Moon jellyfish primarily eat planktonic crustaceans, but they also eat other small plankton including molluscs, fish eggs and smaller jellyfish. They catch their food with sticky mucus that lines the underside of their bells and then direct it into their four stomach pouches with their tentacles.
Moon jellyfish possess stinging cells like other jellyfish, but they primarily use them to deter predators rather than capture prey. Their tentacles are not long and trailing like those generally associated with jellyfish, but instead form a fine fringe along their bell margins. Their specific anatomical features vary by location, with populations occurring on the Pacific coast from San Diego, Calif., to Prince William Sound in Alaska.
Their primary predators are birds, turtles and the much larger lion's mane jellyfish. Moon jellyfish are not hunted by humans, but some are captured for the pet trade and public aquariums. Despite these threats, moon jellyfish are extremely abundant, and their populations are not threatened. In the wild, moon jellyfish appear in very large groups of hundreds of millions of individuals. This is likely coincidental in their habitats, because no known form of communication occurs between these very simple animals. They spawn in these large groups via internal fertilization.