The moon jellyfish, scientifically known as Aurelia aurita, is a common inhabitant of marine environments across the globe. These creatures drift through ocean waters, recognized by their distinctive, translucent appearance. They are often encountered by divers and beachgoers and play a role in ocean ecosystems.
Physical Characteristics
The moon jellyfish possesses a translucent, bell-shaped body that typically ranges from 5 to 40 centimeters in diameter. This bell, or umbrella, is often colorless but can exhibit faint shades of blue, pink, or purple, influenced by its diet. A defining feature visible through the bell are four horseshoe-shaped structures, which are the jellyfish’s reproductive organs, or gonads. These organs are usually prominent and can appear in various colors.
Along the margin of the bell, the moon jellyfish has numerous short, fine, fringed tentacles. Unlike some other jellyfish species, these tentacles are not long and trailing. Extending from the center of the underside of the bell are four frilly oral arms. These arms are equipped with stinging cells and are involved in capturing and transporting food.
Habitat and Behavior
Moon jellyfish are found globally, commonly inhabiting coastal waters, estuaries, and harbors in both temperate and tropical regions. They thrive in nearshore environments where their preferred food sources are abundant. These jellyfish can tolerate a range of water conditions, including varying temperatures and salinities.
Their movement is largely passive, relying on ocean currents to drift through the water. While they are not strong swimmers, moon jellyfish use rhythmic contractions of their bell to pulse and propel themselves, primarily to maintain their position near the water surface. Their diet primarily consists of zooplankton, which includes small crustaceans, fish eggs, and larvae. They capture prey by trapping it in mucus present on their short tentacles and the surface of their bell. Cilia, tiny hair-like structures, then move the entrapped food towards the oral arms and into the mouth for digestion.
Life Cycle and Reproduction
The life cycle of the moon jellyfish is complex, involving both sexual and asexual reproductive stages. The adult jellyfish, known as a medusa, represents the sexually reproductive phase. Male medusae release sperm into the water, which are then taken in by female medusae to fertilize their eggs.
Following fertilization, the eggs develop into small, free-swimming larvae called planulae. These larvae settle onto a hard surface and transform into a sessile polyp stage, known as a scyphistoma. Polyps can reproduce asexually by budding, creating new polyps. Under specific environmental cues, polyps undergo strobilation, segmenting horizontally to bud off tiny, immature jellyfish called ephyrae. These ephyrae are free-swimming and mature into adult medusae, completing the life cycle.
Interaction with Humans
Moon jellyfish possess stinging cells called nematocysts on their tentacles, similar to other jellyfish. Their sting is mild and generally harmless to humans. Most individuals experience little to no reaction, such as slight itching or minor irritation.
These jellyfish are a popular sight in public and private aquariums due to their distinctive appearance and relatively easy care requirements. In marine ecosystems, moon jellyfish play a role in the food chain, serving as a food source for various marine animals, including some sea turtles and ocean sunfish. Occasionally, moon jellyfish appear in large aggregations known as blooms. These blooms are a natural phenomenon, influenced by environmental factors.