With their translucent white bells—which can reach 12 inches in diameter—it’s not difficult to see where moon jellies get their name. Their luminous bells, with a blue-grey transparent disk in the center and glowing, horseshoe-shaped organs, give moon jellies their identifiable appearance.
Moon jellies can be found in temperate and tropical oceans around the world, especially near the surface of shallow bays and harbors. In Maryland, moon jellies can commonly be found in the lower Chesapeake Bay during the summer months. If you stumble upon a moon jelly drifting in the water, there’s no need to panic! Their saucer-shaped bells are fringed with short tentacles, but they deliver a very mild sting.
Their diet consists of zooplankton, which moon jellies trap with their delicate tentacles. When moon jellies are deprived of food, they can shrink to one-tenth of their original size to conserve energy. When food is available, they expand to their normal size.
Their predators include sea turtles and jelly-eating fish, such as tuna, sunfish, butterfish and spiny dogfish. Like many other jelly species, moon jellies have experienced a population boom in recent years. Factors such as overfishing, ocean warming and pollution have negatively impacted populations of their predators, causing jelly populations to grow at an alarming rate and consequently throwing their ecosystems out of balance.
Visit our Living Seashore exhibit to interact with a moon jelly in one of our touchpools!