Editing Abyssal plain (section)

==Biodiversity==
{{ocean habitat topics}}
{{See also|Deep sea communities|Deep sea creature|Deep sea fish|Demersal fish|Benthos}}

Though the plains were once assumed to be vast, [[desert]]-like habitats, research over the past decade or so shows that they teem with a wide variety of [[microbial]] life.<ref name=Scheck2010>{{Cite journal
|author1=Frank Scheckenbach |author2=Klaus Hausmann |author3=Claudia Wylezich |author4=Markus Weitere |author5=Hartmut Arndt |title=Large-scale patterns in biodiversity of microbial eukaryotes from the abyssal sea floor
|journal=Proceedings of the National Academy of Sciences
|volume=107
|issue=1
|pages=115–120
|date=5 January 2010
|pmid=20007768
|pmc=2806785
|doi=10.1073/pnas.0908816106
|bibcode = 2010PNAS..107..115S |doi-access=free }}</ref><ref name=Jorg2007>{{Cite journal
|author1=Jørgensen BB |author2=Boetius A. |title=Feast and famine—microbial life in the deep-sea bed
|journal=Nature Reviews Microbiology 
|volume=5
|issue=10
|pages=770–81
|date = October 2007
|pmid=17828281
|doi=10.1038/nrmicro1745|s2cid=22970703 }}</ref> However, ecosystem structure and function at the deep seafloor have historically been poorly studied because of the size and remoteness of the abyss. Recent [[oceanography|oceanographic]] expeditions conducted by an international group of scientists from the [[Census of Marine Life|Census of Diversity of Abyssal Marine Life]] (CeDAMar) have found an extremely high level of biodiversity on abyssal plains, with up to 2000 species of bacteria, 250 species of [[protozoan]]s, and 500 species of [[invertebrate]]s ([[worm]]s, [[crustacean]]s and [[molluscs]]), typically found at single abyssal sites.<ref name=NOAA>{{Cite web
 |author       = Census of Diversity of Abyssal Marine Life (CeDAMar)
 |url          = http://explore.noaa.gov/abstract-and-bio-census-of-the-diversity-of-abyssal-marine-life-dr-craig-smith
 |title        = Abstract and Bio: Census of the Diversity of Abyssal Marine Life (Dr. Craig Smith)
 |publisher    = Office of Ocean Exploration & Research, National Oceanic and Atmospheric Administration
 |access-date   = 26 June 2010
 |archive-url  = https://web.archive.org/web/20100527223751/http://explore.noaa.gov/abstract-and-bio-census-of-the-diversity-of-abyssal-marine-life-dr-craig-smith/
 |archive-date = 27 May 2010
 |url-status     = dead
}}</ref> New species make up more than 80% of the thousands of seafloor invertebrate species collected at any abyssal station, highlighting our heretofore poor understanding of abyssal diversity and evolution.<ref name=NOAA /><ref name=Glover2002>{{Cite journal
|author=Glover, A.G. |author2=Smith, C.R. |author3=Paterson, G.L.J. |author4=Wilson, G.D.F. |author5=Hawkins, L. |author6=Sheader, M.
|title=Polychaete species diversity in the central Pacific abyss: local and regional patterns and relationships with productivity
|journal=Marine Ecology Progress Series
|volume=240
|pages=157–170
|year=2002
|doi=10.3354/meps240157
|bibcode=2002MEPS..240..157G|doi-access=free
}}</ref><ref name=Martinez2010>{{Cite journal
|author1=Pedro Martínez Arbizu |author2=Horst Kurt Schminke |title=DIVA-1 expedition to the deep sea of the Angola Basin in 2000 and DIVA-1 workshop 2003
|journal=Organisms Diversity & Evolution
|volume=5
|issue=Supplement 1
|pages=1–2
|date=18 February 2005
|doi=10.1016/j.ode.2004.11.009|doi-access=free
}}</ref><ref name=Snelgrove2010>{{Cite journal
|author1=Paul V.R. Snelgrove |author2=Craig R. Smith |title=A riot of species in an environmental calm: the paradox of the species-rich deep-sea floor
|journal=Oceanography and Marine Biology: An Annual Review
|volume=40
|pages=311–342
|year=2002
|id={{INIST|14868518}}}}</ref> Richer biodiversity is associated with areas of known [[phytodetritus]] input and higher organic carbon flux.<ref name=Lambshead2003/>

''[[Abyssobrotula galatheae]]'', a [[species]] of cusk eel in the [[Family (biology)|family]] [[Ophidiidae]], is among the deepest-living species of fish. In 1970, one specimen was [[trawl]]ed from a depth of 8370&nbsp;meters in the [[Puerto Rico Trench]].<ref name="ellis">{{Cite book
|title=Deep Atlantic: Life, Death, and Exploration in the Abyss
|author=Ellis, R.
|publisher=Alfred A. Knopf, Inc
|location=New York
|year=1996
|isbn=978-1-55821-663-1}}</ref><ref name="fishbase">{{FishBase
|genus=Abyssobrotula
|species=galatheae
|date = December 2008|access-date=26 June 2010}}</ref><ref name="nielsen">{{Cite journal
|author=Nielsen, J.G.
|title=The deepest living fish ''Abyssobrotula galatheae'': a new genus and species of oviparous ophidioids (Pisces, Brotulidae)
|journal=Galathea Report
|volume=14
|pages=41–48
|year=1977}}</ref> The animal was dead, however, upon arrival at the surface. In 2008, the [[hadal snailfish]] (''Pseudoliparis amblystomopsis'')<ref name=Pseudoliparis>{{FishBase
|genus=Pseudoliparis
|species=amblystomopsis
|date = March 2009|access-date=26 June 2010}}</ref> was observed and recorded at a depth of 7700&nbsp;meters in the [[Japan Trench]]. In December 2014 a type of snailfish was filmed at a depth of 8145 meters,<ref>{{Cite news |date=2014-12-19 |title=New record for deepest fish |url=https://www.bbc.com/news/science-environment-30541065 |access-date=2024-03-03 |publisher=BBC News |language=en-GB}}</ref> followed in May 2017 by another sailfish filmed at 8178 meters.<ref>{{Cite news |date=Aug 25, 2017 |title=Ghostly fish in Mariana Trench in the Pacific is deepest ever recorded |url=https://www.cbc.ca/news/science/deepest-fish-1.4263003 |access-date=2024-03-02 |work=CBC News}}</ref> These are, to date, the deepest living fish ever recorded.<ref name=Morelle2008/><ref name=Keller2010>{{Cite web
|author=Elizabeth Keller
|year=2010
|url=http://www.extremescience.com/zoom/index.php/life-in-the-deep-ocean/44-deepest-fish
|title=Deepest Fish: Snailfish (''Pseudoliparis amblystomopsis'')
|access-date=26 June 2010| archive-url= https://web.archive.org/web/20100628211038/http://www.extremescience.com/zoom/index.php/life-in-the-deep-ocean/44-deepest-fish| archive-date= 28 June 2010 | url-status= live}}</ref> Other fish of the abyssal zone include the fishes of the family [[Ipnopidae]], which includes the abyssal spiderfish (''[[Bathypterois longipes]]''), tripodfish (''[[Bathypterois grallator]]''), feeler fish (''[[Bathypterois longifilis]]''), and the black lizardfish (''[[Bathysauropsis gracilis]]''). Some members of this family have been recorded from depths of more than 6000&nbsp;meters.<ref name=McGrouther>{{Cite web
|author=Mark McGrouther
|date=22 April 2010
|url=http://australianmuseum.net.au/Spiderfish-Bathypterois-sp/
|title=Spiderfishes, ''Bathypterois spp''
|publisher=Australian Museum
|location=Sydney, NSW
|access-date=26 June 2010}}</ref>

CeDAMar scientists have demonstrated that some abyssal and hadal species have a cosmopolitan distribution. One example of this would be protozoan [[foraminifera]]ns,<ref name=Akimoto>{{Cite journal
|author1=K. Akimoto |author2=M. Hattori |author3=K. Uematsu |author4=C. Kato |title=The deepest living foraminifera, Challenger Deep, Mariana Trench
|journal=Marine Micropaleontology
|volume=42
|issue=1–2
|pages=95–97
|date = May 2001|doi=10.1016/S0377-8398(01)00012-3
|bibcode=2001MarMP..42...95A}}</ref> certain species of which are distributed from the Arctic to the Antarctic. Other faunal groups, such as the [[polychaete]] worms and [[Isopoda|isopod]] crustaceans, appear to be endemic to certain specific plains and basins.<ref name=NOAA /> Many apparently unique [[Taxon|taxa]] of [[nematode]] worms have also been recently discovered on abyssal plains. This suggests that the deep ocean has fostered [[adaptive radiation]]s.<ref name=NOAA /> The taxonomic composition of the nematode fauna in the abyssal Pacific is similar, but not identical to, that of the North Atlantic.<ref name=Lambshead2003/> A list of some of the species that have been discovered or redescribed by CeDAMar can be found [https://web.archive.org/web/20100905112108/http://www.cedamar.org/Species-List here].

Eleven of the 31 described species of ''[[Monoplacophora]]'' (a [[Class (biology)|class]] of [[Mollusca|mollusks]]) live below 2000&nbsp;meters. Of these 11 species, two live exclusively in the hadal zone.<ref name=Schwabe2008>{{Cite book
|author=Enrico Schwab
|title=Bringing light into deep-sea biodiversity (Zootaxa 1866)
|editor1=Pedro Martinez Arbizu |editor2=Saskia Brix |chapter=A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca)
|publisher=Magnolia Press
|location=Auckland, New Zealand
|isbn=978-1-86977-260-4
|year=2008
|pages=205–222
|chapter-url=http://www.mapress.com/zootaxa/2008/f/zt01866p222.pdf
|access-date=26 June 2010}}</ref> The greatest number of monoplacophorans are from the eastern Pacific Ocean along the oceanic trenches. However, no abyssal monoplacophorans have yet been found in the Western Pacific and only one abyssal species has been identified in the Indian Ocean.<ref name=Schwabe2008/> Of the 922 known species of [[chiton]]s (from the ''[[Polyplacophora]]'' class of mollusks), 22 species (2.4%) are reported to live below 2000&nbsp;meters and two of them are restricted to the abyssal plain.<ref name=Schwabe2008/> Although genetic studies are lacking, at least six of these species are thought to be eurybathic (capable of living in a wide range of depths), having been reported as occurring from the [[Littoral zone|sublittoral]] to abyssal depths. A large number of the polyplacophorans from great depths are [[Herbivore|herbivorous]] or [[Xylophagy|xylophagous]], which could explain the difference between the distribution of monoplacophorans and polyplacophorans in the world's oceans.<ref name=Schwabe2008/>

[[Peracarid]] crustaceans, including isopods, are known to form a significant part of the macrobenthic community that is responsible for scavenging on large food falls onto the sea floor.<ref name=CRS2008/><ref name=Debroy2004>{{Cite journal
|author=De Broyer, C. |author2=Nyssen, F. |author3=P. Dauby
|title=The crustacean scavenger guild in Antarctic shelf, bathyal and abyssal communities
|journal=Deep-Sea Research Part II: Topical Studies in Oceanography
|volume=51
|issue=14–16
|pages=1733–1752
|date=July–August 2004
|doi=10.1016/j.dsr2.2004.06.032
|bibcode = 2004DSRII..51.1733D |hdl=2268/34147 |url=http://orbi.ulg.ac.be/handle/2268/34147 |hdl-access=free
}}</ref> In 2000, scientists of the ''Diversity of the deep Atlantic benthos'' (DIVA 1) expedition (cruise M48/1 of the German research vessel RV ''Meteor III'') discovered and collected three new species of the [[Asellota]] [[suborder]] of [[benthic]] isopods from the abyssal plains of the [[Angola Basin]] in the South [[Atlantic Ocean]].<ref>{{harvnb|Mursch|Brenke|Wägele|2008|pp=493–539.}}</ref><ref name=Schmid2002>{{Cite journal
|author=Schmid, C. |author2=Brenke, N. |author3=J.W. Wägele
|s2cid=82476475 |title=On abyssal isopods (Crustacea: Isopoda: Asellota) from the Angola Basin: Eurycope tumidicarpus n.sp. and redescription of Acanthocope galathea Wolff, 1962
|journal=Organisms Diversity & Evolution
|volume=2
|issue=1
|pages=87–88
|year=2002
|doi=10.1078/1439-6092-00030|doi-access=free
}}</ref><ref name=Lowry>{{Cite web
|author=J.K. Lowry
|date=2 October 1999
|url=http://www.crustacea.net/crustace/www/asellota.htm
|title=Crustacea, the Higher Taxa: Description, Identification, and Information Retrieval (Asellota)
|publisher=Australian Museum
|access-date=26 June 2010
|archive-url=https://web.archive.org/web/20090120094611/http://crustacea.net/crustace/www/asellota.htm
|archive-date=20 January 2009
|url-status=dead
}}</ref> In 2003, De Broyer et al. collected some 68,000 peracarid crustaceans from 62 species from baited traps deployed in the [[Weddell Sea]], [[Scotia Sea]], and off the [[South Shetland Islands]]. They found that about 98% of the specimens belonged to the [[Amphipoda|amphipod]] [[Taxonomic rank|superfamily]] ''[[Lysianassidae|Lysianassoidea]]'', and 2% to the isopod family [[Cirolanidae]]. Half of these species were collected from depths of greater than 1000&nbsp;meters.<ref name=Debroy2004/>

In 2005, the [[Japan Agency for Marine-Earth Science and Technology]] (JAMSTEC) remotely operated vehicle, [[Kaikō ROV|KAIKO]], collected sediment core from the Challenger Deep. 432 living specimens of soft-walled foraminifera were identified in the sediment samples.<ref name=Todo2005>{{Cite journal
|author1=Yuko Todo |author2=Hiroshi Kitazato |author3=Jun Hashimoto |author4=Andrew J. Gooday |title=Simple Foraminifera Flourish at the Ocean's Deepest Point
|journal=Science
|volume=307
|issue=5710
|pages=689
|date=4 February 2005
|doi=10.1126/science.1105407
|pmid=15692042|s2cid=20003334 }}</ref><ref name=Roach>{{Cite web
|url=http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html
|archive-url=https://web.archive.org/web/20050205041944/http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html
|url-status=dead
|archive-date=5 February 2005
|title=Life Is Found Thriving at Ocean's Deepest Point
|author=John Roach
|date=3 February 2005
|publisher=National Geographic News
|access-date=26 June 2010}}</ref> Foraminifera are single-celled [[protist]]s that construct shells. There are an estimated 4,000 species of living foraminifera. Out of the 432 organisms collected, the overwhelming majority of the sample consisted of simple, soft-shelled foraminifera, with others representing species of the complex, multi-chambered genera ''[[Leptohalysis]]'' and ''[[Reophax]]''. Overall, 85% of the specimens consisted of soft-shelled [[allogromiids]]. This is unusual compared to samples of sediment-dwelling organisms from other deep-sea environments, where the percentage of organic-walled foraminifera ranges from 5% to 20% of the total. Small organisms with hard calciferous shells have trouble growing at extreme depths because the water at that depth is severely lacking in calcium carbonate.<ref name=Turekian1975>{{Cite journal
|author1=Karl K. Turekian |author2=J. Kirk Cochran |author3=D.P. Kharkar |author4=Robert M. Cerrato |author5=J. Rimas Vaisnys |author6=Howard L. Sanders |author7=J. Frederick Grassle |author8=John A. Allen |title=Slow growth rate of a deep-sea clam determined by 228Ra chronology
|journal=Proceedings of the National Academy of Sciences of the United States of America
|volume=72
|issue=7
|pages=2829–2832
|date = July 1975|doi=10.1073/pnas.72.7.2829
|pmid=1058499
|pmc=432865
|bibcode = 1975PNAS...72.2829T |doi-access=free }}</ref> The giant (5–20&nbsp;cm) foraminifera known as [[Xenophyophorea|xenophyophores]] are only found at depths of 500–10,000 metres, where they can occur in great numbers and greatly increase animal diversity due to their bioturbation and provision of living habitat for small animals.<ref>{{Cite journal|last1=Levin|first1=Lisa A.|last2=Thomas|first2=Cynthia L.|date=December 1988|title=The ecology of xenophyophores (Protista) on eastern Pacific seamounts|url=https://linkinghub.elsevier.com/retrieve/pii/0198014988901227|journal=Deep Sea Research Part A. Oceanographic Research Papers|language=en|volume=35|issue=12|pages=2003–2027|doi=10.1016/0198-0149(88)90122-7|bibcode=1988DSRA...35.2003L|url-access=subscription}}</ref>

While similar lifeforms have been known to exist in shallower oceanic trenches (>7,000&nbsp;m) and on the abyssal plain, the lifeforms discovered in the Challenger Deep may represent independent taxa from those shallower ecosystems. This preponderance of soft-shelled organisms at the Challenger Deep may be a result of selection pressure. Millions of years ago, the Challenger Deep was shallower than it is now. Over the past six to nine million years, as the Challenger Deep grew to its present depth, many of the species present in the sediment of that ancient biosphere were unable to adapt to the increasing water pressure and changing environment. Those species that were able to adapt may have been the ancestors of the organisms currently endemic to the Challenger Deep.<ref name=Todo2005 />

Polychaetes occur throughout the Earth's oceans at all depths, from forms that live as [[plankton]] near the surface, to the deepest oceanic trenches. The robot ocean probe [[Nereus (underwater vehicle)|Nereus]] observed a 2–3&nbsp;cm specimen (still unclassified) of polychaete at the bottom of the Challenger Deep on 31 May 2009.<ref name=Roach /><ref name=Guam>{{Cite web
|author=Bernice Santiago
|date=15 June 2009
|url=http://sciencetech-search.blogspot.com/2009/07/robotic-vehicle-explores-challenger.html
|title=Robotic vehicle explores Challenger Deep
|publisher=Guam Pacific Daily News, Hagatna, Guam
|access-date=26 June 2010}}</ref><ref name=WHOI>{{Cite journal
|author1=Lonny Lippsett |author2=Amy E. Nevala |title=Nereus Soars to the Ocean's Deepest Trench
|journal=Oceanus Magazine
|date=4 June 2009
|url=http://www.whoi.edu/oceanus/viewArticle.do?id=57606
|access-date=26 June 2010
| archive-url= https://web.archive.org/web/20100601172511/http://www.whoi.edu/oceanus/viewArticle.do?id=57606| archive-date= 1 June 2010 | url-status= live}}</ref><ref name=WHOI2>{{Cite web
|author=WHOI Media Relations
|title=Hybrid Remotely Operated Vehicle "Nereus" Reaches Deepest Part of the Ocean
|publisher=[[Woods Hole Oceanographic Institution]]
|date=2 June 2009
|url=http://www.whoi.edu/page.do?pid=24136&tid=282&cid=57586
|access-date=26 June 2010}}</ref> There are more than 10,000 described species of polychaetes; they can be found in nearly every marine environment. Some species live in the coldest ocean temperatures of the hadal zone, while others can be found in the extremely hot waters adjacent to hydrothermal vents.

Within the abyssal and hadal zones, the areas around submarine hydrothermal vents and cold seeps have by far the greatest biomass and biodiversity per unit area. Fueled by the chemicals dissolved in the vent fluids, these areas are often home to large and diverse communities of [[Thermophile|thermophilic]], [[Halophile|halophilic]] and other [[extremophile|extremophilic]] [[prokaryote|prokaryotic]] [[microorganism]]s (such as those of the sulfide-oxidizing genus ''[[Beggiatoa]]''), often arranged in large [[Biofilm|bacterial mats]] near cold seeps. In these locations, chemosynthetic archaea and bacteria typically form the base of the food chain. Although the process of chemosynthesis is entirely microbial, these chemosynthetic microorganisms often support vast ecosystems consisting of complex multicellular organisms through [[symbiosis]].<ref name=MMS3>{{Cite book
 |author1=[[Minerals Management Service]]
 |title=Gulf of Mexico OCS Oil and Gas Lease Sales: 2007–2012. Western Planning Area Sales 204, 207, 210, 215, and 218. Central Planning Area Sales 205, 206, 208, 213, 216, and 222. Draft Environmental Impact Statement. Volume I 
 |editor=Chris C. Oynes 
 |chapter=3: Description of the affected environment 
 |publisher=[[United States Department of the Interior]], [[Minerals Management Service]], Gulf of Mexico OCS Region 
 |location=New Orleans 
 |date=November 2006 
 |pages=3–27–3–31 
 |chapter-url=http://www.gomr.mms.gov/PDFs/2006/2006-062-Vol1.pdf 
 |access-date=20 June 2010 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20090326005638/http://www.gomr.mms.gov/PDFs/2006/2006-062-Vol1.pdf 
 |archive-date=26 March 2009 
}}</ref> These communities are characterized by species such as [[Vesicomyidae|vesicomyid clams]], [[Mytilidae|mytilid]] [[mussel]]s, [[limpet]]s, isopods, [[giant tube worm]]s, [[Alcyonacea|soft corals]], [[eelpout]]s, [[Squat lobster|galatheid crabs]], and [[Alvinocarididae|alvinocarid shrimp]]. The deepest seep community discovered thus far is in the [[Japan Trench]], at a depth of 7700&nbsp;meters.<ref name=Morelle2008/>

Probably the most important ecological characteristic of abyssal ecosystems is energy limitation. Abyssal seafloor communities are considered to be ''food limited'' because [[benthic]] production depends on the input of [[Detritus|detrital]] [[Biotic material|organic material]] produced in the euphotic zone, thousands of meters above.<ref name=Smith2003>Smith, C.R. and Demoupolos, A.W.J. (2003) Ecology of the Pacific ocean floor. In: Ecosystems of the World (Tyler, P.A., ed.), pp. 179–218, Elsevier</ref> Most of the organic flux arrives as an [[marine snow|attenuated rain]] of small particles (typically, only 0.5–2% of net primary production in the euphotic zone), which decreases inversely with water depth.<ref name=Buesseler/> The small particle flux can be augmented by the [[whale fall|fall of larger carcasses]] and downslope transport of organic material near continental margins.<ref name=Smith2003 />