View source for Biology:Diel vertical migration

{{short description| A pattern of daily vertical movement characteristic of many aquatic species }}
[[File:Animation of diel migration.gif|thumb|upright=2| {{center|Daily migration of marine life between the twilight zone<br/>and the ocean surface – animation by NASA{{hsp}}<ref>[https://climate.nasa.gov/blog/2788/this-twilight-zone-is-dark-watery-and-yes-also-full-of-intrigue/ This twilight zone is dark, watery, and yes, also full of intrigue] ''NASA Blog'', 21 August 2018.</ref>}}]]

'''Diel vertical migration''' ('''DVM'''), also known as '''diurnal vertical migration''', is a pattern of movement used by some organisms, such as [[Biology:Copepod|copepod]]s, living in the [[Earth:Ocean|ocean]] and in [[Earth:Lake|lake]]s.  The adjective "diel" (IPA: {{IPAc-en|ˈ|d|aɪ|.|ə|l}}, {{IPAc-en|ˈ|d|iː|.|əl}}) comes from {{Lang-la|diēs|lit= day}}, and refers to a 24-hour period. The [[Biology:Animal migration|migration]] occurs when organisms move up to the uppermost layer of the water at night and return to the bottom of the daylight zone of the oceans or to the [[Biology:Hypolimnion|dense, bottom layer]] of lakes during the day.<ref name=":0"/>  DVM is important to the functioning of [[Biology:Marine food web|deep-sea food webs]] and the [[Biology:Biological pump|biologically-driven sequestration of carbon]].<ref name="Drazen">{{cite journal |last1= Drazen |first1= Jeffrey C. |last2= Sutton |first2= Tracey T. |title=Dining in the Deep: The Feeding Ecology of Deep-Sea Fishes |journal=Annual Review of Marine Science |date=3 January 2017 |volume=9 |issue=1 |pages= 337–366 |doi=10.1146/annurev-marine-010816-060543 |pmid=27814034 |bibcode=2017ARMS....9..337D |url= https://doi.org/10.1146/annurev-marine-010816-060543 |access-date= 21 December 2021 |issn= 1941-1405|doi-access= free }}</ref>

In terms of [[Earth:Biomass (ecology)|biomass]], DVM is the largest synchronous migration in the world.<ref name="Seo">{{cite journal |last1= Seo |first1= Hannah |title=The ups and downs of a great vertical migration |journal= Knowable Magazine |date=3 December 2021 |doi=10.1146/knowable-110421-1 |url= https://knowablemagazine.org/article/living-world/2021/up-downs-great-vertical-migration |access-date= 11 December 2021 |doi-access=free}}</ref><ref name=":0">{{cite web|title=Diel Vertical Migration (DVM)|url= http://funwithkrill.blogspot.com/2011/08/diel-vertical-migration-dvm.html|access-date= 5 April 2012|date= 2011-08-24}}</ref> It is not restricted to any one taxon, as examples are known from [[Biology:Crustacean|crustacean]]s ([[Biology:Copepod|copepod]]s),<ref name="P.B. Holliland, I. Ahlbeck, E. Westlund, S. Hansson 298–307">{{Cite journal|last= P.B. Holliland, I. Ahlbeck, E. Westlund, S. Hansson|date= April 2012|title=Ontogenetic and seasonal changes in diel vertical migration amplitude of the calanoid copepods Eurytemora affinis and Acartia spp. in a coastal area of the northern Baltic proper|journal= Journal of Plankton Research|volume= 34|issue= 4|pages= 298–307|doi= 10.1093/plankt/fbs001 |doi-access= free}}</ref> [[Biology:Mollusca|molluscs]] ([[Biology:Squid|squid]]),<ref>{{Cite journal|last= R. Rosa, B.A. Seibel|date= July–August 2010|title=Metabolic physiology of the Humboldt squid, Dosidicus gigas: Implications for vertical migration in a pronounced oxygen minimum zone|journal= Progress in Oceanography|volume= 86|issue= 1–2|pages= 72–80 |doi= 10.1016/j.pocean.2010.04.004|bibcode=2010PrOce..86...72R}}</ref> and [[Biology:Actinopterygii|ray-finned fishes]] ([[Biology:Trout|trout]]).<ref name="L.F.G. Gutowsky, P.M. Harrison, E.G. Martins, A. Leake, D.A. Patterson, M. Power, S.J. Cooke 365–373">{{Cite journal|last= L.F.G. Gutowsky, P.M. Harrison, E.G. Martins, A. Leake, D.A. Patterson, M. Power, S.J. Cooke|date= August 2013|title= Diel vertical migration hypotheses explain size-dependent behaviour in freshwater piscivore |journal= Animal Behaviour|volume= 86|issue=2|pages=365–373|doi= 10.1016/j.anbehav.2013.05.027 |s2cid= 49544030}}</ref>

The phenomenon may be advantageous for a number of reasons, most typically to access food and to avoid predators.<ref name=":02" /> 
It is triggered by various stimuli, the most prominent being changes in light-intensity,<ref name=":02">{{Cite journal|last= B. Cisewski, V.H. Strass, M. Rhein, S. Kragefsky|date= January 2010|title= Seasonal variation of diel vertical migration of zooplankton from ADCP backscatter time series data in the Lazarev Sea, Antarctica |journal= Deep Sea Research Part I: Oceanographic Research Papers|volume=57|issue=1|pages=78–94|doi= 10.1016/j.dsr.2009.10.005|bibcode= 2010DSRI...57...78C|url= https://epic.awi.de/id/eprint/19768/1/Cis2008b.pdf}}</ref> though evidence suggests that [[Biology:Circadian rhythm|biological clocks]] are an underlying stimulus as well.<ref name="N.S. Hafker, B. Meyer, K.S. Last, D.W. Pond, L. Huppe, M. Taschke 2194–2201">{{Cite journal|last= N.S. Hafker, B. Meyer, K.S. Last, D.W. Pond, L. Huppe, M. Taschke|date= July 2017|title= Circadian clock involvement in zooplankton diel vertical migration|journal= Current Biology|volume= 27|issue= 14|pages= 2194–2201|doi= 10.1016/j.cub.2017.06.025|pmid= 28712565|doi-access= free}}</ref> While this mass migration is generally nocturnal, with the animals ascending from the depths at nightfall and descending at sunrise, the timing can  alter in response to the different cues and stimuli that trigger it. Some unusual events impact vertical migration: DVM can be absent during the [[Astronomy:Midnight sun|midnight sun]] in Arctic regions<ref name="Darnis">{{cite journal |last1= Darnis |first1= G. |last2= Hobbs |first2= L. |last3= Geoffroy |first3= M. |last4= Grenvald |first4= J. C. |last5= Renaud |first5= P. E. |last6= Berge |first6= J. |last7= Cottier |first7= F. |last8= Kristiansen |first8= S. |last9= Daase |first9= M. |last10= Søreide |first10= J. E. |last11= Wold |first11= A. |last12= Morata |first12= N. |last13= Gabrielsen |first13= T. |title= From polar night to midnight sun: Diel vertical migration, metabolism and biogeochemical role of zooplankton in a high Arctic fjord (Kongsfjorden, Svalbard) |journal=Limnology and Oceanography |date= 2017 |volume= 62 |issue= 4 |pages= 1586–1605 |doi= 10.1002/lno.10519 |bibcode= 2017LimOc..62.1586D |s2cid= 56252159 |language= en |issn= 1939-5590|doi-access= free |hdl= 10037/11981 |hdl-access= free }}</ref><ref name="C. Manno, A.K. Pavlov 285–295">{{Cite journal|last=C. Manno, A.K. Pavlov|date= January 2014|title= Living planktonic foraminifera in the Fram Strait (Arctic): absence of diel vertical migration during the midnight sun|journal= Hydrobiologia|volume= 721|pages= 285–295|doi= 10.1007/s10750-013-1669-4|s2cid= 18320084}}</ref> and vertical migration can occur suddenly during a [[Earth:Solar eclipse|solar eclipse]].<ref name="K. Sherman, K.A. Honey 1156–1158">{{Cite journal|last= K. Sherman, K.A. Honey|date= May 1970|title= Vertical movements of zooplankton during a solar eclipse|journal= Nature|volume= 227|issue= 5263|pages= 1156–1158|doi= 10.1038/2271156a0 |pmid= 5451119|bibcode= 1970Natur.227.1156S|s2cid= 4209244}}</ref>  The phenomenon also demonstrates cloud-driven variations.<ref name="Omand">{{cite journal |last1= Omand |first1= Melissa M. |last2= Steinberg |first2= Deborah K. |last3= Stamieszkin |first3= Karen |title= Cloud shadows drive vertical migrations of deep-dwelling marine life |journal= Proceedings of the National Academy of Sciences |date= 10 August 2021 |volume= 118 |issue= 32 |pages= e2022977118 |doi= 10.1073/pnas.2022977118 |pmid= 34349017 |pmc= 8364114 |bibcode= 2021PNAS..11822977O |language= en |issn=0027-8424|doi-access=free }}</ref>

The common swift is an exception among birds in that it ascends and descends into high altitudes at dusk and dawn, similar to the vertical migration of aquatic lifeforms.

==Discovery==
The phenomenon was first documented by French naturalist [[Biography:Georges Cuvier|Georges Cuvier]] in 1817. He noted that ''[[Biology:Daphnia|daphnia]]'', a type of [[Earth:Plankton|plankton]], appeared and disappeared according to a diurnal pattern.<ref name="Seo"/><ref name="Bandara">{{cite journal |last1=Bandara |first1=Kanchana |last2=Varpe |first2=Øystein |last3=Wijewardene |first3=Lishani |last4=Tverberg |first4=Vigdis |last5=Eiane |first5=Ketil |title=Two hundred years of zooplankton vertical migration research |journal=Biological Reviews |date=2021 |volume=96 |issue=4 |pages=1547–1589 |doi=10.1111/brv.12715 |pmid=33942990 |s2cid=233722666 |url=https://doi.org/10.1111/brv.12715 |access-date=11 December 2021 |language=en |issn=1469-185X|hdl=10037/22091 |hdl-access=free }}</ref>

During [[Social:World War II|World War II]] the U.S. Navy was taking sonar readings of the ocean when they discovered the [[Earth:Deep scattering layer|deep scattering layer]] (DSL). While performing sound propagation experiments, the University of California's Division of War Research (UCDWR) consistently had results of the [[Earth:Echo sounding|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.<ref name="Hill"/>

Martin W. Johnson of [[Organization:Scripps Institution of Oceanography|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,&nbsp;that scattered the sonar to create a false or second bottom.<ref name="Seo"/><ref name="Bandara"/><ref name="Hill">{{Cite book|title=Physical Oceanography|last=Hill|first=M.N.|publisher=Harvard University Press|year=2005|pages=499}}</ref>

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 [[Earth:Plankton|plankton]] and some types of [[Earth:Nekton|nekton]] have exhibited some type of vertical migration, although it is not always diel. These migrations may have substantial effects on [[Earth:Mesopredator|mesopredator]]s and apex predators by modulating the concentration and accessibility of their prey (e.g., impacts on the foraging behavior of pinnipeds<ref>{{cite journal|author1=Horning, M. |author2=Trillmich, F. |title=Lunar cycles in diel prey migrations exert a stronger effect on the diving of juveniles than adult Galapagos fur seals|year=1999|journal=Proceedings of the Royal Society B|volume=266|issue=1424 |pages=1127–1132|doi=10.1098/rspb.1999.0753 |pmid=10406130 |pmc=1689955}}</ref>).

==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.<ref name=":0" />
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.<ref name=":02"/>

====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.<ref name=":02"/>

====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.<ref name=":02"/>

===Seasonal===
Organisms are found at different depths depending on what season it is.<ref name="Visser, Andre">{{cite journal | last=Visser | first=Andre |author2=Sigrun Jonasdottir |year=1999 | title=Lipids, buoyancy and the seasonal vertical migration of Calanus finmarchicus | journal=Fisheries Oceanography | volume=8 | pages=100–106 | doi=10.1046/j.1365-2419.1999.00001.x}}</ref> Seasonal changes to the environment may influence changes to migration patterns. Normal diel vertical migration occurs in species of [[Biology:Foraminifera|foraminifera]] 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.<ref name="C. Manno, A.K. Pavlov 285–295"/>  This is not true for all species at all times, however. [[Earth:Zooplankton|Zooplankton]] 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.<ref name="Seo"/>

Larger seasonally-migrating [[Earth:Zooplankton|zooplankton]] such as [[Biology:Overwintering|overwintering]] copepods have been shown to transport a substantial amount of [[Chemistry:Carbon|carbon]] to the [[Earth:Deep sea|deep ocean]] through a process known as the [[Earth:Lipid pump|lipid pump]].<ref name=":1">{{Cite journal|last1=Jónasdóttir|first1=Sigrún Huld|last2=Visser|first2=André W.|last3=Richardson|first3=Katherine|last4=Heath|first4=Michael R.|date=2015-09-29|title=Seasonal copepod lipid pump promotes carbon sequestration in the deep North Atlantic|journal=Proceedings of the National Academy of Sciences|language=en|volume=112|issue=39|pages=12122–12126|doi=10.1073/pnas.1512110112|issn=0027-8424|pmid=26338976|pmc=4593097|doi-access=free}}</ref> The lipid pump is a process that sequesters carbon (in the form of carbon-rich [[Chemistry:Lipid|lipid]]s) out of the surface ocean via the descent of copepods to the deep during autumn.<ref name=":1" /> These copepods accumulate these lipids during late summer and autumn before descending to the deep to overwinter in response to reduced [[Earth:Primary production|primary production]] and harsh conditions at the surface.<ref name=":1" /><ref name=":2">{{Cite journal|last1=Visser|first1=Andre W.|last2=Grønning|first2=Josephine|last3=Jónasdóttir|first3=Sigrún Huld|date=2017|title=Calanus hyperboreus and the lipid pump|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/lno.10492|journal=Limnology and Oceanography|language=en|volume=62|issue=3|pages=1155–1165|doi=10.1002/lno.10492|bibcode=2017LimOc..62.1155V|s2cid=51989153 |issn=1939-5590}}</ref> Furthermore, they rely on these lipid reserves that are [[Biology:Metabolism|metabolized]] for energy to survive through winter before ascending back to the surface in the spring, typically at the onset of a [[Earth:Spring bloom|spring bloom]].<ref name=":1" />

===Ontogenetic===
Organisms spend different stages of their life cycle at different depths.<ref name="Kobari, Toru">{{cite journal | last=Kobari | first=Toru |author2=Tsutomu Ikeda |year=2001 | title=Octogenetic vertical migration and life cycle of Neocalanus plumchrus (Crustacea:Copepoda) in the Oyashio region, with notes on regional variations in body size | journal=Journal of Plankton Research | volume=23 | pages=287–302 | doi=10.1093/plankt/23.3.287 | issue=3| doi-access=free }}</ref> There are often pronounced differences in migration patterns of adult female copepods, like ''[[Biology:Eurytemora|Eurytemora affinis]],'' 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.<ref name="P.B. Holliland, I. Ahlbeck, E. Westlund, S. Hansson 298–307"/>

==Vertical migration stimuli==
There are two different types of factors that are known to play a role in vertical migration, endogenous and exogenous. 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.<ref name="Richards">{{cite journal | last=Richards | first=Shane |author2=Hugh Possingham |author3=John Noye  |year=1996 | title=Diel vertical migration: modeling light-mediated mechanisms | journal=Journal of Plankton Research| volume=18 | pages=2199–2222 | doi=10.1093/plankt/18.12.2199 | issue=12| doi-access=free }}</ref>

=== 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.<ref name="N.S. Hafker, B. Meyer, K.S. Last, D.W. Pond, L. Huppe, M. Taschke 2194–2201"/>

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.<ref name="N.S. Hafker, B. Meyer, K.S. Last, D.W. Pond, L. Huppe, M. Taschke 2194–2201"/>

An experiment was done at the [[Organization:Scripps Institution of Oceanography|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.<ref name="Enright, J.T..">{{cite journal | last=Enright | first=J.T. |author2=W.M. Hammer |year=1967 | title=Vertical Diurnal Migration and Endogenous Rhythmicity | journal=Science | volume=157 | pages=937–941 | jstor= 1722121 | doi=10.1126/science.157.3791.937 | pmid=17792830 | issue=3791| bibcode=1967Sci...157..937E | s2cid=20415350 }}</ref>

====Clock gene expression====

Many organisms, including the copepod ''C. finmarchicus'', have genetic material devoted to maintaining their biological clock. The expression of these genes varies temporally with the expression significantly increasing following dawn and dusk at times of greatest vertical migration. These findings may indicate they work as a molecular stimulus for vertical migration.<ref name="N.S. Hafker, B. Meyer, K.S. Last, D.W. Pond, L. Huppe, M. Taschke 2194–2201"/>

====Body size====

The relative body size of an organism has been found to affect 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.<ref name="L.F.G. Gutowsky, P.M. Harrison, E.G. Martins, A. Leake, D.A. Patterson, M. Power, S.J. Cooke 365–373"/>

===Exogenous factors===
====Light====
"Light is the most common and critical cue for vertical migration".<ref name=":02"/> However, as of 2010,  there had not been sufficient research to determine which aspect of the light field was responsible.<ref name=":02"/> As of 2020, research has suggested that both light intensity and spectral composition of light are important.<ref name="Prins">{{cite journal |last1=Prins |first1=Antoine |last2=Deleris |first2=Paul |last3=Hubas |first3=Cédric |last4=Jesus |first4=Bruno |title=Effect of Light Intensity and Light Quality on Diatom Behavioral and Physiological Photoprotection |journal=Frontiers in Marine Science |date=2020 |volume=7 |pages=203 |doi=10.3389/fmars.2020.00203 |issn=2296-7745|doi-access=free }}</ref>

====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&nbsp;°C over George's Ban''k;'' whereas, in the North Sea they are observed to remain below the gradient.<ref name="Ringelberg 2010 122–127">{{Cite book|title=Diel Vertical Migration of Zooplankton in Lakes and Oceans|url=https://archive.org/details/dielverticalmigr00ring|url-access=limited|last=Ringelberg|first=Joop|publisher=Springer Science|year=2010|isbn=978-90-481-3092-4|location=London New York, USA|pages=[https://archive.org/details/dielverticalmigr00ring/page/n130 122]–127}}</ref>

====Salinity====

Changes in salinity may promote organism to seek out more suitable waters if they happen to be [[Biology:Stenohaline|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.<ref name="Barnes 1993 327–329">{{Cite book|title=Oceanography and Marine Biology, An Annual Review|last=Barnes|first=Margaret|publisher=CRC Press|year=1993|volume=31|location=Boca Raton, Florida, USA|pages=327–329}}</ref> Salinity has also been proposed as a factor that regulates the biogeochemical impact of diel vertical migration.<ref>{{Cite journal |last1=Darnis |first1=G. |last2=Hobbs |first2=L. |last3=Geoffroy |first3=M. |last4=Grenvald |first4=J. C. |last5=Renaud |first5=P. E. |last6=Berge |first6=J. |last7=Cottier |first7=F. |last8=Kristiansen |first8=S. |last9=Daase |first9=M. |last10=E. Søreide |first10=J. |last11=Wold |first11=A. |last12=Morata |first12=N. |last13=Gabrielsen |first13=T. |date=2017 |title=From polar night to midnight sun: Diel vertical migration, metabolism and biogeochemical role of zooplankton in a high Arctic fjord (Kongsfjorden, Svalbard) |journal=Limnology and Oceanography |language=en |volume=62 |issue=4 |pages=1586–1605 |doi=10.1002/lno.10519 |bibcode=2017LimOc..62.1586D |issn=0024-3590|doi-access=free |hdl=10037/11981 |hdl-access=free }}</ref>

==== 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.<ref name="Barnes 1993 327–329"/>

====Predator kairomones====

A predator might release a [[Biology:Kairomone|chemical cue]] which could cause its prey to vertically migrate away.<ref name="von Elert, Eric.">{{cite journal | last=von Elert | first=Eric | author2=Georg Pohnert | year=2000 | title=Diel Predator specificity of kairomones in diel vertical migration of Daphnia: a chemical approach | journal=OIKOS | volume=88 | pages=119–128  | issn=0030-1299 | issue=1 | doi=10.1034/j.1600-0706.2000.880114.x }}{{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> 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 [[Earth:Thermocline|thermocline]], where the fish was not present. This demonstrates the effects of kairomones on ''Daphnia'' DVM''.<ref name="Ringelberg 2010 122–127"/>''

====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.<ref name="Barnes 1993 327–329"/>

==Reasons for vertical migration==
There are many hypotheses as to why organisms would vertically migrate, and several may be valid at any given time.<ref name="Kerfoot, WC">{{cite journal|last=Kerfoot |first=WC |year=1985 |title=Adaptive value of vertical migration: Comments on the predation hypothesis and some alternatives |journal=Contributions in Marine Science |volume=27 |pages=91–113 |url=http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=1587950 |archive-url=https://archive.today/20130121073028/http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=1587950 |url-status=dead |archive-date=2013-01-21 }}</ref>

===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.<ref name="Seo"/>

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.<ref>{{Cite journal|title = Depth-selection behavior and longevity in Daphnia: an evolutionary test for the predation-avoidance hypothesis|journal = Hydrobiologia|date = 2012-11-23|issn = 0018-8158|pages = 87–91|volume = 715|issue = 1|doi = 10.1007/s10750-012-1393-5|first1 = Piotr|last1 = Dawidowicz|first2 = Piotr|last2 = Prędki|first3 = Barbara|last3 = Pietrzak|doi-access = free}}</ref> 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.<ref>{{Cite journal|last1=Onsrud|first1=M.S.R.|last2=Kaartvedt|first2=S.|last3=Røstad|first3=A.|last4=Klevjer|first4=T.A.|date=2004-01-01|title=Vertical distribution and feeding patterns in fish foraging on the krill Meganyctiphanes norvegica|journal=ICES Journal of Marine Science|volume=61|issue=8|pages=1278–1290|doi=10.1016/j.icesjms.2004.09.005|issn=1095-9289|doi-access=free}}</ref>

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. [[Biology:Squid|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.<ref name="Seo"/><ref name="Benoit-Bird">{{cite journal |last1=Benoit-Bird |first1=Kelly J. |last2=Moline |first2=Mark A. |title=Vertical migration timing illuminates the importance of visual and nonvisual predation pressure in the mesopelagic zone |journal=Limnology and Oceanography |date=2021 |volume=66 |issue=8 |pages=3010–3019 |doi=10.1002/lno.11855 |bibcode=2021LimOc..66.3010B |s2cid=236232448 |url=https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lno.11855 |access-date=13 December 2021 |language=en |issn=1939-5590}}</ref>

===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'')  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.<ref name="Benoit-Bird"/><ref name="Sims">{{cite journal |last1=Sims |first1=David W. |last2=Wearmouth |first2=Victoria J. |last3=Southall |first3=Emily J. |last4=Hill |first4=Jacqueline M. |last5=Moore |first5=Pippa |last6=Rawlinson |first6=Kate |last7=Hutchinson |first7=Neil |last8=Budd |first8=Georgina C. |last9=Righton |first9=David |last10=Metcalfe |first10=Julian D. |last11=Nash |first11=Jon P. |last12=Morritt |first12=David |title=Hunt warm, rest cool: bioenergetic strategy underlying diel vertical migration of a benthic shark |journal=Journal of Animal Ecology |date=January 2006 |volume=75 |issue=1 |pages=176–190 |doi=10.1111/j.1365-2656.2005.01033.x |pmid=16903055 |s2cid=39013753 |language=en |issn=0021-8790|doi-access=free }}</ref><ref name="Sogard">{{cite journal |last1=Sogard |first1=Susan M. |last2=Olla |first2=Bori L. |title=Food deprivation affects vertical distribution and activity of a marine fish in a thermal gradient: potential energy-conserving mechanisms |journal=Marine Ecology Progress Series |date=1996 |volume=133 |pages=43–55 |doi=10.3354/meps133043 |bibcode=1996MEPS..133...43S |url=http://www.int-res.com/articles/meps/133/m133p043.pdf |access-date=20 December 2021}}</ref>

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.<ref>{{Cite web |title=Migration in the Ocean Twilight Zone |url=https://twilightzone.whoi.edu/explore-the-otz/migration/ |access-date=2023-11-30 |website=twilightzone.whoi.edu/ |language=en-US}}</ref>

===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.<ref name="Leach">{{cite journal |last1=Leach |first1=Taylor H. |last2=Williamson |first2=Craig E. |last3=Theodore |first3=Nora |last4=Fischer |first4=Janet M. |last5=Olson |first5=Mark H. |title=The role of ultraviolet radiation in the diel vertical migration of zooplankton: an experimental test of the transparency-regulator hypothesis |journal=Journal of Plankton Research |date=3 August 2015 |volume=37 |issue=5 |pages=886–896 |doi=10.1093/plankt/fbv061 |issn=0142-7873|doi-access=free }}</ref><ref name="Williamson">{{cite journal |last1=Williamson |first1=Craig E. |last2=Fischer |first2=Janet M. |last3=Bollens |first3=Stephen M. |last4=Overholt |first4=Erin P. |last5=Breckenridge |first5=Joanne K. |title=Toward a more comprehensive theory of zooplankton diel vertical migration: Integrating ultraviolet radiation and water transparency into the biotic paradigm |journal=Limnology and Oceanography |date=September 2011 |volume=56 |issue=5 |pages=1603–1623 |doi=10.4319/lo.2011.56.5.1603 |bibcode=2011LimOc..56.1603W |s2cid=16088708 |url=https://s3.wp.wsu.edu/uploads/sites/1116/2016/07/Williamson-et-al-Toward-a-comp-theory-of-DVM-integrating-UV-rad-and-water-transp-LO-2011.pdf |access-date=21 December 2021}}</ref>

===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."<ref name="Leach"/><ref name="Williamson"/> 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.<ref>{{Cite journal|title = Does the fish presence influence the diurnal vertical distribution of zooplankton in high transparency lakes?|journal = Hydrobiologia|date = 2012-12-09|issn = 0018-8158|pages = 27–39|volume = 709|issue = 1|doi = 10.1007/s10750-012-1405-5|first1 = Rocco|last1 = Tiberti|first2 = Rocco|last2 = Iacobuzio|s2cid = 18757663|url = https://zenodo.org/record/3412913}}{{Dead link|date=January 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

== 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.<ref name="Darnis"/> 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.<ref name="Greco">{{cite journal |last1=Greco |first1=Mattia |last2=Jonkers |first2=Lukas |last3=Kretschmer |first3=Kerstin |last4=Bijma |first4=Jelle |last5=Kucera |first5=Michal |title=Depth habitat of the planktonic foraminifera Neogloboquadrina pachyderma in the northern high latitudes explained by sea-ice and chlorophyll concentrations |journal=Biogeosciences |date=12 September 2019 |volume=16 |issue=17 |pages=3425–3437 |doi=10.5194/bg-16-3425-2019 |bibcode=2019BGeo...16.3425G |s2cid=203072987 |language=English |issn=1726-4170|doi-access=free }}</ref>  For example ''Neogloboquadrina pachyderma'', and for those species that contain symbionts, like ''Turborotalita quinqueloba'', remain in sunlight to aid photosynthesis.<ref name="C. Manno, A.K. Pavlov 285–295"/> Changes in sea-ice and surface chlorophyll
concentration are found to be stronger determinants of the vertical
habitat of Arctic ''N. pachyderma''.<ref name="Greco"/>

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.<ref name="K. Sherman, K.A. Honey 1156–1158"/>

==Importance for the biological pump==
[[File:Processes in the biological pump.webp|thumb|upright=2| {{center|Biological pump}} Diel vertically migrating krill, smaller zooplankton such as copepods, and fish can actively transport carbon to depth by consuming particulate organic carbon (POC) in the surface layer at night, and metabolising it at their daytime, mesopelagic residence depths. Depending on species life history, active transport may occur on a seasonal basis as well.<ref name=Cavan2019>Cavan, E.L., Belcher, A., Atkinson, A., Hill, S.L., Kawaguchi, S., McCormack, S., Meyer, B., Nicol, S., Ratnarajah, L., Schmidt, K. and Steinberg, D.K. (2019) "The importance of Antarctic krill in biogeochemical cycles". ''Nature communications'', '''10'''(1): 1–13. {{doi|10.1038/s41467-019-12668-7}}. 50px Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

The [[Biology:Biological pump|biological pump]] is the conversion of CO<sub>2</sub> and inorganic nutrients by plant photosynthesis into [[Biology:Particle (ecology)|particulate]] organic matter in the euphotic zone and transference to the deeper ocean.<ref name="Steinberg, Deborah.">{{cite journal | last=Steinberg | first= Deborah |author2=Sarah Goldthwait |author3=Dennis Hansell  |year=2002 | title=Zooplankton vertical migration and the active transport of dissolved organic and inorganic nitrogen in the Sargasso Sea| journal=Deep-Sea Research Part I| volume=49 | pages=1445–1461 | issn=0967-0637 | doi=10.1016/S0967-0637(02)00037-7 | issue=8 | citeseerx= 10.1.1.391.7622 | bibcode= 2002DSRI...49.1445S }}</ref> 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 [[Biology:Marine snow|marine snow]]. 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.<ref name="Steinberg, Deborah."/> 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 [[Biology:Active transport|active transport]]. 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.

[[Earth:Zooplankton|Zooplankton]] and salps 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.<ref name="Steinberg, Deborah."/> 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 [[Earth:Detritus|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.<ref name=":1" /> 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.<ref name=":1" /> The metabolism of these lipids reduces this POC at depth while producing CO<sub>2</sub> as a waste product, ultimately serving as a potentially significant contributor to oceanic [[Earth:Carbon sequestration|carbon sequestration]].<ref name=":1" /> 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 [[Earth:Nutrient cycle|nutrient cycling]],<ref>{{Cite journal|last=Suttle|first=Curtis A.|date=October 2007|title=Marine viruses — major players in the global ecosystem|url=https://www.nature.com/articles/nrmicro1750|journal=Nature Reviews Microbiology|language=en|volume=5|issue=10|pages=801–812|doi=10.1038/nrmicro1750|pmid=17853907|s2cid=4658457|issn=1740-1534}}</ref><ref>{{Cite journal|last1=Eppley|first1=Richard W.|last2=Peterson|first2=Bruce J.|date=December 1979|title=Particulate organic matter flux and planktonic new production in the deep ocean|url=https://www.nature.com/articles/282677a0|journal=Nature|language=en|volume=282|issue=5740|pages=677–680|doi=10.1038/282677a0|bibcode=1979Natur.282..677E|s2cid=42385900|issn=1476-4687}}</ref><ref>{{Cite journal|last1=Siegel|first1=D. A.|last2=Buesseler|first2=K. O.|last3=Doney|first3=S. C.|last4=Sailley|first4=S. F.|last5=Behrenfeld|first5=M. J.|last6=Boyd|first6=P. W.|date=2014|title=Global assessment of ocean carbon export by combining satellite observations and food-web models|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/2013GB004743|journal=Global Biogeochemical Cycles|language=en|volume=28|issue=3|pages=181–196|doi=10.1002/2013GB004743|bibcode=2014GBioC..28..181S|hdl=1912/6668|s2cid=43799803 |issn=1944-9224|hdl-access=free}}</ref> and capture techniques have made it difficult to incorporate it into the global carbon export flux.<ref name=":2" /><ref>{{Cite journal|last1=Kobari|first1=Toru|last2=Steinberg|first2=Deborah K.|last3=Ueda|first3=Ai|last4=Tsuda|first4=Atsushi|last5=Silver|first5=Mary W.|last6=Kitamura|first6=Minoru|date=2008-07-01|title=Impacts of ontogenetically migrating copepods on downward carbon flux in the western subarctic Pacific Ocean|url=https://www.sciencedirect.com/science/article/pii/S096706450800146X|journal=Deep Sea Research Part II: Topical Studies in Oceanography|series=Understanding the Ocean's Biological Pump:results from VERTIGO|language=en|volume=55|issue=14|pages=1648–1660|doi=10.1016/j.dsr2.2008.04.016|bibcode=2008DSRII..55.1648K|issn=0967-0645}}</ref><ref>{{Cite journal|last1=Bradford-Grieve|first1=J. M.|last2=Nodder|first2=S. D.|last3=Jillett|first3=J. B.|last4=Currie|first4=K.|last5=Lassey|first5=K. R.|date=2001-09-01|title=Potential contribution that the copepod Neocalanus tonsus makes to downward carbon flux in the Southern Ocean|url=https://doi.org/10.1093/plankt/23.9.963|journal=Journal of Plankton Research|volume=23|issue=9|pages=963–975|doi=10.1093/plankt/23.9.963|issn=0142-7873}}</ref> 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.<ref name="Wiebe, P.H">{{cite journal | last=Wiebe | first=P.H |author2=L.P. Madin |author3=L.R. Haury |author4=G.R. Harbison |author5=L.M. Philbin |year=1979 | title=Diel Vertical Migration by Salpa aspera and its potential for large-scale particulate organic matter transport to the deep-sea | journal=Marine Biology | volume=53 | pages=249–255 | doi=10.1007/BF00952433 | issue=3| s2cid=85127670 }}</ref>

==See also==
* [[Biology:Krill|Krill]]
* [[Earth:Phytoplankton|Phytoplankton]]
* [[Earth:Primary production|Primary production]]

==References==
{{reflist|30em}}

{{Light Ethology}}
{{diversity of fish}}
{{plankton}}
{{collective animal behaviour}}

[[Category:Aquatic ecology]]
[[Category:Biological oceanography]]
[[Category:Marine biology]]
[[Category:Planktology]]

{{Sourceattribution|Diel vertical migration}}