Moon jellies, scientifically known as Aurelia aurita, are a type of jellyfish found in marine environments worldwide. These invertebrates are recognized by their translucent, moon-like bell, which can reach up to 12 inches (30 cm) in diameter. Four horseshoe-shaped gonads are visible through their bell. They inhabit coastal waters across the Atlantic, Pacific, and Indian Oceans, often congregating in harbors and estuaries.
Their Main Food Sources
Moon jellies are carnivorous filter feeders, consuming small organisms that drift in the water column. Their diet mainly consists of zooplankton, including copepods, crustacean larvae, and protozoans. They also feed on rotifers, diatoms, mollusk larvae, and the eggs and larvae of fish.
Moon jellies are not active hunters and rely on passive capture. Their feeding strategy allows them to consume almost anything small enough to become entangled in their feeding structures. They may even prey on other small gelatinous zooplankton, including smaller jellyfish.
How Moon Jellies Feed
Moon jellies capture food using a specific mechanism. They possess short tentacles lining the edge of their bell, equipped with stinging cells called nematocysts. These nematocysts fire dart-like structures that stun or paralyze their prey.
Once stunned, prey becomes trapped in a layer of mucus covering the moon jelly’s bell and oral arms. Hair-like structures, known as cilia, then move the mucus-laden food towards the mouth, located on the underside of the bell. The food is then transported through branched gastrovascular canals to the central stomach for digestion.
Environmental Impact on Diet
Environmental conditions influence the diet of moon jellies, as they are opportunistic feeders. The availability of their food sources, such as zooplankton, can fluctuate seasonally and geographically. Water temperature also plays a role, with moon jellies thriving in temperatures between 9 and 19 degrees Celsius (48-66 degrees Fahrenheit).
Ocean currents are another factor, as moon jellies are not strong swimmers and drift with the water, which transports their prey directly to them. Their ability to tolerate low dissolved oxygen (hypoxia) conditions gives them an advantage over fish competitors. In such environments, moon jellies can maintain feeding activity, allowing them to flourish when other predators are negatively impacted.
Role in the Marine Food Web
Moon jellies are part of the marine food web, acting as both consumers and a food source for other animals. As predators, they help regulate populations of zooplankton, including copepods and fish larvae. This predation influences plankton community dynamics.
They serve as prey for a variety of larger marine animals, including several species of sea turtles, such as the leatherback turtle, and certain fish like ocean sunfish, tuna, and salmon. Seabirds and some marine mammals also feed on moon jellies. Other jellyfish species are also known to prey upon them.
Beyond their role as predator and prey, moon jellies contribute to nutrient cycling in marine ecosystems. When they die and decompose, they release organic matter and nutrients like nitrogen and phosphorus back into the water. Their waste products also provide nutrients that support the growth of phytoplankton, which forms the base of many oceanic food chains.