![Animation of diel migration](https://upload.wikimedia.org/wikipedia/commons/b/bc/Animation_of_diel_migration.gif)
Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as
copepods, living in the
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
and in
lake
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s. The word ''diel'' comes from the
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''dies''
day, and means a 24-hour period. The
migration
Migration, migratory, or migrate may refer to: Human migration
* Human migration, physical movement by humans from one region to another
** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
occurs when organisms move up to the
uppermost layer of the sea at night and return to the
bottom of the daylight zone of the oceans or to the
dense, bottom layer of lakes during the day.
It is important to the functioning of
deep-sea food webs and the
biologically driven sequestration of carbon.
In terms of
biomass, it is the largest synchronous migration in the world.
It is not restricted to any one taxon as examples are known from
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 can ...
s (
copepods),
molluscs
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estim ...
(
squid), and
ray-finned fishes
Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species.
The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...
(
trout
Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', '' Salmo'' and '' Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salm ...
).
The phenomenon may be advantageous for a number of reasons, most typically to access food and avoid predators.
It is triggered by various stimuli, the most prominent being response to changes in light intensity,
though evidence suggests that
biological clocks are an underlying stimulus as well.
While this mass migration is generally nocturnal, with the animals ascending from the depths at nightfall and descending at sunrise, the timing can be altered in response to the different cues and stimuli that trigger it. Some unusual events impact vertical migration: DVM can be absent during the
midnight sun
The midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the Sun remains visible at the local midnight. When the midnight sun is seen in the Arctic, ...
in Arctic regions
and vertical migration can occur suddenly during a
solar eclipse.
The phenomenon also demonstrates cloud-driven variations.
Discovery
The phenomenon was first documented by French naturalist
Georges Cuvier in 1817. He noted that ''
daphnia
''Daphnia'' is a genus of small planktonic crustaceans, in length. ''Daphnia'' are members of the order Anomopoda, and are one of the several small aquatic crustaceans commonly called water fleas because their saltatory swimming style resembl ...
'', a type of
plankton
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 ...
, appeared and disappeared according to a diurnal pattern.
During
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
the
U.S. Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage o ...
was taking
sonar
Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on o ...
readings of the ocean when they discovered the
deep scattering layer
The deep scattering layer, sometimes referred to as the sound scattering layer, is a layer in the ocean consisting of a variety of marine animals. It was discovered through the use of sonar, as ships found a layer that scattered the sound and w ...
(DSL). While performing sound propagation experiments, the University of California's Division of War Research (UCDWR) consistently had results of the
echo-sounder that showed a distinct reverberation that they attributed to mid-water layer scattering agents. At the time, there was speculation that these readings may be attributed to enemy submarines.
Martin W. Johnson
Martin Wiggo Johnson (September 30, 1893 – November 28, 1984), was an American oceanographer at Scripps Institution of Oceanography. He is known as an author of the landmark reference work ''The Oceans: Their Physics, Chemistry and General B ...
of
Scripps Institution of Oceanography proposed a possible explanation. Working with the UCDWR, the Scripps researchers were able to confirm that the observed reverberations from the echo-sounder were in fact related to the diel vertical migration of marine animals. The DSL was caused by large, dense groupings of organisms, like zooplankton, that scattered the sonar to create a false or second bottom.
Once scientists started to do more research on what was causing the DSL, it was discovered that a large range of organisms were vertically migrating. Most types of
plankton
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 ...
and some types of
nekton
Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms t ...
have exhibited some type of vertical migration, although it is not always diel. These migrations may have substantial effects on
mesopredator
A Mesopredator is a mid-ranking predator in a trophic level, which typically prey on smaller animals. Mesopredators often vary in ecosystems depending on the food web. While there is no definitive measurement for mesopredators, they are usually ref ...
s and
apex predators
An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own.
Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
by modulating the concentration and accessibility of their prey (e.g., impacts on the foraging behavior of
pinnipeds
Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae (whose only living member is the walru ...
).
Types of vertical migration
Diel
This is the most common form of vertical migration. Organisms migrate on a daily basis through different depths in the water column. Migration usually occurs between shallow surface waters of the epipelagic zone and deeper mesopelagic zone of the ocean or hypolimnion zone of lakes.
There are three recognized types of diel vertical migration:
Nocturnal vertical migration
In the most common form, nocturnal vertical migration, organisms ascend to the surface around dusk, remaining at the surface for the night, then migrating to depth again around dawn.
Reverse migration
Reverse migration occurs with organisms ascending to the surface at sunrise and remaining high in the water column throughout the day until descending with the setting sun.
Twilight diel vertical migration
Twilight diel vertical migration involves two separate migrations in a single 24-hour period, with the first ascent at dusk followed by a descent at midnight, often known as the "midnight sink". The second ascent to the surface and descent to the depths occurs at sunrise.
Seasonal
Organisms are found at different depths depending on what season it is.
Seasonal changes to the environment may influence changes to migration patterns. Normal diel vertical migration occurs in species of
foraminifera
Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...
throughout the year in the polar regions; however, during the midnight sun, no differential light cues exist so they remain at the surface to feed upon the abundant phytoplankton, or to facilitate photosynthesis by their symbionts.
This is not true for all species at all times, however.
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 ...
have been observed to resynchronize their migrations with the light of the moon during periods when the sun is not visible, and to stay in deeper waters when the moon is full.
Larger seasonally-migrating
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 ...
such as
overwintering
Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...
copepods have been shown to transport a substantial amount of
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
to the
deep ocean
The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of 200 metres (656 feet) or the point of transition from continental shelves to continental slopes. Conditions within the deep sea are a combin ...
through a process known as the
lipid pump.
The lipid pump is a process that sequesters carbon (in the form of carbon-rich
lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...
s) out of the surface ocean via the descent of copepods to the deep during autumn.
These copepods accumulate these lipids during late summer and autumn before descending to the deep to overwinter in response to reduced
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 ...
and harsh conditions at the surface.
Furthermore, they rely on these lipid reserves that are
metabolized
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
for energy to survive through winter before ascending back to the surface in the spring, typically at the onset of a
spring bloom
The spring bloom is a strong increase in phytoplankton abundance (i.e. stock) that typically occurs in the early spring and lasts until late spring or early summer. This seasonal event is characteristic of temperate North Atlantic, sub-polar, and ...
.
Ontogenetic
Organisms spend different stages of their life cycle at different depths.
There are often pronounced differences in migration patterns of adult female copepods, like ''
Eurytemora affinis
''Eurytemora'' is a genus of copepods in the family Temoridae. The World Register of Marine Species
The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive list of names of ...
,'' which stay at depth with only a small upward movement at night, compared to the rest of its life stages which migrate over 10 meters. In addition, there is a trend seen in other copepods, like ''Acartia spp''. that have an increasing amplitude of their DVM seen with their progressive life stages. This is possibly due to increasing body size of the copepods and the associated risk of visual predators, like fish, as being larger makes them more noticeable.
Vertical migration stimuli
There are two different types of factors that are known to play a role in vertical migration,
endogenous and
exogenous
In a variety of contexts, exogeny or exogeneity () is the fact of an action or object originating externally. It contrasts with endogeneity or endogeny, the fact of being influenced within a system.
Economics
In an economic model, an exogeno ...
. Endogenous factors originate from the organism itself; sex, age, size,
biological rhythms, etc. Exogenous factors are environmental factors acting on the organism such as light, gravity, oxygen, temperature, predator-prey interactions, etc.
Endogenous factors
Endogenous rhythm
Biological clocks are an ancient and adaptive sense of time innate to an organism that allows them to anticipate environmental changes and cycles so they are able to physiologically and behaviorally respond to the expected change.
Evidence of circadian rhythms controlling DVM, metabolism, and even gene expression have been found in copepod species, ''Calanus finmarchicus''. These copepods were shown to continue to exhibit these daily rhythms of vertical migration in the laboratory setting even in constant darkness, after being captured from an actively migrating wild population.
An experiment was done at the
Scripps Institution of Oceanography which kept organisms in column tanks with light/dark cycles. A few days later the light was changed to a constant low light and the organisms still displayed diel vertical migration. This suggests that some type of internal response was causing the migration.
Clock gene expression
Many organisms including the copepod ''C. finmarchicus'', has genetic material devoted to maintaining its biological clock. The expression of these genes varies temporally with the expression significantly increasing following dawn and dusk at times of greatest vertical migration seen in this species. These findings may indicate they work as a molecular stimulus for vertical migration.
Body size
The relative body size of an organism has been found to effect DVM. Bull trout express daily and seasonal vertical migrations with smaller individuals always staying at a deeper layer than the larger individuals. This is most likely due to a predation risk, but is dependent on the individuals own size such that smaller animals may be more inclined to remain at depth.
Exogenous factors
Light
"Light is the most common and critical cue for vertical migration".
However, as of 2010, there had not been sufficient research to determine which aspect of the light field was responsible.
As of 2020, research has suggested that both light intensity and spectral composition of light are important.
Temperature
Organisms will migrate to a water depth with temperatures that best suit the organisms needs, for example some fish species migrate to warmer surface waters in order to aid digestion. Temperature changes can influence swimming behavior of some copepods. In the presence of a strong thermocline some zooplankton may be inclined to pass through it, and migrate to the surface waters, though this can be very variable even in a single species. The marine copepod, ''Calanus finmarchicus,'' will migrate through gradients with temperature differences of 6 °C over George's Ban''k;'' whereas, in the North Sea they are observed to remain below the gradient.
Salinity
Changes in salinity may promote organism to seek out more suitable waters if they happen to be
stenohaline or unequipped to handle regulating their osmotic pressure. Areas that are impacted by tidal cycles accompanied by salinity changes, estuaries for example, may see vertical migration in some species of zooplankton.
Salinity has also been proposed as a factor that regulates the biogeochemical impact of diel vertical migration.
Pressure
Pressure changes have been found to produce differential responses that result in vertical migration. Many zooplankton will react to increased pressure with positive phototaxis, a negative geotaxis, and/or a kinetic response that results in ascending in the water column. Likewise, when there is a decrease in pressure, the zoo plankton respond by passively sinking or active downward swimming to descend in the water column.
Predator kairomones
A predator might release a
chemical cue which could cause its prey to vertically migrate away.
This may stimulate the prey to vertically migrate to avoid said predator. The introduction of a potential predator species, like a fish, to the habitat of diel vertical migrating zooplankton has been shown to influence the distribution patterns seen in their migration. For example, a study used ''Daphnia'' and a fish that was too small to prey of them (''Lebistus reticulatus''), found that with the introduction of the fish to the system the ''Daphnia'' remained below the
thermocline
A thermocline (also known as the thermal layer or the metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) in which temperature changes more drastically with ...
, where the fish was not present. This demonstrates the effects of kairomones on ''Daphnia'' DVM''.
''
Tidal patterns
Some organisms have been found to move with the tidal cycle. A study looked at the abundance of a species of small shrimp, ''Acetes sibogae,'' and found that they tended to move further higher in the water column and in higher numbers during flood tides than during ebb tides experiences at the mouth of an estuary. It is possible that varying factors with the tides may be the true trigger for the migration rather than the movement of the water itself, like the salinity or minute pressure changes.
Reasons for vertical migration
There are many hypotheses as to why organisms would vertically migrate, and several may be valid at any given time.
Predator avoidance
The universality of DVM suggests that there is some powerful common factor behind it.
The connection between available light and DVM has led researchers to theorize that organisms may stay in deeper, darker areas during the day to avoid being eaten by predators who depend on light to see and catch their prey. While the ocean's surface provides an abundance of food, it may be safest for many species to visit it at night.
Light-dependent predation by fish is a common pressure that causes DVM behavior in zooplankton and krill. A given body of water may be viewed as a risk gradient whereby the surface layers are riskier to reside in during the day than deep water, and as such promotes varied longevity among zooplankton that settle at different daytime depths. Indeed, in many instances it is advantageous for zooplankton to migrate to deep waters during the day to avoid predation and come up to the surface at night to feed. For example, the northern krill ''Meganyctiphanes norvegica'' undergoes diel vertical migration to avoid planktivorous fish.
Patterns among migrators seem to support the predator avoidance theory. Migrators will stay in groups as they migrate, a behavior that may protect individuals within the group from being eaten. Groups of smaller, harder to see animals begin their upward migration before larger, easier to see species, consistent with the idea that detectability by visual predators is a key issue. Small creatures may start to migrate upwards as much as 20 minutes before the sun sets, while large conspicuous fish may wait as long as 80 minutes after the sun goes down. Species that are better able to avoid predators also tend to migrate before those with poorer swimming capabilities.
Squid are a primary prey for Risso's dolphins (''
Grampus griseus''), an air-breathing predator, but one that relies on acoustic rather than visual information to hunt. Squid delay their migration pattern by about 40 minutes when dolphins are about, lessening risk by feeding later and for a shorter time.
Metabolic advantages
Another possibility is that predators can benefit from diel vertical migration as an energy conservation strategy. Studies indicate that male dogfish (''
Scyliorhinus canicula
''Scyliorhinus'' is a genus of catsharks in the family Scyliorhinidae. This genus is known in the fossil records from the Cretaceous period, late Albian age to the Pliocene epoch.Carrier, J. C.; Musick, J. A. & Heithaus, M. R. (2004)''Biolo ...
'') follow a "hunt warm - rest cool" strategy that enables them to lower their daily energy costs. They remain in warm water only long enough to obtain food, and then return to cooler areas where their metabolism can operate more slowly.
Alternatively, organisms feeding on the bottom in cold water during the day may migrate to surface waters at night in order to digest their meal at warmer temperatures.
Dispersal and transport
Organisms can use deep and shallow currents to find food patches or to maintain a geographical location.
Avoid UV damage
The sunlight can penetrate into the water column. If an organism, especially something small like a
microbe, is too close to the surface the UV can damage them. So they would want to avoid getting too close to the surface, especially during daylight.
Water transparency
A theory known as the “transparency-regulator hypothesis" predicts that "the relative roles of UV and visual predation pressure will vary systematically across a gradient of lake transparency."
In less transparent waters, where fish are present and more food is available, fish tend to be the main driver of DVM. In more transparent bodies of water, where fish are less numerous and food quality improves in deeper waters, UV light can travel farther, thus functioning as the main driver of DVM in such cases.
Unusual events
Due to the particular types of stimuli and cues used to initiate vertical migration, anomalies can change the pattern drastically.
For example, the occurrence of midnight sun in the Arctic induces changes to planktonic life that would normally perform DVM with a 24-hour night and day cycle. In the summers of the Arctic the Earth's north pole is directed toward the sun creating longer days and at the high latitude continuous day light for more than 24-hours.
Species of foraminifera found in the ocean have been observed to cease their DVM pattern, and rather remain at the surface in favor of feeding on the phytoplankton.
For example ''Neogloboquadrina pachyderma'', and for those species that contain symbionts, like ''Turborotalita quinqueloba'', remain in sunlight to aid photosynthesis.
Changes in sea-ice and surface chlorophyll
concentration are found to be stronger determinants of the vertical
habitat of Arctic ''N. pachyderma''.
There is also evidence of changes to vertical migration patterns during solar eclipse events. In the moments that the sun is obscured during normal day light hours, there is a sudden dramatic decrease in light intensity. The decreased light intensity, replicates the typical lighting experienced at night time that stimulate the planktonic organisms to migrate. During an eclipse, some copepod species distribution is concentrated near the surface, for example ''Calanus finmarchicus'' displays a classic diurnal migration pattern but on a much shorter time scale during an eclipse.
Importance for the biological pump
![Processes in the biological pump](https://upload.wikimedia.org/wikipedia/commons/6/69/Processes_in_the_biological_pump.webp)
The
biological pump
The biological pump (or ocean carbon biological pump or marine biological carbon pump) is the ocean's biologically driven sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sediments.Sigman DM & GH ...
is the conversion of
CO2 and inorganic nutrients by plant photosynthesis into
particulate
Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The te ...
organic matter in the
euphotic 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 ...
and transference to the deeper ocean.
This is a major process in the ocean and without vertical migration it wouldn't be nearly as efficient. The deep ocean gets most of its nutrients from the higher water column when they sink down in the form of
marine snow
In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...
. This is made up of dead or dying animals and microbes, fecal matter, sand and other inorganic material.
Organisms migrate up to feed at night so when they migrate back to depth during the day they defecate large sinking fecal pellets.
Whilst some larger fecal pellets can sink quite fast, the speed that organisms move back to depth is still faster. At night organisms are in the top 100 metres of the water column, but during the day they move down to between 800 and 1000 meters. If organisms were to defecate at the surface it would take the fecal pellets days to reach the depth that they reach in a matter of hours. Therefore, by releasing fecal pellets at depth they have almost 1000 metres less to travel to get to the deep ocean. This is known as
active transport
In cellular biology, ''active transport'' is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellul ...
. The organisms are playing a more active role in moving organic matter down to depths. Because a large majority of the deep sea, especially marine microbes, depends on nutrients falling down, the quicker they can reach the ocean floor the better.
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
salps
A salp (plural salps, also known colloquially as “sea grape”) or salpa (plural salpae or salpas) is a barrel-shaped, planktic tunicate. It moves by contracting, thereby pumping water through its gelatinous body, one of the most efficient ...
play a large role in the active transport of fecal pellets. 15–50% of zooplankton biomass is estimated to migrate, accounting for the transport of 5–45% of particulate organic nitrogen to depth.
Salps are large gelatinous plankton that can vertically migrate 800 meters and eat large amounts of food at the surface. They have a very long gut retention time, so fecal pellets usually are released at maximum depth. Salps are also known for having some of the largest fecal pellets. Because of this they have a very fast sinking rate, small
detritus particles are known to aggregate on them. This makes them sink that much faster. As previously mentioned, the lipid pump represents a substantial flux of POC to the deep ocean in the form of lipids produced by large overwintering copepods.
Through overwintering, these lipids are transported to the deep in autumn and are metabolized at depths below the thermocline through winter before the copepods rise to the surface in the spring.
The metabolism of these lipids reduces this POC at depth while producing CO
2 as a waste product, ultimately serving as a potentially significant contributor to oceanic
carbon sequestration
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in lan ...
.
Although the flux of lipid carbon from the lipid pump has been reported to be comparable to the global POC flux from the biological pump, observational challenges with the lipid pump from deficient
nutrient cycling
A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cycli ...
, and capture techniques have made it difficult to incorporate it into the global carbon export flux.
So while currently there is still much research being done on why organisms vertically migrate, it is clear that vertical migration plays a large role in the active transport of dissolved organic matter to depth.
See also
*
Krill
Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish.
Krill are consi ...
*
Phytoplankton
*
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 ...
References
{{collective animal behaviour
Aquatic ecology
Biological oceanography
Marine biology
Planktology
Animal migration