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Aurelia Aurita: the Moon Jelly

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Aurelia Aurita: the Moon Jelly Aurelia aurita: the Moon Jelly Crystal Franco December 7, 2009 Diagnostic information Aurelia aurita, is of the Phylum Cnidaria, which are characterized by having a polyp and medusa stage, radial symmetry, planula larvae, cnidia, and tentacles around the mouth. Classified under the Class of Scyphozoa qualifies the species as a “true jelly,” that is primarily found in medusoid morphology, with asexual reproduction in the polyp stage via strobilation (Dawson and Martin, Fig. 1. Drawn illustration of Aurelia aurita 2001). It is also of the Order Semaeostomeae, (http://www.sealifebase.org/Photos/PicturesSummary.p Family Ulmaridae, Genus Aurelia, and species hp?StartRow=4&ID=44404&what=species&TotRec=6) Aurelia aurita. The particular species Aurelia aurita is often called “moon jelly,” after its milky, translucent color and shape. The term “jellyfish” also refers to its gelatinous body (Richardson et al, 2009). However, A. aurita is obviously not made of jelly nor a fish species, but instead a free-flowing creature that is able to propel itself though the water with muscular contraction of it’s bell, but is not able move against currents, which technically makes it a 2 Moon Jelly (Aurelia aurita) (www.jellieszone.com) planktonic species. While there are approximately 12 Aurelia subspecies that have below, and are readily visible in females as pink been described, A. aurita is one of two that has and purple clumps. Tiny tentacles surround the been classified as its own distinct species bell shaped dome. Prey becomes stunned by the (Russel 1970). Current studies are using nematocysts (stinging cells) in the tentacles and molecular evidence to identify the organism are then moved via cilia to the mouth which is through genotypic and mitochondria DNA located on the underside of the organism. sequencing (Ki et al., 2008). Identification is Contractions of the bell pulse and propel the further complicated due to the high variation in animal through the water column. However, phenotypic expression of the different life they are unable to overcome current forces, stages. The 5-7 horseshoe shaped rings are the which technically classifies the organism as digestive stomach pouches. The gonads lie just plankton. In most cases, the individuals shrink again when preparing to sexually reproduce and release gametes. It remains difficult to age a specimen, since size averages differ regionally. Typically, medusae life spans range from 4-8months and do no exceed 1 year, though a few exceptions do occur. Age studies have determined that the number of branching points in the radial canals of the water vascular system increase with time, allowing scientist to use this change in physiology to age an individual. While selection occurs at every stage of the life cycle, at any Fig. 3 Shows the life cycle and reproduction cycle given habitat, distribution and abundance is of Aurelia aurita (Muller and Leitz, 2002) dependent on recruitment via sexual reproduction, migration, mortality, and asexual Life History and Basic Ecology reproduction. Mortality has highest impact upon population abundance at the polyp stage. A. aurita is in the class Scyphozoa, which means In the Adriatic Sea, A. aurita has been observed that it will eventually undergo asexual showing diel migrations in pursuit of reproduction via strobilation while in the polyp zooplankton and microbial bacteria (Malej et al., morph, and sexually reproduce as a medusa 2008). At night, the jellyfish could typically be morph. In the Pacific Northwest and other found deeper in the water column, from 24m to temperate regions, the jellyfish asexually 32m. During the day, A. aurita typically strobilates as a polyp during the spring, is able to gathered in the thermocline, which was around a rapidly grow during the summer, and reproduces depth of 20m. The experiment focused on sexually as a medusa in the fall before senescing individuals with a bell diameter of 4.9-11.4 cm, between autumn and winter (Dawson and Martin and they typically found 27 prey items per 2001). The species does show some seasonal medusa. Gut contents of A. aurita contained changes in bell diameter size (Lucas, 2001). larvae of Gastropoda, Bivalva, Cirripedia, Typically medusae are small in size during nauplii, and Appenduculiaria, but were primary winter to early spring, which is a result of composed of copepodites. While they didn’t nutrient and light limitations. Once zooplankton appear to be eating at night, the authors of the and phytoplankton blooms occur in the spring, paper believe migration occurs due to metabolic growth in bell diameter increases exponentially. advantage and tidal distribution avoidance. Other studies have shown that A. aurita may be capable of absorbing dissolved organic matter (Shick, 1973) and even capable of sorting its food to maximize fulfilling its nutritional needs (Dawson and Martin 2001). In some cases, it has also been observed to degrow in times of starvation until sufficient nutrients become available. To catch prey, A. aurita uses it’s cnidea and nematocysts, which are stinging cells found in the tentacles around its mouth to stun and poison their prey (Richardson et al., 2009). Fig. 4 Timing of the appearance of ephyrae, medusae, and plunla- Food particles are then moved via bearing medusae in a variety of Aurelia aurita populations globally cilia to the mouth where they then (Lucas, 2001) enter the digestive tract. Nutrients are then absorbed and stored in the digestive tract of increasing body segmentation in benthic rings that are easily observed in the bell of the polyps of A. aurita. Once, they are through with organism. this process, asexually budding of the benthic The species A. aurita reproduces sexually and strobila produces ephyrae, which are essentially asexually depending on what life stage it is in small jellyfish (Liu et al., 2008). This process (Richardson et al., 2009). Medusae, which are occurs through late winter to early spring. These the commonly known bell shaped forms of the ephyrae then develop into the medusa form of species, are present generally in the spring the species. Studies conducted showed that through fall. They reproduce sexually before there was a negative correlation between senescing. The haloplanktonic larvae then increased temperature and light intensities and develop into polyps, and through the strobilation budding rates. While strobilation proceeded at process, reproduce asexually from winter faster rates, it appears that excess budding rates through the spring. Large blooms of medusae that create larger blooms can occur more during the summer ensure that planulae larvae frequently in temperate regions in comparison to are fertilized before settling and tropical regions. Timing of this process varies metamorphosing into benthic polyps (Hamner globally depending on temperature, nutrients, and Dawson, 2009). Strobilation is the process and light intensity (as depicted in Fig. 4). There appears to have been a worldwide expansion of A. aurita populations, though it is difficult to truly know if the species was native or introduced due to lack of data. However, spread and establishment is easily achievable due to the species wide tolerance of environmental conditions from temperate to tropical regions. (Malej et al., 2007). Studies have shown that the jellyfish prefer positioning themselves near the bottom of the thermocline layers in areas with low salinity and temperatures lower than 19 °C. However, as aforementioned, the jellyfish are quite Fig. 5 Multiple-population relationship between maximum diameter abundant in the tropics. This generalist and medusa abundance of Aurelia aurita (Lucas, 2001). capacity allows them to successfully spread and establish in a great range of ocean water temperatures are likely to facilitate regions. There also seems to be a correlation future blooms. between environment characteristics and A. Also, smaller jellyfish blooms tend to have aurita population size (Dawson and Martin, individuals with large bell diameters relative to 2001). Surveys have found that large bloom of and enclosed system. This may reflect the medusa in temperate regions are generally found organism’s lack of intraspecies competition for in fully or semi-closed environments, which may available nutrient resources. Temperature too be behind key factors of survival such as may be a component influencing the organism’s “reduced advection, dilution and predation growth rate and metabolic processes. There are compared to more habitats” (266, Dawson and also seasonal growth patterns displayed by A. Martin, 2001). Therefore it is reasonable to aurita (Lucas, 2001). Typically, medusae assume that environmental conditions may growth is slow from winter until early spring, decide how large an A. aurita invasion may be. due to temperature and nutrient limitations. High Such blooms are not typically seen in the nutrient concentrations and increased tropics, though the species goes through several temperatures in the water column allow the life cycles a year. Global warming and rising individuals to grow exponentially, until autumn causes the animals to shrink in size with the process of gamete release. A high tolerance for organisms in a commensial relationship, there low dissolved oxygen content also allows the has been reports of planulae larvae settling on jellyfish to prey upon copepods that become substrate in response to cues found in the more susceptible to predation in such conditions environment of settled polyps (Muller and Leitz, (Richardson
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