Krill are small
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s of the
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the
Norwegian
Norwegian, Norwayan, or Norsk may refer to:
*Something of, from, or related to Norway, a country in northwestern Europe
*Norwegians, both a nation and an ethnic group native to Norway
*Demographics of Norway
*The Norwegian language, including the ...
word ', meaning "small
fry of fish", which is also often attributed to species of fish.
Krill are considered an important
trophic level
The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...
connection – near the bottom of the
food chain
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), det ...
. They feed on
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
and (to a lesser extent)
zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
, yet also are the main source of food for many larger animals. In the
Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
, one species, the
Antarctic krill
Antarctic krill (''Euphausia superba'') is a species of krill found in the Antarctic waters of the Southern Ocean. It is a small, swimming crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 ind ...
, ''Euphausia superba'', makes up an estimated
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
of around 379,000,000 tonnes, making it among the species with the largest total biomass. Over half of this biomass is eaten by whales,
seals
Seals may refer to:
* Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly:
** Earless seal, or "true seal"
** Fur seal
* Seal (emblem), a device to impress an emblem, used as a means of a ...
, penguins, seabirds,
squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
, and fish each year. Most krill species display large
daily vertical migrations, thus providing food for predators near the surface at night and in deeper waters during the day.
Krill are fished commercially in the Southern Ocean and in the waters around Japan. The total global harvest amounts to 150,000–200,000 tonnes annually, most of this from the
Scotia Sea
The Scotia Sea is a sea located at the northern edge of the Southern Ocean at its boundary with the South Atlantic Ocean. It is bounded on the west by the Drake Passage and on the north, east, and south by the Scotia Arc, an undersea ridge and i ...
. Most of the krill catch is used for
aquaculture
Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
and
aquarium
An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...
feeds, as
bait in
sport fishing
Recreational fishing, also called sport fishing or game fishing, is fishing for leisure, exercise or competition. It can be contrasted with commercial fishing, which is professional fishing for profit; or subsistence fishing, which is fishing ...
, or in the pharmaceutical industry. In Japan, the Philippines, and Russia, krill are also used for human consumption and are known as in Japan. They are eaten as ''camarones'' in Spain and Philippines. In the Philippines, krill are also known as ''alamang'' and are used to make a salty paste called ''
bagoong
''Bagoóng'' (; ) is a Philippine condiment partially or completely made of either fermented fish (''bagoóng'') or krill or shrimp paste (''alamáng'') with salt. The fermentation process also produces fish sauce known as ''patís''.
The pre ...
''.
Krill are also the main prey of
baleen whale
Baleen whales (systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea (whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in their ...
s, including the
blue whale
The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can ...
.
Taxonomy
Krill belong to the large
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
subphylum
In zoological nomenclature, a subphylum is a taxonomic rank below the rank of phylum.
The taxonomic rank of "subdivision (rank), subdivision" in fungi and plant taxonomy is equivalent to "subphylum" in zoological taxonomy. Some plant taxonomists ...
, the
Crustacea
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
. The most familiar and largest group of crustaceans, the
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
Malacostraca
Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobst ...
, includes the
superorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
Eucarida
Eucarida is a superorder of the Malacostraca, a class of the crustacean subphylum, comprising the decapods, krill, '' Amphionides'' and Angustidontida. They are characterised by having the carapace fused to all thoracic segments, and by the pos ...
comprising the three orders, Euphausiacea (krill),
Decapoda
The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is esti ...
(shrimp, prawns, lobsters, crabs), and the planktonic
Amphionidacea
''Amphionides reynaudii'' is a species of caridean shrimp, whose identity and position in the crustacean system remained enigmatic for a long time. It is a small (less than one inch long) planktonic crustacean found throughout the world's tropic ...
.
The order Euphausiacea comprises two
families
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...
. The more abundant
Euphausiidae
Krill are small crustaceans of the order (biology), order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian language, Norwegian word ', meaning "small Fry (biology), fry of fish", which is also oft ...
contains 10 different
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
with a total of 85 species. Of these, the genus ''
Euphausia
''Euphausia'' is the largest genus of krill, and is placed in the family Euphausiidae. There are 31 species known in this genus, including Antarctic krill (''Euphausia superba'') and ice krill ('' Euphausia crystallorophias'') from the Southern O ...
'' is the largest, with 31 species. The lesser known family, the
Bentheuphausiidae, has only one
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
, ''
Bentheuphausia amblyops
''Bentheuphausia amblyops'', the deep sea krill is a species of krill. ''B. amblyops'' is the only species within its genus, which in turn is the only genus within the family Bentheuphausiidae. All the 85 other species of krill known are classifi ...
'', a
bathypelagic
The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. The bathypelagic ...
krill living in deep waters below . It is considered the most primitive extant krill species.
Well-known species of the Euphausiidae of commercial
krill fisheries include
Antarctic krill
Antarctic krill (''Euphausia superba'') is a species of krill found in the Antarctic waters of the Southern Ocean. It is a small, swimming crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 ind ...
(''Euphausia superba''),
Pacific krill
''Euphausia pacifica'', the North Pacific krill, is a krill, euphausid that lives in the northern Pacific Ocean.
In Japan, ''E. pacifica'' is called ''isada krill'' or ' (ツノナシオキアミ). It is found from Suruga Bay northwards, includi ...
(''E. pacifica'') and
Northern krill
Northern krill (''Meganyctiphanes norvegica'') is a species of krill that lives in the North Atlantic Ocean. It is an important component of the zooplankton, providing food for whales, Pinniped, seals, fish and birds. (In the Southern Ocean, Anta ...
(''Meganyctiphanes norvegica'').
Phylogeny
, the order Euphausiacea is believed to be
monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
due to several unique conserved morphological characteristics (
autapomorphy
In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...
) such as its naked filamentous gills and thin thoracopods
and by molecular studies.
There have been many theories of the location of the order Euphausiacea. Since the first description of ''Thysanopode tricuspide'' by
Henri Milne-Edwards
Henri Milne-Edwards (23 October 1800 – 29 July 1885) was an eminent French zoologist.
Biography
Henri Milne-Edwards was the 27th child of William Edwards, an English planter and colonel of the militia in Jamaica and Elisabeth Vaux, a Frenchw ...
in 1830, the similarity of their biramous thoracopods had led zoologists to group euphausiids and Mysidacea in the order
Schizopoda
Schizopoda is a former Taxonomy (biology), taxonomical classification of a division of the Class (biology), class Malacostraca. Although it was split in 1883 by Johan Erik Vesti Boas into the two distinct order (biology), orders Mysidacea and Eupha ...
, which was split by
Johan Erik Vesti Boas
Johan Erik Vesti Boas (2 July 1855 – 25 January 1935), "Biographical Etymology of Marine Organism Names. B" (biographies of scientists with names beginning "B"), Hans G. Hansson, TJärnö Marine Biological Laboratory, Göteborg University and ...
in 1883 into two separate orders.
Later,
William Thomas Calman
William Thomas Calman (29 December 1871 – 29 September 1952) was a Scottish zoologist, specialising in the Crustacea. From 1927 to 1936 he was Keeper of Zoology at the British Museum (Natural History) (now the Natural History Museum).
Life
...
(1904) ranked the
Mysidacea
The Mysidacea is a group of shrimp-like crustaceans in the superorder Peracarida, comprising the two extant orders Mysida and Lophogastrida and the prehistoric Pygocephalomorpha
The order Pygocephalomorpha is an extinct group of peracarid c ...
in the superorder
Peracarida
The superorder Peracarida is a large group of malacostracan crustaceans, having members in marine, freshwater, and terrestrial habitats. They are chiefly defined by the presence of a brood pouch, or ''marsupium'', formed from thin flattened plat ...
and euphausiids in the superorder
Eucarida
Eucarida is a superorder of the Malacostraca, a class of the crustacean subphylum, comprising the decapods, krill, '' Amphionides'' and Angustidontida. They are characterised by having the carapace fused to all thoracic segments, and by the pos ...
, although even up to the 1930s the order Schizopoda was advocated.
It was later also proposed that order Euphausiacea should be grouped with the
Penaeidae
Penaeidae is a family of marine crustaceans in the suborder Dendrobranchiata, which are often referred to as penaeid shrimp or penaeid prawns. The Penaeidae contain many species of economic importance, such as the tiger prawn, whiteleg shrimp, ...
(family of prawns) in the Decapoda based on developmental similarities, as noted by
Robert Gurney
Robert Gurney (31 July 1879 – 5 March 1950) was a British zoologist from the Gurney family, most famous for his monographs on ''British Freshwater Copepoda'' (1931–1933) and the ''Larvae of Decapod Crustacea'' (1942). He was not affiliated w ...
and
Isabella Gordon
Isabella Gordon OBE FZS FLS (18 May 1901 – 11 May 1988) was a Scottish marine biologist who specialised in carcinology and was an expert in crabs and sea spiders. She worked at the Natural History Museum and received an OBE in 1961.
Ea ...
.
The reason for this debate is that krill share some morphological features of decapods and others of mysids.
Molecular studies have not unambiguously grouped them, possibly due to the paucity of key rare species such as ''Bentheuphausia amblyops'' in krill and ''Amphionides reynaudii'' in Eucarida. One study supports the monophyly of Eucarida (with basal Mysida),
another groups Euphausiacea with Mysida (the Schizopoda),
while yet another groups Euphausiacea with
Hoplocarida
Hoplocarida is a subclass of crustaceans. The only extant members are the mantis shrimp (Stomatopoda), but two other orders existed in the Palaeozoic: Aeschronectida
Aeschronectida is an extinct order of mantis shrimp-like crustacean
Crus ...
.
Timeline
No extant fossil can be unequivocally assigned to Euphausiacea. Some extinct
eumalacostraca
Eumalacostraca is a subclass of crustaceans, containing almost all living malacostracans, or about 40,000 described species. The remaining subclasses are the Phyllocarida and possibly the Hoplocarida. Eumalacostracans have 19 segments (5 cephalic ...
n
taxa
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
have been thought to be euphausiaceans such as ''
Anthracophausia'', ''
Crangopsis
''Crangopsis'' is an extinct genus of crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, a ...
'' – now assigned to the
Aeschronectida
Aeschronectida is an extinct order of mantis shrimp-like crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulida ...
(Hoplocarida)
– and ''Palaeomysis''.
All dating of
speciation
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
events were estimated by
molecular clock
The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleoti ...
methods, which placed the last common ancestor of the krill family Euphausiidae (order Euphausiacea minus ''Bentheuphausia amblyops'') to have lived in the
Lower Cretaceous
Lower may refer to:
*Lower (surname)
*Lower Township, New Jersey
*Lower Receiver (firearms)
*Lower Wick
Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...
about .
Distribution
Krill occur worldwide in all oceans, although many individual species have
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
or
neritic
The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth.
From the point of view of marine biology it forms a relatively stable and well-illuminated ...
(''i.e.,'' coastal) distributions. ''
Bentheuphausia amblyops
''Bentheuphausia amblyops'', the deep sea krill is a species of krill. ''B. amblyops'' is the only species within its genus, which in turn is the only genus within the family Bentheuphausiidae. All the 85 other species of krill known are classifi ...
'', a
bathypelagic
The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. The bathypelagic ...
species, has a
cosmopolitan distribution
In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...
within its deep-sea habitat.
Species of the genus ''
Thysanoessa Thysanoessa
Abstract
''Thysanoessa'' is a genus of the krill that play critical roles in the marine food web. They're abundant in Arctic and Antarctic areas, feeding on zooplankton and detritus to obtain energy. Thysanoessa are responsible for ...
'' occur in both
Atlantic
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
and
Pacific
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
oceans. The Pacific is home to ''
Euphausia pacifica
''Euphausia pacifica'', the North Pacific krill, is a euphausid that lives in the northern Pacific Ocean.
In Japan, ''E. pacifica'' is called ''isada krill'' or ' (ツノナシオキアミ). It is found from Suruga Bay northwards, including all ...
''. Northern krill occur across the Atlantic from the
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...
northward.
Species with neritic distributions include the four species of the genus ''
Nyctiphanes
''Nyctiphanes'' is a genus of krill, comprising four species with an anti-tropical distribution. Based on molecular phylogenetic analyses of the cytochrome oxidase gene and 16S ribosomal DNA, ''Nyctiphanes'' is believed to have evolved during ...
''.
[D'Amato, M.E. ''et al.'':]
Molecular dating and biogeography of the neritic krill ''Nyctiphanes''
", in ''Marine Biology vol. 155, no. 2'', pp. 243–247, August 2008. They are highly abundant along the
upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutr ...
regions of the
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
,
Humboldt,
Benguela
Benguela (; Umbundu: Luombaka) is a city in western Angola, capital of Benguela Province. Benguela is one of Angola's most populous cities with a population of 555,124 in the city and 561,775 in the municipality, at the 2014 census.
History
Por ...
, and
Canarias current systems.
Another species having only neritic distribution is ''E. crystallorophias'', which is endemic to the Antarctic coastline.
Species with endemic distributions include ''
Nyctiphanes capensis
''Nyctiphanes'' is a genus of krill, comprising four species with an anti-tropical distribution. Based on molecular phylogenetic analyses of the cytochrome oxidase gene and 16S ribosomal DNA, ''Nyctiphanes'' is believed to have evolved during ...
'', which occurs only in the Benguela current,
''
E. mucronata'' in the Humboldt current,
and the six ''Euphausia'' species native to the Southern Ocean.
In the Antarctic, seven species are known, one in genus ''Thysanoessa'' (''
T. macrura'') and six in ''Euphausia''. The
Antarctic krill
Antarctic krill (''Euphausia superba'') is a species of krill found in the Antarctic waters of the Southern Ocean. It is a small, swimming crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 ind ...
(''Euphausia superba'') commonly lives at depths reaching , whereas ice krill (''
Euphausia crystallorophias'') reach depth of , though they commonly inhabit depths of at most . Both are found at
latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
s south of
55° S, with ''E. crystallorophias'' dominating south of
74° S and in regions of
pack ice
Drift ice, also called brash ice, is sea ice that is not attached to the shoreline or any other fixed object (shoals, grounded icebergs, etc.).Leppäranta, M. 2011. The Drift of Sea Ice. Berlin: Springer-Verlag. Unlike fast ice, which is "fasten ...
. Other species known in the
Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
are ''
E. frigida'', ''
E. longirostris'', ''
E. triacantha'' and ''
E. vallentini''.
Anatomy and morphology
![Euphausia gills](https://upload.wikimedia.org/wikipedia/commons/6/68/Euphausia_gills.jpg)
Krill are
decapod crustaceans
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
and, as do all crustaceans they have a
chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
ous
external skeleton
An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a Human skeleton, human. In usag ...
. They have the standard
decapod anatomy
The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various g ...
with their bodies made up of three
parts
Part, parts or PART may refer to:
People
*Armi Pärt (born 1991), Estonian handballer
* Arvo Pärt (born 1935), Estonian classical composer
*Brian Part (born 1962), American child actor
*Dealtry Charles Part (1882–1961), sheriff (1926–1927) a ...
: the cephalothorax is composed of the
head
A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...
and the
thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
, which are fused, the
pleon
The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...
, which bears the ten swimming legs, and the
tail fan. This outer shell of krill is transparent in most species.
Krill feature intricate
compound eye
A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which disti ...
s. Some species adapt to different lighting conditions through the use of screening
pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...
s.
They have two
antennae and several pairs of thoracic legs called
pereiopod
The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various g ...
s or
thoracopod The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, plur ...
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.
Krill are decapods, so all species have five pairs of
swimming legs called "swimmerets", very similar to those of a
lobster
Lobsters are a family (biology), family (Nephropidae, Synonym (taxonomy), synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs ...
or
freshwater crayfish.
Most krill are about long as adults. A few species grow to sizes on the order of . The largest krill species, ''Thysanopoda spinicaudata'', lives
deep in the open ocean. Krill can be easily distinguished from other crustaceans such as true
shrimp
Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...
by their externally visible
gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
s.
Except for ''
Bentheuphausia amblyops
''Bentheuphausia amblyops'', the deep sea krill is a species of krill. ''B. amblyops'' is the only species within its genus, which in turn is the only genus within the family Bentheuphausiidae. All the 85 other species of krill known are classifi ...
'', krill are
bioluminescent
Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorganisms including ...
animals having organs called
photophore
A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, ...
s that can emit light. The light is generated by an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
-catalysed
chemiluminescence
Chemiluminescence (also chemoluminescence) is the emission of light (luminescence) as the result of a chemical reaction. There may also be limited emission of heat. Given reactants A and B, with an excited intermediate ◊,
: + -> lozenge -> ...
reaction, wherein a
luciferin
Luciferin (from the Latin ''lucifer'', "light-bearer") is a generic term for the light-emitting compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalyzed reaction with molecular oxygen. The result ...
(a kind of pigment) is activated by a
luciferase
Luciferase is a generic term for the class of oxidative enzymes that produce bioluminescence, and is usually distinguished from a photoprotein. The name was first used by Raphaël Dubois who invented the words ''luciferin'' and ''luciferase'', ...
enzyme. Studies indicate that the luciferin of many krill species is a
fluorescent
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
tetrapyrrole
Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by ( =- or -- units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four car ...
similar but not identical to
dinoflagellate
The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
luciferin and that the krill probably do not produce this substance themselves but acquire it as part of their diet, which contains dinoflagellates. Krill photophores are complex organs with lenses and focusing abilities, and can be rotated by muscles. 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.
Ecology
Feeding
Many krill are
filter feeders
Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...
:
their frontmost
appendage
An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body.
In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...
s, the thoracopods, form very fine combs with which they can filter out their food from the water. These filters can be very fine in species (such as ''Euphausia'' spp.) that feed primarily on
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
, in particular on
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s, which are unicellular
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
. Krill are mostly
omnivorous
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutri ...
,
although a few species are
carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
, preying on small
zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
and fish
larvae
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
.
Krill are an important element of the aquatic
food chain
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), det ...
. Krill convert the
primary production
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
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
Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...
s and larger zooplankton.
Predation
Many animals feed on krill, ranging from smaller animals like fish or penguins to larger ones like
seals
Seals may refer to:
* Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly:
** Earless seal, or "true seal"
** Fur seal
* Seal (emblem), a device to impress an emblem, used as a means of a ...
and
baleen whale
Baleen whales (systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea (whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in their ...
s.
Disturbances of an
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
resulting in a decline in the krill population can have far-reaching effects. During a
coccolithophore
Coccolithophores, or coccolithophorids, are single celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the kingdo ...
bloom in the
Bering Sea
The Bering Sea (, ; rus, Бе́рингово мо́ре, r=Béringovo móre) is a marginal sea of the Northern Pacific Ocean. It forms, along with the Bering Strait, the divide between the two largest landmasses on Earth: Eurasia and The Ameri ...
in 1998, 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
Shearwaters are medium-sized long-winged seabirds in the petrel family Procellariidae
The family Procellariidae is a group of seabirds that comprises the fulmarine petrels, the gadfly petrels, the diving petrels, the prions, and the shearwa ...
population dropped. The incident was thought to have been one reason
salmon
Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
did not spawn that season.
Several single-celled
endoparasitoid
In evolutionary ecology, a parasitoid is an organism that lives in close association with its host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionary strategies within parasitis ...
ic
ciliate
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...
s of the genus ''
Collinia'' can infect species of krill and devastate affected populations. Such diseases were reported for ''
Thysanoessa Thysanoessa
Abstract
''Thysanoessa'' is a genus of the krill that play critical roles in the marine food web. They're abundant in Arctic and Antarctic areas, feeding on zooplankton and detritus to obtain energy. Thysanoessa are responsible for ...
inermis'' in the Bering Sea and also for ''E. pacifica'', ''Thysanoessa spinifera'', and ''T. gregaria'' off the North American Pacific coast. Some
ectoparasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s of the family
Dajidae
The Dajidae are a family of marine isopod crustaceans in the suborder Cymothoida. The original description was made by Giard and Bonnier in 1887. Members of this family are ectoparasites of krill. They resemble a fleshy growth on the krill's bac ...
(epicaridean
isopod
Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...
s) afflict krill (and also shrimp and
mysid
Mysida is an order of small, shrimp-like crustaceans in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a brood pouch or "marsupium" in females. The fact that the larvae are reared in thi ...
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.
Climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
poses another threat to krill populations.
Plastics
Preliminary research indicates krill can digest
microplastic
Microplastics are fragments of any type of plastic less than in length, according to the U.S. National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency. They cause pollution by entering natural ecosystems from a v ...
s under in diameter, breaking them down and excreting them back into the environment in smaller form.
Life history and behavior
![Nauplius Hatching](https://upload.wikimedia.org/wikipedia/commons/a/a9/Nauplius_Hatching.jpg)
The life cycle of krill is relatively well understood, despite minor variations in detail from species to species.
After krill hatch, they experience several larval stages—''
nauplius'', ''
pseudometanauplius
Metanauplius is an early larval stage of some crustaceans such as krill. It follows the nauplius (larva), nauplius stage.
In sac-spawning krill, there is an intermediary phase called pseudometanauplius, a newly hatched form distinguished from old ...
'', ''
metanauplius
Metanauplius is an early larval stage of some crustaceans such as krill. It follows the nauplius stage.
In sac-spawning krill, there is an intermediary phase called pseudometanauplius, a newly hatched form distinguished from older metanauplii by ...
'', ''
calyptopsis'', and ''
furcilia
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a ecdysis, moult, in which the hard exoskeleton is shed to allow the animal to g ...
'', 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
moult
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
repeatedly as they develop, replacing their rigid exoskeleton when it becomes too small. Smaller animals moult more frequently than larger ones.
Yolk
Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...
reserves within their body nourish the larvae through metanauplius stage.
By the calyptopsis stages
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 photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
, 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. After the final furcilia stage, an immature juvenile emerges in a shape similar to an adult, and subsequently develops
gonad
A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...
s and matures sexually.
Reproduction
![Nematoscelis difficilis female](https://upload.wikimedia.org/wikipedia/commons/7/7e/Nematoscelis_difficilis_female.jpg)
During the mating season, which varies by species and climate, the male deposits a
sperm sack at the female's genital opening (named ''thelycum''). The females can carry several thousand eggs in their
ovary
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
, which may then account for as much as one third of the animal's body mass. Krill can have multiple broods in one season, with interbrood intervals lasting on the order of days.
Krill employ two types of spawning mechanism.
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. 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.
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 have been observed, and for ''Meganyctiphanes norvegica'' in the
North Sea
The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...
the inter-moult periods range also from 9 and 28 days but at temperatures between . ''E. superba'' is able to reduce its body size when there is not enough food available, moulting also when its exoskeleton becomes too large. 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.
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.
Subtropical or tropical species' longevity is still shorter, e.g., ''Nyctiphanes simplex'', which usually lives for only six to eight months.
Swarming
![Krill swarm](https://upload.wikimedia.org/wikipedia/commons/1/1f/Krill_swarm.jpg)
Most krill are
swarm
Swarm behaviour, or swarming, is a collective behaviour exhibited by entities, particularly animals, of similar size which aggregate together, perhaps milling about the same spot or perhaps moving ''en masse'' or migrating in some direction. ...
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. 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
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."
Vertical migration
![Pleopods euphausia superba](https://upload.wikimedia.org/wikipedia/commons/0/01/Pleopods_euphausia_superba.jpg)
Krill typically follow a
diurnal 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, apparently to reduce encounters with predators and to conserve energy. Swimming activity in krill varies with stomach fullness. Sated animals that had been feeding at the surface swim less actively and therefore sink below the mixed layer. As they sink they produce
feces
Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...
which implies a role in the Antarctic
carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...
. 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.
Experimental studies using ''
Artemia salina
''Artemia salina'' is a species of brine shrimp – aquatic crustaceans that are more closely related to ''Triops'' and cladocerans than to true shrimp. It belongs to a lineage that does not appear to have changed much in .
''A. salina'' is nati ...
'' as a model suggest that the vertical migrations of krill several hundreds of metres, in groups tens of metres deep, could collectively create enough downward jets of water to have a significant effect on ocean mixing.
Dense swarms can elicit a
feeding frenzy
In ecology, a feeding frenzy occurs when predators are overwhelmed by the amount of prey available. The term is also used as an idiom in the English language.
Examples in nature
For example, a large school of fish can cause nearby sharks, such a ...
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
In biology, exuviae are the remains of an exoskeleton and related structures that are left after ecdysozoans (including insects, crustaceans and arachnids) have moulted. The exuviae of an animal can be important to biologists as they can often b ...
behind as a decoy.
Krill normally swim at a pace of 5–10 cm/s (2–3 body lengths per second), using their swimmerets for propulsion. Their larger migrations are subject to ocean currents. When in danger, they show an
escape reaction
Escape response, escape reaction, or escape behavior is a mechanism by which animals avoid potential predation. It consists of a rapid sequence of movements, or lack of movement, that position the animal in such a way that allows it to hide, freeze ...
called
lobstering – flicking their
caudal structures, the
telson
The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...
and the
uropod
Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion.
Definition
Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...
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 . Their swimming performance has led many researchers to classify adult krill as
micro-nektonic life-forms, i.e., small animals capable of individual motion against (weak) currents. Larval forms of krill are generally considered zooplankton.
Biogeochemical cycles
![Role of Antarctic krill in biogeochemical cycles](https://upload.wikimedia.org/wikipedia/commons/a/ab/Role_of_Antarctic_krill_in_biogeochemical_cycles.webp)
The Antarctic krill is an important species in the context of
biogeochemical cycling
A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and the ...
and in the
Antarctic food web. It plays a prominent role in the Southern Ocean because of its ability to
cycle nutrients and to feed penguins and
baleen
Baleen is a filter-feeding system inside the mouths of baleen whales. To use baleen, the whale first opens its mouth underwater to take in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and ...
and
blue whale
The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can ...
s.
Human uses
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
Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inv ...
.
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.
In 1993, two events caused a decline in krill fishing: Russia exited the industry; and the
(CCAMLR) defined maximum catch quotas for a
sustainable exploitation of Antarctic krill. After an October 2011 review, the Commission decided not to change the quota.
[
The annual Antarctic catch stabilised at around 100,000 tonnes, which is roughly one fiftieth of the CCAMLR catch quota.][ The main limiting factor was probably high costs along with political and legal issues. The Japanese fishery saturated at some 70,000 tonnes.]
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 pristine, they are considered a "clean product".[
In 2018 it was announced that almost every krill fishing company operating in Antarctica will abandon operations in huge areas around the Antarctic Peninsula from 2020, including "buffer zones" around breeding colonies of penguins.
]
Human consumption
Although the total biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
of Antarctic krill may be as abundant as 400 million tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s, the human impact on this keystone species
A keystone species is a species which has a disproportionately large effect on its natural environment relative to its abundance, a concept introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaini ...
is growing, with a 39% increase in total fishing yield to 294,000 tonnes over 2010–2014. Major countries involved in krill harvesting are Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
(56% of total catch in 2014), the Republic of Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korean Peninsula and sharing a land border with North Korea. Its western border is formed by the Yellow Sea, while its east ...
(19%), and China (18%).[
Krill is a rich source of ]protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
and omega-3 fatty acids
Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...
which are under development in the early 21st century as human food, dietary supplement
A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources or that are synthetic in order ...
s as oil capsules, livestock food, and pet food
Pet food is animal feed intended for consumption by pets. Typically sold in pet stores and supermarkets, it is usually specific to the type of animal, such as dog food or cat food. Most meat used for animals is a byproduct of the human food indu ...
. 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
An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...
.[
In 2011, the US ]Food and Drug Administration
The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...
published a letter of no objection for a manufactured krill oil
Krill oil is an extract prepared from a species of Antarctic krill, ''Euphausia superba''. Processed krill oil is commonly sold as a dietary supplement. Two components of krill oil are omega-3 fatty acids similar to those in fish oil, and phosph ...
product to be generally recognized as safe ( GRAS) for human consumption.
Krill (and other planktonic
Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...
shrimp
Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...
, notably ''Acetes
''Acetes'' is a genus of small shrimp that resemble krill, which is native to the western and central Indo-Pacific, the Atlantic coast of the Americas, Pacific coast of South America and inland waters of South America. Although most are from mar ...
'' spp.) are most widely consumed in Southeast Asia, where it is fermented
Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
(with the shells intact) and usually ground finely to make shrimp paste
Shrimp paste or prawn sauce is a fermented condiment commonly used in Southeast Asian and Southern Chinese cuisines. It is primarily made from finely crushed shrimp or krill mixed with salt, and then fermented for several weeks. They are eithe ...
. It can be stir-fried and eaten paired with white rice or used to add umami
Umami ( from ja, 旨味 ), or savoriness, is one of the five basic tastes. It has been described as savory and is characteristic of broths and cooked meats.
People taste umami through taste receptors that typically respond to glutamates and ...
flavors to a wide variety of traditional dishes. The liquid from the fermentation process is also harvested as fish sauce
Fish sauce is a liquid condiment made from fish or krill that have been coated in salt and fermented for up to two years. It is used as a staple seasoning in East Asian cuisine and Southeast Asian cuisine, particularly Myanmar, Cambodia, Laos, P ...
.
See also
* Antarctic krill
Antarctic krill (''Euphausia superba'') is a species of krill found in the Antarctic waters of the Southern Ocean. It is a small, swimming crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 ind ...
* Cold-water shrimp
* Crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
* Krill fishery
The krill fishery is the commercial fishery of krill, small shrimp-like marine animals that live in the oceans world-wide. The present estimate for the biomass of Antarctic krill (''Euphausia superba'') is 379 million tonnes. The total global harv ...
* Krill oil
Krill oil is an extract prepared from a species of Antarctic krill, ''Euphausia superba''. Processed krill oil is commonly sold as a dietary supplement. Two components of krill oil are omega-3 fatty acids similar to those in fish oil, and phosph ...
* Northern krill
Northern krill (''Meganyctiphanes norvegica'') is a species of krill that lives in the North Atlantic Ocean. It is an important component of the zooplankton, providing food for whales, Pinniped, seals, fish and birds. (In the Southern Ocean, Anta ...
References
Further reading
* Boden, Brian P.; Johnson, Martin W.; Brinton, Edward
"Euphausiacea (Crustacea) of the North Pacific"
''Bulletin of the Scripps Institution of Oceanography''. Volume 6 Number 8, 1955.
* Brinton, Edward
"Euphausiids of Southeast Asian waters"
''Naga Report'' volume 4, part 5. La Jolla: University of California, Scripps Institution of Oceanography, 1975.
* Conway, D. V. P.; White, R. G.; Hugues-Dit-Ciles, J.; Galienne, C. P.; Robins, D. B.:
'', ttps://web.archive.org/web/20070927161104/http://www.mba.ac.uk/nmbl/publications/occpub/guide/section13.pdf ''Order'' Euphausiacea Occasional Publication of the Marine Biological Association of the United Kingdom
The Marine Biological Association of the United Kingdom (MBA) is a learned society with a scientific laboratory that undertakes research in marine biology. The organisation was founded in 1884 and has been based in Plymouth since the Citadel Hi ...
No. 15, Plymouth, UK, 2003.
* Everson, I. (ed.): ''Krill: biology, ecology and fisheries''. Oxford, Blackwell Science; 2000. .
*
* Mauchline, J.
Euphausiacea: ''Adults''
, Conseil International pour l'Exploration de la Mer, 1971. Identification sheets for adult krill with many line drawings. PDF
Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...
file, 2 Mb.
* Mauchline, J.
Euphausiacea: ''Larvae''
, Conseil International pour l'Exploration de la Mer, 1971. Identification sheets for larval stages of krill with many line drawings. PDF file, 3 Mb.
* Tett, P.:
', lecture notes from
from Napier University
, mottoeng = Without knowledge, everything is in vain
, established = 1992 – granted University status 1964 – Napier Technical College
, type = Public
, academic_staff = 802
, administrative_staff = 562
, chancellor = Will Whitehorn
, ...
.
* Tett, P.:
Bioluminescence
', lecture notes from the 1999/2000 edition of that same course.
External links
Webcam of Krill Aquarium at Australian Antarctic Division
'Antarctic Energies'
animation by Lisa Roberts
{{Authority control
Malacostraca
Commercial crustaceans
Edible crustaceans
Extant Early Cretaceous first appearances
Taxa named by James Dwight Dana