Cannonball Jellyfish Facts

Scientific Name: Stomolophus meleagris

Cannonball jellyfish washed ashore in South Carolina
This cannonball jellyfish from South Carolina has a brown-rimmed bell.

John Dreyer / Getty Images

The cannonball jellyfish (Stomolophus meleagris) gets its common name from its appearance, which is about the same size and general shape as a cannonball. While the cannonball jellyfish can secrete a toxin, it does not have the long, stinging tentacles normally associated with jellyfish. Instead, it has short oral arms that give rise to its scientific name, which means "many mouthed hunter."

Fast Facts: Cannonball Jellyfish

  • Scientific Name: Stomolophus meleagris
  • Common Names: Cannonball jellyfish, cabbagehead jellyfish, jellyball
  • Basic Animal Group: Invertebrate
  • Size: 7-10 inches wide, 5 inches tall
  • Weight: 22.8 ounces
  • Lifespan: 3-6 months
  • Diet: Carnivore
  • Habitat: Atlantic, Pacific, and Gulf shores
  • Population: Decreasing
  • Conservation Status: Not evaluated

Description

Cannonballs have robust, dome-shaped bells that range from 7 to 10 inches in width and about 5 inches in height. The bell of jellyfish in the Atlantic and Gulf is milky or jelly, often featuring a rim shaded with brown pigment. Cannonball jellyfish from the Pacific are blue. An average cannonball weighs around 22.8 ounces. The cannonball jellyfish has 16 short, forked oral arms and mucus-coated secondary mouth folds or scapulets. The sexes are separate animals, but they look alike.

Cannonball jellyfish from Baja California
Cannonball jellyfish in the Pacific Ocean are blue. Rodrigo Friscione / Getty Images

Habitat and Range

The species lives in estuaries and along coastal shorelines of the Gulf of Mexico, Atlantic Ocean, and Pacific Ocean. In the western Atlantic, it is found from New England to Brazil. It lives in the eastern Pacific from California to Ecuador, and in the western Pacific from the Sea of Japan to the South China Sea. The cannonball thrives in tropical to semi-tropical saltwater with a temperature around 74 degrees Fahrenheit.

Diet

The cannonball jellyfish is a carnivore that feeds on fish eggs, red drum fish larvae, and planktonic larvae of mollusks and snails (veligers). The jellyfish feeds by sucking water into its mouth fold when its bell contracts.

Behavior

Most jellyfish are at the mercy of the wind and waves for movement, but the cannonball uses its oral arms to swim. When the jellyfish is disturbed, it dives deeper into the water and releases toxin-containing mucus. The toxin drives away most predators and may help the cannonball trap and disable small prey.

The jellyfish can sense light, gravity, and touch. While social communication between cannonballs is not well-understood, sometimes the jellyfish form large groups.

Reproduction and Offspring

The cannonball jellyfish life cycle includes sexual and asexual phases. Cannonballs become sexually mature in their medusa state, which is the jellyfish form most people recognize. Male jellyfish eject sperm from their mouths, which are captured by oral arms of females. Special pouches in the oral arms serve as nurseries for the embryos. Three to five hours after fertilization, larvae detach from the pouches and float until they attach themselves to a firm structure. The larvae grow into polyps, which trap small prey with tentacles and reproduce asexually by budding. The offspring detach and become ephyra, which eventually morph into the adult medusa form. The average lifespan of a cannonball jellyfish is 3 to 6 months, but they are preyed upon at all life stages, so few make it to maturity.

Jellyfish life cycle
The jellyfish life cycle includes sexual and asexual phases. Dorling Kindersley / Getty Images

Conservation Status

The International Union for Conservation of Nature (IUCN) has not assigned the cannonball jellyfish a conservation status. The species is ecologically important because it is the primary prey of the endangered leatherback sea turtle (Dermochelys coriacea). The population size varies from year to year. In summer and early autumn, the cannonball jellyfish is the most abundant type of jellyfish off the Atlantic coast from South Carolina to Florida. A study conducted by the South Carolina Department of Natural Resources (SCDNR) from 1989 to 2000 found a steady decline in population numbers.

Threats

Cannonball jellyfish numbers are highly dependent on water temperature. The species is also affected by water pollution, algae blooms, and prey density. Cannonball jellyfish are at risk from overfishing, but some states oversee management plans for commercial fishing of the species.

Cannonball Jellyfish and Humans

Dried cannonball jellyfish are in demand as high-protein food and traditional medicine in Asia. Cannonballs commonly wash ashore off the coast of the southeastern United States. In the rare instances of stings, minor skin and eye irritation may result. However, the toxin the jellyfish release when disturbed can cause cardiac problems in humans and animals, including irregular heartbeat and myocardial conduction problems. While dried jellyfish are safe to eat, it's best to keep children and pets away from live or beached animals.

Sources

  • Corrington, J.D. "Commensal association of a spider crab and a medusa." Biology Bulletin. 53:346-350, 1927. 
  • Fautin, Daphne Gail. "Reproduction of Cnidaria." Canadian Journal of Zoology. 80 (10): 1735–1754, 2002. doi:10.1139/z02-133
  • Hsieh, Y-H.P.; F.M. Leong; Rudloe, J. "Jellyfish as food." Hydrobiologia 451:11-17, 2001. 
  • Shanks, A.L. and W.M. Graham. "Chemical defense in a scyphomedusa." Marine Ecology Progress Series. 45: 81–86, 1988. doi:10.3354/meps045081
  • Toom, P.M.; Larsen, J.B.; Chan, D.S.; Pepper, D.A.; Price, W. "Cardiac effects of Stomolophus meleagris (cabbage head jellyfish) toxin." Toxicon. 13 (3): 159–164, 1975. doi:10.1016/0041-0101(75)90139-7