Nightlight jellyfish

Pelagia noctiluca

ORDER

Semaeostomeae

FAMILY

Pelagiidae

TAXONOMY

Pelagia noctiluca Forskal, 1775, Mediterranean Sea.

Lappet Pelagia

I Aurelia aurita I Pelagia noctiluca

OTHER COMMON NAMES English: Mauve baubler.

PHYSICAL CHARACTERISTICS

The swimming bell usually is less than 3.5 in (9 cm) in diameter. It has a bumpy surface from clusters of stinging cells, which impart a purple or yellowish color to the translucent bell. There are four elongate oral arms and eight long tentacles that alternate with eight rhopalia in the clefts between lappets. There is no polyp stage.

DISTRIBUTION

The medusa is found in tropical to warm temperate Atlantic and Pacific waters and in the Mediterranean Sea. They are present throughout the year in warm waters.

HABITAT

They are found in surface waters of the open ocean, but sometimes can be advected into shallow coastal waters.

BEHAVIOR

This species is unusual among semaeostome scyphomedusae in being bioluminescent. Medusae emit a blue-green light when they are touched or injured. Mucus released from the damaged area continues to glow. The bioluminescence is believed to serve a protective function. Medusae look like glowing balls at night in a boat's wake.

FEEDING ECOLOGY AND DIET

This species has a diverse diet that includes all types of zooplankton, such as crustaceans, mollusk larvae, chaetognaths, pelagic tunicates (larvaceans, salps, and doliolids), siphono-phores, hydromedusae, ctenophores, and fish eggs and larvae. It feeds in the same manner as other semaeostome scyphome-

dusae. Populations of medusae may require a 5-8% diet of zooplankton daily to balance their metabolism.

REPRODUCTIVE BIOLOGY

This species is unusual among semaeostome scyphomedusae in lacking a polyp stage. The larvae develop directly into ephyrae, without ever settling on the bottom. Medusae reproduce throughout the year in tropical waters.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

The nightlight jellyfish periodically develops large populations in the Mediterranean Sea. The medusae can become concentrated near the shore in crowded tourist areas. They have a painful sting, which can cause a severe reaction and has led to two international scientific conferences on jellyfish blooms in the Mediterranean Sea. Dramatic fluctuations in their abundance in the Mediterranean is linked to 12-year climate cycles. ♦

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