By Page Dunning
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., 2001)
Biogeographic Regions:
atlantic ocean 
(native ); mediterranean sea (introduced ).
Habitat
Mnemiopsis leidyi lives in the photic region and can be found from the littoral zone to the pelagic (GESAMP 1997). (GESAMP et al., 1997)
These animals are found in the following types of habitat:
saltwater or marine .
Aquatic Biomes:
pelagic ; coastal ; brackish water .
Other:
intertidal or littoral .
Physical Description
(2.36 in)
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)
Some key physical features:
ectothermic ; heterothermic ; radial symmetry .
Reproduction
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 .
Behavior
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)
Primary Diet:
carnivore (piscivore ); planktivore .
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)
Ways that these animals might be a problem for humans:
crop pest.
Conservation Status
IUCN Red List: [link]:
Not Evaluated.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
This species is not considered to need special conservation efforts, and is an invasive pest in the Mediterranean basin. (GESAMP et al., 1997)
Contributors
Page Dunning (author), Western Maryland College.
Randall L. Morrison (editor), Western Maryland College.
