240,000 cuttlefish in action: Is this Australia's wildest marine spectacle?

An underwater B & S ball is in full swing, and the blokes are outclassing the ladies. Shimmering in neon-pulsing tutus and court-jester headpieces, they saunter seductively, prowling for a female. But the ladies, dressed down and demure in brown, are hard to come by.

One of the world's great mass mating rituals is underway in South Australia, and it's a cornucopia of copulating cuttlefish. Not just any cuttlefish, giant cuttlefish. The sort that grow to the size of toddlers and use flamboyant drag-show moves to woo a mate.

Every year between May and August, the waters off Point Lowly, near Whyalla, play host to the largest-known aggregation of cuttlefish on Earth. Up to 240,000 amass in a colour-bending, shape-shifting mating frenzy so intense, some suitors won't survive. For human voyeurs curious enough to brave the winter chill, the spectacle is one heck of a peep show.

It's peak cuttlefish season when I join Whyalla Diving Services marine biologist Will Farrens for a guided snorkel. Dressed in three layers of neoprene, we shuffle down the rocky shoreline and wriggle into the water. I've been disappointed by marine-life encounters before - when the animals didn't get the curtain call - but this is cephalopod saturation. Within seconds I glimpse my first cuttlefish, then a second, a third, now plumes of them hover above the seabed. Their bodies inflate like technicolour blimps, hemmed by a quivering orbital fin. From their heads, eight long ribbony arms (not to be confused with tentacles) billow forth, and bands of colour ripple across their bodies.

These are the males - the peacocks of the sea - and they're making themselves big, bright and beautiful to score a mate. The competition is fierce; there's one female to every 11 males and only the dandiest, or most cunning, will succeed.

When the male scores a female, he wraps his arms around her head like an Alien "facehugger", and they mate face to face, the male passing a "sperm packet" into her mouth cavity. But she's a promiscuous lady, and will collect numerous packets before choosing the one with which to fertilise her eggs, before depositing them under a rock ledge.

Cuttlefish have lots of love to give. Related to octopus and squid, they have three hearts, blue blood and can change the colour and texture of their skin to attract the opposite sex (and for camouflage). They can also dramatically alter their size and shape, the biggest males reaching up to a metre when fully extended. Cuttlefish have a one-year lifespan and, like salmon, breeding is their closing act. No wonder they make such a song and dance of it.

Will explains how the males that aren't the fairest of the sea resort to trickery to find a mate. They shrink, dull their appearance and retract their arms into a stumpy beard to masquerade as a female. When a male defending his love interest lets his guard down, the imposter sneaks in and does the wild thing right under his belly. Sometimes rivalries turn ugly, and arms will be torn from bodies and eaten, the cuttlefish army long since clearing the seabed of food.

"The majority of them are slowly starving themselves while they're here and that's one of the reasons that they die," Will says. "They're so focused on mating they start metabolising their own body."

I don't witness any cuttlefish cannibalism, but I do see an endless procession of courtship theatrics and lovers' trysts. I watch a female in a headlock, dragged and shunted through the water by a male trying to evade rivals. Another female hides under her companion as he flares his arms to scare away opportunistic males that swarm like buzzards. Some smaller cuttlefish camouflage in rock crevices, and I'm not sure whether they're females taking time out, or diminutive males planning an ambush without consent (it happens).

After an hour, we haul ourselves out of the water. My hands and feet are numb and my lips feel like they've been anesthetised in the dentist's chair. One of my snorkelling buddies drove almost 2500 kilometres from his home in Western Australia to swim with the cuttlefish. When my mouth is working again, I ask him if it was worth the journey. "Definitely worth it, that was amazing," he grins.