What's the weirdest animal in the ocean?
I got to say jellyfish for sure.
Oh, I was right.
Jellyfish.
Wow. That's weird.
They might not have a proper brain, blood or even a heart,
but some jellyfish species can live forever.
What are their secrets to survival?
Hey, Kylie.
How are these things alive?
Jellyfish are really simple creatures.
So, they effectively consist of a layer of tissue
that covers the outside of their body
and a layer of tissue that covers the inside of their body.
In between those two layers of tissue,
is mainly water with a few collagen fibres.
OK...
And they can grow very quickly
because they are effectively 95 per cent water.
Jellyfish are so simple that all they really need to do
is to add more water to their body.
They're almost like a little bit like a water balloon.
A body that's mostly water is great camouflage in the ocean.
And they need to hide because
they can't really see their predators coming.
So, they have very simple eyes.
Jellyfish have eyes? Yes.
But most of them can detect just changes in light intensity
and perhaps light direction.
But they certainly can't form an image.
Mmhmm.
They don't have a well-developed brain.
They've got a very simple nervous system.
So they can probably respond to stimuli,
but they have no cognitive ability.
Who needs eyesight when you can shoot venom?
Underwater cinematographer Dean Cropp
has swum with deadly jellies.
Some jellyfish have stingers.
They've got nematocysts that they can sting you with.
And some are very, very deadly,
especially the box jellyfish which
I grew up with up in far north Queensland.
I've been stung on my foot and it was so painful.
I screamed and I yelled and I said many, many horrible profanities.
The reason their toxin is so, so strong
is it catches animals and feeds on them.
And if that animal isn't immobilised straight away
as it kicks and struggles,
it will just tear that fragile jellyfish apart.
I was lucky because other people
who do get hit on the chest or the neck,
it can cause you lifelong damage
or it can take your life.
There's another variety that's just like the Terminator.
They just won't die.
So, typically with the jellyfish life cycle,
the life cycle goes in one direction.
So, you have the medusa that produced the larvae.
The larvae produce the polyps, and then
the polyps produce the medusae again.
But we found that in some species of jellyfish,
they're actually capable of reversing their life cycle.
Wow.
So, there are some species where the medusa
can actually revert back into being a polyp form.
It can actually just swim back down to the sea floor
and it will just slowly revert back into this tiny little polyp form.
Um... That's....
Yeah. Wow.
So, those polyps could persist
potentially for multiple years.
And it restocks the population of medusae every season.
In theory, it could be immortal,
but in reality, something will eventually kill it,
so it's unlikely to be truly immortal.
Many animals are facing extinction,
but some jellyfish species are exploding.
They gather in masses or blooms.
I had an extraordinary experience with jellyfish
off of the east coast of Newfoundland, Canada,
in Terra Nova National Park.
We accidentally stumbled across this massive, massive bloom.
Wow.
From the surface of the water, all the way down
to about 15 metres of depth were solid jellyfish.
It felt like being in this mass of squishy rubber balls.
It was almost as if it was an organism in and of itself.
Being able to see sort of the beauty and grace
of their swimming, but also to look inside
and see what they've just eaten is incredible.
It was so exciting to be in and amongst them.
I literally wanted to breathe every last breath
out of my tank before getting out of the water.
Bloom encounters seem to be happening more often.
So, the blooms might occur just because of
the aggregation of it is driven by currents.
A female medusa will produce thousands
upon thousands of larvae.
Wow.
So, it's a really prolific way of reproducing.
I think in terms of the weirdness scales,
I thought it couldn't get any weirder
than the four penises on an echidna.
(SCREAMS)
But jellyfish have got to be.
They're immortal. No blood. No ears.
They can grow up this big and never die.
That's weird. (LAUGHS)