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Pelagic zone
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<h2 id="depth-and-layers">Depth and layers</h2> <p>The pelagic zone is subdivided into five vertical regions. From the top down, these are: </p> <h3>Epipelagic (sunlight)</h3> <p class="note">See also: <a href="/facts/Photic_zone/pTrzLGG5">Photic zone</a> and <a href="/facts/Epipelagic_fish/v60cue6L">Epipelagic fish</a></p> <p class="note">From the surface (<a href="/facts/Sea_level/mDhuI7Xe">MSL</a>) down to around 200 m (660 ft)</p> <p>The illuminated zone at the surface of the sea with sufficient light for photosynthesis. Nearly all <a href="/facts/Primary_production/14RzcF5E">primary production</a> in the ocean occurs here, and marine life is concentrated in this zone, including <a href="/facts/Plankton/WGo3LU9T">plankton</a>, <a href="/facts/Sargassum/KUhjp73B">floating seaweed</a>, <a href="/facts/Jellyfish/oLmExpvU">jellyfish</a>, <a href="/facts/Tuna/7HtBI9EL">tuna</a>, many <a href="/facts/Shark/rh5Cotvx">sharks</a> and <a href="/facts/Dolphin/NUxUP7Ph">dolphins</a>. </p> <h3>Mesopelagic (twilight)</h3> <p class="note">See also: <a href="/facts/Mesopelagic_zone/C9y5cjVA">Mesopelagic zone</a> and <a href="/facts/Pelagic_fish/v60cue6L">Pelagic fish § Mesopelagic fish</a></p> <p class="note">From 200 m (660 ft) down to around 1,000 m (3,300 ft)</p> <p>The most abundant organisms thriving into the mesopelagic zone are <a href="/facts/Heterotrophic/wtzlgBtz">heterotrophic</a> bacteria.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> Creatures living in this zone include <a href="/facts/Swordfish/yjNzRNBE">swordfish</a>, <a href="/facts/Squid/wFXpcNUf">squid</a>, <a href="/facts/Anarhichadidae/TzSkx5FB">wolffish</a> and some species of <a href="/facts/Cuttlefish/9AwRKA6M">cuttlefish</a>. Many organisms living here are <a href="/facts/Bioluminescence/IlzgyV4E">bioluminescent</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> Some mesopelagic creatures rise to the epipelagic zone at night to feed.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p> <h3>Bathypelagic (midnight)</h3> <p class="note">See also: <a href="/facts/Bathyal_zone/xxkGTQ5b">Bathyal zone</a> and <a href="/facts/Pelagic_fish/v60cue6L">Pelagic fish § Bathypelagic fish</a></p> <p class="note">From 1,000 m (3,300 ft) down to around 4,000 m (13,000 ft)</p> <p>The name stems from <a href="/facts/Ancient_Greek_language/LIK7NlUh">Ancient Greek</a> <i> βαθύς</i> 'deep'. The ocean is pitch black at this depth apart from occasional <a href="/facts/Bioluminescence/IlzgyV4E">bioluminescent</a> organisms, such as <a href="/facts/Anglerfish/oTpyBSjS">anglerfish</a>. No plants live here. Most creatures survive on <a href="/facts/Detritus/8IjhrXA6">detritus</a> known as "<a href="/facts/Marine_snow/mLM6Ea24">marine snow</a>" falling from the zones above or, like the <a href="/facts/Marine_hatchetfish/Wwnlc54t">marine hatchetfish</a>, by preying on other inhabitants of this zone. Other examples of this zone's inhabitants are <a href="/facts/Giant_squid/jNIw5vaP">giant squid</a>, smaller <a href="/facts/Squid/wFXpcNUf">squid</a>, <a href="/facts/Viperfish/HDEqQa0L">viperfish</a>, <a href="/facts/Saccopharynx/Q2Ks9zk4">gulper eel</a>, and <a href="/facts/Dumbo_octopus/JnqETdqD">dumbo octopus</a>. </p> <h3>Abyssopelagic (abyssal zone)</h3> <p class="note">Main article: <a href="/facts/Abyssal_zone/ec5YEkse">Abyssal zone</a></p> <p class="note">From around 4,000 m (13,000 ft) down to above the <a href="/facts/Ocean_floor/VvxuEWJu">ocean floor</a></p> <p>The name is derived from <a href="/facts/Ancient_Greek_language/LIK7NlUh">Ancient Greek</a> <i> ἄβυσσος</i> 'bottomless' – a holdover from times when the deep ocean was believed to be bottomless. Among the very few creatures living in the cold temperatures, high pressures and complete darkness here are several species of squid; <a href="/facts/Echinoderm/j2rd8qwt">echinoderms</a> including the <a href="/facts/Basket_star/1g97KtMg">basket star</a>, swimming cucumber, and the <a href="/facts/Scotoplanes/kyvufMEe">sea pig</a>; and marine arthropods including the <a href="/facts/Sea_spider/QJyn9BqT">sea spider</a>. Many species at these depths are transparent and eyeless.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h3>Hadopelagic (hadal zone)</h3> <p class="note">Main article: <a href="/facts/Hadal_zone/QXaG9bH2">Hadal zone</a></p> <p>The name is derived from the realm of <a href="/facts/Hades/L8jg3utR">Hades</a>, the <a href="/facts/Greek_underworld/3JMV6eMT">Greek underworld</a>. This is the deepest part of the ocean at more than 6,000 m (20,000 ft) or 6,500 m (21,300 ft), depending on authority. Such depths are generally located in <a href="/facts/Ocean_trench/sbp2PRk4">trenches</a>. </p> <h2 id="pelagic-ecosystem">Pelagic ecosystem</h2> <p>The pelagic ecosystem is based on <a href="/facts/Phytoplankton/tK5MUIkA">phytoplankton</a>. Phytoplankton manufacture their own food using a process of <a href="/facts/Photosynthesis/TMV7w693">photosynthesis</a>. Because they need sunlight, they inhabit the upper, sunlit epipelagic zone, which includes the coastal or <a href="/facts/Neritic_zone/7SW3Ekar">neritic zone</a>. Biodiversity diminishes markedly in the deeper zones below the epipelagic zone as dissolved oxygen diminishes, water pressure increases, temperatures become colder, food sources become scarce, and light diminishes and finally disappears.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h3>Pelagic invertebrates</h3> <p>Some examples of pelagic invertebrates include <a href="/facts/Krill/q11notjt">krill</a>, <a href="/facts/Copepod/TkVLaj0c">copepods</a>, <a href="/facts/Jellyfish/oLmExpvU">jellyfish</a>, <a href="/facts/Decapodiformes/wFXpcNUf">decapod</a> <a href="/facts/Larvae/GKo2FIew">larvae</a>, <a href="/facts/Hyperiid/wLeRHpX4">hyperiid</a> <a href="/facts/Amphipod/cCNathWY">amphipods</a>, <a href="/facts/Rotifer/Gy8DKrFd">rotifers</a> and <a href="/facts/Cladocera/14UTSsAo">cladocerans</a>. </p><p><a href="/facts/Thorson%27s_rule/HyhwBEJl">Thorson's rule</a> states that <a href="/facts/Benthic/N3lM6P7I">benthic</a> <a href="/facts/Marine_invertebrates/Dt72Kb7s">marine invertebrates</a> at low latitudes tend to produce large numbers of eggs developing to widely dispersing pelagic larvae, whereas at high latitudes such organisms tend to produce fewer and larger <a href="/facts/Lecithotrophic/oSgSIVHY">lecithotrophic</a> (yolk-feeding) eggs and larger offspring.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a><a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p> <h3>Pelagic fish</h3> <p class="note">Main article: <a href="/facts/Pelagic_fish/v60cue6L">Pelagic fish</a></p> <p>Pelagic fish live in the <a href="/facts/Water_column/RNQbAVJj">water column</a> of coastal, ocean, and lake waters, but not on or near the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and <a href="/facts/Coral_reef_fish/Rl5lHT6c">coral reef fish</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p><p>Pelagic fish are often <a href="/facts/Fish_migration/obNpLAUD">migratory</a> <a href="/facts/Forage_fish/RJUKYJPb">forage fish</a>, which feed on <a href="/facts/Plankton/WGo3LU9T">plankton</a>, and the larger <a href="/facts/Predatory_fish/WXX1rbDj">predatory fish</a> that follow and feed on the forage fish. Examples of migratory forage fish are <a href="/facts/Herring/QH12ADpV">herring</a>, <a href="/facts/Anchovy/b1HycvUw">anchovies</a>, <a href="/facts/Capelin/KThTIBrf">capelin</a>, and <a href="/facts/Menhaden/tT00eIDH">menhaden</a>. Examples of larger pelagic fish which <a href="/facts/Predation/JEGdrX3f">prey</a> on the forage fish are <a href="/facts/Billfish/c9zRGIY3">billfish</a>, <a href="/facts/Tuna/7HtBI9EL">tuna</a>, and oceanic <a href="/facts/Shark/rh5Cotvx">sharks</a>. </p> <h3>Pelagic reptiles</h3> <p><i><a href="/facts/Yellow-bellied_sea_snake/VbRJ3B3D">Hydrophis platurus</a></i>, the yellow-bellied sea snake, is the only one of the 65 species of <a href="/facts/Hydrophiinae/GyaAAsGW">marine snakes</a> to spend its entire life in the pelagic zone. It bears live young at sea and is helpless on land. The species sometimes forms aggregations of thousands along slicks in surface waters. The yellow-bellied sea snake is the world's most widely distributed snake species. </p><p>Many species of <a href="/facts/Sea_turtle/74lTgK3I">sea turtles</a> spend the first years of their lives in the pelagic zone, moving closer to shore as they reach maturity. </p> <h3>Pelagic birds</h3> <p class="note">See also: <a href="/facts/Seabird/zmMQPeEU">Seabird</a></p> <p>Pelagic birds, also called <i>oceanic birds</i> or <a href="/facts/Seabird/zmMQPeEU">seabirds</a>, live on open seas and oceans rather than inland or around more restricted waters such as rivers and lakes. Pelagic birds feed on planktonic <a href="/facts/Crustacean/PBobIVJP">crustaceans</a>, <a href="/facts/Squid/wFXpcNUf">squid</a> and <a href="/facts/Forage_fish/RJUKYJPb">forage fish</a>. Examples are the <a href="/facts/Atlantic_puffin/XHR2jEuj">Atlantic puffin</a>, <a href="/facts/Macaroni_penguin/HcQ1pzdN">macaroni penguins</a>, <a href="/facts/Sooty_tern/BEAne6d4">sooty terns</a>, <a href="/facts/Shearwater/RJ9ra1J9">shearwaters</a>, and <a href="/facts/Procellariiformes/XNwpA93h">Procellariiformes</a> such as the <a href="/facts/Albatross/k7RUk0Ef">albatross</a>, <a href="/facts/Procellariidae/j2gLube5">Procellariidae</a> and <a href="/facts/Petrel/dBhuUDUS">petrels</a>. </p> <h2 id="further-reading">Further reading</h2> <ul><li>Ryan, Paddy <a href="https://web.archive.org/web/20080619124248/http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/DeepSeaCreatures/en">"Deep-sea creatures"</a> <i>Te Ara – the Encyclopedia of New Zealand</i>, updated 21 September 2007</li> <li><a href="https://www.britannica.com/EBchecked/topic/449062/pelagic-zone">"Pelagic-zone (oceanography)"</a> Encyclopædia Britannica Online. 21 March 2009.</li> <li>Grantham HS, Game ET, Lombard AT, et al. (2011) <a href="http://dx.plos.org/10.1371/journal.pone.0016552">"Accommodating Dynamic Oceanographic Processes and Pelagic Biodiversity in Marine Conservation Planning"</a> <i><a href="/facts/PLOS_One/fTQQQbTr">PLOS One</a></i> 6(2): e16552. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1371%2Fjournal.pone.0016552">10.1371/journal.pone.0016552</a>.</li> <li>Wrobel, David; Mills, Claudia (2003) [1998]. <a href="https://archive.org/details/pacificcoastpela00wrob"><i>Pacific Coast Pelagic Invertebrates: A Guide to the Common Gelatinous Animals</i></a>. Sea Challengers and Monterey Bay Aquarium. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-930118-23-5.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"pelagic (adj.)". Online Etymology Dictionary. Retrieved 17 February 2020. <a href="https://www.etymonline.com/word/pelagic" target="_blank">https://www.etymonline.com/word/pelagic</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Costello, Mark John; Cheung, Alan; De Hauwere, Nathalie (2010). "Surface Area and the Seabed Area, Volume, Depth, Slope, and Topographic Variation for the World's Seas, Oceans, and Countries". Environmental Science & Technology. 44 (23): 8821–8. Bibcode:2010EnST...44.8821C. doi:10.1021/es1012752. PMID 21033734. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Charette, Matthew; Smith, Walter (2010). "The Volume of Earth's Ocean". Oceanography. 23 (2): 112–4. doi:10.5670/oceanog.2010.51. hdl:1912/3862. <a href="https://doi.org/10.5670%2Foceanog.2010.51" target="_blank">https://doi.org/10.5670%2Foceanog.2010.51</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Ocean's Depth and Volume Revealed Archived 23 August 2011 at the Wayback Machine OurAmazingPlanet, 19 May 2010. <a href="http://www.ouramazingplanet.com/oceans-depth-and-volume-revealed-0206/#" target="_blank">http://www.ouramazingplanet.com/oceans-depth-and-volume-revealed-0206/#</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Mazuecos, E.; Arístegui, J.; Vázquez-Domínguez, E.; Ortega-Retuerta, E.; Gasol, J.M.; Reche, I. (2012). "Temperature control of microbial respiration and growth efficiency in the mesopelagic zone of the South Atlantic and Indian Oceans". Deep Sea Research Part I: Oceanographic Research Papers. 95: 131–138. doi:10.3354/ame01583. hdl:10261/95626. <a href="https://doi.org/10.3354%2Fame01583" target="_blank">https://doi.org/10.3354%2Fame01583</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>The Open Ocean - MarineBio.org <a href="https://web.archive.org/web/20100410222157/http://www.marinebio.com/Oceans/open-ocean.asp" target="_blank">https://web.archive.org/web/20100410222157/http://www.marinebio.com/Oceans/open-ocean.asp</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>The Open Ocean - MarineBio.org <a href="https://web.archive.org/web/20100410222157/http://www.marinebio.com/Oceans/open-ocean.asp" target="_blank">https://web.archive.org/web/20100410222157/http://www.marinebio.com/Oceans/open-ocean.asp</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>The Open Ocean - MarineBio.org <a href="https://web.archive.org/web/20100410222157/http://www.marinebio.com/Oceans/open-ocean.asp" target="_blank">https://web.archive.org/web/20100410222157/http://www.marinebio.com/Oceans/open-ocean.asp</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Walker P and Wood E (2005) The Open Ocean (volume in a series called Life in the sea), Infobase Publishing, ISBN 978-0-8160-5705-4. <a href="https://books.google.com/books?id=O0GpAZsmrVAC&q=intitle:The+intitle:Open+intitle:Ocean" target="_blank">https://books.google.com/books?id=O0GpAZsmrVAC&q=intitle:The+intitle:Open+intitle:Ocean</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Thorson, G (1957). "Bottom communities (sublittoral or shallow shelf)". In Hedgpeth, J.W. (ed.). Treatise on Marine Ecology and Palaeoecology. Geological Society of America. pp. 461–534. <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Mileikovsky, S. A. (1971). "Types of larval development in marine bottom invertebrates, their distribution and ecological significance: a re-evaluation". Marine Biology. 10 (3): 193–213. doi:10.1007/BF00352809. S2CID 84623588. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Lal, Brij V.; Fortune, Kate (January 2000). The Pacific Islands: An Encyclopedia. University of Hawaii Press. p. 8. ISBN 978-0-8248-2265-1. <a href="978-0-8248-2265-1" target="_blank">978-0-8248-2265-1</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> </ol>