Common Jellyfish

Aurelia aurita

Family: Ulmaridae | Genus: Aurelia

The common jellyfish, also known as the moon jellyfish or saucer jelly, is among the most widespread and familiar jellyfish species worldwide. It belongs to the phylum Cnidaria, class Scyphozoa and order Semaeostomeae.

Aurelia aurita is recognised by its translucent, umbrella-shaped bell, which can reach up to 50 cm in diameter. Around the edge, it has short tentacles and eight evenly spaced sensory structures known as rhopalia. From above, four horseshoe-shaped gonads are clearly visible—often pink or reddish in colour—making the species easy to identify.

Geographical distribution

A circumglobal species, it occurs in oceans worldwide, except in extremely cold polar waters.

Habitat

Found in the pelagic zone—the open water column of the ocean—this species occurs both offshore and near the coast, most often in surface waters.

In particular, environments typically include:

Temperate or warm waters
Plenty of plankton
Ocean currents that help transport it

Lifestyle and behaviour

Movement is driven by gentle, rhythmic contractions of the bell, creating a steady pulsing motion. However, it is not a strong swimmer and is often carried along by ocean currents. Individuals may be seen alone or gathered in large groups, sometimes forming blooms or swarms.

Social behaviour:

Can occur as solitary individuals.
Forms large aggregations when environmental conditions are favourable.

Daily activity:

Usually found in surface waters.
Drifts mainly with plankton and currents.

Reproduction:

Alternates between sexual (medusa stage) and asexual (polyp stage) reproduction.
Larvae (planulae) settle on a substrate and develop into polyps; through strobilation, these release ephyrae, which grow into adult jellyfish.

Relationship with its environment:

Plays an important role in marine food webs.
Populations may increase when natural predators decline or environmental conditions shift, such as milder winters and warmer summers.

Diet

In the wild

Zooplankton.
Small crustaceans, ctenophores and diatoms.
Captures prey using stinging tentacles or sticky mucus on the bell.

Under human care

Cultured plankton.
Small marine organisms, mainly nauplii.

Conservation status

The common jellyfish (Aurelia aurita) has not yet been assessed by the Red List of the International Union for Conservation of Nature.

Main threats:

Although not formally evaluated, marine pollution is known to affect jellyfish populations and may alter ecosystem balance