Editing Pelagic zone

{{Short description|Water column of the open ocean}}
{{Redirect-multi|2|Pelagic|Open sea|the writer|Vasa Pelagić|the marketplace|OpenSea|ocean not controlled by any sovereign territory, also called the "high seas"|International waters}}
{{Use dmy dates|date=August 2020}}
[[File:Pelagiczone.svg|thumb| {{center|Layers of the pelagic zone (scaled)}}]]
{{ocean habitat topics}}

The '''pelagic zone''' consists of the [[water column]] of the '''open ocean''' and can be further divided into regions by [[Depth (coordinate)|depth]]. The word ''pelagic'' is derived {{etymology|grc|''{{wikt-lang|grc|πέλαγος}}'' ({{grc-transl|πέλαγος}})|open sea}}.<ref>{{OEtymD|pelagic  |access-date=2020-02-17}}</ref> The pelagic zone can be thought of as an imaginary [[cylinder]] or water column between the [[photic zone|surface of the sea]] and the [[seabed|bottom]].

Conditions in the water column change with depth: pressure increases; temperature and light decrease; salinity, oxygen, micronutrients (such as iron, magnesium and calcium) all change. In a manner analogous to [[Atmosphere of Earth#Stratification|stratification in the Earth's atmosphere]], the water column can be divided vertically into up to five different layers (illustrated in the diagram), with the number of layers depending on the depth of the water.

[[Marine life]] is affected by [[bathymetry]] (underwater topography) such as the seafloor, shoreline, or a submarine [[seamount]], as well as by proximity to the boundary between the ocean and the atmosphere at the ocean surface, which brings light for photosynthesis, predation from above, and wind stirring up waves and setting currents in motion. The pelagic zone refers to the open, free waters away from the shore, where marine life can swim freely in any direction unhindered by [[topography|topographical]] constraints.

The [[oceanic zone]] is the deep open ocean beyond the [[continental shelf]], which contrasts with the inshore waters near the [[coast]], such as in [[estuary|estuaries]] or on the continental shelf. Waters in the oceanic zone plunge to the depths of the [[abyssal zone|abyssopelagic]] and further to the [[hadal zone|hadopelagic]]. Coastal waters are generally the relatively shallow epipelagic. Altogether, the pelagic zone occupies {{convert|1.33|e9km3|e6cumi|abbr=unit}}, with a mean depth of {{cvt|3.68|km|mi}} and maximum depth of {{cvt|11|km|mi}}.<ref>{{cite journal |last1=Costello |first1=Mark John |last2=Cheung |first2=Alan |last3=De Hauwere |first3=Nathalie |year=2010 |title=Surface Area and the Seabed Area, Volume, Depth, Slope, and Topographic Variation for the World's Seas, Oceans, and Countries |journal=Environmental Science & Technology |doi=10.1021/es1012752 |pmid=21033734 |bibcode=2010EnST...44.8821C |volume=44 |issue=23 |pages=8821–8}}</ref><ref>{{cite journal |last1=Charette |first1=Matthew |last2=Smith |first2=Walter |year=2010 |title=The Volume of Earth's Ocean |journal=Oceanography  |hdl=1912/3862 |doi=10.5670/oceanog.2010.51 |volume=23 |issue=2 |pages=112–4|doi-access=free |bibcode=2010Ocgpy..23b.112C |hdl-access=free }}</ref><ref>[http://www.ouramazingplanet.com/oceans-depth-and-volume-revealed-0206/# Ocean's Depth and Volume Revealed] {{Webarchive|url=https://web.archive.org/web/20110823051211/http://www.ouramazingplanet.com/oceans-depth-and-volume-revealed-0206/ |date=23 August 2011 }} ''OurAmazingPlanet'', 19 May 2010.</ref> Pelagic life decreases as depth increases. 

The pelagic zone contrasts with the [[benthic zone|benthic]] and [[demersal zone|demersal]] zones at the bottom of the sea. The benthic zone is the ecological region at the very bottom, including the sediment surface and some subsurface layers. Marine organisms such as [[clam]]s and [[crab]]s living in this zone are called [[benthos]]. Just above the benthic zone is the demersal zone. [[Demersal fish]] can be divided into [[demersal fish#Benthic fish|benthic fish]], which are denser than water and rest on the bottom, and [[demersal fish#Benthopelagic fish|benthopelagic fish]], which swim just above the bottom. Demersal fish are also known as [[bottom feeder]]s and [[groundfish]].

==Depth and layers==
The pelagic zone is subdivided into five vertical regions. From the top down, these are:

===Epipelagic (sunlight)===
{{See also|Photic zone|Epipelagic fish}}
{{Hatnote|From the surface ([[sea level|MSL]]) down to around {{cvt|200|m|ft}}}}

The illuminated zone at the surface of the sea with sufficient light for photosynthesis. Nearly all [[primary production]] in the ocean occurs here, and marine life is concentrated in this zone, including [[plankton]], [[Sargassum|floating seaweed]], [[jellyfish]], [[tuna]], many [[shark]]s and [[dolphin]]s.{{Citation needed|date=January 2021}}

===Mesopelagic (twilight)===
{{See also|Mesopelagic zone|Pelagic fish#Mesopelagic fish}}
{{Hatnote|From {{cvt|200|m|ft}} down to around {{cvt|1000|m|ft}}}}

The most abundant organisms thriving into the mesopelagic zone are [[heterotrophic]] bacteria.<ref>{{cite journal |last1=Mazuecos |first1=E. |last2=Arístegui |first2=J. |last3=Vázquez-Domínguez |first3=E. |last4=Ortega-Retuerta |first4=E. |last5=Gasol |first5=J.M. |last6=Reche |first6=I. |year=2012 |title=Temperature control of microbial respiration and growth efficiency in the mesopelagic zone of the South Atlantic and Indian Oceans. |journal=Deep Sea Research Part I: Oceanographic Research Papers |doi=10.3354/ame01583 |volume=95 |pages=131–138|doi-access=free |hdl=10261/95626 |hdl-access=free }}</ref> Creatures living in this zone include [[swordfish]], [[squid]], [[Anarhichadidae|wolffish]] and some species of [[cuttlefish]]. Many organisms living here are [[bioluminescence|bioluminescent]].<ref name="marinebio.com">[https://web.archive.org/web/20100410222157/http://www.marinebio.com/Oceans/open-ocean.asp The Open Ocean - MarineBio.org]</ref> Some mesopelagic creatures rise to the epipelagic zone at night to feed.<ref name="marinebio.com"/>

===Bathypelagic (midnight)===
{{See also|Bathyal zone|Pelagic fish#Bathypelagic fish}}
{{Hatnote|From {{cvt|1000|m|ft}} down to around {{cvt|4000|m|ft}}}}

The name stems {{ety|grc|[[wikt:βαθύς|βαθύς]]|deep}}. The ocean is pitch black at this depth apart from occasional [[bioluminescence|bioluminescent]] organisms, such as [[anglerfish]]. No plants live here. Most creatures survive on [[detritus]] known as "[[marine snow]]" falling from the zones above or, like the [[marine hatchetfish]], by preying on other inhabitants of this zone. Other examples of this zone's inhabitants are [[giant squid]], smaller [[squid]], [[viperfish]], [[Saccopharynx|gulper eel]], and [[dumbo octopus]].

===Abyssopelagic (abyssal zone)===
{{Main|Abyssal zone}}
{{Hatnote|From around {{cvt|4000|m|ft}} down to above the [[ocean floor]]}}

The name is derived {{ety|grc|[[wikt:ἄβυσσος|ἄβυσσος]]|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; [[echinoderm]]s including the [[basket star]], swimming cucumber, and the [[Scotoplanes|sea pig]]; and marine arthropods including the [[sea spider]]. Many species at these depths are transparent and eyeless.<ref name="marinebio.com"/>

===Hadopelagic (hadal zone)===
{{Main|Hadal zone}}

The name is derived from the realm of [[Hades]], the [[Greek underworld]]. This is the deepest part of the ocean at more than {{cvt|6000|m|ft}} or {{cvt|6500|m|ft}}, depending on authority. Such depths are generally located in [[ocean trench|trenches]].{{Citation needed|date=January 2021}}

==Pelagic ecosystem==
The pelagic ecosystem is based on [[phytoplankton]]. Phytoplankton manufacture their own food using a process of [[photosynthesis]]. Because they need sunlight, they inhabit the upper, sunlit epipelagic zone, which includes the coastal or [[neritic zone]]. 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.<ref>Walker P and Wood E (2005) [https://books.google.com/books?id=O0GpAZsmrVAC&q=intitle:The+intitle:Open+intitle:Ocean ''The Open Ocean''] (volume in a series called ''Life in the sea''), Infobase Publishing, {{ISBN|978-0-8160-5705-4}}.</ref>

===Pelagic invertebrates===
Some examples of pelagic invertebrates include [[krill]], [[copepod]]s, [[jellyfish]], [[Decapodiformes|decapod]] [[larvae]], [[hyperiid]] [[amphipod]]s, [[rotifer]]s and [[cladocera]]ns.

[[Thorson's rule]] states that [[benthic]] [[marine invertebrates]] 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 [[lecithotrophic]] (yolk-feeding) eggs and larger offspring.<ref name="Thorson">{{cite book |editor1-first=J.W. |editor1-last=Hedgpeth |last1=Thorson |first1=G |year=1957 |chapter=Bottom communities (sublittoral or shallow shelf) |title=Treatise on Marine Ecology and Palaeoecology |publisher=Geological Society of America |pages=461–534}}</ref><ref name="Mileikovsky">{{cite journal |last1=Mileikovsky |first1=S. A. |year=1971 |title=Types of larval development in marine bottom invertebrates, their distribution and ecological significance: a re-evaluation |journal=Marine Biology |doi=10.1007/BF00352809 |volume=10 |issue=3 |pages=193–213|bibcode=1971MarBi..10..193M |s2cid=84623588 }}</ref>

===Pelagic fish===
{{Main|Pelagic fish}}

'''Pelagic fish''' live in the [[water column]] 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 [[coral reef fish]].<ref name="Lal8">{{cite book |last1=Lal |first1=Brij V. |author-link1=Brij Lal (historian) |last2=Fortune |first2=Kate |date=January 2000 |title=The Pacific Islands: An Encyclopedia |publisher=University of Hawaii Press |isbn=978-0-8248-2265-1 |page=8 |url=https://books.google.com/books?id=T5pPpJl8E5wC&pg=PA8}}</ref>

Pelagic fish are often [[fish migration|migratory]] [[forage fish]], which feed on [[plankton]], and the larger [[predatory fish]] that follow and feed on the forage fish. Examples of migratory forage fish are [[herring]], [[anchovy|anchovies]], [[capelin]], and [[menhaden]]. Examples of larger pelagic fish which [[predation|prey]] on the forage fish are [[billfish]], [[tuna]], and oceanic [[shark]]s.{{Citation needed|date=January 2021}}

===Pelagic reptiles===
[[File:Diomedea exulans in flight - SE Tasmania.jpg|thumb|right| The pelagic [[wandering albatross]] (''Diomedea exulans'') ranges over huge areas of ocean and can circle the globe.]]

''[[Yellow-bellied sea snake|Hydrophis platurus]]'', the yellow-bellied sea snake, is the only one of the 65 species of [[Hydrophiinae|marine snake]]s 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.{{Citation needed|date=January 2021}}

Many species of [[sea turtle]]s spend the first years of their lives in the pelagic zone, moving closer to shore as they reach maturity.{{Citation needed|date=January 2021}}

===Pelagic birds===
{{See also|Seabird}}

'''Pelagic birds''', also called ''oceanic birds'' or [[seabird]]s, live on open seas and oceans rather than inland or around more restricted waters such as rivers and lakes. Pelagic birds feed on planktonic [[crustacean]]s, [[squid]] and [[forage fish]]. Examples are the [[Atlantic puffin]], [[macaroni penguin]]s, [[sooty tern]]s, [[shearwater]]s, and [[Procellariiformes]] such as the [[albatross]], [[Procellariidae]] and [[petrel]]s.{{Citation needed|date=January 2021}}

{{aquatic layer topics}}
[[File:Representative ocean animal life.jpg|thumb|upright=2|left| Some representative ocean animals (not drawn to scale) within their approximate depth-defined ecological habitats. [[Marine microorganisms]] also exist on the surfaces and within the tissues and organs of the diverse life inhabiting the ocean, across all ocean habitats. The animals rooted to or living on the ocean floor are not pelagic but are [[benthic]] animals.<ref name=Apprill2017>Apprill, A. (2017)"Marine animal microbiomes: toward understanding host–microbiome interactions in a changing ocean". ''Frontiers in Marine Science'', '''4''': 222. {{doi|10.3389/fmars.2017.00222}}. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

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==References==
{{Reflist}}

==Further reading==
* Ryan, Paddy [https://web.archive.org/web/20080619124248/http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/DeepSeaCreatures/en "Deep-sea creatures"] ''Te Ara – the Encyclopedia of New Zealand'', updated 21 September 2007
* [https://www.britannica.com/EBchecked/topic/449062/pelagic-zone "Pelagic-zone (oceanography)"] Encyclopædia Britannica Online. 21 March 2009.
* Grantham HS, Game ET, Lombard AT, et al. (2011) [http://dx.plos.org/10.1371/journal.pone.0016552 "Accommodating Dynamic Oceanographic Processes and Pelagic Biodiversity in Marine Conservation Planning"] ''[[PLOS One]]'' '''6'''(2): e16552. {{doi|10.1371/journal.pone.0016552}}.
* {{cite book |last1=Wrobel |first1=David |last2=Mills |first2=Claudia |date=2003 |orig-year=1998 |title=Pacific Coast Pelagic Invertebrates: A Guide to the Common Gelatinous Animals |publisher=Sea Challengers and Monterey Bay Aquarium |isbn=0-930118-23-5 |url-access=registration |url=https://archive.org/details/pacificcoastpela00wrob}}

{{physical oceanography|expanded=other}}
{{aquatic ecosystem topics|expanded=none}}
{{Biomes}}
{{Authority control}}

[[Category:Aquatic biomes]]
[[Category:Fisheries science]]
[[Category:Oceanographical terminology]]
[[Category:Oceanography]]