Mauve Stinger Pelagia noctiluca
Mauve stinger, Pelagia noctiluca, is a jellyfish in the family Pelagiidae and the only currently recognized species in the genus Pelagia. It is typically known in English as the mauve stinger, but other common names are purple-striped jelly (causing potential confusion with chrysaora colorata), purple stinger, purple people eater, purple jellyfish, luminous jellyfish and night-light jellyfish. Pelagia noctiluca can be described as a marine organism with the ability to glow in the dark (bioluminescence). It is found worldwide in tropical and warm temperate seas, although it is suspected that records outside the North Atlantic region, which includes the Mediterranean sea and Gulf of Mexico represent closely related but currently unrecognized species. A fairly small and variably coloured species, both its tentacles and (unusual among jellyfish) bell are covered in stinging cells. Stinging incidents are common, painful and the symptoms may continue for a considerable time after the encounter, but they are generally not dangerous.

When large numbers of this oceanic species are washed ashore, the local economy can be affected because tourists avoid the beaches and fishers are stung while trying to retrieve their nets, which can be clogged by the jellyfish. Additionally, swarms of Pelagia noctiluca have been recorded wiping out entire fish farms. Because of this, it has become one of the most studied jellyfish species. This jellyfish is best known from the North Atlantic region, ranging from 4th parallel north (just north of Equator) to the North Sea and Atlantic Canada, including the Mediterranean and Gulf of Mexico. The swimming ability of Pelagia noctiluca is limited and as a result large swarms (also known as blooms) of this oceanic species are occasionally carried by the wind or current to inshore areas, sometimes ending up stranded on beaches.

This also means that the species sometimes appears in waters outside its normal temperature preference, with records as far north as the Shetland Islands and the Norwegian deep. It generally occurs at water temperatures between 10 and 27 °C. but below 11 °C. it stops pulsating. It mostly ranges from the surface to a depth of 150 m. but has been recorded to 1,400 m. Pelagia noctiluca partakes in the diel vertical migration, occurring near the surface at night and deeper during the day. Local populations fluctuate greatly and the species may go virtually unrecorded in a region for years, only to suddenly reappear in huge swarms. On occasion, a swarm may cover tens of square kilometers, include millions of Pelagia noctiluca, and reach densities of more than 500 individuals per m3
(extract from Wikipedia)