttlefish for every single female giant cuttlefish! Large dominant male cuttlefish carve out territories with aggressive posturing and insanely bright flashing color displays. Smaller males (who do not wish to be ripped apart), distract the alpha male cuttlefish by adapting the color schemes of female cuttlefish and courting him. They then abruptly change color and pay (rapid) court to the polyandrous females. The female stores sperm packets from several males and she chooses the paternity of her offspring only after she lays her eggs. Cuttlefish are semelparous—they mate only once, and then they immediately die. The whole beautiful horrifying op-art orgy in the waters around Point Lowly is of paramount importance—and is also reckoned to be one of the unrivaled diving spectacles of the world.
Unfortunately all of the Spenser Gulf cuttlefish tend to be in one place at once. Since they only reproduce one time, they are very vulnerable to fisherman, who, up until the mid nineties, descended upon the area, captured most of the cuttlefish, and chopped them into bate for snappers. When one cohort was removed, the next was seriously attenuated!
Fortunately the spawning waters of Spenser Gulf are now a protected refuge, yet hydrological changes, agricultural run-off, and industrial development could still threaten the entire population. Perhaps the other Australian Giant Cuttlefish (who conduct their romantic affairs in a more disparate manner) are on to something.