Mnemiopsis leidyi

Geographic Range

Mnemiopsis leidyi is native from the eastern shores of the United States to the West Indies. It also has invaded Eurasian waters of the Mediterranean, Black Sea, Azov Sea, Caspian Sea, and the Sea of Marmara (GESAMP 1997).

The limits of distribution are in temperatures between 1.3^(oC) to 32^(oC) and salt concentrations ranging from 3.4ppt to 75ppt, with water temperature being the most significant limiting factor.

Mnemiopsis leidyi is able to live in oxygen poor waters and is not significantly harmed by water pollution. In addition, this organism thrives in brackish water that has a high concentration of organic material suspended in it (Ginn et. al 2001). (GESAMP, et al., 1997; Ginn, et al., Feb. 27, 2001)


Mnemiopsis leidyi lives in the photic region and can be found from the littoral zone to the pelagic (GESAMP 1997). (GESAMP, et al., 1997)

Physical Description

Mnemiopsis leidyi is related to jellyfish. However, it does not have tentacles, nor does it sting. The sea walnut is approximately 6cm long and 10cm wide, and is characterized by wart-like bumps on its body. This organism is also capable of bioluminescence and studies are being done to determine its function (Tennessee 1998). The estimated biomass of the Black Sea population in the summer of 1989 was 30x10^(6) tons (GESAMP 1997). (GESAMP, et al., 1997; Tennessee Aquarium, 1998)

  • Average length
    6 cm
    2.36 in


Mnemiopsis leidyi has both male and female reproductive organs and is able to fertilize itself (GESAMP 1997). It is reproductively mature 13 days after hatching (Kideys 1994). When food is plentiful and the water temperature is between 19-23°C, Mnemiopsis leidyi will spawn. Spawning only occurs at night and involves each organism releasing about 8,000 eggs. After fertilization, the embryo is fully developed after only 20 hours (GESAMP 1997). (GESAMP, et al., 1997; Kideys, 1994)

  • Key Reproductive Features
  • simultaneous hermaphrodite
  • oviparous
  • Average number of offspring
  • Average age at sexual or reproductive maturity (female)
    13 days
  • Average age at sexual or reproductive maturity (male)
    13 days


They are motile organisms. No concrete evidence has been obtained as of yet to say whether or not they are social animals. Studies are being done to see if the bioluminescence is a form of communication (Wampler 1997).

Food Habits

Mnemiopsis leidyi is a generalized feeder and eats fish eggs and larva, kilka (a collective name for sardine-like fish), anchovies, zooplankton, and horse mackerel (Radler 2000).

The feeding behavior entails swimming slowly to pump water over the mucus-covered lobes that trap food (Ginn et. al 2001). Mnemiopsis leidyi continues to consume food after its stomach chamber is full. This is possible because the excess food is ejected as a ball of mucus. When there is no food available, Mnemiopsis leidyi is able to survive for up to three weeks by reducing its body size (GESAMP 1997). (GESAMP, et al., 1997; Radler, 10/20/00)

  • Animal Foods
  • fish
  • eggs
  • aquatic crustaceans
  • cnidarians
  • other marine invertebrates
  • zooplankton

Economic Importance for Humans: Negative

The invasion of this species into the Black Sea has done significant harm to commercial fishing there, and control efforts are being made. These efforts include the introduction of specialist predator comb-jellies in the genus Beroe (GESAMP 1997). (GESAMP, et al., 1997)

  • Negative Impacts
  • crop pest

Conservation Status

This species is not considered to need special conservation efforts, and is an invasive pest in the Mediterranean basin. (GESAMP, et al., 1997)


Page Dunning (author), Western Maryland College, Randall L. Morrison (editor), Western Maryland College.


Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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brackish water

areas with salty water, usually in coastal marshes and estuaries.


an animal that mainly eats meat


the nearshore aquatic habitats near a coast, or shoreline.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


an animal that mainly eats fish


an animal that mainly eats plankton

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


GESAMP, , IMO, FAO, UNESCO-IOC, WMO. 1997. "Opportunistic Settlers and the Problem of the Ctenophore Mnemiopsis leidyi Invasion in the Black Sea." (On-line). Accessed May 1, 2001 at

Ginn, J., T. Miller, L. Sanford. Feb. 27, 2001. "Effects of Small-scale Turbulence on Ingestion Rates and Swimming Speeds of the Ctenophore Mnemiopsis leidyi" (On-line). Accessed May 1, 2001 at

Kideys, A. 1994. Recent Dramatic Changes in the Black Sea Ecosystem: The Reason for the Sharp Decline in Turkish Anchovy Fisheries. Journal of Marine Systems, 5: 171-181.

Radler, D. 10/20/00. Predator Destroys Black Sea Fishing, Moves to Caspian. Daily University Science News,

Tennessee Aquarium, 1998. "Mnemiopsis leidyi" (On-line). Accessed May 1, 2001 at

Zaika, V., N. Revkov. 1995. Anatomy of Gonads and Propagation of Ctenophore Mnemiopsis in the Black Sea. Hydrobiol Journal, 31: 9-14.