The Jellyfish Aurelia

FRENCh name : Aurelie Moon

English name : Jellyfish Aurelia

latinE NAME : Aurelia aurita

Geographic distribution: this jellyfish is widespread throughout the oceans, with the exception of the extremely cold waters at the north and south poles.

Habitat: Aurelia aurita often swims on the surface of the water, in the open seas or near coasts. It likes the polluted waters of ports as well as waters with high salinity, where the water temperature is higher. Its planula (ciliated larvae) settle on the substrate in port and industrial areas areas where they turn into a type of polyp called a scyphistoma, which later turns into a medusa (an adult jellyfish).

Size:the umbrella shaped bell (body) of an Aurelia aurita jellyfish can reach 40 cm in diameter.

Longevity: its lifespan is less than a year.

Diet: the Aurelia aurita jellyfish feeds on young herring alevins and a group of jellyfish can decimate an entire shoal. It feeds mostly on small crustaceans (copepods, which make up 90% of plankton). However, they are quite opportunistic and will eat whatever they can find, including other jellyfish. Aurelia will even eat their own larvae. To grow and reproduce a jellyfish must consume several times its bodyweight per day.

Moving around: while jellyfish generally drift with the currents, they are also capable of a sort of jet propulsion. They swim by contracting their bell (expelling water) then, by relaxing their muscles, their bell reopens (taking in water). The Aurelia aurita jellyfish can both float and swim and cannot hold its position against ocean currents. It is a constituent of ocean plankton.

Biology: Aurelia aurita is translucent white with a nuance of blue. It is made up of water (generally more than 95%). It has a digestive system with a mouth between its tentacles, light sensitive organs, muscles and nerves. Its stinging cells are like miniature harpoon guns, each one with its own supply of venom. Looking a little like a four leaf clover, four darker zones surrounding the stomach can easily be made out in the centre of its bell. In males these zones are a soft purple colour, whereas in females they are whitish.

Reproduction:the lifecycle of this jellyfish is complex but goes through one fixed lifecycle stage, a tiny polyp. Polyps live on the sea bed, attached to a rock where they multiply through a process of budding to create a colony. With the change of season the polyp transforms and its crown of tentacles detaches to become a tiny jellyfish larva, which will eventually grow into the jellyfish that we are all familiar with. Jellyfish are both male and female and inseminate each other. After insemination their larvae are deposited on the sea bed where they turn into a new polyp, and the cycle can begin again!

Predators: turtles, petrels, gulls, fish and other jellyfish.