Meet Our Moon Jellyfish: Celestial Drifters of the Sea

As a carnivorous sea creature, the moon jellyfish diet consists mostly of small organisms like zooplankton, mollusks, crustaceans, copepods and little fish. These organisms get caught on their bells or tentacles and are then moved down into their stomachs.

Since moon jellies have relatively clear bodies, they can sometimes turn the same color as the food they’ve just eaten!

Moon jellyfish are quite small. Their bells are about the size of a large dinner plate and typically measure between 5cm and 40cm in length. Their short tentacles only grow between 1cm and 5cm long. 

They’re not as giant as other commonly-sighted jellies like the lion’s mane jellyfish, which can reach up to 200cm (6ft5) in length.

The moon jellyfish's life span is quite short. It’s about 8 to 12 months in the wild and about a year in captivity. 

Another interesting fact about this sea drifter is that the moon jellyfish life cycle consists of two stages: polyp and medusa. The ‘medusa’ stage is the adult bell-shaped jelly we see floating in the sea, whereas its ‘polyp’ stage is how the moon jelly forms after fertilization: a small stalk that attaches to a rock and divides into buds. These buds then break free and turn into adult jellies.

The moon jellyfish live in the coastal waters of North and South America, Eurasia, Southern Greenland and Australia. They like swimming in warm tropical and oceanic coastal waters and thrive best in waters with temperatures around 63.5°F. 

Moon jellies are robust creatures and can even live in water with a very low salt content (as low as 0.6%). They can be found floating just below the surface, but they often range in depths between 200m and 1,000m. 

Moon jellyfish reproduction happens via external fertilization. The adult male moon jelly releases strands of sperm that are ingested by the females. 

After fertilization, the female moon jellies grow the larvae on their tentacles and later release them to settle on the seabed and develop into polyps. During the polyp stage, the larvae clone and eventually swim away to grow into mature moon jellyfish.

The moon jellyfish has a few predators, including birds, fish like the chum salmon, sunfish and butterfish, sea turtles, and other jellyfish. Humans can also be classified as moon jellyfish predators, as some places consider these jellies a delicacy.

Moon jellyfish aren’t classified as endangered, but can be under threat of ecosystem eradication and plastic pollution.

Yes, the moon jellyfish can sting, but it’s a pretty mild sting for humans and has little to no effects. Their tentacles have stinging cells called cnidoblasts, which are primarily used for capturing and paralyzing their prey. 

If you’re ever stung by a moon jellyfish, rinse the affected area with saltwater (not freshwater), remove any tentacles from your skin, and then apply vinegar or rubbing alcohol to the affected area.