The Spencer Gulf hugged the rocky coastline revealing a landscape that was typically Australian – silhouettes of kangaroos were littered amongst a backdrop of rugged native shrubbery. As dusk approached, the warm breeze kicked up an onshore surge against the broken red shoreline. The ocean was murky, choppy, and uninviting. I looked at my newly minted husband, with raised eyebrows, “well, this is it – the place I’ve always wanted to dive more than anywhere else in the world”. We exchanged dubious looks and returned to the car with dampened spirits. The plan was to return in the morning with all our SCUBA gear to explore the only known mass breeding aggregation of giant cuttlefish. As we departed from the dive site, bouncing across the red-soiled road, I reassured myself that everything would look different in the morning light. 

Sure enough, on returning the following daybreak, we were greeted by a completely different coastline. The bay was lapis lazuli, the deep blue of a precious a gemstone, and from the shore to the horizon the water was a peaceful millpond. The only intermittent disturbances came from a pod of feeding dolphins, some hundred feet from the shoreline. We suited up and lugged our regalia of SCUBA gear down the steep wooden staircase, across the rocky beach, and immersed ourselves into the chilly South Australian water. 

We’d only dived down two metres when we came across our first sighting. A pair of giant Australian cuttlefish amongst the weedy reef-bed. The male was mate guarding—peacefully hovering beside the female—a behaviour that typically occurs after mating, to protect the female from potential rivals. The male, almost twice the size of the female, slowly undulated his eight arms as they transformed in colour from amethyst purple to emerald green. At the same time, intense bands of dark and light patterns swept across his body, creating an effect aptly named the “passing cloud”.  This mesmerising display of hypnotic patterning is the main way that male cuttlefish communicate. Meanwhile, his petite lady friend, floating beside him, stared at me with one curious eye, as her elongated black pupil contracted to form an unearthly W-shape. The two giant cuttlefish gazed at us in peaceful inquisitiveness, and we gaped back in awe through our plate-glass masks, whilst the four of us swayed gently to the ebb of the shallow tide. The entire scene was beyond surreal, astonishingly beautiful, and strangely familiar, yet wholly out of this world. 

I’ve dived with these creatures many times before, yet their eccentric appearance and anthropogenic curiosity still never cease to astound me. Whilst I stayed fixated on that vibrant couple, I completely failed to notice the rest of my surroundings. When I eventually tore my eyes away from them, my initial surprise was such that the overwhelming joy manifested into a sharp gasp of air that escaped out my regulator. Before me was a scene that I was not familiar with— hordes of cuttlefish, in a rainbow-coloured swarm, filled the water column. They swayed and twirled and flashed their colours dynamically. We were diving in a cuttlefish disco!  

Every southern winter (May–August), thousands of cuttlefish aggregate at this rocky shoreline with one thing on their mind – finding a mate. Although I had read much about this phenomenon—experiencing it was simply mind-blowing.

The aggregation is highly skewed towards males, averaging four males to every one female. These odds create fierce competition between the fellas. Meaning that large males must use brilliantly coloured postures and displays to vie for females, and when fights cannot be ‘visually’ settled they can escalate to physical aggression. Whereas small males, who have little chance of winning through muscle power, employ a seriously sneaky trick to stay in the game. To get past the biggest males, they draw in their arms and transform their vibrant green and purple hues to more closely resemble the mottled colouration of a female—that’s right, they frock-up as ladies! This cross-dressing tactic not only deflects physical aggression from larger males but also impresses the ladies enough for the smaller males to be successful in mating. At the end of the day, the ladies have all the power over what suitor she chooses to mate with. The fact that cross-dressing endures is a clear sign that in the world of cuttlefish – it’s not all about size.

We spent the next eighty minutes mesmerized by the sheer abundance of cuttlefish in this underwater wonderland. Feverishly pointing in one direction and then the other, trying to soak in and share every moment of those dynamic displays that were taking place in this colossal battle for love. We not only saw colourful battles, but also males mimicking females, and on several occasions, we witnessed the ultimate act – mating. Cuttlefish mating occurs in a head-to-head position, as both males and females open their arms and entwine them. The male then uses a specialized arm to deposit packets of sperm inside the mouth of the female. At a later stage, the female can produce eggs inside her mouth, fertilise them using the packet of sperm, and then use her arms to attach the fertilised eggs to suitable rocky substrates. Our dive was early in the season, but we were lucky enough to still see a handful of these grape-sized translucent eggs, swaying from the rock beds. Approximately four months after our dive, from those same eggs, will hatch miniaturized, but fully-formed, cardboard cut-outs of adult cuttlefish. 

The shallow dive meant that our air consumption was low; meaning we could’ve stayed down there for hours! But in the end, my teeth were chattering as the icy waters got the best of me, and the harsh realities of the frigid water pulled me out of my spellbound state. When we finally surfaced, shivering and numb, I looked over at my husband with the widest grin and exclaimed “again!!”