Being underwater when the aggregation is happening is kind of being like at a cuttlefish nightclub.

There's displaying that looks like pirouettes and dancing.

There's also some physical attack happening, which kind of looks like boxers having a go and just so much color, and you're kind of invisible to them at that time.

They have absolutely no interest in what you're doing, and they've just got the one thing on their mind.

They're there to breed.

It's an event like no other on Earth.

Every winter off the coast of South Australia, thousands of giant cuttlefish gather in a glowing, chaotic battle royale to win a mate.

But to stand out and survive in the world's weirdest single scene, these shapeshifters will have to rely on some of the most bizarre and brilliant tactics in the animal kingdom.

The Giant Australian Cuttlefish, also known as Sepia apama are the largest cuttlefish in the world.

They grow to about half a meter down in Whyalla in South Australia.

And then as you get into warmer waters like New South Wales, they can get up to a meter long.

They have three hearts and blue blood.

They're so unlike us.

I've never met a cuttlefish that I didn't like.

So I think that they have beautiful charisma.

They often really want to interact with you.

I call them the Labradors of the sea.

Giant cuttlefish are found across the Great Southern Reef in Australia.

Every winter, the giant cuttlefish within the Upper Spencer Gulf come to this eight kilometers stretch of coastline to mate and lay their eggs.

There's tens of thousands of these individuals, all within that small section of coast, which is something that is not seen anywhere else in the world.

You would not expect something like this to be happening in the shallow waters, just near what is otherwise a very industrial town.

The juxtaposition between what's above the water and you go underwater, and it's just the beautiful kelps and seaweeds.

And then emerging out of that, all of the cuttlefish.

And the reason why they're all going to that one spot is due to that awesome habitat for the egg laying.

It's sort of this combination of really large, flat rocks.

So the way females lay their eggs is they attach them to the undersides of rocks where they're a little bit sheltered, those eggs need to be protected from the elements and from predators.

So sort of all of those crevices under the flat rocks is what they're looking for.

But then also the way that the rocks are layered and the way that there's lots of gaps in there, it gives the cuttlefish plenty of space to hide within those rocks.

The cuttlefish mate in a face to face embrace, and the male will pass a sperm packet to fertilize the egg of the female.

On average, it's about four males to one female, but it can range up to 11 males to one female.

So as you can imagine, there's a lot of fighting and displaying going around so that the males can win the female's attention.

With so much competition, attracting a mate can be challenging.

Giant cuttlefish are experts in camouflage, adeptly changing their colors and skin texture to blend seamlessly with their surroundings.

When it comes to mating, they utilize these color transformations to communicate and stand out from the crowd.

So they communicate through changes in color and changes in body posture.

And this is done by special cells on their skin called chromatophores.

That kind of, imagine a plastic bag that can expand and contract with muscles around them.

And inside the little plastic bag there's pigments of color, but the cool thing is, is that they can do this in the blink of an eye.

So they can change their entire body pattern in milliseconds.

Another really cool thing about cuttlefish skin is that they can make it smooth or bumpy through the use of a thing called papillae, and these are hydrostat cells that they can use to make their skin look like bumpy algae, or just really smooth, like our own skin.

And it's the same type of thing that we have on our tongue that makes our tongue bumpy.

At the aggregation, you will just typically see dozens and dozens of cuttlefish performing these really intricate social displays and social behaviors, all trying to out compete to get access to females.

And if you're out on a snorkel, it's sort of just like watching a soap opera.

So the biggest males are putting on like an underwater light show.

And they've got three different displays that they display to one another that essentially means I'm bigger and I'm stronger.

Back off.

I want this female.

And they progress through different levels of aggression.

So they might start with an approach, and I'm going to wave my arms in front of you.

And then they can turn into more of a rigid body with a shovel shaped kind of face.

And then the big one, which really means I'm about to attack, is this lateral display, where they turn side on and they stretch out their body and their arms so they look really big, and they open their eyes and they wave their arms around as well.

So in all of the displays, they're usually also producing a passing cloud display, which looks like white and dark bands moving over the body of the animal.

And these can get quite progressively intense, the more aggressive the display.

The best case scenario is if males can just settle the fight without physically touching each other.

And that's what this displays are about And that's why there's a level of aggression that escalates the fight.

The large numbers at Whyalla mean the small males don't stand a chance when it comes to fighting the big males.

So they've developed this really unique strategy.

They sneakily change the color of their skin and draw in their arms so they look like a female.

And it's what's known as sexual mimicry.

So essentially these small males will swim around and see a larger male guarding a female.

And the larger male is duped.

He has no idea that that cross-dressing male is a male.

And then he can just get in there and mate with the female.

And I think the little sneaky males sire about 30 to 35% of the female's eggs.

So it is a successful strategy.

I've never seen that strategy anywhere else in this particular species.

Giant cuttlefish have one of the largest brains to body size ratio in all invertebrates.

So in all animals without a backbone.

And the brains are even larger than some reptiles and fish.

We also know that cuttlefish have incredible memories, and a particular type of memory that has been shown in cuttlefish is the ability to remember the past.

And this is called episodic memory.

So when that plays out in the wild, where they could use this type of memory might be to remember where their favorite meal was in their environment.

It could also help them potentially at the mating aggregation, to remember who they had mated with and how long ago.

Cuttlefish have a very short life cycle.

They're called the rock stars of the sea because they live fast and die young.

They only live for about 1 to 2 years.

Cuttlefish actually only have one breeding season and then they die.

So after they mate with multiple partners over the space of two months, then their body just starts deteriorating.

Any given year.

the population is highly dependent on the previous year.

They are a boom and bust species, meaning populations do flux.

In good years.

the population may go up quite a lot, and when conditions aren't so great, the populations can crash dramatically.

So in the past there's been fishing pressure put on the aggregation site, before we really knew about how important the aggregation was.

It was targeted by recreational and commercial fishers taking hundreds of tonnes of cuttlefish every winter just because they were so abundant.

Thankfully, the giant cuttlefish of the Upper Spencer Gulf Marine Park are now fully protected.

And so within the Cuttlefish Coast Sanctuary, there's absolutely no fishing allowed.

It is a bit weird when you're telling people, this is something that you've really got to go and see, it's like animals having sex, but that's essentially what's going on.

And what's quite special is just the fact that they're so fiercely competitive.

It's almost too much to absorb and take in.

When I'm down there watching cuttlefish just changing color in front of me, it just feels like I'm on a different planet.

It honestly feels like you're just watching aliens under the sea.

There are so many knowledge gaps about this species that you could just spend you could spend your whole life researching them and still have so many more questions.