Moon Jelly
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, and are
common to the waters off California, Japan, the East Coast of the
United States as well as Europe. The animal can be large (up to 15
cm across), translucent and often considered beautiful for the
patterns of color within its body. It feeds by stinging small
medusans, plankton and mollusks with its tentacles and bringing
them into its body for digestion, but is capable of only limited
motion; like other jellies it drifts with the current.
Moon Jelly,
Aurelia aurita
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 (Gilbertson, 1999). 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).
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 40 cm (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
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
Loggerhead Sea Turtle (Caretta
caretta), and the hydromedusae (Aequorea victoria) (Arai, 1997).
Another cause of death is by fisheries of A. aurita for food in countries such
as China, Philippines, Thailand, Malaysia, and Indonesia. They are
hunted by birds also. They defend themselves by stinging with their
tentacles (Arai, 1997).
There are possible metazoan parasites that attack A. aurita (Arai, 1997).
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).
Issue #259
