Diferencia entre revisiones de «Euphausiacea»
Contenido eliminado Contenido añadido
Bibliografía adicional. |
Taxonomía |
||
Línea 1:
{{Ficha de taxón
| name = Kril
| image = Meganyctiphanes norvegica2.jpg
| image_caption = ''[[Meganyctiphanes norvegica]]''
| regnum = [[Animalia]]
Línea 28 ⟶ 27:
}}
Los '''eufausiáceos'''{{refn|El orden Euphausiacea se denomina, según los autores, como «eufausiáceos», como «eufáusidos» o como «eufásidos».|group=n}} ('''Euphausiacea''') son un [[
El kril puede encontrarse en todos los océanos del mundo y está considerado una importante conexión de [[nivel trófico]], casi al final de la [[Cadena trófica|cadena alimenticia]], porque se alimenta de [[fitoplancton]] y, en menor medida, de [[zooplancton]], con un tamaño adecuado para muchos animales más grandes, para los cuales constituye la mayor parte de su dieta. En el [[océano Antártico]], una especie, el [[Euphausia superba|kril antártico]] (''Euphausia superba'')), constituye una [[biomasa]] estimada de alrededor de 379 000 000 de toneladas,<ref>{{cita publicación |nombre=A. |apellido=Atkinson |nombre2=V. |apellido2=Siegel |nombre3=E. A. |apellido3=Pakhomov |nombre4=M. J. |apellido4=Jessopp |nombre5=V. |apellido5=Loeb |título=A re-appraisal of the total biomass and annual production of Antarctic krill |publicación=Deep-Sea Research I |año=2009 |volumen=56 |páginas=727-740 |url=http://www.iced.ac.uk/documents/Atkinson%20et%20al,%20Deep%20Sea%20Research%20I,%202009.pdf |doi=10.1016/j.dsr.2008.12.007}}</ref> lo que la convierte en una de las especies con mayor biomasa del planeta, de la cual más de la mitad es consumida por [[Mysticeti|ballenas barbadas]], [[Phocidae|focas]], [[Spheniscidae|pingüinos]], [[Teuthida|calamares]] y [[Pez|peces]] cada año. La mayoría de las especies de eufausiáceos realizan grandes migraciones verticales diarias, lo que proporciona alimento a los depredadores cerca de la superficie por la noche y en aguas más profundas durante el día.
== Taxonomía ==
Los eufausiáceos (Euphausiacea) son un [[Orden (biología)|orden]] de [[Arthropoda|artrópodos]] incluidos dentro del gran sub[[filo]] [[Crustacea]]. El grupo con más familias y más numeroso de crustáceos, la [[Clase (biología)|clase]] [[Malacostraca]], incluye el superorden [[Eucarida]] que comprende tres órdenes: Euphausiacea (kril), [[Decapoda]] (camarones, cangrejos, langostas) y [[Amphionidacea]].
El orden se divide en dos [[Familia (biología)|familias]]. La más abundante es Euphausiidae, que contiene 10 [[Género (biología)|géneros]] con un total de 86 [[especie]]s;<ref>{{ITIS|id=95500 |taxón=Euphausiidae}}</ref><ref name="Letterio">{{cita publicación |nombre=Letterio |apellido=Guglielmo |nombre2=Antonia |apellido2=Granata |nombre3=Rosanna |apellido3=Guglielmo |título=Orden Euphausiacea |publicación=Ibero Diversidad Entomológica |año=2015 |número=86A |páginas=1-20 |issn=2386-7183 |editorial=Sociedad Entomológica Aragonesa |url=http://sea-entomologia.org/IDE@/revista_86A.pdf}}</ref> de estos, el género ''[[Euphausia]]'' es el mayor, con 31 especies.<ref>{{ITIS|id=95501 |taxón=Euphausia}}</ref><ref>{{Cita web |url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=110671 |título=Euphausiidae Dana, 1852 |nombre=Volker |apellido=Siegel |año=2017 |sitioweb=World Euphausiacea database |editorial=[[Registro Mundial de Especies Marinas]] |fechaacceso=1 de noviembre de 2017}}</ref> La familia menos conocida, Bentheuphausiidae, tiene una sola especie, ''[[Bentheuphausia amblyops]]'', un kril [[Zona batial|batipelágico]] que vive en aguas por debajo de los 1000 m de profundidad y se considera la especie de kril más primitiva que existe.<ref>{{cita publicación |nombre=Edward |apellido=Brinton |título=The distribution of Pacific euphausiids |publicación=Bulletin of the Scripps Institution of Oceanography |volumen=8 |número=2 |páginas=51-270 |año=1962 |url=https://escholarship.org/content/qt6db5n157/qt6db5n157.pdf}}</ref>
Las especies más conocidas, sobre todo por ser objeto de pesca comercial, son el [[Euphausia superba|kril antártico]] (''Euphausia superba''), el [[Euphausia pacifica|kril del Pacífico]] (''Euphausia pacifica'') y el [[Meganyctiphanes norvegica|kril del norte]] (''Meganyctiphanes norvegica'').<ref name="nicol">{{cita publicación |nombre=S. |apellido=Nicol |nombre2=Y. |apellido2=Endo |año=1999 |título=Krill fisheries: Development, management and ecosystem implications |publicación=Aquatic Living Resources |volumen=12 |número=2 |páginas=105-120 |doi=10.1016/S0990-7440(99)80020-5}}</ref>
=== Filogenia ===
{{Cuadro imagen
|título=Propuesta de filogenia de Euphausiacea<ref name="Maas">{{cita publicación |nombre=Andreas |apellido=Maas |nombre2=Dieter |apellido2=Waloszek |año=2001 |título=Larval development of ''Euphausia superba'' Dana, 1852 and a phylogenetic analysis of the Euphausiacea |url=http://biosys-serv.biologie.uni-ulm.de/Downloadfolder/PDFs%20Team/2001_Maas&Waloszek_Euphausia.pdf |publicación=Hydrobiologia |volumen=448 |páginas=143-169 |doi=10.1023/A:1017549321961}}</ref>
|pie=El taxón marcado (♣) posiblemente parafilético debido a ''Nematobrachion''. Los marcados (♦) difieren de Casanova (1984),<ref name="casanova">{{cita publicación |nombre=Bernadette |apellido=Casanova |año=1984 |título=Phylogénie des Euphausiacés (Crustacés Eucarides) |idioma=francés |títulotrad=Phylogeny of the Euphausiacea (Crustacea: Eucarida) |publicación=Bulletin du Muséum National d'Histoire Naturelle |volumen=4 |páginas=1077-1089}}</ref> donde ''Pseudoeuphausia'' es hermano de ''Nyctiphanes'', ''Euphausia'' es hermano de ''Thysanopoda'' y ''Nematobrachion'' es hermano de ''Stylocheiron''.
|contenido=
{{clado| style=font-size:75%;line-height:75%
|label1=Euphausiacea
|1={{clado
|label1=Bentheuphausiidae
|1=''[[Bentheuphausia amblyops|Bentheuphausia]]''
|label2= Euphausiidae
|2={{clado
|1=''[[Thysanopoda]]'' (♣)
|2=''[[Nematobrachion]]'' (♦)
|label3=Euphausiinae
|3={{clado
|1=''[[Northern krill|Meganyctiphanes]]''
|label2=Euphausiini (♦)
|2={{clado
|1=''[[Pseudeuphausia]]''
|2=''[[Euphausia]]''
}}
|label3=Nematoscelini
|3={{clado
|1=''[[Nyctiphanes]]''
|label2=Nematoscelina
|2={{clado
|1=''[[Nematoscelis]]''
|2=''[[Thysanoessa]]''
|3=''[[Tessarabrachion]]''
|4=''[[Stylocheiron]]''
}}
}}
}}
}}
}}
}}
}}
Se cree que el orden Euphausiacea es [[monofilético]] debido a que conserva varias características morfológicas únicas ([[autoapomorfia]]), como branquias filamentosas desnudas y toracópodos delgados,<ref name="casanova03">{{cita publicación |nombre=Bernadette |apellido=Casanova |título=Ordre des Euphausiacea Dana, 1852 |publicación=Crustaceana |volumen=76 |número=9 |año=2003 |páginas=1083-1121 |doi=10.1163/156854003322753439 |jstor=20105650}}</ref> y por estudios moleculares.<ref>{{cita publicación |nombre=M. Eugenia |apellido=D'Amato |nombre2=Gordon W. |apellido2=Harkins |nombre3=Tulio |apellido3=de Oliveira |nombre4=Peter R. |apellido4=Teske |nombre5=Mark J. |apellido5=Gibbons |año=2008 |título=Molecular dating and biogeography of the neritic krill ''Nyctiphanes'' |url=http://www.bioafrica.net/manuscripts/AmatoMarineBiology.pdf |publicación=Marine Biology |volumen=155 |número=2 |páginas=243-247 |doi=10.1007/s00227-008-1005-0}}</ref><ref name="Jarman">{{cita publicación |nombre=Simon N. |apellido=Jarman |año=2001 |título=The evolutionary history of krill inferred from nuclear large subunit rDNA sequence analysis |publicación=Biological Journal of the Linnean Society |volumen=73 |número=2 |páginas=199-212 |doi=10.1111/j.1095-8312.2001.tb01357.x |url=https://academic.oup.com/biolinnean/article-pdf/73/2/199/16718073/j.1095-8312.2001.tb01357.x.pdf}}</ref><ref>{{cita publicación |nombre=Xin |apellido=Shen |nombre2=Haiqing |apellido2=Wang |nombre3=Minxiao |apellido3=Wang |nombre4=Bin |apellido4=Liu |año=2011 |título=The complete mitochondrial genome sequence of ''Euphausia pacifica'' (Malacostraca: Euphausiacea) reveals a novel gene order and unusual tandem repeats |publicación=Genome |volumen=54 |número=11 |páginas=911-922 |doi=10.1139/g11-053 |pmid=22017501}}</ref>
Ha habido muchas propuestas sobre la ubicación del orden Euphausiacea. Desde la primera descripción de ''Thysanopode tricuspide'' realizada por [[Henri Milne-Edwards]] en 1830, la similitud de sus [[Tórax (artrópodos)|toracópodos]] birrámeos había llevado a los zoólogos a agrupar a los eufausiáceos y [[Mysidacea|misidáceos]] (Mysidacea) en el orden Schizopoda, que fue dividido por [[Johan Erik Vesti Boas|Boas]] en 1883 en dos órdenes separados.<ref name="Boas">{{cita publicación |nombre=Johan Erik Vesti |apellido=Boas |año=1883 |título=Studien über die Verwandtschaftsbeziehungen der Malakostraken |idioma=alemán |publicación=Morphologisches Jahrbuch |volumen=8 |páginas=485-579}}</ref> En 1904 [[William Thomas Calman]] clasificó los misidáceos en el superorden [[Peracarida]] y los eufausiáceos en el superorden [[Eucarida]], aunque hasta la década de 1930 se abogó por el orden Schizopoda.<ref name="casanova03"/> Posteriormente también se propuso que el orden Euphausiacea debería agruparse con [[Penaeidae]] (familia de langostinos) en Decapoda en base a sus similitudes de desarrollo, tal como lo consideraron Robert Gurney e Isabella Gordon.<ref name="Gurney">{{cita libro |nombre=Robert |apellido=Gurney |año=1942 |editorial=Ray Society |título=Larvae of Decapod Crustacea |url=https://decapoda.nhm.org/pdfs/12852/12852.pdf}}</ref><ref>{{cita publicación |nombre=Isabella |apellido=Gordon |año=1955 |título=Systematic position of the Euphausiacea |publicación=Nature |volumen=176 |número=4489 |página=934 |doi=10.1038/176934a0 |bibcode=1955Natur.176..934G}}</ref> La razón de este debate es que el kril comparte algunas características morfológicas de los decápodos y otras de los misidáceos.<ref name="casanova03"/>
Los estudios moleculares no hay permitido su agrupación de manera inequívoca, posiblemente debido a la escasez de especies clave escasas como ''Bentheuphausia amblyops'' en Euphausiacea y ''Amphionides reynaudii'' en Eucarida. Un estudio apoya la monofilia de Eucarida (con el orden Mysida basal),<ref name="Spears, T. 2005">{{cita publicación |nombre=Trisha |apellido=Spears |nombre2=Ronald W. |apellido2=DeBry |nombre3=Lawrence G. |apellido3=Abele |nombre4=Katarzyna |apellido4=Chodyl |año=2005 |título=Peracarid monophyly and interordinal phylogeny inferred from nuclear small-subunit ribosomal DNA sequences (Crustacea: Malacostraca: Peracarida) |publicación=Proceedings of the Biological Society of Washington |volumen=118 |número=1 |páginas=117-157 |doi=10.2988/0006-324X(2005)118[117:PMAIPI]2.0.CO;2 |url=http://decapoda.nhm.org/pdfs/10231/10231.pdf}}</ref> otros agrupan Euphausiacea con Mysida (Schizopoda),<ref name="Jarman"/> mientras que otros agrupan Euphausiacea con [[Hoplocarida]].<ref>{{cita publicación |nombre=K. |apellido=Meland |nombre2=E. |apellido2=Willassen |año=2007 |título=The disunity of “Mysidacea” (Crustacea) |publicación=Molecular Phylogenetics and Evolution |volumen=44 |número=3 |páginas=1083-1104 |doi=10.1016/j.ympev.2007.02.009 |pmid=17398121}}</ref>
Ningún [[fósil]] existente puede asignarse inequívocamente a Euphausiacea. Se ha considerado que algunos taxones [[Eumalacostraca|eumalacostráceos]] extintos podrían ser eufausiáceos, como ''Anthracophausia'', ''Crangopsis'' —actualmente asignado a Aeschronectida ([[Hoplocarida]])—<ref name="Maas">{{cita publicación |nombre=Andreas |apellido=Maas |nombre2=Dieter |apellido2=Waloszek |año=2001 |título=Larval development of ''Euphausia superba'' Dana, 1852 and a phylogenetic analysis of the Euphausiacea |url=http://biosys-serv.biologie.uni-ulm.de/Downloadfolder/PDFs%20Team/2001_Maas&Waloszek_Euphausia.pdf |publicación=Hydrobiologia |volumen=448 |páginas=143-169 |doi=10.1023/A:1017549321961}}</ref> o ''Palaeomysis''.<ref name="Schram86">{{cita libro |nombre=Frederick R. |apellido=Schram |año=1986 |título=Crustacea |isbn=0-19-503742-1 |editorial=Oxford University Press}}</ref> Todas las fechas de los procesos de [[especiación]] se estimaron mediante la técnica de [[reloj molecular]], que ubicaron al último ancestro común de la familia de krils Euphausiidae (orden Euphausiacea menos ''Bentheuphausia amblyops'') como que vivió en el [[Cretácico inferior]] hace unos 130 millones de años.<ref name="Jarman"/>
== Distribución ==
{{En desarrollo|Furado}}
<!--
[[Archivo:Krill swarm.jpg|thumb|left|A krill swarm]]
Krill occur worldwide in all oceans, although many individual species have [[endemism|endemic]] or [[neritic]] (''i.e.,'' coastal) distributions. ''[[Bentheuphausia amblyops]]'', a [[Bathyal zone|bathypelagic]] species, has a [[cosmopolitan distribution]] within its deep-sea habitat.<ref>{{cita publicación |author1=J. J. Torres |author2=J. J. Childress |año=1985 |título=Respiration and chemical composition of the bathypelagic euphausiid ''Bentheuphausia amblyops'' |publicación=[[Marine Biology (journal)|Marine Biology]] |volumen=87 |número=3 |páginas=267-272 |doi=10.1007/BF00397804}}</ref>
Species of the genus ''[[Thysanoessa]]'' occur in both [[Atlantic Ocean|Atlantic]] and [[Pacific Ocean|Pacific]] oceans.<ref>{{cite WoRMS |author=Volker Siegel |año=2011 |título=''Thysanoessa'' Brandt, 1851 |id=110679 |fechaacceso=June 18, 2011}}</ref> The Pacific is home to ''[[Euphausia pacifica]]''. Northern krill occur across the Atlantic from the [[Mediterranean Sea]] northward.
Species with neritic distributions include the four species of the genus ''[[Nyctiphanes]]''.<ref name="damato">D'Amato, M.E. ''et al.'': "[http://www.bioafrica.net/manuscripts/AmatoMarineBiology.pdf Molecular dating and biogeography of the neritic krill ''Nyctiphanes'']", in ''Marine Biology vol. 155, no. 2'', pp. 243-247, August 2008.</ref> They are highly abundant along the [[upwelling]] regions of the [[California Current|California]], [[Humboldt Current|Humboldt]], [[Benguela Current|Benguela]], and [[Canary Current|Canarias]] [[Ocean current|current system]]s.<ref>{{cita web |author=Volker Siegel |año=2011 |título=''Nyctiphanes'' Sars, 1883 |editor=V. Siegel |work=World Euphausiacea database |editorial=[[World Register of Marine Species]] |url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=110677 |fechaacceso=June 18, 2011}}</ref><ref name="mauchline"/><ref name="gut2005">{{cita publicación |author1=Jaime Gómez-Gutiérrez |author2=Carlos J. Robinson |año=2005 |título=Embryonic, early larval development time, hatching mechanism and interbrood period of the sac-spawning euphausiid ''Nyctiphanes simplex'' Hansen |publicación=[[Journal of Plankton Research]] |volumen=27 |número=3 |páginas=279-295 |doi=10.1093/plankt/fbi003}}</ref> Another species having only neritic distribution is ''E. crystallorophias'', which is endemic to the Antarctic coastline.<ref name="jarman2002">{{cita publicación |author1=S. N. Jarman |author2=N. G. Elliott |author3=S. Nicol |author4=A. McMinn |año=2002 |título=Genetic differentiation in the Antarctic coastal krill ''Euphausia crystallorophias'' |publicación=[[Heredity (journal)|Heredity]] |volumen=88 |páginas=280-287 |pmid=11920136 |doi=10.1038/sj.hdy.6800041 |número=4}}</ref>
Species with endemic distributions include ''[[Nyctiphanes capensis]]'', which occurs only in the Benguela current,<ref name="damato"/> ''[[Euphausia mucronata|E. mucronata]]'' in the Humboldt current,<ref name="escribano">{{cita publicación |author1=R. Escribano |author2=V. Marin |author3=C. Irribarren |año=2000 |título=Distribution of ''Euphausia mucronata'' at the upwelling area of Peninsula Mejillones, northern Chile: the influence of the oxygen minimum layer |publicación=[[Scientia Marina]] |volumen=64 |número=1 |páginas=69-77 |url=http://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/viewFile/741/758 |doi=10.3989/scimar.2000.64n169}}</ref> and the six ''Euphausia'' species native to the Southern Ocean.
In the Antarctic, seven species are known,<ref>{{cita web |author=P. Brueggeman |url=http://www.peterbrueggeman.com/nsf/fguide/arthropoda10.html |título=''Euphausia crystallorophias'' |work=Underwater Field Guide to Ross Island & McMurdo Sound, Antarctica |editorial=[[University of California, San Diego]]}}</ref> one in genus ''Thysanoessa'' (''[[Thysanoessa macrura|T. macrura]]'') and six in ''Euphausia''. The [[Antarctic krill]] (''Euphausia superba'') commonly lives at depths reaching {{convert|100|m|ft|-1|abbr=on}},<ref>{{cita web |url=http://marinebio.org/species.asp?id=518 |título=Krill, ''Euphausia superba'' |editorial=[[MarineBio.org]] |fechaacceso=February 25, 2009}}</ref> whereas ice krill (''[[Euphausia crystallorophias]]'') reach depth of {{convert|4000|m|ft|-2|abbr=on}}, though they commonly inhabit depths of at most {{convert|300|-|600|m|ft|-2|abbr=on}}.<ref>{{cita publicación |author=J. A. Kirkwood |título=A Guide to the Euphausiacea of the Southern Ocean |publicación=ANARE Research Notes |año=1984 |volumen=1 |páginas=1-45}}</ref> Both are found at [[latitude]]s south of [[55th parallel south|55° S]], with ''E. crystallorophias'' dominating south of [[74th parallel south|74° S]]<ref>{{cita publicación |author1=A. Sala |author2=M. Azzali |author3=A. Russo |url=http://www.icm.csic.es/scimar/download.php/Cd/c6d5ca7c8572ce508582edcd1793cf93/IdArt/3031 |título=Krill of the Ross Sea: distribution, abundance and demography of ''Euphausia superba'' and ''Euphausia crystallorophias'' during the Italian Antarctic Expedition (January-February 2000) |publicación=[[Scientia Marina]] |volumen=66 |número=2 |páginas=123-133 |año=2002 |doi=10.3989/scimar.2002.66n2123}}</ref> and in regions of [[pack ice]]. Other species known in the [[Southern Ocean]] are ''[[Euphausia frigida|E. frigida]]'', ''[[Euphausia longirostris|E. longirostris]]'', ''[[Euphausia triacantha|E. triacantha]]'' and ''[[Euphausia vallentini|E. vallentini]]''.<ref>{{cita publicación |author1=G. W. Hosie |author2=M. Fukuchi |author3=S. Kawaguchi |url=http://www.noc.soton.ac.uk/CLIVAR/organization/southern/expertgroup/Hosie%20et%20al%20P&O%202003.pdf |título=Development of the Southern Ocean Continuous Plankton Recorder survey |publicación=[[Progress in Oceanography]] |volumen=58 |páginas=263-283 |año=2003 |doi=10.1016/j.pocean.2003.08.007 |número=2-4}}</ref>{{Clear}}
== Anatomy and morphology ==
[[Archivo:Krillanatomykils.jpg|thumb|Krill anatomy explained, using ''[[Euphausia superba]]'' as a model]]
Krill are crustaceans and have a [[chitin]]ous [[exoskeleton]] made up of three tagmata: the cephalon (head), the [[pereion]] (fused to the cephalon to form a cephalothorax), and the [[pleon]]. This outer shell of krill is transparent in most species. Krill feature intricate [[compound eye]]s; some species adapt to different lighting conditions through the use of screening [[pigment]]s.<ref>{{cita web |author=E. Gaten |url=http://www.le.ac.uk/biology/gat/northernkrill.html |título=''Meganyctiphanes norvegica'' |fechaacceso=February 25, 2009 |editorial=[[University of Leicester]]}}</ref> They have two [[antenna (biology)|antennae]] and several pairs of thoracic legs called [[pereiopod]]s or [[thoracopod]]s, so named because they are attached to the thorax; their number varies among genera and species. These thoracic legs include feeding legs and grooming legs. Additionally all species have five pairs of swimming legs called [[pleopod]]s or "swimmerets", very similar to those of a [[lobster]] or [[freshwater crayfish]]. Most krill are about {{convert|1|-|2|cm|in|1}} long as adults; a few species grow to sizes on the order of {{convert|6|-|15|cm|in|1}}. The largest krill species is the bathypelagic ''Thysanopoda spinicauda''.<ref>{{cita publicación |author=E. Brinton |título=''Thysanopoda spinicauda'', a new bathypelagic giant euphausiid crustacean, with comparative notes on ''T. cornuta'' and ''T. egregia'' |publicación=[[Journal of the Washington Academy of Sciences]] |volumen=43 |páginas=408-412 |año=1953}}</ref> Krill can be easily distinguished from other crustaceans such as true [[shrimp]] by their externally visible [[gill]]s.<ref name="tafi2008">{{cita web |editorial=Tasmanian Aquaculture & Fisheries Institute |url=http://www.tafi.org.au/zooplankton/imagekey/malacostraca/euphausiacea/ |título=Euphausiacea |fechaacceso=June 6, 2010}}</ref>
[[Archivo:Euphausia gills.jpg|left|thumb|The [[gill]]s of krill are externally visible.]]
Except for ''[[Bentheuphausia amblyops]]'', krill are [[bioluminescence|bioluminescent]] animals having organs called [[photophore]]s that can emit light. The light is generated by an [[enzyme]]-catalysed [[chemiluminescence]] reaction, wherein a [[luciferin]] (a kind of pigment) is activated by a [[luciferase]] enzyme. Studies indicate that the luciferin of many krill species is a [[fluorescence|fluorescent]] [[Polypyrrole|tetrapyrrole]] similar but not identical to [[dinoflagellate]] luciferin<ref>{{cita publicación |author=O. Shimomura |pmid=7676855 |título=The roles of the two highly unstable components F and P involved in the bioluminescence of euphausiid shrimps |publicación=Journal of Bioluminescence and Chemiluminescence |volumen=10 |número=2 |páginas=91-101 |año=1995 |doi=10.1002/bio.1170100205}}</ref> and that the krill probably do not produce this substance themselves but acquire it as part of their diet, which contains dinoflagellates.<ref>{{cita publicación |author1=J. C. Dunlap |author2=J. W. Hastings |author3=O. Shimomura |año=1980 |título=Crossreactivity between the light-emitting systems of distantly related organisms: novel type of light-emitting compound |publicación=[[Proceedings of the National Academy of Sciences]] |volumen=77 |número=3 |páginas=1394-1397 |doi=10.1073/pnas.77.3.1394 |pmid=16592787 |jstor=8463 |pmc=348501}}</ref> Krill photophores are complex organs with lenses and focusing abilities, and can be rotated by muscles.<ref>{{cite book |author1=P. J. Herring |author2=E. A. Widder |url=http://www.isbc.unibo.it/Files/BC_PlanktonNekton.htm |chapter=Bioluminescence in Plankton and Nekton |editor1=J. H. Steele |editor2=S. A. Thorpe |editor3=K. K. Turekian |título=Encyclopedia of Ocean Science |volumen=1 |páginas=308-317 |editorial=[[Academic Press]], San Diego |año=2001 |isbn=0-12-227430-X}}</ref> The precise function of these organs is as yet unknown; possibilities include mating, social interaction or orientation and as a form of counter-illumination camouflage to compensate their shadow against overhead ambient light.<ref>{{cite conference|author1=S. M. Lindsay |author2=M. I. Latz |título=Experimental evidence for luminescent countershading by some euphausiid crustaceans |conference=American Society of Limnology and Oceanography (ASLO) Aquatic Sciences Meeting |location=Santa Fe |año=1999}}</ref><ref>{{cita publicación |author=Sönke Johnsen |título=The Red and the Black: bioluminescence and the color of animals in the deep sea |publicación=[[Integrative and Comparative Biology]] |volumen=4 |número=2 |páginas=234-246 |año=2005 |url=http://www.biology.duke.edu/johnsenlab/pdfs/pubs/blcolor.pdf |format=[[Portable Document Format|PDF]] |doi=10.1093/icb/45.2.234}}</ref>
== Ecology ==
{{see also|Carbon sequestration|biological pump}}
===Feeding===
Many krill are [[filter feeding|filter feeders]]:<ref name="mauchline"/> their frontmost [[appendage]]s, the thoracopods, form very fine combs with which they can filter out their food from the water. These filters can be very fine indeed in those species (such as ''Euphausia'' spp.) that feed primarily on [[phytoplankton]], in particular on [[diatom]]s, which are unicellular [[algae]]. Krill are mostly [[omnivorous]],<ref name="cripps">{{cita publicación |author1=G. C. Cripps |author2=A. Atkinson |año=2000 |título=Fatty acid composition as an indicator of carnivory in Antarctic krill, ''Euphausia superba'' |publicación=Canadian Journal of Fisheries and Aquatic Sciences |volumen=57 |número=S3 |páginas=31-37 |doi=10.1139/f00-167}}</ref> although a few species are [[carnivorous]], preying on small [[zooplankton]] and fish [[larvae]].<ref name="saether">{{cita publicación |author1=Olav Saether |author2=Trond Erling Ellingsen |author3=Viggo Mohr |año=1986 |título=Lipids of North Atlantic krill |publicación=[[Journal of Lipid Research]] |volumen=27 |páginas=274-285 |pmid=3734626 |url=http://www.jlr.org/content/27/3/274.full.pdf |format=[[Portable Document Format|PDF]] |número=3}}</ref>
Krill are an important element of the aquatic [[food chain]]. Krill convert the [[primary production]] of their prey into a form suitable for consumption by larger animals that cannot feed directly on the minuscule algae. Northern krill and some other species have a relatively small filtering basket and actively hunt [[copepod]]s and larger zooplankton.<ref name="saether"/>
===Predation===
Many animals feed on krill, ranging from smaller animals like [[fish]] or [[penguin]]s to larger ones like [[pinniped|seals]] and [[baleen whale]]s.<ref name="noaa_krill">{{cita web |author=M. J. Schramm |url=http://sanctuaries.noaa.gov/news/features/1007_krill.html |título=Tiny Krill: Giants in Marine Food Chain |editorial=NOAA National Marine Sanctuary Program |fecha=October 10, 2007 |fechaacceso=June 4, 2010}}</ref>
Disturbances of an [[ecosystem]] resulting in a decline in the krill population can have far-reaching effects. During a [[coccolithophore]] bloom in the [[Bering Sea]] in 1998,<ref>{{cita web |author=J. Weier |url=http://earthobservatory.nasa.gov/Features/Coccoliths/bering_sea.php |título=Changing currents color the Bering Sea a new shade of blue |editorial=[[National Oceanic and Atmospheric Administration|NOAA]] Earth Observatory |año=1999 |fechaacceso=June 15, 2005}}</ref> for instance, the diatom concentration dropped in the affected area. Krill cannot feed on the smaller coccolithophores, and consequently the krill population (mainly ''E. pacifica'') in that region declined sharply. This in turn affected other species: the [[shearwater]] population dropped. The incident was thought to have been one reason [[salmon]] did not spawn that season.<ref>{{cite book |author1=R. D. Brodeur |author2=G. H. Kruse |author3=P. A. Livingston |author4=G. Walters |author5=J. Ianelli |author6=G. L. Swartzman |author7=M. Stepanenko |author8=T. Wyllie-Echeverria |título=Draft Report of the FOCI International Workshop on Recent Conditions in the Bering Sea |páginas=22-26 |editorial=[[National Oceanic and Atmospheric Administration|NOAA]] |año=1998}}</ref>
[[Climate change]] poses another threat to krill populations.<ref>{{cite news |author=Rusty Dornin |url=http://www.cnn.com/EARTH/9707/06/krill.kill/ |título=Antarctic krill populations decreasing |editorial=[[CNN]] |fecha=July 6, 1997 |fechaacceso=June 18, 2011}}</ref> Several single-celled [[endoparasitoid]]ic [[ciliate]]s of the genus ''Collinia'' can infect species of krill and devastate affected populations. Such diseases were reported for ''Thysanoessa inermis'' in the Bering Sea and also for ''E. pacifica'', ''Thysanoessa spinifera'', and ''T. gregaria'' off the North American Pacific coast.<ref>{{cite news |author=J. Roach |url=http://news.nationalgeographic.com/news/2003/07/0717_030717_krillkiller.html |título=Scientists discover mystery krill killer |editorial=[[National Geographic News]] |fecha=17 July 2003}}</ref><ref>{{cita publicación |author1=J. Gómez-Gutiérrez |author2=W. T. Peterson |author3=A. de Robertis |author4=R. D. Brodeur |título=Mass mortality of krill caused by parasitoid ciliates |publicación=[[Science (journal)|Science]] |volumen=301 |número=5631 |página=339 |año=2003 |pmid=12869754 |doi=10.1126/science.1085164 }}</ref> Some [[ectoparasite]]s of the family [[Dajidae]] (epicaridean [[isopod]]s) afflict krill (and also shrimp and [[mysid]]s); one such parasite is ''Oculophryxus bicaulis'', which was found on the krill ''Stylocheiron affine'' and ''S. longicorne''. It attaches itself to the animal's eyestalk and sucks blood from its head; it apparently inhibits the host's reproduction, as none of the afflicted animals reached maturity.<ref>{{cita publicación |author1=J. D. Shields |author2=J. Gómez-Gutiérrez |doi=10.1016/0020-7519(95)00126-3 |título=''Oculophryxus bicaulis'', a new genus and species of dajid isopod parasitic on the euphausiid ''Stylocheiron affine'' Hansen |publicación=[[International Journal for Parasitology]] |volumen=26 |número=3 |páginas=261-268 |año=1996}}</ref>
== Life history and behavior ==
[[Archivo:Nauplius Hatching.jpg|thumb|A [[nauplius (larva)|nauplius]] of ''[[Euphausia pacifica]]'' hatching, emerging backwards from the egg]]
The life cycle of krill is relatively well understood, despite minor variations in detail from species to species.<ref name="Gurney"/><ref name="mauchline">{{cite book |author1=J. Mauchline |author2=L. R. Fisher |año=1969 |título=The Biology of Euphausiids |series=Advances in Marine Biology |volumen=7 |editorial=[[Academic Press]] |isbn=978-7-7708-3615-2 }}</ref> After krill hatch, they experience several larval stages—''[[nauplius (larva)|nauplius]]'', ''[[pseudometanauplius]]'', ''[[metanauplius]]'', ''[[calyptopsis]]'', and ''[[furcilia]]'', each of which divides into sub-stages. The pseudometanauplius stage is exclusive to species that lay their eggs within an ovigerous sac: so-called "sac-spawners". The larvae grow and [[ecdysis|moult]] repeatedly as they develop, replacing their rigid exoskeleton when it becomes too small. Smaller animals moult more frequently than larger ones. [[Yolk]] reserves within their body nourish the larvae through metanauplius stage. By the calyptopsis stages [[cellular differentiation|differentiation]] has progressed far enough for them to develop a mouth and a digestive tract, and they begin to eat phytoplankton. By that time their yolk reserves are exhausted and the larvae must have reached the [[photic zone]], the upper layers of the ocean where algae flourish. During the furcilia stages, segments with pairs of swimmerets are added, beginning at the frontmost segments. Each new pair becomes functional only at the next moult. The number of segments added during any one of the furcilia stages may vary even within one species depending on environmental conditions.<ref>{{cita publicación |author=M. D. Knight |url=http://www.calcofi.org/newhome/publications/CalCOFI_Reports/v25/pdfs/Vol_25_Knight.pdf |título=Variation in larval morphogenesis within the Southern California Bight population of ''Euphausia pacifica'' from Winter through Summer, 1977-1978 |publicación=CalCOFI Report |volumen=XXV |año=1984}}</ref> After the final furcilia stage, an immature juvenile emerges in a shape similar to an adult, and subsequently develops [[gonad]]s and matures sexually.<ref name="fao_factsheet">{{cita web |editorial=[[Food and Agriculture Organization]] |url=http://www.fao.org/fishery/species/3393/en |work=Species factsheet |título=''Euphausia superba'' |fechaacceso=June 4, 2010}}</ref>
===Reproduction===
During the mating season, which varies by species and climate, the male deposits a [[spermatophore|sperm sack]] at the female's genital opening (named ''thelycum''). The females can carry several thousand eggs in their [[ovary]], which may then account for as much as one third of the animal's body mass.<ref>{{cita publicación |author1=R. M. Ross |author2=L. B. Quetin |título=How productive are Antarctic krill? |publicación=[[BioScience]] |volumen=36 |número=4 |páginas=264-269 |año=1986 |doi=10.2307/1310217 |jstor=1310217}}</ref> Krill can have multiple broods in one season, with interbrood intervals lasting on the order of days.<ref name="gut2005"/><ref name="cuzin">{{cita publicación |author=Janine Cuzin-Roudy |año=2000 |título=Seasonal reproduction, multiple spawning, and fecundity in northern krill, ''Meganyctiphanes norvegica'', and Antarctic krill, ''Euphausia superba'' |publicación=[[Canadian Journal of Fisheries and Aquatic Sciences]] |volumen=57 |número=S3 |páginas=6-15 |doi=10.1139/f00-165}}</ref>
[[Archivo:Nematoscelis difficilis female.jpg|thumb|left|The head of a female krill of the sac-spawning species ''[[Nematoscelis difficilis]]'' with her brood sac. The eggs have a diameter of {{convert|0.3|-|0.4|mm}}.]]
Krill employ two types of spawning mechanism.<ref name="gut2005"/> The 57 species of the genera ''Bentheuphausia'', ''Euphausia'', ''Meganyctiphanes'', ''Thysanoessa'', and ''Thysanopoda'' are "broadcast spawners": the female releases the fertilised eggs into the water, where they usually sink, disperse, and are on their own. These species generally hatch in the nauplius 1 stage, but have recently been discovered to hatch sometimes as metanauplius or even as calyptopis stages.<ref>{{cita publicación |author=J. Gómez-Gutiérrez |url=http://plankt.oxfordjournals.org/cgi/content/abstract/24/12/1265 |título=Hatching mechanism and delayed hatching of the eggs of three broadcast spawning euphausiid species under laboratory conditions |publicación=[[Journal of Plankton Research]] |volumen=24 |número=12 |páginas=1265-1276 |año=2002 |doi=10.1093/plankt/24.12.1265}}</ref> The remaining 29 species of the other genera are "sac spawners", where the female carries the eggs with her, attached to the rearmost pairs of thoracopods until they hatch as metanauplii, although some species like ''Nematoscelis difficilis'' may hatch as nauplius or pseudometanauplius.<ref>{{cite book |author1=E. Brinton |author2=M. D. Ohman |author3=A. W. Townsend |author4=M. D. Knight |author5=A. L. Bridgeman |url=http://species-identification.org/species.php?species_group=euphausiids&menuentry=inleiding |título=Euphausiids of the World Ocean |editorial=World Biodiversity Database CD-ROM Series, [[Springer Verlag]] |año=2000 |isbn=3-540-14673-3}}</ref>
===Moulting===
Moulting occurs whenever a specimen outgrows its rigid exoskeleton. Young animals, growing faster, moult more often than older and larger ones. The frequency of moulting varies widely by species and is, even within one species, subject to many external factors such as latitude, water temperature, and food availability. The subtropical species ''Nyctiphanes simplex'', for instance, has an overall inter-moult period of two to seven days: larvae moult on the average every four days, while juveniles and adults do so, on average, every six days. For ''E. superba'' in the Antarctic sea, inter-moult periods ranging between 9 and 28 days depending on the temperature between {{convert|−1|and|4|C|F}} have been observed, and for ''Meganyctiphanes norvegica'' in the [[North Sea]] the inter-moult periods range also from 9 and 28 days but at temperatures between {{convert|2.5|and|15|C|F}}.<ref>{{cita publicación |author=F. Buchholz |url=http://www.informaworld.com/smpp/content~content=a713644430~db=all |título=Experiments on the physiology of Southern and Northern krill, ''Euphausia superba'' and ''Meganyctiphanes norvegica'', with emphasis on moult and growth - a review |publicación=[[Marine and Freshwater Behaviour and Physiology]] |volumen=36 |número=4 |páginas=229-247 |año=2003 |doi=10.1080/10236240310001623376}}</ref> ''E. superba'' is able to reduce its body size when there is not enough food available, moulting also when its exoskeleton becomes too large.<ref>{{cita publicación |author1=H.-C. Shin |author2=S. Nicol |url=http://www.int-res.com/abstracts/meps/v239/p157-167/ |título=Using the relationship between eye diameter and body length to detect the effects of long-term starvation on Antarctic krill ''Euphausia superba'' |publicación=[[Marine Ecology Progress Series]] |volumen=239 |páginas=157-167 |año=2002 |doi=10.3354/meps239157}}</ref> Similar shrinkage has also been observed for ''E. pacifica'', a species occurring in the Pacific Ocean from polar to temperate zones, as an adaptation to abnormally high water temperatures. Shrinkage has been postulated for other temperate-zone species of krill as well.<ref>{{cita publicación |author1=B. Marinovic |author2=M. Mangel |url=http://people.ucsc.edu/~msmangel/MM.pdf |título=Krill can shrink as an ecological adaptation to temporarily unfavourable environments |publicación=[[Ecology Letters]] |volumen=2 |páginas=338-343 |año=1999}}</ref>{{Clear}}
===Lifespan===
Some high-latitude species of krill can live for more than six years (e.g., ''Euphausia superba''); others, such as the mid-latitude species ''Euphausia pacifica'', live for only two years.<ref name="nicol" /> Subtropical or [[Tropics|tropical]] species' longevity is still shorter, e.g., ''Nyctiphanes simplex'', which usually lives for only six to eight months.<ref>{{cita publicación|doi=10.3354/meps119063 |author=J. G. Gómez |título=Distribution patterns, abundance and population dynamics of the euphausiids''Nyctiphanes simplex'' and ''Euphausia eximia'' off the west coast of Baja California, Mexico |publicación=[[Marine Ecology Progress Series]] |volumen=119 |páginas=63-76 |año=1995 |url=http://www.int-res.com/articles/meps/119/m119p063.pdf |format=[[Portable Document Format|PDF]]}}</ref>
===Swarming===
Most krill are [[swarm]]ing animals; the sizes and densities of such swarms vary by species and region. For ''Euphausia superba'', swarms reach 10,000 to 60,000 individuals per cubic meter.<ref>{{cite book|author1=U. Kils |author2=P. Marshall |chapter=Der Krill, wie er schwimmt und frisst - neue Einsichten mit neuen Methoden ("''The Antarctic krill - how it swims and feeds - new insights with new methods''") |editor1=I. Hempel |editor2=G. Hempel |título=Biologie der Polarmeere - Erlebnisse und Ergebnisse (''Biology of the Polar Oceans Experiences and Results'') |editorial=[[Fischer Verlag]]|año=1995 |páginas=201-210 |isbn=3-334-60950-2}}</ref><ref>{{cite book |author=R. Piper |título=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals |editorial=[[Greenwood Press (publisher)|Greenwood Press]] |año=2007 |isbn=0-313-33922-8}}</ref> Swarming is a defensive mechanism, confusing smaller predators that would like to pick out individuals. In 2012, Gandomi and Alavi presented what appears to be a [[Swarm intelligence#Krill herd algorithm|successful stochastic algorithm]] for modelling the behaviour of krill swarms. The algorithm is based on three main factors: " (i) movement induced by the presence of other individuals (ii) foraging activity, and (iii) random diffusion."<ref name=kha2012>{{cita publicación |first1=A.H. |last= Gandomi |first2=A.H. |last2=Alavi |título= Krill Herd Algorithm: A New Bio-Inspired Optimization Algorithm |url=http://www.sciencedirect.com/science/article/pii/S1007570412002171?v=s5 |publicación= Communications in Nonlinear Science and Numerical Simulation |doi=10.1016/j.cnsns.2012.05.010|año=2012 |volumen=17 |número=12 |páginas=4831 }}</ref>
===Vertical migration===
Krill typically follow a [[diurnality|diurnal]] [[Diel vertical migration|vertical migration]]. It has been assumed that they spend the day at greater depths and rise during the night toward the surface. The deeper they go, the more they reduce their activity,<ref>{{cita publicación |author1=J. S. Jaffe |author2=M. D. Ohmann |author3=A. de Robertis |url=http://jaffeweb.ucsd.edu/files/pubs/Sonar%20estimates%20of%20daytime%20activity%20levels%20of%20Euphausia%20pacifica%20in%20Saanich%20Inlet.pdf |título=Sonar estimates of daytime activity levels of ''Euphausia pacifica'' in Saanich Inlet |publicación=[[Canadian Journal of Fisheries and Aquatic Sciences]] |volumen=56 |páginas=2000-2010 |año=1999 |doi=10.1139/cjfas-56-11-2000 |número=11}}</ref> apparently to reduce encounters with predators and to conserve energy. Swimming activity in krill varies with stomach fullness. Satiated animals that had been feeding at the surface swim less actively and therefore sink below the mixed layer.<ref>{{cita publicación|author1=Geraint A. Tarling |author2=Magnus L. Johnson |año=2006 |título=Satiation gives krill that sinking feeling |publicación=[[Current Biology]] |volumen=16 |número=3 |páginas=83-84 |doi=10.1016/j.cub.2006.01.044 |pmid=16461267}}</ref> As they sink they produce [[feces]] which implies a role in the Antarctic carbon cycle. Krill with empty stomachs swim more actively and thus head towards the surface. Vertical migration may be a 2-3 times daily occurrence. Some species (e.g., ''Euphausia superba'', ''E. pacifica'', ''E. hanseni'', ''Pseudeuphausia latifrons'', and ''Thysanoessa spinifera'') form surface swarms during the day for feeding and reproductive purposes even though such behaviour is dangerous because it makes them extremely vulnerable to predators.<ref name="howard">{{cite book |author=Dan Howard |chapter=Krill|chapter-url=http://pubs.usgs.gov/circ/c1198/chapters/133-140_Krill.pdf |páginas=133-140 |editor1=Herman A. Karl |editor2=John L. Chin |editor3=Edward Ueber |editor4=Peter H. Stauffer |editor5=James W. Hendley II |url=http://pubs.usgs.gov/circ/c1198/ |título=Beyond the Golden Gate - Oceanography, Geology, Biology, and Environmental Issues in the Gulf of the Farallones |editorial=[[United States Geological Survey]] |id=Circular 1198 |año=2001 |fechaacceso=October 8, 2011}}</ref>
[[Archivo:Pleopods euphausia superba.jpg|right|thumb|Beating [[pleopod]]s of a swimming [[Antarctic krill]]]]
Dense swarms can elicit a [[feeding frenzy]] among fish, birds and mammal predators, especially near the surface. When disturbed, a swarm scatters, and some individuals have even been observed to moult instantaneously, leaving the [[exuvia]] behind as a decoy.<ref>{{cita web |author=D. Howard |url=http://oceanexplorer.noaa.gov/explorations/02quest/background/krill/krill.html |título=Krill in Cordell Bank National Marine Sanctuary |editorial=[[National Oceanic and Atmospheric Administration]]|fechaacceso=June 15, 2005}}</ref>
Krill normally swim at a pace of 5-10 cm/s (2-3 body lengths per second),<ref>{{cita publicación |publicación=ICES Journal of Marine Science |año=2005 |volumen=62 |número=1 |páginas=25-32 |doi=10.1016/j.icesjms.2004.07.027 |título=New target-strength model indicates more krill in the Southern Ocean |author1=David A. Demer |author2=Stéphane G. Conti }}</ref> using their swimmerets for propulsion. Their larger migrations are subject to ocean currents. When in danger, they show an [[escape reaction]] called [[Caridoid escape reaction|lobstering]] - flicking their [[Caudal (anatomical term)|caudal]] structures, the [[telson]] and the [[uropod]]s, they move backwards through the water relatively quickly, achieving speeds in the range of 10 to 27 body lengths per second, which for large krill such as ''E. superba'' means around {{convert|0.8|m/s|ft/s|0|abbr=on}}.<ref>{{cita publicación |author=U. Kils |título=Swimming behavior, swimming performance and energy balance of Antarctic krill ''Euphausia superba''|url=http://www.zuckerspeicher.de/ecoscope/biomass3.htm |publicación=BIOMASS Scientific Series 3, [[BIOMASS Research Series]]|páginas=1-122 |año=1982}}</ref> Their swimming performance has led many researchers to classify adult krill as [[nekton|micro-nektonic]] life-forms, i.e., small animals capable of individual motion against (weak) currents. Larval forms of krill are generally considered zooplankton.<ref>{{cita publicación |author1=S. Nicol |author2=Y. Endo |url=http://www.fao.org/docrep/003/w5911e/w5911e00.htm |título=Krill Fisheries of the World |publicación=[[Food and Agriculture Organization|FAO]] Fisheries Technical Paper |volumen=367 |año=1997}}</ref>
==Human uses ==
{{see also|Krill fishery}}
[[Archivo:Krillmeatkils.jpg|thumb|left|Deep frozen plates of [[Antarctic krill]] for use as animal feed and raw material for cooking]]
===Harvesting history===
Krill have been harvested as a food source for humans and domesticated animals since at least the 19th century, and possibly earlier in Japan, where it was known as ''okiami''. Large-scale fishing developed in the late 1960s and early 1970s, and now occurs only in Antarctic waters and in the seas around Japan. Historically, the largest krill fishery nations were Japan and the Soviet Union, or, after the latter's dissolution, [[Russia]] and [[Ukraine]].<ref name="pri">{{cita web|author1=Grossman, Elizabeth |título=Scientists consider whether krill need to be protected from human over-hunting|url=https://www.pri.org/stories/2015-07-14/scientists-consider-whether-krill-need-be-protected-human-over-hunting|editorial=Public Radio International (PRI)|fechaacceso=1 April 2017|fecha=14 July 2015}}</ref> The harvest peaked, which in 1983 was about 528,000 tonnes in the Southern Ocean alone (of which the Soviet Union took in 93%), is now managed as a precaution against overfishing.<ref>{{cita web |título=Krill fisheries and sustainability: Antarctic krill (Euphausia superba)|url=https://www.ccamlr.org/en/fisheries/krill-fisheries-and-sustainability|editorial=Commission for the Conservation of Antarctic Marine Living Resources|fechaacceso=1 April 2017|fecha=23 April 2015}}</ref>
In 1993, two events caused a decline in krill fishing: Russia exited the industry; and the [[Convention for the Conservation of Antarctic Marine Living Resources]] (CCAMLR) defined maximum catch quotas for a [[sustainable fisheries|sustainable exploitation]] of Antarctic krill. After an October 2011 review, the Commission decided not to change the quota.<ref name=nature/>
The annual Antarctic catch stabilised at around 100,000 tonnes, which is roughly one fiftieth of the CCAMLR catch quota.<ref name=ccamlr/> The main limiting factor was probably high costs along with political and legal issues.<ref>{{cita publicación|author=Minturn J. Wright |título=The Ownership of Antarctica, its Living and Mineral Resources |publicación=Journal of Law and the Environment |año=1987 |volumen=4 |número=2 |páginas=49-78 |url=http://heinonline.org/HOL/Page?handle=hein.journals/jlen4&div=14&collection=journals&set_as_cursor=0&men_tab=srchresults}}</ref> The Japanese fishery saturated at some 70,000 tonnes.<ref name="nicol2">{{cita publicación |author1=S. Nicol |author2=J. Foster |título=Recent trends in the fishery for Antarctic krill |publicación=Aquatic Living Resources |volumen=16 |páginas=42-45 |año=2003 |doi=10.1016/S0990-7440(03)00004-4}}</ref>
Although krill are found worldwide, fishing in Southern Oceans are preferred because the krill are more "catchable" and abundant in these regions. Particularly in Antarctic seas which are considered as [[wikt:pristine|pristine]], they are considered a "clean product".<ref name=pri/>
===Human consumption===
Although the total [[biomass]] of Antarctic krill may be as abundant as 400 million [[tonne]]s, the human impact on this [[keystone species]] is growing, with a 39% increase in total fishing yield to 294,000 tonnes over 2010–2014.<ref name="ccamlr">{{cita web |título=Krill - biology, ecology and fishing|url=https://www.ccamlr.org/en/fisheries/krill-%E2%80%93-biology-ecology-and-fishing|editorial=Commission for the Conservation of Antarctic Marine Living Resources|fechaacceso=1 April 2017|fecha=28 April 2015}}</ref> Major countries involved in krill harvesting are [[Norway]] (56% of total catch in 2014), the [[Republic of Korea]] (19%), and [[China]] (18%).<ref name=ccamlr/>
Krill is a rich source of [[protein]] and [[omega-3 fatty acids]] which are under development in the early [[21st Century]] as human food, [[dietary supplement]]s as oil capsules, [[livestock]] food, and [[pet food]].<ref name=pri/><ref name="nature">{{cita publicación|pmid=20811427|año=2010|author1=Schiermeier|first1=Q |título=Ecologists fear Antarctic krill crisis|publicación=Nature|volumen=467|número=7311|páginas=15|doi=10.1038/467015a|url=http://www.nature.com/news/2010/100901/full/467015a.html}}</ref><ref name="noaa">{{cita web|url=https://swfsc.noaa.gov/textblock.aspx?Division=AERD&id=11462 |título=Why krill?|editorial=Southwest Fisheries Science Center, US National Oceanic and Atmospheric Administration|fecha=22 November 2016|fechaacceso=1 April 2017}}</ref> Krill tastes salty with a somewhat stronger fish flavor than shrimp. For mass-consumption and commercially prepared products, they must be peeled to remove the inedible [[exoskeleton]].<ref name=noaa/>
In 2011, the US [[Food and Drug Administration]] published a letter of no objection for a manufactured [[krill oil]] product to be [[generally recognized as safe]] ([[GRAS]]) for human consumption.<ref>{{cita web|url=http://www.fda.gov/Food/IngredientsPackagingLabeling/GRAS/NoticeInventory/ucm267323.htm|editorial=US FDA|author=Cheeseman MA|fecha=22 July 2011 |título=Krill oil: Agency Response Letter GRAS Notice No. GRN 000371|fechaacceso=3 June 2015}}</ref>
-->
== Ecología ==
Línea 46 ⟶ 180:
El kril es una especie clave del ecosistema antártico. Su rol en el ecosistema fue mencionado tempranamente por Bellingshausen en 1820 quien hace referencia a su abundancia y su importancia como alimento de pingüinos, luego por Webster en 1834 quien indicó que los pingüinos alimentaban a sus crías en isla Decepción con "kril" ("pequeño pez" en noruego) y Mac Nab en 1839 asoció los cambios en coloración del agua que producen las grandes concentraciones de eufausiáceos con agrupamientos de ballenas (Marr 1962).
Los kril adultos se agrupan en gigantescos cardúmenes, que pueden extenderse por kilómetros con miles de individuos concentrados por metro cúbico de agua. Los bancos de estos crustáceos suelen tener densidades de 20 kg/m³. Esta conducta gregaria hace que el kril sea una especie atractiva para su explotación comercial.
Se alimentan filtrando con sus patas plumosas las diminutas [[diatomea]]s del agua. Emiten una luz azul verdosa que, posiblemente les sirve para reunirse en el momento de desovar. Del kril se alimentan [[Pisces|peces]], [[aves]] y, muy especialmente, las [[Balaenidae|ballenas]], las cuales pueden consumir dos toneladas de una vez. Según la especie, permanecen en superficie o bajan hasta profundidades de 2 km.
Línea 60 ⟶ 194:
== Interés económico ==
[[Archivo:Krillmeatkils.jpg|right|thumb
El kril es recolectado para el consumo humano (''[[okiami]]'', en japonés) y ha sido cultivado desde el siglo XIX, aunque probablemente en [[Japón]] lo fuera antes. A partir de la década de los sesenta se ha pescado en gran cantidad en aguas antárticas y en mares adyacentes a [[Japón]]. El interés por la pesca de kril comenzó en la década de 1960, y las mayores capturas ocurrieron a principio de los años ochenta, llegando al máximo en [[1983]], cuando se capturaron más de 528 000 [[tonelada]]s solamente en el [[océano Glaciar Antártico]], de las cuales el 93 % correspondían a la Unión Soviética. En [[1993]], dos elementos propiciaron el descenso en su explotación: primero, Rusia abandonó sus operaciones (debido a la ruptura de la Unión Soviética, que obligó a la flota fuertemente subsidiada a dejar de operar); y segundo, la Comisión para la Conservación de los Recursos Vivos Marinos Antárticos ([[CCRVMA]]) definió un umbral de captura máximo para garantizar una [[explotación sostenible]]. Hoy en día, los estados que aún comercian con este recurso son Japón, [[Corea del Sur]], Ucrania y [[Polonia]].
Línea 66 ⟶ 200:
Las capturas de kril Antártico han incrementado substancialmente en los últimos años, llegando a un máximo de 282.000 toneladas en la temporada 2013 - 2014, concentrándose repetitivamente en ciertas áreas. La pesquería de kril Antártico podría convertirse en la pesquería global más grande, con el potencial de afectar significativamente a la estructura trófica del ecosistema marino Antártico.
==
;Notas
{{listaref|group=n}}
;Referencias
{{listaref|2}}
Línea 80 ⟶ 217:
== Enlaces externos ==
{{
{{wikispecies
* [http://www.ecoscope.com/krill «Microscopio virtual» de krill antártico], Department of Marine and Coastal Sciences, Rutgers University
| |||