Sea stars might look harmless - cute even -- lounging around in tide pools,
showing off their pretty colors... but no, they’re actually hunters,
voracious predators, that scour the oceans for prey.
Ooo… what’s that delicious smell?
Mmm… mussels!
Sea stars, also called starfish, don’t have a nose, they sniff with their feet.
They have hundreds, sometimes thousands of feet, running along their undersides from their mouth
to the tips of their flexible arms.
What they don’t have is a brain.
So how do they figure out which way to go to find a meal?
Well, they leave that up to their feet too.
See the long skinny ones on the ends? They’re extra sensitive.
A few of them start creeping towards the smell of the mussel.
They move using an elaborate system that harnesses the most plentiful resource around: seawater.
The sea star pulls water in through a sieve plate on its topside,
and pumps it down its arms.
It fills these bulb-shaped ampullae.
Each individual ampulla is connected to a tube foot.
Together, the foot and ampulla look kind of like an eyedropper.
A disc at the end of the foot clamps onto surfaces around it -- not by
suction like you might expect -- but by secreting strong, sticky glue.
The ampullae squeeze water into the tube feet, extending them like long balloons.
When the tube feet contract, they drag the whole
starfish along with them, and push water back up into the ampullae.
Then the disc secretes other chemicals to let go.
A single tube foot isn’t so strong on its own, but a whole army of them provide some serious grip.
Check this out.
You can see a few tube feet get a whiff of that savory mussel.
They start crawling towards it.
Eventually this whole arm gets going.
Whichever arm pulls the hardest takes the lead.
As the sea star builds speed it takes on an adorable little… bounce.
It’s the sea star’s version of a gallop.
Instead of just dragging themselves along,
the tube feet stiffen, lifting the star up mid-stride and then vaulting forward.
No one tube foot is setting the pace.
When you’re all connected to the same starfish it’s just easier to move when your neighbor moves.
When they get going like they also skip the glue, to stay light on their feet.
It’s called an emergent pattern.
Order from chaos. No brain required.
Each of these little tube feet has a fierce independent streak.
But the success of starfish in oceans the whole
world over -- shows us that sometimes it's best to just go with the flow.
Did you know about starfishes' other tube-footed relatives?
Like sea urchins and sand dollars.
Also - PBS Digital Studios has a new science series called Overview -
think Deep Look, but with drones!
Overview combines mesmerizing aerial footage
with in-depth storytelling to reveal our planet's secrets.
Head to the PBS Terra channel, and tell them Deep Look sent you!