moon jellyfish

Aurelia aurita

Aurelia aurita (moon jelly, moon jellyfish, common jellyfish, saucer jelly) is one of a suite of more than ten morphologically nearly identical jellyfish species in the genus Aurelia. In general, it is nearly impossible to identify Aurelia medusae without genetic sampling, so most of what follows about "Aurelia aurita", should actually be considered to be information about the genus, not any particular species. The medusa is translucent, usually about 25-40 cm across, and can be recognized by its four horseshoe-shaped gonads that are easily seen through the top of the bell. It feeds by stinging small medusae, plankton and mollusks with its nematocyst-laden tentacles and bringing the prey into its body for digestion, but is capable of only limited motion; like other jellies it drifts with the current.

Distribution

The cosmopolitan genus Aurelia is found throughout most of the world's oceans, from the tropics to as far north as 70° latitude and as far south as 40°. (J.E. Purcell, et al. 2001). The species Aurelia aurita, whose distribution has been confirmed by Michael Dawson using genetic analysis, is found along the eastern Atlantic coast of Northern Europe and the western Atlantic coast of North America in New England and Eastern Canada. In general, Aurelia is an inshore genus that can be found in estuaries and harbors (Russell, 1953). It lives in ocean water temperatures ranging from −6 °C to 31 °C; with optimum temperatures of 9 °C to 19 °C (Rodriguez, 1996). A. aurita prefers temperate seas with consistent currents (Rodriguez, 1996). It has be found in waters with salinity as low as 3 ppt salinity, but is typically found only in water with salinity above 23 ppt.

Feeding

A. aurita and other Aurelia species feed on plankton that includes organisms such as mollusks, crustaceans, tunicate larvae, rotifers, young polychaetes, protozoans, diatoms, eggs, fish eggs, and other small organisms. Occasionally, they are also seen feeding on gelatinous zooplankton such as hydromedusae and ctenophores (Rodriguez, 1996). Both the adult medusae and larvae of Aurelia have nematocysts to capture prey and also to protect themselves from predators. The food is tied with mucus, and then it is passed down by ciliated action down into the gastrovascular cavity where digestive enzymes from serous cell break down the food. There is little known about the requirements for particular vitamins and minerals, but due to the presence of some digestive enzymes, we can deduce in general that A. aurita can process carbohydrates, proteins, and lipids (Arai, 1997).

Filtering Grid of Tentacles on the Bell Margin

Click on the images for higher resolutions.


High resolution in situ image of an undulating live Aurelia in the Baltic showing the grid of tentacles which are slowly pulled through the water. The motion is so slow that copepods can not sense it and don't react with an escape response

Higher magnification showing a prey item, probably a copepod

The prey is then drawn to the body by contracting the tentacles in a corkscrew fashion (image taken with an ecoSCOPE).

Body system

A. aurita does not have respiratory parts such as gills, lungs, or trachea. Since it is a small organism, it respires by diffusing oxygen from water through the thin membrane. Within the gastrovascular cavity, low oxygenated water can be expelled and high oxygenated water can come in by ciliated action, thus increasing the diffusion of oxygen through cell (Rees, 1966). The large surface area membrane to volume ratio helps A. aurita to diffuse more oxygen and nutrients into the cells.

The basic body plan of A. aurita consists of several parts. The species lack respiratory, excretory, and circulatory systems (Arai, 1997). The adult medusa of A. aurita, with a transparent look, has an umbrella margin membrane and tentacles that are attached to the bottom (Russell, 1953). It has four bright circular gonads that are under the stomach (J.E. Purcell, et al. 2001). Food travels through the muscular manubrium while the radial canals help disperse the food (Russell 1963). There is a middle layer of mesoglea, gastrodervascular cavity with gastrodermis, and epidermis (Solomon, 2002). There is a nerve net that is responsible for contractions in swimming muscles and feeding responses (Arai, 1997). Adult medusa can have a diameter up to 40 cm (Arai, 1997). The sexes are differentiated between males and females in the medusa stage (Arai, 1997). The young stage, planula, has small ciliated cells and would settle at the bottom of the water where it would change into strobila and then float off as ephyra (Gilbertson, 1999). There is an increasing size from starting stage planula to ephyra, from less than 1 cm in planula stage to 1 cm in ephyra stage (Russell, 1953).

Predators

The death of the organism sometimes is brought about after reproduction, leaving the gonads open to infection and degradation (Arai, 1997). A. aurita have been food for a wide variety of predators including the Ocean Sunfish (Mola mola), the Leatherback Sea Turtle (Dermochelys coriacea), a hydromedusa (Aequorea victoria) (Arai, 1997) and the scyphomedusa Phacellophora camtschatica (Towanda and Thuesen, 2006). They are hunted by birds also.

A. aurita is food in countries such as China, Philippines, Thailand, Malaysia, and Indonesia.

There are possible metazoan parasites that attack A. aurita (Arai, 1997).

References

Further References

  • Arai, M. N. 1997. A Functional Biology of Scyphozoa. Chapman and Hall, London, 68-206.
  • Dawson, M.N. 2003. Macro-morphological variation among cryptic species of the moon jellyfish, "Aurelia" (Cnidaria: Scyphozoa). Marine Biology 143: 369-379.
  • Gilbertson, L. 1999. Zoology Laboratory Manual 4th edition. McGraw-Hill Inc, CA, 9.2-9.7.
  • Moen, F.E. and E. Svensen. 2004. Marine fish & invertebrates of Northern Europe. AquaPress: Southend-on-Sea. ISBN 0-9544060-2-8. 608 pp.
  • Purcell, J. E., W.M. Graham, and H.J. Dumont (Eds.). 2001. Jellyfish Blooms: Ecological and Societal Importance. Kluwer Academic Publishers, Dordrecht, 229-273.
  • Rees, W. J. 1996. The Cnidaria and Their Evolution. Academic Press Inc, NY, 77-104.
  • Rodriguez, R. J. February 1996. "Aurelia aurita (Saucer Jelly, Moon Jelly, Common Sea Jelly Jellyfish) Narrative."
  • Russell, F. S. 1953. The Medusae of the British Isles II. Syndics of Cambridge University Press, London, 81-186.
  • Solomon, E. P., L. R. Berg, and W. W. Martin. 2002. Biology 6th edition. Brooks/Cole Publishing, CA, 602-608.
  • Towanda, T. and E.V. Thuesen. 2006. Ectosymbiotic behavior of Cancer gracilis and its trophic relationships with its host Phacellophora camtschatica and the parasitoid Hyperia medusarum. Marine Ecology Progress Series 315, 221-236.
  • National Center for Biotechnology Information. October 23, 2001.

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