Jellyfish blooms can have significant impact on community structure. Some carnivorous jellyfish species prey on zooplankton while others graze on primary producers. [110] Reductions in zooplankton and ichthyoplankton due to a jellyfish bloom can ripple through the trophic levels. High-density jellyfish populations can outcompete other predators and reduce fish recruitment. [111] Increased grazing on primary producers by jellyfish can also interrupt energy transfer to higher trophic levels. [112] Most jellyfish do not have specialized systems for osmoregulation, respiration and circulation, and do not have a central nervous system. Nematocysts, which deliver the sting, are located mostly on the tentacles; true jellyfish also have them around the mouth and stomach. [33] Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis. They have limited control over their movement, but can navigate with the pulsations of the bell-like body; some species are active swimmers most of the time, while others largely drift. [34] Instead, they swallow their prey whole. Once the food is in their stomach, enzymes will break down the materials and absorb the nutrients.

Yong, Ed (6 June 2011). "Jellyfish shift ocean food webs by feeding bacteria with mucus and excrement". Discover Magazine. Archived from the original on 6 November 2018 . Retrieved 3 October 2018. Magma jellyfish - An extremely rare kind of jellyfish made entirely of magma that gets bigger when hit, making them extremely hard to defeat. In the DS version of SpongeBob's Atlantis SquarePantis, they are only seen in the magma stage at the Volcano of Mu. Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are anchored to the seabed by stalks rather than being mobile. The bell can pulsate to provide propulsion for highly efficient locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish have a complex life cycle. The medusa is normally the sexual phase, which produces planula larvae; these then disperse widely and enter a sedentary polyp phase, before reaching sexual maturity. a b Mills, C. E. (8 November 2010). "Ctenophores". University of Washington . Retrieved 28 August 2018. The stinging cells used by jellyfish to subdue their prey can injure humans. Thousands of swimmers worldwide are stung every year, with effects ranging from mild discomfort to serious injury or even death. When conditions are favourable, jellyfish can form vast swarms, which can be responsible for damage to fishing gear by filling fishing nets, and sometimes clog the cooling systems of power and desalination plants which draw their water from the sea.Further information: Bioluminescence and Green fluorescent protein The hydromedusa Aequorea victoria was the source of green fluorescent protein, studied for its role in bioluminescence and later for use as a marker in genetic engineering.

Mills, C. E. (2001). "Jellyfish blooms: are populations increasing globally in response to changing ocean conditions?" (PDF). Hydrobiologia. 451: 55–68. doi: 10.1023/A:1011888006302. S2CID 10927442. Archived (PDF) from the original on 3 March 2016. As a jellyfish drifts through the water, it captures the surrounding planktons in their stingers with ease. CrustaceansJellyfish Fields, a major location in the SpongeBob SquarePants universe, is home to over 10 million jellyfish, according to the episode "Jellyfish Hunter." However, some may drift into Bikini Bottom but are seldom a nuisance to its denizens. Most choose to steer clear of them however, due to the potential health risk they pose due to their ability to sting. Currie, B.; Ho, S.; Alderslade, P. (1993). "Box-jellyfish, Coca-Cola and old wine". Medical Journal of Australia. 158 (12): 868. doi: 10.5694/j.1326-5377.1993.tb137688.x. PMID 8100984. S2CID 19857333. Jellyfish play an essential role in the ocean’s food chain. They consume a variety of smaller organisms, including microscopic plankton, various crustaceans, and even other jellyfish. Omori, Makoto; Kitamura, Minoru (2004). "Taxonomic review of three Japanese species of edible jellyfish (Scyphozoa: Rhizostomeae)" (PDF). Plankton Biology and Ecology. 51 (1): 36–51. Archived (PDF) from the original on 23 March 2012. Jellyfish are hosts to a wide variety of parasitic organisms. They act as intermediate hosts of endoparasitic helminths, with the infection being transferred to the definitive host fish after predation. Some digenean trematodes, especially species in the family Lepocreadiidae, use jellyfish as their second intermediate hosts. Fish become infected by the trematodes when they feed on infected jellyfish. [123] [124] Relation to humans Global harvest of jellyfish in thousands of tonnes as reported by the FAO [125] Fisheries