Moon Jellies!

Updated: Jul 19


The moon jellyfish features a translucent bell with a fringe of short tentacles that measures 10 to 16 inches in diameter. The nematocysts border the tentacles (stinging cells). The gonads (reproductive organs) of most moon jellies are horseshoe-shaped, but a few have three or five. Depending on the animal's nutrition, the bell and gonads can be translucent white, pink, blue, or purple. The jellyfish's oral arms are fringed and longer than its tentacles.


The species can be found in tropical and subtropical oceans all over the world. It's common along North America's and Europe's Atlantic coasts. Moon jellyfish can survive the lower salinity of estuaries and bays and are common in coastal and epipelagic environments.


The moon jellyfish is a carnivore that eats protozoa, diatoms, eggs, crustaceans, mollusks, and worms, among other zooplankton. The jelly is not a good swimmer, preferring to keep near the water's surface with its small tentacles. Plankton becomes trapped in the mucus that coats the animal and is then transferred through the cilia into the animal's oral cavity for digestion. If a moon jellyfish is starving, it absorbs its own tissue and shrinks. When food becomes available, they return to their usual size.

Reproduction and Offspring

There is a sexual and asexual component to the jellyfish life cycle. Each adult (also known as a medusa) is either male or female. Jellyfish release sperm and eggs into the water in the open ocean. Fertilized eggs develop and grow as planula in the water for a few days before attaching to the seafloor and become polyps. The polyp has the appearance of an upside-down medusa. Polyps produce clones that develop into mature medusae asexually. Aurelia jellyfish reproduce over several months in the wild. They grow susceptible to disease and tissue damage as the summer progresses, because of the strain of reproduction and dwindling food supply. The average lifespan of a moon jellyfish is six months, while captive specimens can live for years. The moon jellyfish, like the "immortal jellyfish" can reverse its lifecycle and grow younger rather than older.

Conservation Status

The IUCN has not assigned a conservation status to the moon jelly. Adult populations spike or "bloom" in July and August, indicating that the jellyfish are plentiful. The moon jellyfish thrives in water with a lower than typical dissolved oxygen concentration. When the temperature or pollution rises, the amount of dissolved oxygen decreases. Predators of jellyfish, leatherback turtles and ocean sunfish, cannot survive the same conditions. They are vulnerable to over fishing and climate change, and may perish if they consume floating plastic bags that look like jellyfish. As a result, the number of jellyfish is projected to increase.


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