Pacific Moon Jellyfish, Aurelia labiata

Pacific Moon Jellyfish, Aurelia labiate. Underwater photograph taken in the coastal waters off Monterey, California, February 2022. Photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny:  The Pacific Moon Jellyfish, Aurelia labiata (Chamisso and Eysenhardt, 1821), is a member of the Ulmaridae Family of Jellyfish. The genus Aurelia is one of fourteen genera in the Ulmaridae Family, and there are twenty-six species in the Aurelia genus. They are also known as the Greater Moon Jellyfish and in Mexico as Medusa Luna. All species in the Aurelia genus are known as moon jellies and this causes some confusion. Until recently the Pacific Moon Jelly was lumped in with the Moon Jelly, Aurelia aurica, which has a cosmopolitan distribution, but is often considered an Atlantic Ocean species. Many sources still fail to recognize this division.

Morphology: The Pacific Moon Jellyfish has a dish or bowl-shaped bell with scalloping along the rim. There are sixteen scallops, though they are often hard to differentiate in living specimens. The bell is translucent and is usually white in color. Depending on the animal’s food source, the bell may be tinged with pink, purple, or yellow. The reproductive organs are visible through the top of the bell, in the shape of a four-leaf clover. The four oral arms and the tentacles are short. Pacific Moon Jellies reach a maximum of 40 cm (15.7 inches) in diameter.

Habitat and Distribution:  Pacific Moon Jellyfish are normally found near the surface, but can be found at depths up to 1,000 m (3,280 feet). The Pacific Moon Jelly is found in the temperate to tropical waters of the Eastern Pacific.  Prior confusion of this species with Aurelia aurica, and that these species do overlap in range makes it difficult to establish accurate range limitations along Mexico’s Pacific coast. Pacific Moon Jellies range from Alaska to the northern  Baja Peninsula. Neither species has been recorded from the Gulf of California. The Pacific Moon Jelly can be distinguished from Aurelia aurica by its slightly larger size and by having sixteen versus eight scallops along the rim of the bell.

Diet: Pacific Moon Jellyfish are suspension feeders that consume crustacean larvae, planktonic fish eggs, fish larvae, mollusk larvae, and other small jellyfish.

Predators: Pacific Moon Jellyfish are preyed upon by sea birds, fish, sea turtles and other jellyfish.

Reproduction:  Pacific Moon Jellyfish are gonochoric (male or female for life). They can reproduce asexually, through budding, or sexually. Sexual reproduction occurs through males releasing sperm filaments from their oral arms into the water. These sperm filaments are picked up by females. The sperm is carried to the females gastric pouch by cilliary currents. The fertilized eggs can be seen as gray, teardrop-shaped clumps on the female’s manubrium (the stalk hanging down which supports the mouth and oral arms). After a short time, these egg clumps drop off and attach to the bottom substrate to continue development.

Ecosystem Interactions: Pacific Moon Jellyfish are known to host the Longnose Spider Crab, Libinia dubia, and the planktonic amphipod, Hyperia galba. These crustaceans shelter in the bell and tentacles of the Pacific Moon Jelly and consume the jelly’s food as well as the jelly itself.

Human Interactions:  Pacific Moon Jellyfish have nematocysts that contain a toxin that they use to capture prey and to repel predators. This toxin poses no threat to humans, though contact with the skin or eyes may result in irritation in sensitive individuals. From a conservation perspective the Pacific Moon Jellyfish has not been formally evaluated. They are fairly common, with a wide distribution, and should therefore be considered a species of Least Concern.

Synonyms:  Aurelia (Aurelissa) labiata and Aurellia labiata