Mom, Where Do Baby Jellyfish Come From?
When grown-up jellyfish love each other very much, they make huge numbers of teeny-tiny potato-shaped larvae. Those larvae grow into little polyps that cling to rocks and catch prey with their stinging tentacles. But their best trick is when they clone themselves by morphing into a stack of squirming jellyfish pancakes.
TRANSCRIPT
There’s a reason the ocean is full of jellyfish.
These creatures have mastered the ability to multiply themselves again and again.
Adult moon jellies grow to the size of dinner plates.
A mature jellyfish like this is called a medusa for its resemblance to the ancient Greek monster with snakes for hair.
But instead of snakes, this medusa has stinging tentacles that paralyze its prey.
It’s hard to tell by looking at them but there are male and female moon jellies.
The males release sperm into the water.
And the females collect it to fertilize their eggs.
Those eggs turn into larvae called planulae that mom sends out into the world.
They look like fuzzy little potatoes.
Each planula does its best to settle on something solid — like rock – and develops into this, a polyp the size of a pea.
The polyp clings to the rock with a sticky foot, like a miniature version of its colorful cousin, the sea anemone.
Its stinging tentacles catch prey that float by, like these tiny crustaceans.
With each mouthful it grows.
See that budding out of its side?
It’s a little clone!
After a few days the clone pops off, and settles in right next door.
The polyps make more polyps.
And more …
Until they form a whole neighborhood of clones …
So how do they go from tiny polyp stuck on a rock to giant medusa gliding through the open ocean?
When the water begins to cool at the end of summer, they go through yet another change.
They slow down, stop hunting and develop these ridges along their sides.
Over a few weeks, the ridges get more and more pronounced, until the polyp looks like a stack of pancakes.
Each individual pancake, called an ephyra, is a clone with the potential to grow into an adult.
That’s right, it’s a whole extra round of cloning called strobilation.
It begins with a twitch.
The ephyrae flex and convulse.
They impatiently work to free themselves … from themselves.
The next ones in line can’t wait for their turn either.
So they help push things along.
After all that effort, the ephyra on the very end finally breaks free.
Sometimes jellyfish are so successful that they explode in number, creating a jellyfish bloom.
That’s great for predators like barnacles that snatch them up when they’re young … and for sea turtles that scarf down the grown-ups.
That’s why moon jellies play the odds.
By making babies that clone themselves, and clone themselves again, jellies multiply their chances that some will make it all the way.
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