Moon Jelly
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| Moon Jelly | ||||||||||||||
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| Aurelia aurita |
Moon Jelly (Aurelia aurita) are the most common Jellyfish species found in the genus Aurelia. Other species found in the genus Aurelia besides A. aurita are: A. labiata, A. limbata, Aurelia sp. They can be found in the Atlantic Ocean, the Arctic Ocean and the Pacific Ocean.
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General biology
The cosmopolitan Aurelia aurita is found throughout the tropics and as far north as 70° latitude and as far south as 40°. (J.E. Purcell, et al. 2001). In addition to frequenting the North American coast, they are usually found all around the coasts of the British Isles (Russell, 1953). In general, A. aurita is an inshore species that can be found in places like estuaries and harbors (Russell, 1953). They live in ocean water temperatures that range from -6° to 31° Celsius; with optimum temperatures of 9-19° Celsius (Rodriguez, 1996). A. aurita prefers mildly cold salt water with consistent currents (Rodriguez, 1996). They can be found in 3% salinity water but are typically found only in water with 6% salinity (Russell, 1953).
Life cycle
A. aurita first starts out with an ovum from a female medusa and a sperm from a different medusa to form a zygote. The zygote then turns into a blastula, then gastrula, and then planula (Gilbertson, 1999).
The planula settles on the bottom and attaches itself onto a reef for a while (Gilbertson, 1999). The planula then grows and changes into a small polyp called a scyphistoma. The scyphistoma grows and becomes a strobila with small buds on the top layers. Each of the buds breaks off and forms an ephyra. The ephyra enlarges and matures to become the last stage, adult medusa. The strobila stage can reproduce by asexual fission (Gilbertson, 1999).
From mid July to October is when the growth of A. aurita at its highest. The ephyra and medusa stage can last approximately 14 months, although some medusae die earlier in the winter (Aria, 1997).
A. aurita has a complicated life cycle that has two main stages. In the polyp stage they reproduce asexually while the medusa stage they reproduce sexually.
The major tolerance and adaptability of A. aurita explains its presence worldwide. Medusae appear more frequently in shallow water that is open to the ocean with limited waves. The intermediate planula stage generally stays in water that is around 20 feet deep. The scyphistomas can be located in mussel beds. A. aurita medusae can survive in polluted, nutrient-poor, and airless environments. The polyps can survive in oxygen levels that are three times normal for several days, giving them a higher chance of living in case of a sudden change in the water oxygen.
Feeding
A. aurita species feed on zooplankton that includes organisms such as "mollusks, crustaceans, tunicate larvae, copepods, rotifers, nematodes, young polychaetes, protozoans, diatoms, eggs, fish eggs, and other small jellies." (Rodriguez, 1996). Occasionally, they would be seen feeding on hydromedusa and ctenophores (Rodriguez, 1996). Larvae of A. aurita have special nematocysts to capture prey and also to protect themselves from predators (Arai, 1997). The food is tied with mucus, and then it passed down by ciliated action down into the gastrovascular cavity where digestive enzymes from serous cell would break down the food (Arai, 1997). 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 species consume carbohydrates, proteins, and lipids (Arai, 1997).
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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 (Aria, 1997). Adult medusa can have a diameter up to 40cm (Arai, 1997). The sexes are can be 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
Aurelia aurita are known to be eaten by a wide variety of predators, including the ocean sunfish (Mola mola), the leatherback sea turtle (Dermochelys coriacea), the scyphomedusa Phacellophora camtschatica,and a very large hydromedusa (Aequorea victoria). Recently it was reported from the Red Sea that Aurelia aurita was seasonally preyed upon by two herbivorous fish. Moon jellies are also fed upon by sea birds, which may be more interested in the amphipods and other small arthropods that frequent the bells of Aurelia, but in any case, birds do some substantial amount of damage to these jellyfish that often are found just at the surface of bays.
Aurelia jellyfish naturally die after living and reproducing for several months. It is probably rare for these moon jellies to live more than about six months in the wild, although specimens cared for in public aquarium exhibits typically live several to many years. In the wild, the warm water at the end of summer combines with exhaustive daily reproduction and lower natural levels of food for tissue repair, leaving these jellyfish more susceptible to bacterial and other disease problems that likely lead to the demise of most individuals. Such problems are responsible for the demise of many smaller species of jellyfish.
Aurelia aurita interaction
Beside from being a source of food for human consumption, A. aurita species also "represent an important step in pelagic organic matter transformations" (Rodriguez, 1996). On the bad side, A. aurita species could ruin the fish markets for human, creating a tidal effect that may hurt the fish population either indirectly or directly by feeding on fish larvae (Arai, 1997).
References
- Arai, M. N.1997. A Functional Biology of Scyphozoa. Chapman and Hall, London, 68-206.
- Gilbertson, L. 1999. Zoology Laboratory Manual 4th edition. McGraw-Hill Inc, CA, 9.2-9.7.
- 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." [1] (http://animaldiversity.ummz.umich.edu/accounts/aurelia/a._aurita$narrative.html)
- 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.
- National Center for Biotechnology Information. October 23, 2001. [2] (http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi)