Gelatinous zooplankton

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Jellyfish are slow swimmers, and most species form part of the plankton. Traditionally jellyfish have been viewed as trophic dead ends, minor players in the marine food web, gelatinous organisms with a body plan largely based on water that offers little nutritional value or interest for other organisms apart from a few specialised predators such as the ocean sunfish and the leatherback sea turtle.[7][1] That view has recently been challenged. Jellyfish, and more gelatinous zooplankton in general, which include salps and ctenophores, are very diverse, fragile with no hard parts, difficult to see and monitor, subject to rapid population swings and often live inconveniently far from shore or deep in the ocean. It is difficult for scientists to detect and analyse jellyfish in the guts of predators, since they turn to mush when eaten and are rapidly digested.[7] But jellyfish bloom in vast numbers, and it has been shown they form major components in the diets of tuna, spearfish and swordfish as well as various birds and invertebrates such as octopus, sea cucumbers, crabs and amphipods.[8][1] "Despite their low energy density, the contribution of jellyfish to the energy budgets of predators may be much greater than assumed because of rapid digestion, low capture costs, availability, and selective feeding on the more energy-rich components. Feeding on jellyfish may make marine predators susceptible to ingestion of plastics."[1]

According to a 2017 study, narcomedusae consume the greatest diversity of mesopelagic prey, followed by physonect siphonophores, ctenophores and cephalopods.[9] The importance of the so called "jelly web" is only beginning to be understood, but it seems medusae, ctenophores and siphonophores can be key predators in deep pelagic food webs with ecological impacts similar to predator fish and squid. Traditionally gelatinous predators were thought ineffectual providers of marine trophic pathways, but they appear to have substantial and integral roles in deep pelagic food webs.[9]

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  Gelatinous zooplankton like this narcomedusan can be key predators in deep pelagic food webs
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  Narcomedusa ingesting a salp chain
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  Helmet jellyfish feeding on an armhook squid
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  Trachymedusa with a large red mysid in its gut

Thaliaceans, a class of tunicates, play an important role in the ecology of the sea. Their dense faecal pellets sink to the bottom of the oceans and this may be a major part of the worldwide carbon cycle.[10]

Because of its fragile structure, image acquisition of gelatinous zooplankton requires the assistance of computer visioning. Automated recognition of zooplankton in sample deposits is possible by utilising technologies such as Tikhonov regularization, support vector machines and genetic programming.[11]

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  Deep-red jellyfish, a hydrozoan found in the Arctic Ocean at depths below 1,000 m (3,300 ft).[12]
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  The doliolid is a gelatinous tunicate, found everywhere on continental shelves
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  The salp, another example of a gelatinous tunicate, is often found in the form of a colonial chain

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  The Beroe ctenophore, mouth gaping, preys on other ctenophores
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  Marrus orthocanna, a pelagic colonial siphonophore

• Jelly-falls

• Plankton Chronicles Short documentary films & photos
• Ocean Explorer: Gelatinous zooplankton from the Arctic Ocean
• Jellyfish and other gelatinous zooplankton
• PLANKTON NET: information on all types of plankton including gelatinous zooplankton
• Deep-sea gelatinous zooplankton from The Deep (Nouvian, 2007)