Hot on the heels of yesterday’s post of the Moon Jellies From Outer Space comes this video from the Oregon Coast Aquarium, showing…baby moon jellies! (But not in outer space, alas.)
Jellyfish have a cool life cycle, involving both sessile (stationary) and motile phases. Here’s how it looks:
The phase we all recognize as “jellyfish” is the adult medusa phase. Medusae produce sperm and eggs, which mix together in the water column to eventually result in a free-swimming planula larva. The larva heads for someplace solid, hopefully in a good current that will bring nutrients past. There it attaches and transforms into the scyphistoma, which looks and behaves a lot like a tiny sea anemone. (It should not surprise you that sea anemones and jellyfish are in the same phylum.) It feeds on passing bits of plankton and, when environmental conditions are right, buds off a whole stack of individual juvenile jellies, all connected together. This stack pulses, creating an energetic movement which eventually breaks loose the topmost baby jelly. The moment this jelly is freed from the stack and begins swimming, it’s called an ephyra.
If you’ve ever heard of “jellyfish blooms,” when a particular body of water suddenly becomes jammed full of jellyfish, this is the reason why. Once the strobilae start releasing the ephyrae, vast swarms of tiny jellies are set free, to feed and grow into the adult form. If the food is plentiful, they grow very quickly.
The Oregon Coast Aquarium is raising moon jelly ephyrae right now, and produced a video of the little aliens being fed a diet of newly hatched brine shrimp. There’s not a lot of action, since moon jellies don’t actually pursue their prey, but simply swim around as food sticks to them. Still, they get big points for sheer cuteness. Most people don’t realize that marine invertebrates can be cute, but this video proves it.
Hat tip to Kay.