Jelly-falls are marine

carbon cycling The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major component ...

events whereby

gelatinous zooplankton Gelatinous zooplankton are fragile animals that live in the water column in the ocean. Their delicate bodies have no hard parts and are easily damaged or destroyed. Gelatinous zooplankton are often transparent. All jellyfish are gelatinous zoopla ...

, primarily

cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...

ns, sink to the seafloor and enhance carbon and nitrogen fluxes via rapidly sinking

particulate organic matter Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 to 2 millimeters. Particulate organic carbon (POC) is ...

. These events provide nutrition to

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

megafauna In terrestrial zoology, the megafauna (from Greek μέγας ''megas'' "large" and New Latin ''fauna'' "animal life") comprises the large or giant animals of an area, habitat, or geological period, extinct and/or extant. The most common threshold ...

and

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. Jelly-falls have been implicated as a major “gelatinous pathway” for the sequestration of labile biogenic carbon through the biological pump. These events are common in protected areas with high levels of primary production and water quality suitable to support cnidarian species. These areas include

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

and several studies have been conducted in

fjords of Norway This list of Norwegian fjords shows many of the fjords in Norway. In total, there are about 1,190 fjords in Norway and the Svalbard islands. The sortable list includes the lengths and locations of those fjords. Fjords See also * List of gla ...

Initiation

Jelly-falls are primarily made up of the decaying corpses of

Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...

and Thaliacea (

Pyrosomida Pyrosomes, genus ''Pyrosoma'', are free-floating colonial tunicates that usually live in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or cone-shaped colonies up to long, ...

Doliolida The Doliolida are an order of small marine animals of the subphylum Tunicata. They are in the class Thaliacea, which also includes the salps and pyrosomes. The doliolid body is small, typically 1–2 mm long, and barrel-shaped; it featu ...

, and

Salp A salp (plural salps, also known colloquially as “sea grape”) or salpa (plural salpae or salpas) is a barrel-shaped, planktic tunicate. It moves by contracting, thereby pumping water through its gelatinous body, one of the most efficient ...

ida). Several circumstances can trigger the death of gelatinous organisms which would cause them to sink. These include high levels of primary production that can clog the feeding apparatuses of the organisms, a sudden temperature change, when an old bloom runs out of food, when predators damage the bodies of the jellies, and

parasitism Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...

. In general, however, jelly-falls are linked to jelly-blooms and primary production, with over 75% of the jelly falls in subpolar and temperate regions occurring after spring blooms, and over 25% of the jelly-falls in the tropics occurring after upwelling events. With global climates shifting towards creating warmer and more acidic oceans, conditions not favored by non-resilient species, jellies are likely to grow in population sizes. Eutrophic areas and dead zones can become jelly hot spots with substantial blooms. As the climate changes and ocean waters warm, jelly blooms become more prolific and the transport of

jelly-carbon Gelatinous zooplankton are fragile animals that live in the water column in the ocean. Their delicate bodies have no hard parts and are easily damaged or destroyed. Gelatinous zooplankton are often transparent. All jellyfish are gelatinous zoopla ...

to the lower ocean increases. With a possible slowing of the classic biological pump, the transport of carbon and nutrients to the deep sea through jelly-falls may become more and more important to deep ocean.

Decomposition

The

decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is e ...

process starts after death and can proceed in the water column as the gelatinous organisms are sinking. Decay happens faster in the tropics than in temperate and subpolar waters as a result of warmer temperatures. In the tropics, a jelly-fall may take less than 2 days to decay in warmer, surface water, but as many as 25 days when it is lower than 1000 m deep. However, lone gelatinous organisms may spend less time on the sea floor as one study found that jellies could be decomposed by

scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...

s in the Norwegian deep sea in under two and a half hours. Decomposition of jelly-falls is largely aided by these kinds of

s. In general,

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea ...

s, such as sea stars, have emerged as the primary consumer of jelly-falls, followed by

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s and fish. However, which scavengers find their way to jelly-falls is highly reliant on each ecosystem. For example, in an experiment in the Norwegian deep sea, hagfish were the first scavengers to find the traps of decaying jellies, followed by squat lobsters, and finally decapod shrimp. Photographs taken off the coast of Norway on natural jelly-falls also revealed caridean shrimp feeding on jelly carcasses. With increased populations and blooms becoming more common, with favorable conditions and a lack of other filter feeders in the area to consume

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

, environments with jellies present will have carbon pumps be more primarily supplied with jelly-falls. This could lead to issues of habitats with established biological pumps succumbing to nonequilibrium as the presence of jellies would change the food web as well as changes to the amount of carbon deposited into the sediment. Finally, decomposition is aided by the microbial community. In a case study on the

Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...

, the number of bacteria increased in the presence of jelly-falls, and the bacteria were shown to preferentially use nitrogen released from decaying jelly carcasses while mostly leaving carbon. In a study conducted by Andrew Sweetman in 2016, it was discovered using core samples of the sediment in Norwegian fjords, the presence of jelly-falls significantly impacted the biochemical process of these benthic communities. Bacteria consume jelly carcasses rapidly, removing opportunities of acquiring sustenance for bottoming feeding

macrofauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is ''funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zool ...

, which has impacts traveling up the trophic levels. In addition, with the exclusion of scavengers, jelly-falls develop a white layer of bacteria over the decaying carcasses and emit a black residue over the surrounding area, which is from sulfide. This high level of microbial activity requires a lot of oxygen, which can lead zones around jelly-falls to become hypoxic and inhospitable to larger scavengers.

Research challenges

Researching jelly-falls relies on direct observational data such as video, photography, or benthic trawls. A complication with trawling for jelly-falls is the gelatinous carcass easily falls apart and as a result, opportunistic photography, videography, and chemical analysis have been primary methods of monitoring. This means that jelly-falls are not always observed in the time period in which they exist. Because jelly-falls can be fully processed and degraded within a number of hours by scavengers and the fact that some jelly-falls will not sink below 500 m in tropical and subtropical waters, the importance and prevalence of jelly-falls may be underestimated.

References

{{reflist, 30em Aquatic ecology Biological oceanography Chemical oceanography Biogeochemistry