The struggle to survive in our green seas
can have far-reaching consequences.
Once a year, one particular meadow in Australia
is transformed.
Around the first full moon of winter,
an army materialises.
Spider crabs.
For the past year, they've been feeding in deeper waters.
Now, they march across the seagrass plains.
Hundreds of thousands of them.
They clamber over one another,
creating great mounds
nearly 100 metres long.
They're not seeking mates.
Neither are they laying eggs.
They have come here in order to grow.
Like all crabs, their bodies are enclosed in a hard, unexpandable shell.
So to grow, they have to break out of it.
And that allows the soft one that has developed beneath to expand.
It will take days for the new shell to harden.
Its legs are so limp that they won't work properly.
The crab is unprotected
and in great danger.
A smooth stingray.
It's huge – about four metres long.
It wants a soft, freshly moulted crab
that will be easier to eat.
The crabs try to stick together.
But now, disturbed by the ray,
they're scattering.
A newly moulted crab
is too weak to keep up with the crowd.
The safest place is right in the middle of the pile.
That is why they have all assembled here.
There is safety in numbers.
But the vast majority of the crabs escape.
And within the next few days,
they will be ready to return to the depths
and resume their lonely wanderings in search of food.
This is no graveyard,
but the triumph of 100,000 crabs
successfully moulted.