Marine Invertebrates of Bermuda
Moon Jelly (
By Andrew Bishop
James B. Wood and Abel Valdivia (Eds)
The moon jellyfish
is a scyphozoan distinguished by its transparent bell, in which conspicuous purple gonads form a clover like shape. An omnipresent zooplankton of the sea, moon jellies are found solitary and in swarms anywhere between latitudes 70°N and 40°S, and are often considered pests because of their tendency to mass-consume the larvae of commercially important fish . Although denoted as costly gluttons by managers of local fishing companies, they are well respected among marine biologists for their high degree of plasticity, in regards to the myriad of marine environments which moon jellies successfully inhabit.
have a complex life history involving multiple metamorphoses, and reproduce both sexually – where fertilization results in the eventual release of planula larvae - and asexually – where strobilation produces multiple developing medusae. Unlike other scyphozoans, female moon jellies brood fertilized eggs on the ma! nubrium before release of the hatched larvae into the water column. Recent research has focused on how the water flow patterns which
generate in order to move, also help the organism catch prey.
Moon jellyfish are known for their ability to thrive in a variety marine environments, which significantly differ in salinity, temperature, and water flow rates (Lucas 2001). They frequent reefs and shallow coastal waters, such as inlets, bays, and estuaries, and can radically alter the population dynamics of particular habitats by consuming zooplankton in mass proportions (Dawson and Jacobs 2001, Lucas 2001). Because
larvae require a shallow substrate for colonization, moon jellies are less commonly found in the deep ocean (Lucas 2001).
travel via “jetting”, in which the bell contracts to decrease water volume and push water outward, thus propelling the organism forward (Dabiri et al. 2005). This phase is complimented by the “bell relaxation phase”, in which water flows back into the bell in order to renew the swimming cycle. While moon jellies are planktonic, jetting allows them to actively travel across coastal waters, and can significantly increase the number of prey which they encounter. Moon jellies are not highly selective feeders (Lucas 2001), and prey upon a variety of zooxplankton - including copepods, cladocerans, larvaceans, and bivalves (Hansson 2005). They capture prey using the nematocysts and mucus found on their tentacles and oral arms, and subsequently transport the immobilized prey along the marginal groove of the oral arm, through the mouth, and into their gastric pouches for digestion; the transport process takes approximately 5-15 minutes (The Jellies Zone). The s! tomach region also contains nematocysts, which restrain captured prey that have not been completely incapacitated (The Jellies Zone).
Common predators of
are both the nudibranch
(Henroth 1985), and the scyphozoans
(Lucas 2001). The nudibranch eats moon jellies in their polyp stage, and specific areas have been documented where
are almost completely reliant on
polyps for food. This dependence can in turn drastically reduce moon jelly abundance (Henroth 1985). The scyphozoan
in their medusa stage, and utilizes their fellow jellyfish as a valuable carbon resource (Hansson 1997). Fish and turtles have also been known to prey upon moon jellies (Lucas 2001).
The life cycle of the moon jelly consists of several phases, and both the number of phases, as well as the respective duration, can vary among different moon jelly populations (Lucas 2001). The most prominent phase is always the medusa stage, which can last up to a year (Dawson et al. 2001). During this time period, medusae sexually reproduce via embryogenesis to create large numbers of motile planula larvae (Kroiher et al. 2000, Lucas 2001). Reproduction generally occurs when medusae are at their peak biomass, and parent medusae will often dwindle and die after the process is complete (Lucas 2001). Within a few days of their release, planula larvae colonize shallow benthos habitats, and proceed to morph into filter feeding polyps (Dawson et al. 2001). Like the medusae, polyps are “generalist’ feeders, and are capable of surviving fairly long periods of starvation (Lucas 2001). The polyps then either bud to form more polyps, or undergo strobilation, which produces juven! ile medusae, termed ephyra (Kroiher et al. 2000). Strobilation generally occurs in early spring, and can produce up to 30 ephyra per polyp (Lucas 2001). Ephyra will then grow, feeding on copepepods, phytoplankton, and particulate organic matter, until they are fully functioning, sexually mature medusae (Bamstedt et al. 2001).
As evident by this life cycle,
reproduce both asexually and sexually. Asexual reproduction occurs during the polyp stage, when the polyp either strobilates to produce ephyra, or simply buds to produce more polyps (Kroiher et al. 2000). During strobilation, “transversal constrictions” first appear in the top region of the polyp, and migrate basally to section the polyp into distinct, equally subdivided segments (Kroiher et al. 2000). These fissures intensify until the segments break off, each forming an ephyra. Larger polyps create more numerous ephyra, yet ephyra size tends to remain constant regardless of polyp size. After strobilation is complete, a portion of the basal region of the polyp remains attached to the substrate, and eventually reforms into a complete polyp. Strobilation can be induced both in the lab and in the field by a decrease in temperature (Kroiher et al. 2000).
Like the majority of scyphozoans,
are gonochoristic and sexually reproduce by spawning (Lucas 2001). Oocytes develop simultaneously among most populations; however, oogenesis does not occur at set intervals (Lucas and Lawes 1998).
are unique among their class, in that the female medusae brood developing planulae beneath their oral arms (Ishii and Takagi 2003). Brooding time varies among different populations of
; a period of 7-11 days has been documented in moon jelly populations in Tokyo Bay (Ishii and Takagi 2003). The number of planula larvae produced by medusae is heavily influenced by the abundance of food in the area, and therefore significantly oscillates between different populations (Lucas and Lawes 1998). In general, planula larvae are smaller, yet produced in higher numbers, in areas of high food availability (Lucas and Lawes 1998). Analogously, planula larvae tend to be larger, yet less abundan! t, in food limited habitats. All planula larvae swim by the use of cilia, and are lecithotrophic, meaning they are released from eggs which contain yolk (Lucas 2001).
was the subject of a recent study which examined the flow patterns which jellyfish produce when jetting, and how these patterns allow for effective feeding (Dabiri et al. 2005). It was determined that
generate both a “starting vortex”, when pushing water out of the bell, and a “stopping vortex”, when allowing water back into the bell (Dabiri et al. 2005). The merging of these vortexes pushes water past the organism’s feeding appendages, allowing the scyphozoan to swim and catch prey simultaneously
are considered to be an annoyance by many local fisheries, because they often deplete the larvae of commercially important fish species by either predation or food competition (Dawson and Jacobs 2001). Moon jellies can also induce algae blooms, by mass consuming herbivorous zooplankton, and subsequently decreasing predation pressures on phytoplankton (Lucas 2001). These blooms can have a severely negative effect on local tourist and fishing industries.
There are no laws concerning moon jelly fish in Bermuda (Wood and Jackson 2005).
My interest in moon jellies stems from all the memories I have of finding them washed up on the shore in South Carolina and Florida when I was a child. I always remember being told not to touch them because of their tentacles, and wondering how exactly it was that they managed to end up stranded on the beach.
Bamstedt, U., Wild, B., and M. B. Martinussen. 2001. Significance of food type for growth of ephyrae
Dabiri, J. O., Colin, S. P., Costello, J. H., and M. Gharib. 2005. Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses.
Journal of Experimental Biology
Dawson, M. N., and D. K. Jacobs. 2001. Molecular Evidence for Cryptic Species of
Hansson, L. J. 2006. A method for in situ estimation of prey selectivity and predation rate in large plankton, exemplified with the jellyfish
Journal of MarineBiology and Ecology
Hansson, L. J. 1997. Capture and digestion of the scyphozoan jellyfish
and prey response to predator contact.
Journal of Plankton Research
Henroth, L., and F. Groendahl. 1985. On the Biology of
. Predation by
(Gatropoda, Opisthobranchia), a major factor regulating the development of
populations in the Gullmar Fjord, western Sweden.
Ishii, H., and A. Takagi. 2003. Development time of planula larvae on the oral arms of the scyphomedusa
Journal of Plankton Research
Kroiher, M., Siefker, B., and S. Berking. 2000. Induction of segmentation in polyps of
(Scyphozoa, Cnidaria) into medusae and formation of mirror- image medusa anlagen.
Int. J. Dev. Biol
Lucas, C. H., and S. Lawes. 1998. Sexual Reproduction of the scyphomedusae
in relation to temperature and variable food supply.
Lucas, C. H. 2001. Reproduction and life history strategies of the common jellyfish,
, in relation to its ambient environment.
"The Jellies Zone". Wrobel, D. “Scyphomedusae”. 3 March 2006.< http://jellieszone.com/ Index.html>.
Wood, J. and K. Jackson. 2005. Bermuda, In: Caribbean marine Biodiversity., Miloslavich, P. and E. Klein Eds. De Stech Publications Inc. pp 19-35.
The Jellies Zone
Animal Diversity Web