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Encyclopedia > Krill
Euphausiacea
A Northern krill (Meganyctiphanes norvegica)
A Northern krill (Meganyctiphanes norvegica)
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Superorder: Eucarida
Order: Euphausiacea
Dana, 1852
Families

Krill are shrimp-like marine invertebrate animals. These small crustaceans are important organisms of the zooplankton, particularly as food for baleen whales, Mantas, whale sharks, Crabeater seals and other seals, and a few seabird species that feed almost exclusively on them. Their scientific name is Euphausiids, after their taxonomic order Euphausiacea. The name Krill comes from the Norwegian word krill meaning "young fry of fish". Image File history File links Download high resolution version (1750x1000, 145 KB) A Northern krill (Meganyctiphanes norvegica). ... Binomial name Meganyctiphanes norvegica Northern Krill (Meganyctiphanes norvegica) is a crustacean that lives in the North Atlantic Ocean. ... Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (parasitic to flatworms, echinoderms, etc. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - Trilobites (extinct) Subphylum Chelicerata Arachnida - Spiders, Scorpions, etc. ... Classes Remipedia Cephalocarida Branchiopoda Ostracoda Maxillopoda Malacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum. ... Orders Subclass Eumalacostraca  Superorder Eucarida   Order Amphionidacea   Order Decapoda - crabs, shrimp   Order Euphausiacea - krill  â€ Superorder Pancarida   â€ Order Thermosbaenacea  Superorder Peracarida   Order Amphipoda - amphipods   Order Cumacea - cumaceans   Order Isopoda - pillbugs, sowbugs   Order Lophogastrida   Order Mictacea   Order Mysida   â€ Order Spelaeogriphacea   Order Tanaidacea  Superorder Syncarida   Order Anaspidacea   Order Bathynellacea   â€ Order Palaeocaridacea   Order Stygocaridacea... Orders Decapoda Euphausiacea Amphionidacea Eucarida is a superorder of crustaceans, comprising the decapods, krill and Amphionides. ... James Dwight Dana (February 12, 1813 - April 14, 1895) was an American geologist, mineralogist and zoologist. ... 1852 was a leap year starting on Thursday (see link for calendar). ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Species Many, see text. ... Binomial name Meganyctiphanes norvegica (M. Sars, 1856) Northern krill (Meganyctiphanes norvegica) is a crustacean that lives in the North Atlantic Ocean. ... E. W. L. Holt Ernest William Lyons Holt (October 17, 1864 – June 10, 1922) was an eminent British marine naturalist and biologist specialized in ichthyology, the study of fish. ... Walter Medley Tattersall (November 8, 1882 - October 5, 1948) was a British zoologist and marine biologist, famous for his study of mysids. ... Species (Calman, 1896) (Ortmann, 1893) Hansen, 1911 Nematobrachion is a genus of krill, small shrimp-like invertebrate animals living in the oceans. ... William Thomas Calman (December 29, 1871 - September 29, 1952) was a Scottish zoologist, specialising in the Crustacea. ... Species see text Nematoscelis is a genus of krill, small shrimp-like invertebrate animals living in the oceans. ... Georg Ossian Sars (April 20, 1837 - April 9, 1927) was a Norwegian marine biologist. ... Species G. O. Sars, 1883 Hansen 1911 (Bell 1853) Hansen 1911 Nyctiphanes is a genus of krill, small shrimp-like invertebrate animals living in the oceans. ... Species G. O. Sars 1883 Wang and Chen 1963 Pseudeuphausia is a genus of krill, small shrimp-like invertebrate animals living in the oceans. ... Hans Jacob Hansen (August 10, 1855 - June 26, 1936) was a Danish zoologist. ... Species see text Stylocheiron is a genus of krill, small shrimp-like invertebrate animals living in the oceans. ... Binomial name Tessarabrachion oculatus Hansen, 1911 Tessarabrachion oculatus is a species of krill, small shrimp-like invertebrate animals living in the oceans. ... Species Several, see text. ... Johann Friedrich von Brandt (May 25, 1802 - July 15, 1879) was a German naturalist. ... Species Several, see text. ... Pierre André Latreille. ... Binomial name Bentheuphausia amblyops G. O. Sars, 1883 Bentheuphausia amblyops is a species of krill, small shrimp-like crustaceans living in the ocean. ... Superfamilies and families Alpheoidea Alpheidae - snapping shrimps Barbouriidae Hippolytidae Ogyrididae Atyoidea Atyidae Bresilioidea Agostocarididae Alvinocarididae Bresiliidae Disciadidae Mirocarididae Campylonotoidea Bathypalaemonellidae Campylonotoidae Crangonoidea Crangonidae Glyphocrangonidea Galatheacaridoidea Galatheacarididae Nematocarcinoidea Eugonatonotidae Nematocarcinidae Rhynchocinetidae Xiphocarididae Oplophoroidea Oplophoridae Palaemonoidea Anchistioididae Desmocarididae Euryrhynchidae Gnathophyllidae Hymenoceridae Kakaducarididae Palaemonidae Typhlocarididae Pandaloidea Pandalidae Thalassocarididae Pasiphaeoidea Pasiphaeidae Procaridoidea Procarididae Processoidea... Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. ... Classes Class Branchiopoda Subclass Phyllopoda Subclass Sarsostraca Class Remipedia Order Enantiopoda Order Nectiopoda Class Cephalocarida Order Brachypoda Class Maxillopoda Subclass Mystacocarida Subclass Copepoda Subclass Branchiura Subclass Pentastomida Subclass Tantulocarida Subclass Thecostraca Infraclass Cirripedia Class Ostracoda Order Metacopina Subclass Myodocopa Subclass Podocopa Class Malacostraca Subclass Eumalacostraca Subclass Hoplocarida Subclass Phyllocarida The... Photomontage of plankton organisms Plankton is the aggregate community of weakly swimming but mostly drifting small organisms that inhabit the water column of the ocean, seas, and bodies of freshwater. ... Families Balaenidae Balaenopteridae Eschrichtiidae Neobalaenidae Scientifically known as the Mysticeti, the baleen whales, also called whalebone whales or great whales, form a suborder of the order cetacea. ... Binomial name Manta birostris Dondorff, 1798 The manta ray, or giant manta, is the largest of the rays, ranging up to 6. ... Binomial name Rhincodon typus (Smith, 1828) The whale shark (Rhincodon typus) is a distinctively-marked member of the subclass Elasmobranchii of the class Chondrichthyes. ... Binomial name Lobodon carcinophagus Hombron & Jacquinot, 1842 The Crabeater Seal, Lobodon carcinophagus, is one of the most remarkable, though least known, of the mammals of the world. ... Families Odobenidae Otariidae Phocidae Pinnipeds (fin-foots, lit. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ...


Krill occur in all oceans of the world. They are considered a keystone species near the bottom of the food chain because they feed on phytoplankton and zooplankton, converting these into a form suitable for many larger animals for whom krill makes up the largest part of their diet. Most of the species display large daily vertical migrations making a significant amount of biomass available as food for predators near the surface at night and in deeper waters during the day. A keystone predator may prevent a particular prey species from overrunning an ecosystem. ... Food chains and food webs or food networks describe the feeding relationships between species in a biotic community. ... Diagrams of some typical phytoplankton Phytoplankton refers to the autotrophic component of the plankton that drifts in the water column. ... Biomass is organic non-fossil material, collectively. ...


Commercial fishing of krill is done in the Southern Ocean and in the waters around Japan. The total global production amounts to 150 – 200,000 tonnes annually. Most krill is used for aquaculture and aquarium feeds, as bait in sport fishing, or in the pharmaceutical industry. In Japan and Russia, krill is also used for human consumption and known as okiami (オキアミ)1 in Japan. The examples and perspective in this article may not represent a worldwide view. ... For other uses, see Aquarium (disambiguation). ... Bait is any substance used to attract prey, especially fish. ...

Contents


Taxonomy

The order Euphausiacea is split into two families. The family Bentheuphausiidae has only one species, Bentheuphausia amblyops, a bathypelagic krill living in deep waters below 1,000 m. It is considered the most primitive living species of all krill.[Brin62] The other family — the Euphausiidae — contains ten different genera with a total of 85 species. Of these, the genus Euphausia is the largest, with 31 species.[ITIS] Binomial name Bentheuphausia amblyops G. O. Sars, 1883 Bentheuphausia amblyops is a species of krill, small shrimp-like crustaceans living in the ocean. ... Binomial name Bentheuphausia amblyops G. O. Sars, 1883 Bentheuphausia amblyops is a species of krill, small shrimp-like crustaceans living in the ocean. ... The pelagic zone is the part of the open sea or ocean comprising the water column, i. ... Genera Euphausia Dana, 1852 Meganyctiphanes Holt and W. M. Tattersall, 1905 Nematobrachion Calman, 1905 Nematoscelis G. O. Sars, 1883 Nyctiphanes G. O. Sars, 1883 Pseudeuphausia Hansen, 1910 Stylocheiron G. O. Sars, 1883 Tessarabrachion Hansen, 1911 Thysanoessa Brandt, 1851 Thysanopoda Latreille, 1831 The family of the Euphausiidae is the largest family... In biology, a genus (plural genera) is a taxonomic grouping. ... Species Many, see text. ...


Well-known species—mainly because they are subject to commercial krill fishery—include Antarctic krill (Euphausia superba), Pacific krill (Euphausia pacifica) and Northern krill (Meganyctiphanes norvegica).
Krill fishery is the commercial fishery of krill, small shrimp-like marine animals that live in the oceans world-wide. ... Binomial name Euphausia superba Dana, 1850 The Antarctic krill (Euphausia superba ) is a species of krill found in the Antarctic waters of the Southern Ocean. ... Binomial name Euphausia pacifica Hansen, 1911 Pacific krill, Euphausia pacifica, is a euphausid that lives in the Pacific Ocean. ... Binomial name Meganyctiphanes norvegica Northern Krill (Meganyctiphanes norvegica) is a crustacean that lives in the North Atlantic Ocean. ...


Distribution

A krill swarm
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A krill swarm

Krill occur worldwide in all oceans; most species have transoceanic distribution and several species have endemic or neritic restricted distribution. Species of the genus Thysanoessa occur in both the Atlantic and the Pacific Ocean, which is also home to Euphausia pacifica. Northern krill occurs across the Atlantic, from the north to the Mediterranean Sea. The four species of the genus Nyctiphanes are highly abundant along the upwelling regions of the California, Humbolt, Benguela, and Canarias Current Systems, where occur most of the largest fisheries activities of fish, molluscs and crustaceans. Download high resolution version (1732x1188, 1246 KB)Many krill. ... Download high resolution version (1732x1188, 1246 KB)Many krill. ... In biology and ecology endemic means exclusively native to a place or biota, in contrast to cosmopolitan or one of various ways of being not native (e. ... Species Several, see text. ... Euphausia pacifica is small zooplankton organism in the Pacific. ... Binomial name Meganyctiphanes norvegica Northern Krill (Meganyctiphanes norvegica) is a crustacean that lives in the North Atlantic Ocean. ... Satellite image The Mediterranean Sea is a part of the Atlantic Ocean almost completely enclosed by land, on the north by Europe, on the south by Africa, and on the east by Asia. ... Species G. O. Sars, 1883 Hansen 1911 (Bell 1853) Hansen 1911 Nyctiphanes is a genus of krill, small shrimp-like invertebrate animals living in the oceans. ...


In the Antarctic, seven species are known:[Bru] one of the genus Thysanoessa (T. macrura) and six species of the genus Euphausia. The Antarctic krill (Euphausia superba) commonly lives at depths up to 100 m,[MarineBio] whereas Ice krill (Euphausia crystallorophias) has been recorded at a depth of 4,000 m but commonly lives in depths at most 300 to 600 m deep.[Kir84] Both are found at latitudes south of 55° S; with E. crystallorophias dominating south of 74° S[SAR02] and in regions of pack ice. Other species known in the Southern Ocean are E. frigida, E. longirostris, E. triacantha, and E. vallentini.[HFK03]
Antarctica (Greek, antarktikos: opposite the Arctic[1]) is a continent encircling the Earths South Pole, surrounded by the Southern Ocean and divided in two by the Transantarctic Mountains. ... Binomial name Euphausia superba Dana, 1850 The Antarctic krill (Euphausia superba ) is a species of krill found in the Antarctic waters of the Southern Ocean. ... Latitude, sometimes denoted by the Greek letter φ, gives the location of a place on Earth north or south of the Equator. ... An icebreaker navigates some through young (1 year) sea ice Sea ice is formed from ocean water that freezes. ...


Morphology

Krill anatomy explained, using Euphausia superba as a model
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Krill anatomy explained, using Euphausia superba as a model

Krill are crustaceans and have a chitinous exoskeleton made up of three segments: the cephalon (head), thorax, and the abdomen. The first two segments are fused into one segment, the cephalothorax. This outer shell of krill is nearly transparent. Krill feature intricate compound eyes; some species can adapt to different lighting conditions through the use of screening pigments.[Gat05] They have two antennae and several pairs of thoracic legs called pereiopods or thoracopods (so named because they are attached to the thorax; their number varies among genera and species). These thoracic legs include the feeding legs and the grooming legs. Additionally all species have five swimming legs called pleopods or "swimmerets". Most krill are about 1 to 2 cm long as adults, a few species grow to sizes of the order of 6 to 15 cm. The largest krill species is the mesopelagic Thysanopoda spinicauda.[Brin53] Krill can be easily distinguished from other crustaceans such as true shrimps by their externally visible gills. antarctic krill anatomy graph by uwe kils gfdl from Kils & Klages 1979 File links The following pages link to this file: Talk:Antarctic krill Krill Decapod anatomy User:Kils/gallery ... antarctic krill anatomy graph by uwe kils gfdl from Kils & Klages 1979 File links The following pages link to this file: Talk:Antarctic krill Krill Decapod anatomy User:Kils/gallery ... Binomial name Euphausia superba Dana, 1850 Krill is the Norwegian word for whale food. ... Classes Remipedia Cephalocarida Branchiopoda Ostracoda Maxillopoda Malacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum. ... Structure of chitin molecule In biology, chitin (pronounced keye-tin) is one of the main components in the cell walls of fungi, the exoskeletons of insects and other arthropods, and in some other animals. ... An exoskeleton, in contrast to an endoskeleton, is an external anatomical feature that supports and protects an animals body. ... The abdomen is a part of the body. ... The cephalothorax is an anatomical term used of arachnid and malacostracan arthropods for the first major body section. ... Compound eye of a dragonfly Compound eye of Antarctic krill as imaged by an electron microscope A compound eye is a visual organ found in certain arthropods such as insects and crustaceans. ... In biology, pigment is any material resulting in color in plant or animal cells which is the result of selective absorption. ... Antennae (singular antenna), are the paired appendages connecting to the first (and in crustaceans also to the second) segment of the head of the members of all subphyla of the arthropods except Chelicerata. ... Antennules Pereiopods Carapace Pleopods Uropods Telson The body of a decapod crustacean is made up of nineteen body segments grouped into two main body parts, the cephalothorax and the abdomen. ... Thoracopod is the leg of crustacean used for walking, swimming feeding or filtration. ... Antennules Pereiopods Carapace Pleopods Uropods Telson The body of a decapod crustacean is made up of nineteen body segments grouped into two main body parts, the cephalothorax and the abdomen. ... The pelagic zone is the part of the open sea or ocean comprising the water column, i. ... Superfamilies and families Alpheoidea Alpheidae - snapping shrimps Barbouriidae Hippolytidae Ogyrididae Atyoidea Atyidae Bresilioidea Agostocarididae Alvinocarididae Bresiliidae Disciadidae Mirocarididae Campylonotoidea Bathypalaemonellidae Campylonotoidae Crangonoidea Crangonidae Glyphocrangonidea Galatheacaridoidea Galatheacarididae Nematocarcinoidea Eugonatonotidae Nematocarcinidae Rhynchocinetidae Xiphocarididae Oplophoroidea Oplophoridae Palaemonoidea Anchistioididae Desmocarididae Euryrhynchidae Gnathophyllidae Hymenoceridae Kakaducarididae Palaemonidae Typhlocarididae Pandaloidea Pandalidae Thalassocarididae Pasiphaeoidea Pasiphaeidae Procaridoidea Procarididae Processoidea... gills of a Smooth Newt Gills inside of a tuna head In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. ...

The gills of krill are externally visible.
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The gills of krill are externally visible.

Many krill are filter feeders: their front-most extremities, 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 diatoms, which are unicellular algae. However, it is believed that all krill species are mostly omnivorous and some few species are carnivorous preying small zooplankton and fish larvae. Image File history File links Euphausia_gills. ... Image File history File links Euphausia_gills. ... gills of a Smooth Newt Gills inside of a tuna head In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. ... Filter feeders (also known as suspension feeders) are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized structure, such as the baleen of baleen whales. ... Diagrams of some typical phytoplankton Phytoplankton refers to the autotrophic component of the plankton that drifts in the water column. ... Diatoms are a major group of eukaryotic algae, and are one of the most common types of phytoplankton. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Omnivores are organisms that consume both plants and animals. ... This article deals with meat-eating animals. ...


Except for the Bentheuphausia amblyops species, krill are bioluminescent animals having organs called photophores that are able to emit light. The light is generated by an enzyme-catalyzed chemoluminescence 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 fluorescent tetrapyrrole similar but not identical to dinoflagellate luciferin[Shi95] and that the krill probably do not produce this substance themselves but acquire it as part of their diet that contains dinoflagellates.[DHS80] Krill photophores are complex organs with lenses and focusing abilities, and they can be rotated by muscles.[HW01] The precise function of these organs is as yet unknown; they might have a purpose in mating, social interaction or in orientation. Some researchers (e.g. Lindsay & Latz[LL99] or Johnsen[John05]) have proposed that krill use the light as a form of counter-illumination camouflage to compensate their shadow against the ambient light from above to make themselves more difficult to be seen by predators from below.
Bioluminescence is the production and emission of light by a living organism as the result of a chemical reaction during which chemical energy is converted to light energy. ... A photophore is a light-emitting organ which appears as luminous spots on various marine fishes. ... Lightsticks Chemoluminescence (sometimes chemiluminescence) is the emission of light (luminescence) as the result of a chemical reaction. ... Luciferin is a generic name for light emitting pigments found in organisms capable of bioluminescence, like fireflies, deep sea fish and microbes. ... In biology, pigment is any material resulting in color in plant or animal cells which is the result of selective absorption. ... Luciferase is a generic name for enzymes commonly used in nature for bioluminescence. ... Ribbon diagram of the catalytically perfect enzyme TIM. An enzyme is a protein that catalyzes, or speeds up, a chemical reaction. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... A Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. ... Classes Dinophyceae Noctiluciphyceae Syndiniophyceae The dinoflagellates are a large group of flagellate protists. ... It has been suggested that Copulation be merged into this article or section. ... Anolis caroliensis showing blending camouflage and counter-shading. ...


Behaviour

Most krill are swarming animals; the size and density of such swarms vary greatly depending on the species and the region. Of Euphausia superba, swarms containing up to 10,000 to 30,000 individuals per cubic meter have been reported.[KM95] Swarming is a defensive mechanism, confusing smaller predators that would like to pick out single individuals. School of juvenile herring - many fish have the opercula wide open for ram feeding and you can see the red gills The term swarm (schooling or swarming) is applied to fish, birds and insects and describes a behavior of an aggregation (school) of animals of similar size and body orientation...


Krill typically follow a diurnal vertical migration. They spend the day at greater depths and rise during the night towards the surface. The deeper they go, the more they reduce their activity,[JODR99] apparently to reduce encounters with predators and to conserve energy. Some species (e.g. Euphausia superba, E. pacifica, E. hanseni, Pseudeuphausia latifrons, or Thysanoessa spinifera) also 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. Diel means in the course of the day. Thus a diel variation is a variation that occurs regularly every day or most days. ...

Beating pleopods of a swimming Antarctic krill.
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Beating pleopods of a swimming Antarctic krill.

Dense swarms may elicit a feeding frenzy among predators such as fish or birds, especially near the surface, where escape possibilities for the krill are limited. When disturbed, a swarm scatters, and some individuals have even been observed to molt instantaneously, leaving the exuvia behind as a decoy.[How05] Image File history File links The pleopods (swimming legs, or swimmerets) of a krill (here a member of Euphausia superba, the Antarctic krill). ... Image File history File links The pleopods (swimming legs, or swimmerets) of a krill (here a member of Euphausia superba, the Antarctic krill). ... Antennules Pereiopods Carapace Pleopods Uropods Telson The body of a decapod crustacean is made up of nineteen body segments grouped into two main body parts, the cephalothorax and the abdomen. ... Binomial name Euphausia superba Dana, 1850 The Antarctic krill (Euphausia superba ) is a species of krill found in the Antarctic waters of the Southern Ocean. ... Feeding frenzy is a ecological term used to describe a situation where oversaturation of a supply of food leads to rapid feeding by predatory animals. ... In birds, moulting or molting is the routine shedding of old feathers. ... Exuvia of an Antarctic krill. ...


Krill normally swim at pace of a few centimetres per second (0.2 – 10 body lengths per second[Ign99]), using their swimmerets for propulsion. Their larger migrations are subject to the currents in the ocean. When in danger, they show an escape reaction called lobstering: flipping their caudal appendages, i.e. the telson and uropods, they move backwards through the water relatively quickly, achieving speeds in the range of 10 to 27 body lengths per second,[Ign99] which for large krill such as E. superba means around 0.8 m/s.[Kils82] Their swimming performance has led many researchers to classify adult krill as micro-nektonic lifeforms, i.e. small animals capable of individual motion against (weak) currents. Larval forms of krill are generally considered zooplankton.[NE97, ch. 2]
The metre, or meter (symbol: m) is the SI base unit of length. ... Escape reaction (startle reaction) is a term used in behavior physiology to describe the details of the flight of attacked animals (predator/prey relationship). ... Lobstering. ... The telson is the last division of the body of a crustacean. ... Antennules Pereiopods Carapace Pleopods Uropods Telson The body of a decapod crustacean is made up of nineteen body segments grouped into two main body parts, the cephalothorax and the abdomen. ... Nekton is the grouping of organisms that live in the water column of the ocean and freshwater lakes. ... Photomontage of plankton organisms Plankton is the aggregate community of weakly swimming but mostly drifting small organisms that inhabit the water column of the ocean, seas, and bodies of freshwater. ...


Life cycle

A nauplius of Euphausia pacifica hatching, emerging backwards from the egg.
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A nauplius of Euphausia pacifica hatching, emerging backwards from the egg.

The general life-cycle of krill has been the subject of several studies (e.g. Guerny 1942,[Gue42] or Mauchline & Fisher 1969[MF69]) performed on a variety of species and is thus relatively well understood, although there are minor variations in details from species to species. When krill hatch from the eggs, they go through several larval stages called the nauplius, pseudometanauplius, metanauplius, calyptopsis, and furcilia stages, each of which is sub-divided into several sub-stages. The pseudometanauplius stage is exclusive of species that lay their eggs within an ovigerous sac (so-called sac-spawners). The larvae grow and molt multiple times during this process, shedding their rigid exoskeleton and growing a new one whenever it becomes too small. Smaller animals molt more frequently than larger ones. Until and including the metanauplius stage, the larvae nourish on yolk reserves within their body. Only by the calyptopsis stages, differentiation has progressed far enough for them to develop a mouth and a digestive tract, and they begin to feed upon phytoplankton. By that time, the larvae must have reached the photic zone, the upper layers of the ocean where algae flourish, for their yolk reserves are exhausted by then and they would starve otherwise. 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 molt. The number of segments added during any one of the furcilia stages may vary even within one species depending on environmental conditions.[Kn84] Image File history File links A nauplius of the krill Euphausia pacifica hatching, emerging backwards from the egg. ... Image File history File links A nauplius of the krill Euphausia pacifica hatching, emerging backwards from the egg. ... The nauplius larva of a prawn A nauplius is the larva of many kinds of crustaceans. ... Euphausia pacifica is small zooplankton organism in the Pacific. ... The nauplius larva of a prawn A nauplius is the larva of many kinds of crustaceans. ... A pseudometanauplius of the krill species Nematoscelis difficilis hatches using the push-off hatching technique. ... A metanauplius of the krill species Nematoscelis difficilis hatches using the push-off hatching technique. ... Ecdysis is the molting of the cuticula in arthropods and related groups (Ecdysozoa). ... The egg yolk is the yellow inside an egg. ... Embryonic stem cells differentiate into cells in various body organs. ... Diagrams of some typical phytoplankton Phytoplankton refers to the autotrophic component of the plankton that drifts in the water column. ... The photic zone is the depth of the water, whether in a lake or an ocean, that is exposed to sufficient sunlight for photosynthesis to occur. ...


After the final furcilia stage, the krill emerges in a shape similar to an adult, but is still immature. During the mating season, which varies depending on the species and the climate, the male deposits a sperm package at the genital opening (named thelycum) of the female. 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.[RQ86] Krill can have multiple broods in one season, with interbrood periods of the order of days. A spermatophore is a capsule or mass created by males of various invertebrate species, containing spermatozoa and transferred in entirety to the female during sex. ... Human female internal reproductive anatomy Ovaries are egg-producing reproductive organs found in female organisms. ...

The head of a female krill of the sac-spawning species Nematoscelis difficilis with her brood sac. The eggs have a diameter of 0.3 – 0.4 mm.
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The head of a female krill of the sac-spawning species Nematoscelis difficilis with her brood sac. The eggs have a diameter of 0.3 – 0.4 mm.

There are two types of spawning mechanisms.[Gom02a] The 57 species of the genera Bentheuphausia, Euphausia, Meganyctiphanes, Thysanoessa, and Thysanopoda are "broadcast spawners": the female eventually just releases the fertilized eggs into the water, where they usually sink into deeper waters, disperse, and are on their own. These species generally hatch in the nauplius 1 stage, but recently have been discovered to hatch sometimes as metanauplius or even as calyptopis stages.[Gom02b] The remaining 29 species of the other genera are "sac spawners", where the female carries the eggs with her attached to its rearmost pairs of thoracopods until they hatch as metanauplii, although some species like Nematoscelis difficilis may hatch as nauplius or pseudometanauplius.[B+2000] Image File history File links The head of female krill of the sac-spawning species Nematoscelis difficilis with her brood sac. ... Image File history File links The head of female krill of the sac-spawning species Nematoscelis difficilis with her brood sac. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ...


Some high latitude species of krill can live up to more than six years (e.g. Euphausia superba); others, such as the as mid-latitude species Euphausia pacifica, live only for two years.[NE97] Subtropical or tropical species' longevity is still smaller, like e.g. Nyctiphanes simplex that usually lives only for six to eight months.[Gom05] Latitude, sometimes denoted by the Greek letter φ, gives the location of a place on Earth north or south of the Equator. ... A tropic is either of two circles of latitude: Tropic of Cancer, at 23½°N Tropic of Capricorn, at 23½°S Tropic is also the name of a town in Utah, United States. ...


Molting occurs whenever the animal outgrows its rigid exoskeleton. Young animals, growing faster, therefore molt more often than older and larger ones. The frequency of molting varies wildly from species to species and is, even within one species, subject to many external factors such as the latitude, the water temperature, or the availability of food. The subtropical species Nyctiphanes simplex, for instance, has an overall intermolt period in the range of two to seven days: larvae molt on the average every three days, while juveniles and adults do so on the average every five days. For E. superba in the Antarctic sea, intermolt periods ranging between 9 and 28 days depending on the temperature between -1°C to 4°C have been observed, and for Meganyctiphanes norvegica in the North Sea the intermolt periods range also from 9 and 28 days but at temperatures between 2.5°C to 15°C.[Buch03] E. superba is known to be able to reduce its body size when there is not enough food available, molting also when its exoskeleton becomes too large.[SN02] 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, and has been postulated for other temperate species of krill, too.[MM99]
A degree Celsius (°C) is a unit of temperature named after the Swedish astronomer Anders Celsius (1701-1744), who first proposed a similar system in 1742. ...


Ecology

NASA SeaWiFS satellite image of the large phytoplankton bloom in the Bering Sea in 1998.
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NASA SeaWiFS satellite image of the large phytoplankton bloom in the Bering Sea in 1998.

Krill are an important element of the food chain. Antarctic krill feed directly on phytoplankton, converting the primary production energy into a form suitable for consumption by larger animals that cannot feed directly on the minuscule algae, but that can feed upon krill. Some species like the Northern krill have a smaller feeding basket and hunt for copepods and larger zooplankton. Many other animals feed on krill, ranging from smaller animals like fish or penguins to larger ones like seal and even baleen whales. NASA SeaWiFS image taken on April 25, 1998, showing the coccolithophore bloom in the Bering Sea. ... NASA SeaWiFS image taken on April 25, 1998, showing the coccolithophore bloom in the Bering Sea. ... NASA logo Listen to this article · (info) This audio file was created from an article revision dated 2005-09-01, and does not reflect subsequent edits to the article. ... SeaWiFS stands for Sea-viewing Wide Field-of-view Sensor. ... The term bloom can refer to the following things: Blooming soccer club from Santa Cruz - Bolivia Bloom (novel) is a science fiction novel by Wil McCarthy. ... The Bering (or Imarpik) Sea is a body of water above, and separted from, the north Pacific Ocean Ocean by the Alaska Peninsula and Aleutian Islands. ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean. ... Food chains and food webs or food networks describe the feeding relationships between species in a biotic community. ... Binomial name Euphausia superba Dana, 1850 The Antarctic krill (Euphausia superba ) is a species of krill found in the Antarctic waters of the Southern Ocean. ... Diagrams of some typical phytoplankton Phytoplankton refers to the autotrophic component of the plankton that drifts in the water column. ... Global oceanic and terrestrial primary production, from September 1997 to August 1998. ... Orders Calanoida Cyclopoida Gelyelloida Harpacticoida Misophrioida Monstrilloida Mormonilloida Platycopioida Poecilostomatoida Siphonostomatoida Copepods are small animals living in the sea and nearly every freshwater habitat. ... Photomontage of plankton organisms Plankton is the aggregate community of weakly swimming but mostly drifting small organisms that inhabit the water column of the ocean, seas, and bodies of freshwater. ... Atlantic herring, Clupea harengus: the most abundant species of fish in the world. ... This article is about penguin birds. ... Families Odobenidae Otariidae Phocidae Pinnipeds (fin-foots, lit. ... Families Balaenidae Balaenopteridae Eschrichtiidae Neobalaenidae Scientifically known as the Mysticeti, the baleen whales, also called whalebone whales or great whales, form a suborder of the order cetacea. ...


Disturbances of an ecosystem resulting in a decline of the krill population can have far-reaching effects. During a coccolithophore bloom in the Bering Sea in 1998,[Wei99] for instance, the diatom concentration dropped in the affected area. However, 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, and the incident was even thought to have been a reason for salmon not returning to the rivers of western Alaska in that season.[Br+98] In ecology, the word ecosystem is an abbreviation of the term, ecological system. ... Coccolithophores are single-celled algae belonging to the haptophytes. ... The Bering (or Imarpik) Sea is a body of water above, and separted from, the north Pacific Ocean Ocean by the Alaska Peninsula and Aleutian Islands. ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean. ... Diatoms are a major group of eukaryotic algae, and are one of the most common types of phytoplankton. ... Genera Procellaria Calonectris Puffinus †See also fulmar, prion, petrel Shearwaters are medium-sized long-winged seabirds. ... The Chinook or King Salmon is the largest salmon in North America and can grow up to 58 long and 126 pounds. ... Official language(s) English Capital Juneau Largest city Anchorage Area  - Total  - Width  - Length  - % water  - Latitude  - Longitude Ranked 1st 663,267 mi² / 1 717 854 km² 808 mi / 1300 km 1,479 mi / 2380 km 13. ...


Other factors besides predators and food availability also can influence the mortality rate in krill populations. There are several single-celled endoparasitoidic ciliates of the genus Collinia that can infect different species of krill and cause mass dying in affected populations. Such diseases have been reported for Thysanoessa inermis in the Bering Sea, but also for E. pacifica, Thysanoessa spinifera, and T. gregaria off the North-American Pacific coast.[Roa03] There are also some ectoparasites of the family Dajidae that afflict krill (and also shrimps and mysids); one such parasite is Oculophryxus bicaulis which has been found on the krill Stylocheiron affine and S. longicorne. It attaches itself to the eyestalk of the animal and sucks blood from its head; it is believed that it inhibits the reproduction of its host as none of the afflicted animals found reached maturity.[SG96] SEM image of endoparasitoidic ciliates of the genus Collinia, which can cause mass mortality in affected krill populations. ... Classes & Subclasses Class Karyorelictea Class Heterotrichea (e. ... A parasite is an organism that lives in or on the living tissue of a host organism at the expense of that host. ... Superfamilies and families Alpheoidea Alpheidae - snapping shrimps Barbouriidae Hippolytidae Ogyrididae Atyoidea Atyidae Bresilioidea Agostocarididae Alvinocarididae Bresiliidae Disciadidae Mirocarididae Campylonotoidea Bathypalaemonellidae Campylonotoidae Crangonoidea Crangonidae Glyphocrangonidea Galatheacaridoidea Galatheacarididae Nematocarcinoidea Eugonatonotidae Nematocarcinidae Rhynchocinetidae Xiphocarididae Oplophoroidea Oplophoridae Palaemonoidea Anchistioididae Desmocarididae Euryrhynchidae Gnathophyllidae Hymenoceridae Kakaducarididae Palaemonidae Typhlocarididae Pandaloidea Pandalidae Thalassocarididae Pasiphaeoidea Pasiphaeidae Procaridoidea Procarididae Processoidea... Any of various small, shrimplike, chiefly marine crustaceans of the order Mysidacea, the females of which carry their eggs in a pouch beneath the thorax. ... For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ...


See also: Carbon sequestration, biological pump.
Carbon sequestration from a fossil-fuel power station A carbon dioxide sink or CO2 sink is a carbon reservoir that is increasing in size, and is the opposite of a carbon source. The main sinks are the oceans and growing vegetation. ... In oceanic biogeochemistry, the biological pump is the sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone to the oceans interior. ...


Economy

Main article: Krill fishery. Krill fishery is the commercial fishery of krill, small shrimp-like marine animals that live in the oceans world-wide. ...

Deep frozen plates of Antarctic krill for use as animal feed and raw material for cooking
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Deep frozen plates of Antarctic krill for use as animal feed and raw material for cooking

Krill has been harvested as a food source for both humans (okiami) and their domesticated animals since the 19th century, in Japan maybe even earlier. Large-scale fishing developed only 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, the Russian Federation and Ukraine. A peak in krill harvest had been reached in 1983 with more than 528,000 tonnes in the Southern Ocean alone (of which the Soviet Union produced 93%). In 1993, two events led to a drastic decline in krill production: first, Russia abandoned its operations, and second, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) defined maximum catch quotas for a sustainable exploitation of Antarctic krill. Nowadays, the largest krill fishing nations in the Antarctic are Japan, followed by South Korea, Ukraine, and Poland.[NE97] The annual catch in Antarctic waters seems to have stabilized around 100,000 tonnes of krill, which is roughly one fiftieth of the CCAMLR catch quota[CCAMLR]. The main limiting factor is probably the high cost associated with Antarctic operations. The fishery around Japan appears to have saturated at some 70'000 tonnes.[NF03] Image File history File links krill meat plates image user:Uwe kils gfdl self File links The following pages link to this file: Krill Krill fishery ... Image File history File links krill meat plates image user:Uwe kils gfdl self File links The following pages link to this file: Krill Krill fishery ... Binomial name Euphausia superba Dana, 1850 The Antarctic krill (Euphausia superba ) is a species of krill found in the Antarctic waters of the Southern Ocean. ... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... Fishing is the activity of hunting for fish. ... The 1960s decade refers to the years from 1960 to 1969, inclusive. ... The 1970s decade refers to the years from 1970 to 1979, inclusive. ... Greek ἀνταρκτικός, opposite the arctic) is a continent surrounding the Earths South Pole. ... Krill fishery is the commercial fishery of krill, small shrimp-like marine animals that live in the oceans world-wide. ... The Convention for the Conservation of Antarctic Marine Living Resources is part of the Antarctic Treaty System. ... Sustainable - the ability to maintain into perpetuity. ...


Experimental small-scale harvesting is being carried out in other areas, too, e.g. fishing for Euphausia pacifica off British Columbia or harvesting Meganyctiphanes norvegica, Thysanoessa raschii and Thysanoessa inermis in the Gulf of St. Lawrence. These experimental operations produce only a few hundred tonnes of krill per year. Nicol & Foster[NF03] consider it unlikely that any new large-scale harvesting operations in these areas will be started due to the opposition from local fishing industries and conservation groups. Euphausia pacifica is small zooplankton organism in the Pacific. ... Motto: Splendor Sine Occasu (Latin: Splendour without diminishment) Official languages English Capital Victoria Largest city Vancouver Lieutenant-Governor Iona Campagnolo Premier Gordon Campbell (BC Liberal) Parliamentary representation  - House seat  - Senate seats 36 6 Area Total  â€¢ Land  â€¢ Water    (% of total)  Ranked 5th 944,735 km² 925,186 km² 19,549 km... The Gulf of Saint Lawrence, the worlds largest estuary, is the outlet of North Americas Great Lakes via the Saint Lawrence River into the Atlantic Ocean. ...


Krill taste salty and somewhat stronger than shrimp. For mass-consumption and commercially prepared products, they must be peeled because their exoskeleton contains fluorides, which are toxic in high concentrations.[Hab97] Excessive intake of okiami may cause diarrhea.
Superfamilies and families Alpheoidea Alpheidae - snapping shrimps Barbouriidae Hippolytidae Ogyrididae Atyoidea Atyidae Bresilioidea Agostocarididae Alvinocarididae Bresiliidae Disciadidae Mirocarididae Campylonotoidea Bathypalaemonellidae Campylonotoidae Crangonoidea Crangonidae Glyphocrangonidea Galatheacaridoidea Galatheacarididae Nematocarcinoidea Eugonatonotidae Nematocarcinidae Rhynchocinetidae Xiphocarididae Oplophoroidea Oplophoridae Palaemonoidea Anchistioididae Desmocarididae Euryrhynchidae Gnathophyllidae Hymenoceridae Kakaducarididae Palaemonidae Typhlocarididae Pandaloidea Pandalidae Thalassocarididae Pasiphaeoidea Pasiphaeidae Procaridoidea Procarididae Processoidea... An exoskeleton, in contrast to an endoskeleton, is an external anatomical feature that supports and protects an animals body. ... A fluoride ion is the ionic form of fluorine. ... Diarrhea (American English) or diarrhoea (Commonwealth English) is a condition in which the sufferer has frequent and watery, chunky, or loose bowel movements (from the ancient Greek word διαρροή = leakage; lit. ...


Footnotes

Note 1: The scientific name Euphausiacea is okiamime (オキアミ目) in Japanese.


References

The referencing system used in this article follows the alpha.bst style of BibTeX. The BibTeX logo BibTeX is a tool for formatting lists of references used by the LaTeX document preparation system. ...