Editing Jellyfish (section)

== Ecology ==
=== Diet ===
Jellyfish are, like other cnidarians, generally carnivorous (or parasitic),<ref name="Brusca296">{{cite book | last=Brusca | first=Richard | title=Invertebrates | publisher=Sinauer Associates | year=2016 | isbn=978-1-60535-375-3 | page=296 |quote=All cnidarians are carnivores (or parasites). Typically, nematocyst-laden feeding tentacles capture animal prey and carry it to the mouth region where it is ingested whole.}}</ref> feeding on planktonic organisms, crustaceans, small fish, fish eggs and larvae, and other jellyfish, ingesting food and voiding undigested waste through the mouth. They hunt passively using their tentacles as drift lines, or sink through the water with their tentacles spread widely; the tentacles, which contain nematocysts to stun or kill the [[Predation|prey]], may then flex to help bring it to the mouth.<ref name=Ruppert /> Their swimming technique also helps them to capture prey; when their bell expands it sucks in water which brings more potential prey within reach of the tentacles.<ref>{{cite web |url=http://www.nbcnews.com/id/44523885/ns/world_news-world_environment/t/bigger-jellyfish-are-inheriting-ocean-study-finds/#.U7MlOmeKCcw |title=Bigger jellyfish inheriting the ocean, study finds |website=msnbc.com |access-date=3 December 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140714121949/http://www.nbcnews.com/id/44523885/ns/world_news-world_environment/t/bigger-jellyfish-are-inheriting-ocean-study-finds/#.U7MlOmeKCcw |archive-date=14 July 2014|date=2011-09-15 }}</ref>

A few species such as ''[[Aglaura hemistoma]]'' are omnivorous, feeding on microplankton which is a mixture of [[zooplankton]] and [[phytoplankton]] (microscopic plants) such as [[dinoflagellate]]s.<ref>{{cite web |last1=Davies |first1=C.H. |last2=Slotwinski |first2=A.S. |title=Australian Marine Zooplankton-Jellyfish, Cladocerans |url=http://www.imas.utas.edu.au/__data/assets/pdf_file/0017/401264/AustralianZooplanktonGuide_JellyfishCladocerans.pdf |publisher=Institute for Marine and Antarctic Studies, University of Tasmania |access-date=12 October 2018}}</ref> Others harbour [[mutualism (biology)|mutualistic]] algae ([[Zooxanthellae]]) in their tissues;<ref name=Ruppert /> the spotted jellyfish (''[[Mastigias papua]]'') is typical of these, deriving part of its nutrition from the products of [[photosynthesis]], and part from captured zooplankton.<ref>{{cite journal |title=Variegated mesocosms as alternatives to shore-based planktonkreisels: notes on the husbandry of jellyfish from marine lakes |journal=Journal of Plankton Research |first=Michael N. |last=Dawson |volume=22 |issue=9 |pages=1673–1682 |year=2000 |doi=10.1093/plankt/22.9.1673|doi-access=free }}</ref><ref name="Dawson2001">{{cite book |url=https://books.google.com/books?id=iQSTgX1UkdUC&pg=PA131 |title=Jellyfish swarms, tourists, and the Christ-child |journal=[[Hydrobiologia]] |publisher=Springer |first1=Mike N. |last1=Dawson |first2=Laura E. |last2=Martin |last3=Lolita K |first3=Lolita K. |last4=Penland |volume=451 |pages=131–144 |date=May 2001 |isbn=978-0-7923-6964-6 |doi=10.1023/A:1011868925383|s2cid=1679552 }}</ref> The [[Cassiopea|upside-down jellyfish]] (''Cassiopea andromeda'') also has a symbiotic relationship with [[microalgae]], but captures tiny animals to supplement their diet. This is done by releasing tiny balls of living cells composed of [[mesoglea]]. These use cilia to drive them through water and stinging cells which stun the prey. The blobs also seems to have digestive capabilities.<ref>{{cite web |url=https://www.discovermagazine.com/planet-earth/venomous-snot-helps-these-jellyfish-sting-without-their-tentacles |title=Venomous Snot Helps These Jellyfish Sting Without Their Tentacles |author=Nemo, Leslie |date=13 February 2020 |work=Discover |access-date=11 July 2021}}</ref>

=== Predation ===
Other species of jellyfish are among the most common and important jellyfish predators. Sea anemones may eat jellyfish that drift into their range. Other predators include [[tuna]]s, sharks, [[swordfish]], sea turtles and penguins.<ref>{{cite news | last=Yin | first=Steph | date=September 29, 2017 | title=Who's Eating Jellyfish? Penguins, That's Who | url=https://www.nytimes.com/2017/09/29/science/penguins-eating-jellyfish.html | newspaper=[[The New York Times]] | archive-url=https://web.archive.org/web/20171001051212/https://www.nytimes.com/2017/09/29/science/penguins-eating-jellyfish.html | archive-date=1 October 2017 | access-date=4 October 2017 }}</ref><ref>{{cite journal |last1=Thiebot |first1=Jean-Baptiste |last2=Arnould |first2=John P. Y. |last3=Gómez-Laich |first3=Agustina |last4=Ito |first4=Kentaro |last5=Kato |first5=Akiko |last6=Mattern |first6=Thomas |last7=Mitamura |first7=Hiromichi |last8=Noda |first8=Takuji |last9=Poupart |first9=Timothée |last10=Quintana |first10=Flavio |last11=Raclot |first11=Thierry |last12=Ropert-Coudert |first12=Yan |last13=Sala |first13=Juan E |last14=Seddon |first14=Philip J. |last15=Sutton |first15=Grace J. |last16=Yoda |first16=Ken |last17=Takahashi |first17=Akinori |display-authors=3|s2cid=90152409 |title=Jellyfish and other gelata as food for four penguin species – insights from predator-borne videos |journal=Frontiers in Ecology and the Environment |year=2017 |doi=10.1002/fee.1529 |volume=15 |issue=8 |pages=437–441|bibcode=2017FrEE...15..437T }}</ref> Jellyfish washed up on the beach are consumed by foxes, other terrestrial mammals and birds.<ref>{{cite book |author=Gershwin, Lisa-Ann |title=Jellyfish: A Natural History |url=https://books.google.com/books?id=PVRFDwAAQBAJ&pg=PA140 |year=2016 |publisher=University of Chicago Press |isbn=978-0-226-28767-6 |page=140}}</ref> In general however, few animals prey on jellyfish; they can broadly be considered to be [[apex predator|top predators]] in the food chain. Once jellyfish have become dominant in an ecosystem, for example through overfishing which removes predators of jellyfish larvae, there may be no obvious way for the previous balance to be restored: they eat fish eggs and juvenile fish, and compete with fish for food, preventing fish stocks from recovering.<ref>{{cite book |author=Gershwin, Lisa-Ann |title=Stung!: On Jellyfish Blooms and the Future of the Ocean |url={{google books |plainurl=y |id=4jEJKlpSVf8C|page=274}} |year=2013 |publisher=University of Chicago Press |isbn=978-0-226-02010-5 |pages=274–|url-status=live |archive-url=https://web.archive.org/web/20160806072537/https://books.google.com/books?id=4jEJKlpSVf8C&pg=PA274 |archive-date=6 August 2016}}</ref>

=== Symbiosis ===
Some small fish are immune to the stings of the jellyfish and live among the tentacles, serving as bait in a fish trap; they are safe from potential predators and are able to share the fish caught by the jellyfish.<ref>{{cite web |url=http://tolweb.org/treehouses/?treehouse_id=4296 |title=The jellyfish |author=colugo7 |year=2006 |website=Tree of Life Web Project |access-date=7 June 2018 |archive-date=12 June 2018 |archive-url=https://web.archive.org/web/20180612140910/http://tolweb.org/treehouses/?treehouse_id=4296 |url-status=dead }}</ref> The [[cannonball jellyfish]] has a symbiotic relationship with ten different species of fish, and with the [[Libinia dubia|longnose spider crab]], which lives inside the bell, sharing the jellyfish's food and nibbling its tissues.<ref>{{cite web |author1=Griffin, DuBose B. |author2=Murphy, Thomas M. |title=Cannonball Jellyfish |publisher=South Carolina Department of Natural Resources |url=http://www.dnr.sc.gov/cwcs/pdf/Cannonballjellyfish.pdf |access-date=7 June 2018 |archive-date=19 January 2008 |archive-url=https://web.archive.org/web/20080119191254/https://www.dnr.sc.gov/cwcs/pdf/Cannonballjellyfish.pdf |url-status=dead }}</ref>

=== Blooms ===
{{Main|Jellyfish bloom}}

[[File:Jellyfish population trends by LME.jpg|thumb|Map of population trends of native and invasive jellyfish.<ref name="brotz">{{cite journal |journal=Hydrobiologia |title=Increasing jellyfish populations: trends in Large Marine Ecosystems |year=2012 |volume=688 |author1=Brotz, Lucas |author2=Cheung, William W. L. |author3=Kleisner, Kristin |author4=Pakhomov, Evgeny |author5=Pauly, Daniel |display-authors=3|doi=10.1007/s10750-012-1039-7 |pages=3–20|doi-access=free }}</ref>
<br />Circles represent data records; larger circles denote higher certainty of findings.<br />
{{legend|#E51A1D|Increase (high certainty)}}{{legend|#F1A341|Increase (low certainty)}}
{{legend|#4DAF4A|Stable/variable}}{{legend|#377CB5|Decrease}}{{legend|#CCCCCA|No data}}]]

Jellyfish form large masses or blooms in certain environmental conditions of [[ocean current]]s, [[nutrient]]s, sunshine, temperature, season, prey availability, reduced predation and [[oxygen]] concentration. Currents collect jellyfish together, especially in years with unusually high populations. Jellyfish can detect [[marine current]]s and swim against the current to congregate in blooms.<ref>{{cite news |last1=Gill |first1=Victoria |title=Jellyfish 'can sense ocean currents' |url=https://www.bbc.co.uk/news/science-environment-30936192 |access-date=26 January 2015 |agency=BBC News |url-status=live |archive-url=https://web.archive.org/web/20150126020804/http://www.bbc.co.uk/news/science-environment-30936192 |archive-date=26 January 2015}}</ref><ref>{{cite journal | last=Hays | first=Graeme C. | title=Ocean currents and marine life | journal=Current Biology | volume=27 | issue=11 | year=2017 | doi=10.1016/j.cub.2017.01.044 | pages=R470–R473|pmid=28586681| doi-access=free | bibcode=2017CBio...27.R470H | hdl=10536/DRO/DU:30100274 | hdl-access=free }}</ref> Jellyfish are better able to survive in nutrient-rich, oxygen-poor water than competitors, and thus can feast on plankton without competition. Jellyfish may also benefit from saltier waters, as saltier waters contain more [[iodine]], which is necessary for polyps to turn into jellyfish. Rising sea temperatures caused by [[climate change]] may also contribute to jellyfish blooms, because many species of jellyfish are able to survive in warmer waters.<ref>{{cite web |last=Shubin |first=Kristie |access-date =19 November 2009 |date =10 December 2008 |title =Anthropogenic Factors Associated with Jellyfish Blooms – Final Draft II |url=http://jrscience.wcp.muohio.edu/fieldcourses08/PapersMarineEcologyArticles/AnthropogenicFactorsAssocA.html |url-status=live |archive-url=https://web.archive.org/web/20100614184618/http://jrscience.wcp.muohio.edu/fieldcourses08/PapersMarineEcologyArticles/AnthropogenicFactorsAssocA.html |publisher= Tropical Field Courses: Western Program: Miami University|archive-date=14 June 2010 }}</ref> Increased nutrients from agricultural or urban [[Runoff (water)|runoff]] with nutrients including nitrogen and phosphorus compounds increase the growth of phytoplankton, causing [[eutrophication]] and [[algal bloom]]s. When the phytoplankton die, they may create [[Dead zone (ecology)|dead zones]], so-called because they are [[Hypoxia (environmental)|hypoxic]] (low in oxygen). This in turn kills fish and other animals, but not jellyfish,<ref>{{cite web|url=https://oceanservice.noaa.gov/facts/deadzone.html|title=What is a dead zone?|publisher=National Ocean Service|access-date=3 October 2018}}</ref> allowing them to bloom.<ref>{{cite web|url=http://blogs.discovermagazine.com/notrocketscience/2011/06/06/jellyfish-shift-ocean-food-webs-by-feeding-bacteria-with-mucus-and-excrement/|title=Jellyfish shift ocean food webs by feeding bacteria with mucus and excrement|last1=Yong|first1=Ed|date=6 June 2011|publisher=Discover Magazine|access-date=3 October 2018|archive-date=6 November 2018|archive-url=https://web.archive.org/web/20181106190642/http://blogs.discovermagazine.com/notrocketscience/2011/06/06/jellyfish-shift-ocean-food-webs-by-feeding-bacteria-with-mucus-and-excrement/|url-status=dead}}</ref><ref name="WaPost">{{Cite web|title=Jellyfish blooms could be sign of ailing seas|url=http://www.eurocbc.org/page727.html|access-date=2023-02-10|website=www.eurocbc.org}}</ref> Jellyfish populations may be expanding globally as a result of land runoff and [[overfishing]] of their [[predation|natural predators]].<ref>{{cite journal|last1=Hays|first1=G. C.|last2=Bastian|first2=T.|last3=Doyle|first3=T. K.|last4=Fossette|first4=S.|last5=Gleiss|first5=A. C.|last6=Gravenor|first6=M. B.|last7=Hobson|first7=V. J.|last8=Humphries|first8=N. E.|last9=Lilley|first9=M. K. S.|last10=Pade|first10=N. G.|last11=Sims|first11=D. W.|display-authors=3|year=2011|title=High activity and Lévy searches: jellyfish can search the water column like fish|url=http://www.swan.ac.uk/bs/turtle/reprints/Hays_etal_PRSB_doi_2011.pdf|url-status=live|journal=Proceedings of the Royal Society B|volume=279|issue=1728|pages=465–473|doi=10.1098/rspb.2011.0978|pmc=3234559|pmid=21752825|archive-url=https://web.archive.org/web/20121225074206/http://www.swan.ac.uk/bs/turtle/reprints/Hays_etal_PRSB_doi_2011.pdf|archive-date=25 December 2012}}</ref><ref>{{cite journal|last1=Pauly|first1=D.|last2=Christensen|first2=V.|last3=Dalsgaard|first3=J.|last4=Froese|first4=R.|last5=Torres Jr|first5=F.|display-authors=3|year=1998|title=Fishing down marine food webs|url=http://umanitoba.ca/institutes/natural_resources/pdf/pauly_fishing_down_marine_food_webs.pdf|url-status=live|journal=Science|volume=279|issue=5352|pages=860–863|bibcode=1998Sci...279..860P|doi=10.1126/science.279.5352.860|pmid=9452385|archive-url=https://web.archive.org/web/20120710184954/http://umanitoba.ca/institutes/natural_resources/pdf/pauly_fishing_down_marine_food_webs.pdf|archive-date=10 July 2012}}</ref> Jellyfish are well placed to benefit from disturbance of marine ecosystems. They reproduce rapidly; they prey upon many species, while few species prey on them; and they feed via touch rather than visually, so they can feed effectively at night and in turbid waters.<ref>{{cite journal|last1=Richardson|first1=A. J.|last2=Bakun|first2=A.|last3=Hays|first3=G. C.|last4=Gibbons|first4=M. J.|year=2009|title=The jellyfish joyride: causes, consequences and management responses to a more gelatinous future|url=http://www.swan.ac.uk/bs/turtle/reprints/Richardson_et_al_2009_TREE_-_The_Jellyfish_Joyride.pdf|journal=Trends in Ecology & Evolution|volume=24|issue=6|pages=312–322|doi=10.1016/j.tree.2009.01.010|pmid=19324452|bibcode=2009TEcoE..24..312R }}{{Dead link|date=February 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite journal|last1=Aksnes|first1=D. L.|last2=Nejstgaard|first2=J.|last3=Sædberg|first3=E.|last4=Sørnes|first4=T.|year=2004|title=Optical control of fish and zooplankton populations|journal=Limnology and Oceanography|volume=49|issue=1|pages=233–238|bibcode=2004LimOc..49..233A|doi=10.4319/lo.2004.49.1.0233|doi-access=free}}</ref> It may be difficult for [[fish stocks]] to re-establish themselves in marine ecosystems once they have become dominated by jellyfish, because jellyfish feed on plankton, which includes [[fish eggs]] and [[fish larvae|larvae]].<ref>{{cite journal|last1=Lynam|first1=C. P.|last2=Gibbons|first2=M. J.|last3=Axelsen|first3=B. E.|last4=Sparks|first4=C. A. J.|last5=Coetzee|first5=J.|last6=Heywood|first6=B. G.|last7=Brierley|first7=A. S.|display-authors=3|year=2006|title=Jellyfish overtake fish in a heavily fished ecosystem|url=https://www.st-andrews.ac.uk/~perg/Lynam_et_al_Current_Biology_16_2006.pdf|url-status=live|journal=Current Biology|volume=16|issue=13|pages=492–493|doi=10.1016/j.cub.2006.06.018|pmid=16824906|s2cid=62793057|archive-url=https://web.archive.org/web/20110323010524/http://www.st-andrews.ac.uk/~perg/Lynam_et_al_Current_Biology_16_2006.pdf|archive-date=23 March 2011|doi-access=free|bibcode=2006CBio...16.R492L }}</ref><ref>{{cite journal|last1=Pauly|first1=D.|last2=Graham|first2=W.|last3=Libralato|first3=S.|last4=Morissette|first4=L.|last5=Palomares|first5=M. L. D.|display-authors=3|year=2009|title=Jellyfish in ecosystems, online databases, and ecosystem models|url=http://filaman.ifm-geomar.de/home/pages/JellyfishInEcosystems_publication.pdf|url-status=dead|journal=Hydrobiologia|volume=616|pages=67–85|doi=10.1007/s10750-008-9583-x|s2cid=12415790|archive-url=https://web.archive.org/web/20130712214856/http://www.uamshealth.com/?id=11935&sid=1|archive-date=12 July 2013}}</ref><ref name="WaPost" />
[[File:Aurelia aurita (auge24eu).jpg|thumb|[[Aurelia aurita|Moon jellyfishes]] can live in northern hemisphere seas,<ref>{{cite journal |last1=Dawson |first1=M. N. |first2=A. |last2=Sen Gupta |first3=M. H. |last3=England |year=2005 |title=Coupled biophysical global ocean model and molecular genetic analyses identify multiple introductions of cryptogenic species |journal=[[Proceedings of the National Academy of Sciences of the United States of America|Proc. Natl. Acad. Sci. USA]] |volume=102 |issue=34 |pages=11968–73 |doi=10.1073/pnas.0503811102 |pmid=16103373 |pmc=1189321|bibcode=2005PNAS..10211968D |doi-access=free }}</ref><ref>{{cite journal |last=Dawson |first=M. N. |year=2003 |title=Macro-morphological variation among cryptic species of the moon jellyfish, ''Aurelia'' (Cnidaria: Scyphozoa) |journal=[[Marine Biology (journal)|Marine Biology]] |volume=143 |issue=2 |pages=369–79 |doi=10.1007/s00227-003-1070-3 |bibcode=2003MarBi.143..369D |s2cid=189820003 }}</ref> such as the [[Baltic Sea]].<ref name="navandi" /><ref name="haaretz" />]]

As suspected at the turn of this century,<ref>{{cite journal |last1=Briand |first1=Frederic |last2=Boero |first2=Ferdinando |title=Gelatinous zooplankton outbreaks - an overview on jellyfish blooms |journal=CIESM Monographs |date=2001 |volume=14 |page=5-17 |url=https://www.researchgate.net/publication/365366204}}</ref><ref>{{cite journal|last1=Mills|first1=C. E.|year=2001|title=Jellyfish blooms: are populations increasing globally in response to changing ocean conditions?|url=http://faculty.washington.edu/cemills/jellyblooms2001.pdf|url-status=live|journal=Hydrobiologia|volume=451|pages=55–68|doi=10.1023/A:1011888006302|s2cid=10927442|archive-url=https://web.archive.org/web/20160303171345/http://faculty.washington.edu/cemills/jellyblooms2001.pdf|archive-date=3 March 2016}}</ref> jellyfish blooms are increasing in frequency. Between 2013 and 2020 the [[Mediterranean Science Commission]] monitored on a weekly basis the frequency of such outbreaks in coastal waters from Morocco to the Black Sea, revealing a relatively high frequency of these blooms nearly all year round, with peaks observed from March to July and often again in the autumn. The blooms are caused by different jellyfish species, depending on their localisation within the Basin: one observes a clear dominance of ''[[Pelagia noctiluca]]'' and ''[[Velella velella]]'' outbreaks in the western Mediterranean, of ''[[Rhizostoma pulmo]]'' and ''[[Rhopilema nomadica]]'' outbreaks in the eastern Mediterranean, and of ''[[Aurelia aurita]]'' and ''[[Mnemiopsis leidyi]]'' outbreaks in the Black Sea.<ref>{{Cite web|title=CIESM GIS|url=https://www.ciesm.org/gis/JW/build/JellyBlooms.php|access-date=2023-02-10|website=www.ciesm.org}}</ref>  

Some jellyfish populations that have shown clear increases in the past few decades are [[invasive species]], newly arrived from other habitats: examples include the [[Black Sea]], [[Caspian Sea]], [[Baltic Sea]], central and eastern [[Mediterranean Sea|Mediterranean]], Hawaii, and tropical and subtropical parts of the West Atlantic (including the [[Caribbean Sea|Caribbean]], [[Gulf of Mexico]] and Brazil).<ref name="navandi">{{cite journal |author1=Abed-Navandi, D. |author2=Kikinger, R. |year=2007 |title=First record of the tropical scyphomedusa ''Phyllorhiza punctata'' von Lendenfeld, 1884 (Cnidaria: Rhizostomeae) in the Central Mediterranean Sea |journal=Aquatic Invasions |volume=2 |issue=4 |pages=391–394 |url=http://elnais.ath.hcmr.gr/PDF/Abel_Navanti_Phylorizapunctata.pdf |doi=10.3391/ai.2007.2.4.7 |url-status=live |archive-url=https://web.archive.org/web/20120917090718/http://elnais.ath.hcmr.gr/PDF/Abel_Navanti_Phylorizapunctata.pdf |archive-date=17 September 2012|doi-access=free }}</ref><ref name="haaretz">{{cite news |url=https://www.haaretz.com/1.5065394 |title=World's Most Invasive Jellyfish Spreading Along Israel Coast |author=Rinat, Zafrir |date=15 June 2009 |newspaper=Haaretz |access-date=13 October 2018}}</ref>

Jellyfish blooms can have significant impact on community structure. Some carnivorous jellyfish species prey on zooplankton while others graze on primary producers.<ref>{{Cite journal|last1=Purcell|first1=J.|last2=Arai|first2=M.|date=2001|title=Interactions of pelagic cnidarians and ctenophores with fish: a review|journal=Hydrobiologia|volume=541|pages=27–44|doi=10.1007/978-94-010-0722-1|isbn=978-94-010-3835-5|s2cid=27615539|editor1-last=Purcell|editor1-first=J. E|editor2-last=Graham|editor2-first=W. M|editor3-last=Dumont|editor3-first=H. J}}</ref> 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.<ref>{{Cite journal|last1=Brodeur|first1=Richard D.|last2=Link|first2=Jason S.|last3=Smith|first3=B.E.|last4=Ford|first4=M.D.|last5=Kobayashi|first5=D.R.|last6=Jones|first6=T.T.|display-authors=3|date=2016|title=Ecological and Economic Consequences of Ignoring Jellyfish: A Plea for Increased Monitoring of Ecosystems|journal=Fisheries|volume=41|issue=11|pages=630–637|doi=10.1080/03632415.2016.1232964|bibcode=2016Fish...41..630B }}</ref> Increased grazing on primary producers by jellyfish can also interrupt energy transfer to higher trophic levels.<ref>{{Cite journal|last1=Ruzicka|first1=J.J.|last2=Brodeur|first2=R.D.|last3=Emmett|first3=R.L.|last4=Steele|first4=J.H.|last5=Zamon|first5=J.E.|last6=Morgan|first6=C.A.|last7=Thomas|first7=A.C.|last8=Wainwright|first8=T.C.|display-authors=3|date=2012|title=Interannual variability in the Northern California Current food web structure: changes in energy flow pathways and the role of forage fish, euphausiids, and jellyfish|journal=Progress in Oceanography|volume=102|pages=19–41|doi=10.1016/j.pocean.2012.02.002|bibcode=2012PrOce.102...19R}}</ref>

During blooms, jellyfish significantly alter the nutrient availability in their environment. Blooms require large amounts of available organic nutrients in the water column to grow, limiting availability for other organisms.<ref name="Pitt-2009">{{Cite journal|last1=Pitt|first1=Kylie|last2=Welsh|first2=David|last3=Condon|first3=Robert|date=January 2009|title=Influence of jellyfish blooms on carbon, nitrogen and phosphorus cycling and plankton production|journal=Hydrobiologia|volume=616|pages=133–149|doi=10.1007/s10750-008-9584-9|s2cid=22838905}}</ref> Some jellyfish have a symbiotic relationship with single-celled dinoflagellates, allowing them to assimilate inorganic carbon, phosphorus, and nitrogen creating competition for phytoplankton.<ref name="Pitt-2009" /> Their large biomass makes them an important source of dissolved and particulate organic matter for microbial communities through excretion, mucus production, and decomposition.<ref name="brotz" /><ref>{{Cite journal|last1=Condon|first1=Robert H.|last2=Duarte|first2=Carlos M.|last3=Pitt|first3=Kylie A.|last4=Robinson|first4=Kelly L.|last5=Lucas|first5=Cathy H.|last6=Sutherland|first6=Kelly R.|last7=Mianzan|first7=Hermes W.|last8=Bogeberg|first8=Molly|last9=Purcell|first9=Jennifer E.|last10=Decker|first10=Mary Beth|last11=Uye|first11=Shin-ichi|display-authors=3|date=2013-01-15|title=Recurrent jellyfish blooms are a consequence of global oscillations|journal=Proceedings of the National Academy of Sciences|volume=110|issue=3|pages=1000–1005|doi=10.1073/pnas.1210920110|pmid=23277544|pmc=3549082|bibcode=2013PNAS..110.1000C|doi-access=free}}</ref> The microbes break down the organic matter into inorganic ammonium and phosphate. However, the low carbon availability shifts the process from production to respiration creating low oxygen areas making the dissolved inorganic nitrogen and phosphorus largely unavailable for primary production.

These blooms have very real impacts on industries. Jellyfish can outcompete fish by utilizing open niches in over-fished fisheries.<ref>{{Cite journal|last1=Lynam|first1=Christopher P.|last2=Gibbons|first2=Mark J.|last3=Axelsen|first3=Bjørn E.|last4=Sparks|first4=Conrad A. J.|last5=Coetzee|first5=Janet|last6=Heywood|first6=Benjamin G.|last7=Brierley|first7=Andrew S.|display-authors=3|date=2006-07-11|title=Jellyfish overtake fish in a heavily fished ecosystem|journal=Current Biology |volume=16|issue=13|pages=R492–493|doi=10.1016/j.cub.2006.06.018|pmid=16824906|s2cid=62793057|doi-access=free|bibcode=2006CBio...16.R492L }}</ref> Catch of jellyfish can strain fishing gear and lead to expenses relating to damaged gear. Power plants have been shut down due to jellyfish blocking the flow of cooling water.<ref>{{Cite journal|last1=Masilamani|first1=J|last2=Jesudoss|first2=K|last3=Kanavillil|first3=Nandakumar|last4=Satpathy|first4=K.K.|last5=Nair|first5=K|last6=Azariah|first6=J|display-authors=3|date=2000-09-10|title=Jellyfish ingress: A threat to the smooth operation of coastal power plants|url=https://www.researchgate.net/publication/236844536|journal=Current Science|volume=79|pages=567–569}}</ref> Blooms have also been harmful for tourism, causing a rise in stings and sometimes the closure of beaches.<ref name="Purcell-2007">{{Cite journal|last1=Purcell|first1=Jennifer E.|last2=Uye|first2=Shin-ichi|last3=Lo|first3=Wen-Tseng|date=2007-11-22|title=Anthropogenic causes of jellyfish blooms and their direct consequences for humans: a review|journal=Marine Ecology Progress Series|volume=350|pages=153–174|doi=10.3354/meps07093|bibcode=2007MEPS..350..153P|doi-access=free}}</ref>

Jellyfish form a component of [[jelly-falls]], events where gelatinous [[zooplankton]] fall to the seafloor, providing food for the [[benthic]] organisms there.<ref>{{Cite journal |last1=Sweetman |first1=Andrew K. |last2=Smith |first2=Craig R. |last3=Dale |first3=Trine |last4=Jones |first4=Daniel O. B. |date=2014 |title=Rapid scavenging of jellyfish carcasses reveals the importance of gelatinous material to deep-sea food webs |journal=Proceedings of the Royal Society B: Biological Sciences |volume=281 |issue=1796 |page=20142210 |doi=10.1098/rspb.2014.2210 |pmid=25320167 |pmc=4213659}}</ref> In temperate and subpolar regions, jelly-falls usually follow immediately after a bloom.<ref>{{Cite journal |last1=Lebrato |first1=Mario |last2=Pahlow |first2=Markus |last3=Oschlies |first3=Andreas |last4=Pitt |first4=Kylie A. |last5=Jones |first5=Daniel O. B. |last6=Molinero |first6=Juan Carlos |last7=Condon |first7=Robert H. |display-authors=3 |date=2011 |title=Depth attenuation of organic matter export associated with jelly falls |journal=Limnology and Oceanography |volume=56 |issue=5 |pages=1917–1928 |doi=10.4319/lo.2011.56.5.1917|url=http://oceanrep.geomar.de/12648/1/1917.pdf |bibcode=2011LimOc..56.1917L |hdl=10072/43275 |s2cid=3693276 |hdl-access=free }}</ref>

=== Habitats ===
[[File:Common jellyfish swimming close to shore.jpg|thumb|upright|A common Scyphozoan jellyfish seen near beaches in the Florida Panhandle]]

Most jellyfish are marine animals, although a few hydromedusae inhabit [[freshwater]]. The best known freshwater example is the [[Cosmopolitan distribution|cosmopolitan]] hydrozoan jellyfish, ''[[Craspedacusta sowerbii]]''. It is less than an inch (2.5&nbsp;cm) in diameter, colorless and does not sting.<ref>{{cite web|url=http://www.nobanis.org/files/factsheets/Craspedacusta_sowerbyi.pdf |title=Invasive Alien Species Fact Sheet: ''Craspedacusta sowerbyi'' |last=Didžiulis |first=Viktoras |archive-url=https://web.archive.org/web/20140517210230/http://www.nobanis.org/files/factsheets/Craspedacusta_sowerbyi.pdf |publisher=NOBANIS |archive-date=17 May 2014 |url-status=live |access-date=16 June 2016 }}</ref> Some jellyfish populations have become restricted to coastal saltwater lakes, such as [[Jellyfish Lake]] in Palau.<ref>{{Cite book |url=https://books.google.com/books?id=iQSTgX1UkdUC&pg=PA131 |title=Jellyfish swarms, tourists, and the Christ-child |journal=[[Hydrobiologia]] |first1=Mike N. |last1=Dawson |first2=Laura E. |last2=Martin |first3=Lolita K. |last3=Penland |volume=451 |pages=131–144 |year=2001 |isbn=978-0-7923-6964-6 |doi=10.1023/A:1011868925383|s2cid=1679552 }}</ref> Jellyfish Lake is a [[marine lake]] where millions of golden jellyfish (''Mastigias'' spp.) migrate horizontally across the lake daily.<ref name="Dawson2001" />

Although most jellyfish live well off the ocean floor and form part of the plankton, a few species are closely associated with the bottom for much of their lives and can be considered [[benthic]]. The upside-down jellyfish in the genus ''[[Cassiopea]]'' typically lie on the bottom of shallow lagoons where they sometimes pulsate gently with their umbrella top facing down. Even some deep-sea species of hydromedusae and scyphomedusae are usually collected on or near the bottom. All of the [[stauromedusae]] are found attached to either seaweed or rocky or other firm material on the bottom.<ref>{{cite journal |last=Mills |first=C. E. |author2=Hirano, Y. M. |title=Stauromedusae |journal=Encyclopedia of Tidepools and Rocky Shores |year=2007 |pages=541–543}}</ref>

Some species explicitly adapt to [[tide|tidal]] flux. In [[Roscoe Bay Provincial Park|Roscoe Bay]], jellyfish ride the current at ebb tide until they hit a [[gravel bar]], and then descend below the current. They remain in still waters until the tide rises, ascending and allowing it to sweep them back into the bay. They also actively avoid fresh water from mountain snowmelt, diving until they find enough salt.<ref name=angier2dec />

=== Parasites ===
Jellyfish are [[host (biology)|hosts]] to a wide variety of parasitic organisms. They act as intermediate hosts of endoparasitic [[helminth]]s, with the infection being transferred to the definitive host fish after [[predation]]. Some [[digenea]]n [[trematode]]s, 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.<ref>{{cite journal|last1=Kondo |first1=Yusuke |last2=Ohtsuka |first2=Susumu |last3=Hirabayashi |first3=Takeshi |last4=Okada |first4=Shoma |last5=Ogawa |first5=Nanako O. |last6=Ohkouchi |first6=Naohiko |last7=Shimazu |first7=Takeshi |last8=Nishikawa |first8=Jun |display-authors=3|title=Seasonal changes in infection with trematode species utilizing jellyfish as hosts: evidence of transmission to definitive host fish via medusivory |journal=Parasite |volume=23 |year=2016 |page=16 |doi=10.1051/parasite/2016016 |url=https://www.parasite-journal.org/articles/parasite/full_html/2016/01/parasite150043/parasite150043.html|pmid=27055563 |pmc=4824873 |url-status=live |archive-url=https://web.archive.org/web/20171104045257/https://www.parasite-journal.org/articles/parasite/full_html/2016/01/parasite150043/parasite150043.html |archive-date=4 November 2017 }}</ref><ref>{{cite web |author=Leung, Tommy |url=http://dailyparasite.blogspot.fr/2016/05/opechona-olssoni.html |title=''Opechona olssoni'' |publisher=Blog: Parasite of the Day |date=26 May 2016|access-date=1 June 2016 |url-status=live |archive-url=https://web.archive.org/web/20160630161725/http://dailyparasite.blogspot.fr/2016/05/opechona-olssoni.html |archive-date=30 June 2016}}</ref>