Sea Nettle Facts

The sea nettle is a group of jellyfish in the genus Chrysaora. The jellyfish gets its common name from its sting, which resembles that from a nettle or bee. The scientific name Chrysaora comes from Greek mythology, referring to Chrysaor, who was the son of Poseidon and the Gorgon Medusa and brother of Pegasus. Chrysaor's name means "he who has a golden sword." Many sea nettles have vivid golden coloration.

Species

There are 15 known sea nettle species:

• Chrysaora achlyos: Black sea nettle
• Chrysaora africana
• Chrysaora chesapeakei
• Chrysaora chinensis
• Chrysaora colorata: Purple-striped jelly
• Chrysaora fulgida
• Chrysaora fuscescens: Pacific sea nettle
• Chrysaora helvola
• Chrysaora hysoscella: Compass jellyfish
• Chrysaora lactea
• Chrysaora melanaster: Northern sea nettle
• Chrysaora pacifica: Japanese sea nettle
• Chrysaora pentastoma
• Chrysaora plocamia: South American sea nettle
• Chrysaora quinquecirrha: Atlantic sea nettle

Description

The size, color, and tentacle number of sea nettles depends on the species. Sea nettle bells can reach 3 feet in diameter, with oral arms and tentacles trailing as far as 20 feet. However, most specimens only reach 16-20 inches in diameter, with proportionally shorter arms and tentacles.

Sea nettles are radially symmetrical. The jellyfish is the animal's medusa stage. The mouth is at the center beneath the bell and is surrounded by tentacles that capture food. The bell may be semi-transparent or opaque, sometimes with stripes or spots. The tentacles and oral arms are often more deeply colored than the bell. Colors include off-white, gold, and reddish-gold.

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Habitat and Range

Sea nettles live in oceans worldwide. They are pelagic animals, subject to ocean currents. While they occur throughout the water column, they are particularly abundant near the surface of coastal waters.

Diet

Like other jellyfish, sea nettles are carnivores. They catch prey by paralyzing or killing them with their tentacles. The tentacles are covered with nematocysts. Each nematocyst has a cnidocil (trigger) that injects venom upon contact. The oral arms then transport the prey to the mouth, partially digesting it on the way. The mouth opens to an oral cavity that is lined with fibrous vessels that surround the victim, break it apart, and complete digestion. Nettles eat zooplankton, salps, crustaceans, snails, fish and their eggs, and other jellyfish.

Behavior

Sea nettles expand and contract muscles in their bells, ejecting jets of water to swim. While their stokes aren't powerful enough to overcome strong currents, nettles can move up and down the water column. Eye spots or ocelli on the bell and tentacles allow the animal to see light and dark, but not form images. Statocysts help the nettle orient itself with respect to gravity.

Reproduction and Offspring

The sea nettle life cycle includes both sexual and asexual reproduction. Fertilized eggs hatch into rounded, ciliated larvae called planulae. Within two to three hours, the planulae swim to a sheltered object and attach themselves. Planulae developed into tentacled polyps called scyphistomes. If conditions are suitable, the polyps bud off to release clones in a process called strobilation. The strobilia bud off and develop into ephyra. Ephyra have tentacles and oral arms. Ephyra transition into male and female medusae (the "jellyfish" form). Some species may reproduce by broadcast spawning. In others, females hold eggs in their mouths and capture sperm released by the male into the water. The female retains the fertilized eggs, planulae, and polyps on her oral arms, eventually releasing the polyps so they can attach elsewhere and develop. In captivity, sea nettles live as medusae for 6 to 18 months. In the wild, their life expectancy is likely between 6 months and one year.

Conservation Status

Like many invertebrates, sea nettles have not been evaluated by the International Union for Conservation of Nature (IUCN) for a conservation status. Populations of coastal species appear to be increasing. Researchers believe this is a result of nutrients released by urban runoff and climate change.

Sea Nettles and Humans

While painful, sea nettle stings are not lethal to people unless they are allergic to the venom. Stings normally hurt for up to 40 minutes. Applying vinegar to the sting site neutralizes the venom. Antihistamines and over-the-counter pain medication relieve the pain and swelling. In addition to tourism, sea nettles also affect the fishing industry. The medusae clog fishing nets and eat eggs and fry, reducing the number of fish that make it to adulthood. Sea nettles are relatively easy to maintain in captivity and are often featured in public aquariums.

Sources

• Caravati, E. Martin. Medical Toxicology. Lippincott Williams & Wilkins. (2004). ISBN 978-0-7817-2845-4.
• Gaffney, Patrick M.; Collins, Allen G.; Bayha, Keith M. (2017-10-13). "Multigene phylogeny of the scyphozoan jellyfish family Pelagiidae reveals that the common U.S. Atlantic sea nettle comprises two distinct species (Chrysaora quinquecirrha and C. chesapeakei)". PeerJ. 5: e3863. (October 13, 2017). doi:10.7717/peerj.3863
• Martin, J. W.; Gershwin, L. A.; Burnett, J. W.; Cargo, D. G.; Bloom, D. A. "Chrysaora achlyos, a Remarkable New Species of Scyphozoan from the Eastern Pacific". The Biological Bulletin. 193 (1): 8–13. (1997). doi:10.2307/1542731
• Morandini, André C. and Antonio C. Marques. "Revision of the genus Chrysaora Péron & Lesueur, 1810 (Cnidaria: Scyphozoa)". Zootaxa. 2464: 1–97. (2010).