View source for Plankton

{{Short description|Organisms living in water or air that are drifters on the current or wind}}
{{About|the marine organisms|other uses}}
{{pp-pc}}
[[File:Marine microplankton.jpg|thumb|upright=1.35| {{center|'''[[Marine microplankton|Marine microplankton and mesoplankton]]'''}} Part of the contents of one dip of a [[hand net]]. The image contains diverse planktonic organisms, ranging from [[photosynthetic]] [[cyanobacteria]] and [[diatom]]s to many different types of [[zooplankton]], including both [[holoplankton]] (permanent residents of the plankton) and [[meroplankton]] (temporary residents of the plankton, e.g., [[fish egg]]s, crab larvae, worm larvae).]]

'''Plankton''' are the diverse collection of [[organism]]s that drift in [[Hydrosphere|water]] (or [[atmosphere|air]]) but are unable to actively propel themselves against [[ocean current|current]]s (or [[wind]]).<ref>{{cite book |last1 = Lalli |first1 = C. |last2=Parsons |first2=T. |year=1993 |title=Biological Oceanography: An Introduction |publisher = Butterworth-Heinemann |isbn = 0-7506-3384-0}}</ref><ref>{{cite journal |last=Smith |first=David J. |date=July 2013 |title=Aeroplankton and the Need for a Global Monitoring Network |journal=BioScience |volume=63 |issue=7 |pages=515–516 |s2cid=86371218 |doi=10.1525/bio.2013.63.7.3 |doi-access=free }}</ref> The individual organisms constituting plankton are called '''plankters'''.<ref>{{cite web |title=plankter |url=https://www.ahdictionary.com/word/search.html?q=plankter |website=American Heritage Dictionary |publisher=Houghton Mifflin Harcourt Publishing Company |access-date=9 November 2018 |archive-url=https://web.archive.org/web/20181109153109/https://www.ahdictionary.com/word/search.html?q=plankter |archive-date=9 November 2018 |url-status=dead }}</ref> In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as [[bivalve]]s, [[fish]], and [[baleen whale]]s.

Marine plankton include [[bacteria]], [[archaea]], [[algae]], [[protozoa]], microscopic [[fungi]],<ref name="Lawton-2024-02-10">{{cite journal |last1=Lawton |first1=Graham |title=Fungi ahoy! |journal=New Scientist |date=10 February 2024 |volume=261 |issue=3477 |pages=37–39 |doi=10.1016/S0262-4079(24)00274-4|bibcode=2024NewSc.261b..37L }}</ref> and drifting or floating [[animal]]s that inhabit the [[saltwater]] of [[ocean]]s and the [[brackish]] waters of [[estuaries]]. [[fresh water|Freshwater]] plankton are similar to marine plankton, but are found in lakes and rivers. Mostly, plankton just drift where currents take them, though some, like [[jellyfish]], swim slowly but not fast enough to generally overcome the influence of currents.

Although plankton are usually thought of as inhabiting water, there are also airborne versions that live part of their lives drifting in the atmosphere. These ''[[aeroplankton]]'' include [[plant spore]]s, [[pollen]] and wind-scattered [[seed]]s. They may also include microorganisms swept into the air from terrestrial dust storms and oceanic plankton swept into the air by [[sea spray]].

Though many planktonic [[species]] are [[microscopic scale|microscopic]] in size, ''plankton'' includes organisms over a wide range of sizes, including large organisms such as jellyfish.<ref>{{cite web |url= http://www.institut-ocean.org/images/articles/documents/1354542960.pdf |title= Microzooplankton: the microscopic (micro) animals (zoo) of the plankton |last=Dolan |first=John |date= November 2012 |publisher=[[Institut océanographique]] |access-date=16 January 2014 |archive-url= https://web.archive.org/web/20160304081019/http://www.institut-ocean.org/images/articles/documents/1354542960.pdf |archive-date=4 March 2016 |url-status= dead }}</ref> This is because plankton are defined by their [[ecological niche]] and level of [[motility]] rather than by any [[phylogenetics|phylogenetic]] or [[taxonomy (biology)|taxonomic]] classification. The "plankton" category differentiates these organisms from those that float on the water's surface, called ''[[neuston]],'' those that can swim against a current, called ''[[nekton]]'', and those that live on the deep sea floor, called ''[[benthos]]''.

== Terminology ==
[[File:Neuston, Plankton, Nekton, Benthos.jpg|thumb|upright=1.3| {{center|Plankton (organisms that drift with water currents) can be contrasted with  [[nekton]] (organisms that swim against water currents), [[neuston]] (organisms that live at the ocean surface) and [[benthos]] (organisms that live at the ocean floor).}}]]

The name ''plankton'' was coined by German marine biologist [[Victor Hensen]] in 1887 from shortening the word ''halyplankton'' from [[Greek language|Greek]] {{lang|grc|ᾰ̔́λς}} ''háls'' "sea" and {{lang|grc|πλανάω}} ''planáō'' to  "drift" or "wander".<ref>{{cite journal |last=Hansen |first=Victor |year=1887 |title=Uber die Bestimmung des Plankton's oder des im Meere treibenden Materials an Pflanzen und Thieren |trans-title=On the determination of the plankton or the material floating in the sea on plants and animals |url=https://www.biodiversitylibrary.org/item/108760#page/17/mode/1up |language=de |journal=Fünfter Bericht der Kommission zur Wissenschaftlichen Untersuchung der Deutschen Meere |volume=12 |issue=12–16 |location=Berlin, Germany |publisher=Paul Parey |pages=1–108 |via=Biodiversity Heritage Library}}</ref>{{rp|1}} While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day (a behavior called [[diel vertical migration]]), their horizontal position is primarily determined by the surrounding water movement, and plankton typically flow with [[ocean current]]s. This is in contrast to [[nekton]] organisms, such as [[fish]], [[squid]] and [[marine mammal]]s, which can swim against the ambient flow and control their position in the environment.

Within the plankton, [[holoplankton]] spend their entire [[biological life cycle|life cycle]] as plankton (e.g. most [[algae]], [[copepod]]s, [[salp]]s, and some [[jellyfish]]). By contrast, [[meroplankton]] are only planktic for part of their lives (usually the [[larva]]l stage), and then graduate to either a nektic (swimming) or [[benthos|benthic]] (sea floor) existence. Examples of meroplankton include the larvae of [[sea urchin]]s, [[starfish]], [[crustacean]]s, marine [[worm]]s, and most [[fish]].<ref>{{cite book |last1=Karleskint |first1=George |last2=Turner |first2=Richard |last3=Small |first3=James |date=2013 |chapter= 17: The Open Sea |title=Introduction to Marine Biology |edition=4th |publisher= Brooks/Cole |pages=442–443 |isbn=978-1-133-36446-7}}</ref>

The [[abundance (ecology)|amount]] and [[species distribution|distribution]] of plankton depends on available nutrients, the [[water column|state of water]] and a large amount of other plankton.<ref name="Book-2013">{{cite book |last1=Agrawai |first1=Anju |last2=Gopnal |first2=Krishna |title= Biomonitoring of Water and Waste Water |url= https://books.google.com/books?id=Cf4_AAAAQBAJ&q=Plankton+abundance+and+distribution+are+strongly+dependent+on+factors+such+as+ambient+nutrient+concentrations,+the+physical+state+of+the+water+column,+and+the+abundance+of+other+plankton.&pg=PA34 |date=2013 |publisher=Springer India |page=34 |isbn=978-8-132-20864-8 |access-date= 2 April 2018 }}</ref>

The study of plankton is termed [[planktology]] and a planktonic individual is referred to as a plankter.<ref>{{cite encyclopedia |url=http://www.britannica.com/EBchecked/topic/463117/plankter |title= Plankter – marine biology |encyclopedia=Encyclopædia Britannica}}</ref> The adjective ''planktonic'' is widely used in both the scientific and popular literature, and is a generally accepted term. However, from the standpoint of prescriptive grammar, the less-commonly used ''planktic'' is more strictly the correct adjective. When deriving English words from their Greek or Latin roots, the gender-specific ending (in this case, "-on" which indicates the word is neuter) is normally dropped, using only the root of the word in the derivation.<ref name="Emiliani, C.">{{cite journal |last=Emiliani |first=C. |year=1991 |title=Planktic/Planktonic, Nektic/Nektonic, Benthic/Benthonic |journal= Journal of Paleontology |volume=65 |pages= 329 |jstor=1305769 |issue=2 |doi=10.1017/S0022336000020576 |bibcode=1991JPal...65..329E |s2cid=131283465 }}</ref>

<gallery mode=packed style=float:left heights=160px>
File:Diatoms through the microscope.jpg|Some marine [[diatom]]s — a key [[phytoplankton]] group
File:hyperia.jpg | The [[amphipoda|amphipod]] ''[[Hyperia macrocephala]]'' – part of the [[zooplankton]]
</gallery>
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== Trophic groups ==
{{plankton sidebar|trophic}}

Plankton are primarily divided into broad functional (or [[trophic level]]) groups:   
*'''[[Phytoplankton]]''' (from Greek ''phyton'', or plant) are [[autotroph]]ic [[prokaryote|prokaryotic]] or [[eukaryote|eukaryotic]] [[algae]] that live near the water surface where there is sufficient [[light]] to support [[photosynthesis]]. Among the more important groups are the [[diatom]]s, [[cyanobacteria]], [[dinoflagellate]]s, and [[coccolithophore]]s.
*'''[[Zooplankton]]''' (from Greek ''zoon'', or animal) are small [[protozoa]]ns or [[metazoa]]ns (e.g. [[crustacean]]s and other [[animal]]s) that feed on other plankton. Some of the [[egg]]s and [[larva]]e of larger nektonic animals, such as fish, crustaceans, and [[annelid]]s, are included here.
*'''[[Mycoplankton]]''' include [[fungi]] and [[Fungus#Fungus-like organisms|fungus-like organisms]], which, like bacterioplankton, are also significant in [[remineralisation]] and [[nutrient cycling]].<ref>{{cite book |last1=Wang |first1=G. |last2= Wang, X. |last3= Liu |first3=X. |last4=Li |first4= Q. |editor-last=Raghukumar |editor-first=Chandralata |date=2012 |chapter=Diversity and biogeochemical function of planktonic fungi in the ocean |title=Biology of Marine Fungi |url=https://books.google.com/books?id=1kE5OpuGp9YC |publisher=Springer Berlin Heidelberg |pages=71–88 |isbn=978-3-642-23342-5}}</ref>
*'''[[Bacterioplankton]]''' include [[bacteria]] and [[archaea]], which play an important role in remineralising organic material down the water column (note that prokaryotic phytoplankton are also bacterioplankton).
*'''[[Virioplankton]]''' are [[Marine virus|viruses]]. Viruses are more abundant in the plankton than bacteria and archaea, though much smaller.<ref>{{cite journal |last1=Wommack |first1=K.E. |last2=Colwell |first2=R.R. |date=March 2000 |title=Virioplankton: viruses in aquatic ecosystems |journal=Microbiology and Molecular Biology Reviews |volume=64 |issue=1 |pages=69–114 |doi=10.1128/MMBR.64.1.69-114.2000 |pmid=10704475 |pmc=98987 }}</ref><ref>{{cite web |title=Plankton |url=https://education.nationalgeographic.org/resource/plankton/ |website=Resource Library |publisher=[[National Geographic]] |access-date=13 September 2019}}</ref>

=== Mixoplankton ===
{{further|Marine microorganisms#Mixotrophs|Mixotrophic dinoflagellate}}

*'''[[Mixotroph]]s'''. Plankton have traditionally been categorized as [[Autotroph|producer]], [[Heterotroph|consumer]], and recycler groups, but some plankton are able to benefit from more than just one trophic level. In this mixed trophic strategy—known as mixotrophy—organisms act as both producers and consumers, either at the same time or switching between modes of nutrition in response to ambient conditions. This makes it possible to use photosynthesis for growth when nutrients and light are abundant, but switch to eating phytoplankton, zooplankton or each other when growing conditions are poor. Mixotrophs are divided into two groups; constitutive mixotrophs (CMs) which are able to perform photosynthesis on their own, and non-constitutive mixotrophs (NCMs) which use [[phagocytosis]] to engulf phototrophic prey that are either kept alive inside the host cell, which benefits from its photosynthesis, or they digested, except for the [[plastid]]s, which continue to perform photosynthesis ([[kleptoplasty]]).<ref>{{cite journal| url = https://academic.oup.com/plankt/article/40/6/627/5165357| title = Modelling mixotrophic functional diversity and implications for ecosystem function - Oxford Journals| journal = Journal of Plankton Research| date = November 2018| volume = 40| issue = 6| pages = 627–642| doi = 10.1093/plankt/fby044| last1 = Leles| first1 = Suzana Gonçalves}}</ref>
Recognition of the importance of mixotrophy as an ecological strategy is increasing,<ref>{{cite journal |last1=Hartmann |first1=M. |last2=Grob |first2=C. |last3=Tarran |first3=G.A. |last4=Martin |first4=A.P. |last5=Burkill |first5=P.H. |last6=Scanlan |first6=D.J. |last7=Zubkov |first7=M.V. |date=2012 |title=Mixotrophic basis of Atlantic oligotrophic ecosystems |journal=Proc. Natl. Acad. Sci. USA |volume=109 |issue=15 |pages=5756–5760 |doi=10.1073/pnas.1118179109 |pmid=22451938 |pmc=3326507 |bibcode=2012PNAS..109.5756H |doi-access=free }}</ref> as well as the wider role this may play in marine [[biogeochemistry]].<ref>{{cite journal |last1=Ward |first1=B.A. |last2=Follows |first2=M.J. |date=2016 |title=Marine mixotrophy increases trophic transfer efficiency, mean organism size, and vertical carbon flux |journal=Proc. Natl. Acad. Sci. USA |volume=113 |issue=11 |pages=2958–2963 |doi=10.1073/pnas.1517118113 |pmid=26831076 |pmc=4801304 |bibcode=2016PNAS..113.2958W |doi-access=free }}</ref> Studies have shown that mixotrophs are much more important for marine ecology than previously assumed and comprise more than half of all microscopic plankton.<ref>{{cite magazine| url = https://www.the-scientist.com/news-opinion/mixing-it-up-in-the-web-of-life-65431| title = Mixing It Up in the Web of Life| magazine = The Scientist Magazine| access-date = <!-- unknown, too far back -->| archive-date = 2021-01-21| archive-url = https://web.archive.org/web/20210121092951/https://www.the-scientist.com/news-opinion/mixing-it-up-in-the-web-of-life-65431| url-status = dead}}</ref><ref>{{cite web| url = https://theconversation.com/uncovered-the-mysterious-killer-triffids-that-dominate-life-in-our-oceans-67387| title = Uncovered: the mysterious killer triffids that dominate life in our oceans| date = 3 November 2016}}</ref> Their presence acts as a buffer that prevents the collapse of ecosystems during times with little to no light.<ref>{{Cite web |url=https://www.astrobio.net/news-exclusive/catastrophic-darkness/ |title=Catastrophic Darkness |work=Astrobiology Magazine |access-date=2019-11-27 |archive-url=https://web.archive.org/web/20150926012623/http://www.astrobio.net/news-exclusive/catastrophic-darkness/ |archive-date=2015-09-26 |url-status=dead }}</ref>

== Size groups ==
[[File:Plankton species diversity.jpg|thumb|upright=1.75| {{center|'''Plankton species diversity'''}} Diverse assemblages consist of [[unicellular]] and [[multicellular]] organisms with different sizes, shapes, feeding strategies, ecological functions, life cycle characteristics, and environmental sensitivities.<ref>Chust, G., Vogt, M., Benedetti, F., Nakov, T., Villéger, S., Aubert, A., Vallina, S.M., Righetti, D., Not, F., Biard, T. and Bittner, L.(2017) "''Mare incognitum'': A glimpse into future plankton diversity and ecology research". ''Frontiers in Marine Science'', '''4''': 68. {{doi|10.3389/fmars.2017.00068|doi-access=free}}.</ref> {{center|<small>Courtesy of Christian Sardet/CNRS/[[Tara expedition]]s</small>}}]]

Plankton are also often described in terms of size. Usually the following divisions are used:{{hsp}}<ref>{{cite book| last = Omori | first = M.   | author2=Ikeda, T. | year=1992   | title = Methods in Marine Zooplankton Ecology   | publisher = Krieger Publishing Company   | location = Malabar, USA   | isbn = 978-0-89464-653-9}}</ref> 
::{| class="wikitable"
|width="120"| '''Group'''
|width="100"| '''Size range'''<br />&nbsp;&nbsp;&nbsp;&nbsp;([[Equivalent spherical diameter|ESD]])
|width="350"| '''Examples'''
|-
| Megaplankton     ||&gt; 20&nbsp;cm               || [[metazoan]]s; ''e.g.'' [[jellyfish]]; [[Ctenophora (phylum)|ctenophores]]; [[salp]]s and [[pyrosome]]s (pelagic [[Tunicata]]); [[Cephalopoda]]; [[Amphipoda]]
|-
| Macroplankton    || 2→20&nbsp;cm            || [[metazoans]]; ''e.g.'' [[Pteropoda]]; [[Chaetognath]]s; [[Euphausiacea]] ([[krill]]); [[Medusae]]; [[Ctenophora (phylum)|ctenophores]]; [[salp]]s, doliolids and [[pyrosome]]s (pelagic [[Tunicata]]); [[Cephalopoda]]; [[Janthina]] and [[Recluzia]] (two genera of gastropods); [[Amphipoda]]
|-
| Mesoplankton     || 0.2→20&nbsp;mm            || [[metazoan]]s; ''e.g.'' [[copepod]]s; [[Medusae]]; [[Cladocera]]; [[Ostracoda]]; [[Chaetognath]]s; [[Pteropoda]]; [[Tunicata]]
|-
| Microplankton    || 20→200 [[Micrometre|μm]] || large [[eukaryote|eukaryotic]] [[protist]]s; most [[phytoplankton]]; [[Protozoa]] [[Foraminifera]]; [[tintinnid]]s; other [[ciliate]]s; [[Rotifera]]; juvenile [[metazoan]]s – [[crustacean|Crustacea]] ([[copepod]] nauplii)
|-
| Nanoplankton     || 2→20&nbsp;μm             || small [[eukaryotic]] [[protist]]s; small [[diatom]]s; small [[flagellate]]s; [[Pyrrophyta]]; [[Chrysophyta]]; [[Chlorophyta]]; [[Xanthophyta]]
|-
| [[Picoplankton]] || 0.2→2&nbsp;μm            || small [[eukaryotic]] [[protist]]s; [[bacterium|bacteria]]; [[Chrysophyta]]
|-
| Femtoplankton    || &lt; 0.2&nbsp;μm         || [[marine virus]]es
|-
|}
   
However, some of these terms may be used with very different boundaries, especially on the larger end. The existence and importance of nano- and even smaller plankton was only discovered during the 1980s, but they are thought to make up the largest proportion of all plankton in number and diversity.

The microplankton and smaller groups are [[microorganism]]s and operate at low [[Reynolds number]]s, where the viscosity of water is more important than its mass or inertia.
<ref>{{cite book |author=Dusenbery, David B. |title=Living at micro scale: the unexpected physics of being small |publisher=Harvard University Press |location= Cambridge |year=2009 |isbn=978-0-674-03116-6 }}</ref>

<gallery mode="packed" style="float:left" heights="220px">
File:Plankton size.png| {{center|'''Plankton sizes by taxonomic groups'''{{hsp}}<ref>{{cite journal |doi = 10.1371/journal.pbio.1001177|title = A Holistic Approach to Marine Eco-Systems Biology|year = 2011|last1 = Karsenti|first1 = Eric|last2 = Acinas|first2 = Silvia G.|last3 = Bork|first3 = Peer|last4 = Bowler|first4 = Chris|last5 = De Vargas|first5 = Colomban|last6 = Raes|first6 = Jeroen|last7 = Sullivan|first7 = Matthew|last8 = Arendt|first8 = Detlev|last9 = Benzoni|first9 = Francesca|last10 = Claverie|first10 = Jean-Michel|last11 = Follows|first11 = Mick|last12 = Gorsky|first12 = Gaby|last13 = Hingamp|first13 = Pascal|last14 = Iudicone|first14 = Daniele|last15 = Jaillon|first15 = Olivier|last16 = Kandels-Lewis|first16 = Stefanie|last17 = Krzic|first17 = Uros|last18 = Not|first18 = Fabrice|last19 = Ogata|first19 = Hiroyuki|last20 = Pesant|first20 = Stéphane|last21 = Reynaud|first21 = Emmanuel Georges|last22 = Sardet|first22 = Christian|last23 = Sieracki|first23 = Michael E.|last24 = Speich|first24 = Sabrina|last25 = Velayoudon|first25 = Didier|last26 = Weissenbach|first26 = Jean|last27 = Wincker|first27 = Patrick|journal = PLOS Biology|volume = 9|issue = 10|pages = e1001177|pmid = 22028628|pmc = 3196472 | doi-access=free }}</ref>}}|alt=Plankton sizes by taxonomic groups
</gallery>

{{clear}}

==Habitat groups==

===Marine plankton===
Marine plankton includes [[Marine prokaryotes|marine bacteria and archaea]], [[algae]], [[protozoa]] and drifting or floating animals that inhabit the saltwater of oceans and the brackish waters of estuaries.

===Freshwater plankton===
Freshwater plankton are similar to marine plankton, but are found inland in the freshwaters of lakes and rivers.

===Aeroplankton===
<gallery mode="packed" style="float:right" heights="220px">
File:Ocean mist and spray 2.jpg|[[Sea spray]] containing [[marine microorganisms]] can be swept high into the atmosphere and may travel the globe as [[aeroplankton]] before falling back to earth.
</gallery>
{{main|Aeroplankton}}

[[Aeroplankton]] are tiny lifeforms that float and drift in the air, carried by the [[Air current|current]] of the [[wind]]; they are the [[atmospheric]] [[analogy (biology)|analogue]] to oceanic plankton. Most of the living things that make up aeroplankton are very small to [[Microscope|microscopic]] in size, and many can be difficult to identify because of their tiny size. Scientists can collect them for study in traps and sweep nets from [[aircraft]], kites or balloons.<ref>A. C. Hardy and P. S. Milne (1938) Studies in the Distribution of Insects by Aerial Currents. Journal of Animal Ecology, 7(2):199-229</ref> Aeroplankton is made up of numerous [[Microorganism|microbes]], including [[virus]]es, about 1000 different species of [[bacteria]], around 40,000 varieties of [[Fungus|fungi]], and hundreds of species of [[protist]]s, [[algae]], [[moss]]es and [[Marchantiophyta|liverworts]] that live some part of their life cycle as aeroplankton, often as [[spore]]s, [[pollen]], and wind-scattered [[seed]]s. Additionally, peripatetic microorganisms are swept into the air from terrestrial dust storms, and an even larger amount of airborne marine microorganisms are propelled high into the atmosphere in sea spray. Aeroplankton deposits hundreds of millions of airborne viruses and tens of millions of bacteria every day on every square meter around the planet.

The [[sea surface microlayer]], compared to the sub-surface waters, contains elevated concentration of [[bacteria]] and [[viruses]].<ref name=Liss2005>{{cite book | last=Liss | first=P. S. | title=The sea surface and global change | publisher=Cambridge University Press | publication-place=Cambridge New York | year=1997 | isbn=978-0-521-56273-7 | oclc=34933503}}</ref><ref name="blanchard">Blanchard, D.C., 1983. The production, distribution and bacterial enrichment of the sea-salt aerosol. In: Liss, P.S., Slinn, W.G.N. ŽEds.., Air–Sea Exchange of Gases and Particles. D. Reidel Publishing Co., Dordrecht, Netherlands, pp. 407–444.</ref> These materials can be transferred from the sea-surface to the atmosphere in the form of wind-generated aqueous [[aerosol]]s due to their high vapour tension and a process known as [[volatilisation]].<ref name="wallace">Wallace Jr., G.T., Duce, R.A., 1978. Transport of particulate organic matter by bubbles in marine waters. Limnol. Oceanogr. 23 Ž6., 1155–1167.</ref> When airborne, these [[microbes]] can be transported long distances to coastal regions. If they hit land they can have an effect on animal, vegetation and human health.<ref name="WHO">WHO, 1998. Draft guidelines for safe recreational water environments: coastal and fresh waters, draft for consultation. World Health Organization, Geneva, EOSrDRAFTr98 14, pp. 207–299.</ref> Marine aerosols that contain viruses can travel hundreds of kilometers from their source and remain in liquid form as long as the humidity is high enough (over 70%).<ref name="klassen">Klassen, R. D., & Roberge, P. R. (1999). Aerosol transport modeling as an aid to understanding atmospheric corrosivity patterns. Materials & Design, 20, 159–168.</ref><ref name="moorthy">Moorthy, K. K., Satheesh, S. K., & Krishna Murthy, B.V. (1998). Characteristics ofspectral optical depths and size distributions of aerosols over tropical oceanic regions. Journal of Atmospheric and Solar–Terrestrial Physics, 60, 981–992.
</ref><ref>Chow, J. C., Watson, J. G., Green, M. C., Lowenthal, D. H., Bates, B., Oslund, W., & Torre, G. (2000). Cross-border transport and spatial variability of suspended particles in Mexicali and California's Imperial Valley. Atmospheric Environment, 34, 1833–1843.</ref> These aerosols are able to remain suspended in the atmosphere for about 31 days.<ref name="aller">Aller, J., Kuznetsova, M., Jahns, C., Kemp, P. (2005) The sea surface microlayer as a source of viral and bacterial enrichment in marine aerosols. Journal of aerosol science. Vol. 36, pp. 801–812.</ref> Evidence suggests that bacteria can remain viable after being transported inland through aerosols. Some reached as far as 200 meters at 30 meters above sea level.<ref name="marks"/> The process which transfers this material to the atmosphere causes further enrichment in both bacteria and viruses in comparison to either the SML or sub-surface waters (up to three orders of magnitude in some locations).<ref name="marks">Marks, R., Kruczalak, K., Jankowska, K., & Michalska, M. (2001). Bacteria and fungi in air over the GulfofGdansk and Baltic sea. Journal of Aerosol Science, 32, 237–250.</ref>

===Geoplankton===
{{see also|Geoplankton}}

Many animals live in terrestrial environments by thriving in transient often microscopic bodies of water and moisture, these include [[rotifer]]s and [[gastrotrich]]s which lay resilient eggs capable of surviving years in dry environments, and some of which can go dormant themselves. Nematodes are usually microscopic with this lifestyle. Water bears, despite only having lifespans of a few months, famously can enter suspended animation during dry or hostile conditions and survive for decades. This allows them to be ubiquitous in terrestrial environments despite needing water to grow and reproduce. Many microscopic crustacean groups like [[copepod]]s and [[Amphipoda|amphipods]] (of which [[Talitridae|sandhoppers]] are members) and [[Ostracod|seed shrimp]] are known to go dormant when dry and live in transient bodies of water too<ref name=":0" />

==Other groups==

===Gelatinous zooplankton===
[[File:Jellyfish swarm.jpg|thumb|upright=1|left| Jellyfish are gelatinous zooplankton.<ref name=Hays2018>{{cite journal |doi = 10.1016/j.tree.2018.09.001|title = A Paradigm Shift in the Trophic Importance of Jellyfish?|year = 2018|last1 = Hays|first1 = Graeme C.|last2 = Doyle|first2 = Thomas K.|last3 = Houghton|first3 = Jonathan D.R.|journal = Trends in Ecology & Evolution|volume = 33|issue = 11|pages = 874–884|pmid = 30245075| bibcode=2018TEcoE..33..874H |s2cid = 52336522|url = https://pure.qub.ac.uk/en/publications/a-paradigm-shift-in-the-trophic-importance-of-jellyfish(6158fa15-32f8-4167-9574-dbc08266b588).html|author1-link = Graeme Hays}}</ref>]]
{{main|Gelatinous zooplankton}}

[[Gelatinous zooplankton]] are fragile animals that live in the water column in the ocean. Their delicate bodies have no hard parts and are easily damaged or destroyed.<ref>{{aut|Lalli, C.M. & Parsons, T.R.}} (2001) ''Biological Oceanography''. Butterworth-Heinemann.</ref> Gelatinous zooplankton are often transparent.<ref>{{aut|Johnsen, S.}} (2000) Transparent Animals. ''Scientific American'' '''282''': 62–71.</ref> All [[jellyfish]] are gelatinous zooplankton, but not all gelatinous zooplankton are jellyfish. The most commonly encountered organisms include [[ctenophore]]s, [[Jellyfish|medusae]], [[salps]], and [[Chaetognatha]] in coastal waters. However, almost all marine phyla, including [[Annelida]], [[Mollusca]] and [[Arthropoda]], contain gelatinous species, but many of those odd species live in the open ocean and the deep sea and are less available to the casual ocean observer.<ref>{{aut|Nouvian, C.}} (2007) ''The Deep''. University of Chicago Press.</ref>

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===Ichthyoplankton===
{{main|Ichthyoplankton}}
[[File:Salmonlarvakils 2.jpg|thumb|Salmon egg hatching into a ''sac fry''. In a few days, the sac fry will absorb the yolk sac and start feeding on smaller plankton.]]

[[Ichthyoplankton]] are the [[Fish eggs|eggs]] and [[larvae]] of fish. They are mostly found in the sunlit zone of the [[water column]], less than 200 metres deep, which is sometimes called the [[epipelagic]] or [[photic zone]]. Ichthyoplankton are [[planktonic]], meaning they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into [[Juvenile fish|juveniles]]. Fish larvae are part of the [[zooplankton]] that eat smaller plankton, while fish eggs carry their food supply. Both eggs and larvae are themselves eaten by larger animals.<ref name=NOAA>[http://swfsc.noaa.gov/textblock.aspx?Division=FRD&id=6210 What are Ichthyoplankton?] Southwest Fisheries Science Center, NOAA. Modified 3 September 2007. Retrieved 22 July 2011.</ref><ref name=Moser2006>{{Cite book|url=https://books.google.com/books?id=Qdzg0Vfql2sC&pg=PA269|title = The Ecology of Marine Fishes: California and Adjacent Waters|pages = 269–319|isbn = 9780520932470|last1 = Allen|first1 = Dr. Larry G.|last2 = Horn|first2 = Dr. Michael H.|date = 15 February 2005| publisher=University of California Press }}</ref> Fish can produce high numbers of eggs which are often released into the open water column. Fish eggs typically have a diameter of about {{convert|1|mm}}. The newly hatched young of oviparous fish are called [[larva]]e. They are usually poorly formed, carry a large [[yolk sac]] (for nourishment), and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed [[metamorphosis]]) to become juveniles. During this transition larvae must switch from their yolk sac to feeding on [[zooplankton]] prey, a process which depends on typically inadequate zooplankton density, starving many larvae. In time fish larvae become able to swim against currents, at which point they cease to be plankton and become [[juvenile fish]].

===Holoplankton===
{{main|Holoplankton}}
[[File:Tomopteriskils.jpg|thumb|left| ''[[Tomopteris]]'', a holoplanktic [[bioluminescence]] [[polychaete]] worm<ref>{{cite book | author = Harvey, Edmund Newton | title = Bioluminescence | publisher = Academic Press | year = 1952 }}</ref>]]

[[Holoplankton]] are organisms that are planktic for their entire life cycle. Holoplankton can be contrasted with [[meroplankton]], which are planktic organisms that spend part of their life cycle in the [[benthic zone]]. Examples of holoplankton include some [[diatom]]s, [[radiolarian]]s, some [[dinoflagellate]]s, [[foraminifera]], [[amphipod]]s, [[krill]], [[copepod]]s, and [[salp]]s, as well as some [[gastropod]] mollusk species. Holoplankton dwell in the [[pelagic zone]] as opposed to the [[benthic zone]].<ref name=Anderson>{{cite web|last=Anderson|first=Genny|title=Marine Plankton|url=http://marinebio.net/marinescience/03ecology/mlplankton.htm|work=Marine Science|access-date=2012-04-04}}</ref> Holoplankton include both [[phytoplankton]] and [[zooplankton]] and vary in size. The most common plankton are [[protist]]s.<ref name=Talks>{{cite web|last=Talks|first=Ted|title=Zooplankton|url=http://marinebio.org/oceans/zooplankton.asp|archive-url=http://webarchive.loc.gov/all/20171207180052/https://marinebio.org/oceans/zooplankton/|url-status=dead|archive-date=2017-12-07|work=Marine Life/Marine Invertebrates|access-date=2012-04-04}}</ref>

{{clear}}

===Meroplankton===
[[File:Larva de phyllosoma.jpg|thumb|right| {{center|[[Phyllosoma|Larva stage]] of a spiny lobster}}]]
{{main|Meroplankton}}

[[Meroplankton]] are a wide variety of aquatic organisms that have both planktonic and [[Benthic zone|benthic]] stages in their life cycles. Much of the meroplankton consists of [[larva]]l stages of larger organisms.<ref name=":0">{{Cite journal|last1=Stübner|first1=E. I.|last2=Søreide|first2=J. E.|date=2016-01-27|title=Year-round meroplankton dynamics in high-Arctic Svalbard|url=https://academic.oup.com/plankt/article/38/3/522/2223522|journal=Journal of Plankton Research|volume=38|issue=3|pages=522–536|doi=10.1093/plankt/fbv124|doi-access=free}}</ref> Meroplankton can be contrasted with [[holoplankton]], which are planktonic organisms that stay in the [[pelagic zone]] as plankton throughout their entire life cycle.<ref>{{Cite web|title=Plankton|url=https://www.britannica.com/science/plankton|access-date=2020-06-13|website=Britannica}}</ref> After some time in the plankton, many meroplankton graduate to the [[nekton]] or adopt a [[benthos|benthic]] (often [[Sessility (zoology)|sessile]]) lifestyle on the [[seafloor]]. The larval stages of benthic [[invertebrate]]s make up a significant proportion of planktonic communities.<ref>{{Cite journal|last1=Ershova|first1=E. A.|last2=Descoteaux|first2=R.|date=2019-08-13|title=Diversity and Distribution of Meroplanktonic Larvae in the Pacific Arctic and Connectivity With Adult Benthic Invertebrate Communities|journal=Frontiers in Marine Science|volume=6|doi=10.3389/fmars.2019.00490|s2cid=199638114|doi-access=free|hdl=10037/16483|hdl-access=free}}</ref> The planktonic larval stage is particularly crucial to many benthic invertebrates in order to [[Dispersal vector|disperse]] their young. Depending on the particular species and the environmental conditions, larval or juvenile-stage meroplankton may remain in the pelagic zone for durations ranging from hours to months.<ref name=":0" />

===Pseudoplankton===
{{main|Pseudoplankton}}

[[Pseudoplankton]] are organisms that attach themselves to planktonic organisms or other floating objects, such as drifting wood, [[buoyant]] shells of organisms such as ''[[Spirula]]'', or man-made [[flotsam]]. Examples include [[goose barnacle]]s and the bryozoan ''[[Jellyella]]''. By themselves these animals cannot [[Buoyancy|float]], which contrasts them with true planktonic organisms, such as ''[[Velella]]'' and the [[Portuguese Man o' War]], which are buoyant. Pseudoplankton are often found in the guts of filtering [[Zooplankton|zooplankters]].<ref>{{cite book|title=Coral Reef Ecology|first=Yuri I. |last=Sorokin|publisher=Springer Science & Business Media|date=12 March 2013|page=96|isbn=9783642800467 |url=https://books.google.com/books?id=hKvrCAAAQBAJ}}</ref>

===Tychoplankton===
{{main|Tychoplankton}}

[[Tychoplankton]] are organisms, such as free-living or attached [[Benthos|benthic organism]]s and other non-planktonic organisms, that are carried into the plankton through a disturbance of their benthic habitat, or by winds and currents.<ref name=Margulis_2009>{{cite book|last1=Chapman|first1=Michael J. | first2=Lynn | last2=Margulis | author-link=Lynn Margulis|title=Kingdoms and Domains: An Illustrated Guide to the Phyla of Life on Earth|url=https://archive.org/details/fivekingdomsillu00marg_711|url-access=limited|year=2009|publisher=Academic Press/Elsevier|location=Amsterdam|isbn=978-0123736215|pages=[https://archive.org/details/fivekingdomsillu00marg_711/page/n619 566]|edition=[4th ed.].}}</ref> This can occur by direct [[turbulence]] or by disruption of the substrate and subsequent entrainment in the water column.<ref name=Margulis_2009/><ref>{{Cite book |url=https://archive.org/details/encyclopediabiol00simb |title=Encyclopedia of biological invasions |publisher=University of California Press |year=2011 |isbn=978-0520264212 |editor-last=Simberloff |editor-first=Daniel |location=Berkeley |pages=[https://archive.org/details/encyclopediabiol00simb/page/n760 736] |editor-last2=Rejmanek |editor-first2=Marcel |url-access=limited}}</ref> Tychoplankton are, therefore, a primary subdivision for sorting planktonic organisms by duration of lifecycle spent in the plankton, as neither their entire lives nor particular reproductive portions are confined to planktonic existence.<ref name=Kennish_2003>{{cite book|editor-last=Kennish|editor-first=Michael J.|title=Estuarine Research, Monitoring, and Resource Protection|year=2004|publisher=CRC Press|location=Boca Raton, Fla.|isbn=978-0849319600|pages=194|url=http://www.crcpress.com/product/isbn/0849319609|archive-url=https://archive.today/20130120014208/http://www.crcpress.com/product/isbn/0849319609|url-status=dead|archive-date=2013-01-20}}</ref> Tychoplankton are sometimes called ''accidental plankton''.

===Mineralized plankton===
{{See also|protist shells|biomineralization}}

<gallery mode="packed" caption="Some planktons are protected with mineralized shells or [[Test (biology)|tests]]." style="float:left">
File:Diatom Helipelta metil.jpg|[[Diatom]]s have glass shells ([[frustule]]s) and produce much of the world's oxygen.
File:Haeckel Spumellaria detail.png| The elaborate [[silica]] shells of microscopic [[marine radiolarian]]s can eventually produce [[opal]]. 
File:Coccolithus pelagicus.jpg| [[Coccolithophore]]s have [[chalk]] plates called [[coccoliths]], and produced the [[Cliffs of Dover]].
File:Cwall99 lg.jpg| Planktonic [[algae bloom]] of [[coccolithophore]]s off the southern coast of England
File:Planktic Foraminifera of the northern Gulf of Mexico.jpg| [[Foraminiferan]]s have [[calcium carbonate]] shells and produced the [[limestone]] in the [[Great Pyramids]].
</gallery>

{{Clear}}

== Distribution ==
[[File:Plankton satellite image.jpg|thumb|400px|right| {{center|World concentrations of surface ocean chlorophyll as viewed by satellite during the northern spring, averaged from 1998 to 2004. Chlorophyll is a marker for the distribution and abundance of phytoplankton.}}]]

Apart from aeroplankton, plankton inhabits oceans, seas, lakes and ponds. Local abundance varies horizontally, vertically and seasonally. The primary cause of this variability is the availability of light. All plankton ecosystems are driven by the input of solar energy (but see [[chemosynthesis]]), confining [[primary production]] to surface waters, and to geographical regions and seasons having abundant light.

A secondary variable is nutrient availability. Although large areas of the [[tropics|tropical]] and [[sub-tropical]] oceans have abundant light, they experience relatively low primary production because they offer limited nutrients such as [[nitrate]], [[phosphate]] and [[silicate]]. This results from large-scale [[ocean current|ocean circulation]] and water column [[Ocean stratification|stratification]]. In such regions, primary production usually occurs at greater depth, although at a reduced level (because of reduced light).

Despite significant [[macronutrient]] concentrations, some ocean regions are unproductive (so-called [[HNLC|HNLC regions]]).<ref>{{Cite journal   
| last = Martin | first = J.H. 
| author2=Fitzwater, S.E. | year=1988
| title = Iron-deficiency limits phytoplankton growth in the Northeast Pacific Subarctic
| journal= Nature | volume=331 | pages=341–343
| doi= 10.1038/331341a0 | issue=6154
| bibcode=1988Natur.331..341M
| s2cid = 4325562 
}}</ref> The [[micronutrient]] [[iron]] is deficient in these regions, and [[iron fertilization|adding it]] can lead to the formation of phytoplankton [[algal bloom]]s.<ref>{{Cite journal   
| last1 = Boyd | first1 = P.W. | year=2000   
| title = A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by fertilization   
| journal=Nature | volume=407 | pages=695–702   
| doi = 10.1038/35037500 | pmid = 11048709   
| last2 = Watson | first2 = AJ   
| last3 = Law | first3 = CS   
| last4 = Abraham | first4 = ER   
| last5 = Trull | first5 = T   
| last6 = Murdoch | first6 = R   
| last7 = Bakker | first7 = DC   
| last8 = Bowie | first8 = AR   
| last9 = Buesseler | first9 = KO   
| issue = 6805 
| display-authors = 1   | bibcode = 2000Natur.407..695B 
| s2cid = 4368261 }}</ref> Iron primarily reaches the ocean through the deposition of dust on the sea surface. Paradoxically, oceanic areas adjacent to unproductive, [[arid]] land thus typically have abundant phytoplankton (e.g., the eastern [[Atlantic Ocean]], where [[trade winds]] bring dust from the [[Sahara Desert]] in north [[Africa]]).

While plankton are most abundant in surface waters, they live throughout the water column. At depths where no primary production occurs, [[zooplankton]] and [[bacterioplankton]] instead consume organic material sinking from more productive surface waters above. This flux of sinking material, so-called [[marine snow]], can be especially high following the termination of [[spring bloom]]s.

The local distribution of plankton can be affected by wind-driven [[Langmuir circulation]] and the [[Langmuir circulation#Biological effects|biological effects]] of this physical process.

== Ecological significance ==

===Food chain===
{{ external media
| float  = right
| width  = 260px
| video1 = [https://www.youtube.com/watch?v=xFQ_fO2D7f0 The Secret Life of Plankton] - ''YouTube''
}}
{{see also|marine food web}}

As well as representing the lower levels of a [[food chain]] that supports commercially important [[Fishery|fisheries]], plankton [[ecosystem]]s play a role in the [[biogeochemical cycle]]s of many important [[chemical element]]s, including the ocean's [[carbon cycle]].<ref>{{Cite FTP |last= Falkowski |first=Paul G. |year=1994 |url= ftp://marine.calpoly.edu/Needles/SPRING%2009/papers/2-Falkowski.pdf |title=The role of phytoplankton photosynthesis in global biogeochemical cycles |volume=39 |issue=3 |pages=235–258 |doi= 10.1007/BF00014586 |pmid=24311124 |bibcode=1994PhoRe..39..235F |server= Photosynthesis Research |url-status= dead |s2cid=12129871 }}</ref> Fish larvae mainly eat zooplankton, which in turn eat phytoplankton<ref name="sciencedirect.com">{{Cite journal |last1=James |first1=Alex |last2=Pitchford |first2=Jonathan W. |last3=Brindley |first3=John |date=2003-02-01 |title=The relationship between plankton blooms, the hatching of fish larvae, and recruitment |url=https://www.sciencedirect.com/science/article/pii/S0304380002003113 |journal=Ecological Modelling |language=en |volume=160 |issue=1 |pages=77–90 |doi=10.1016/S0304-3800(02)00311-3 |bibcode=2003EcMod.160...77J |issn=0304-3800|url-access=subscription }}</ref>

===Carbon cycle===
{{see also|ocean carbon cycle|biological pump}}

Primarily by grazing on phytoplankton, zooplankton provide [[carbon]] to the planktic [[foodweb]], either [[Cellular respiration|respiring]] it to provide [[metabolism|metabolic]] energy, or upon death as [[Biomass (ecology)|biomass]] or [[detritus]]. Organic material tends to be [[density|denser]] than [[seawater]], so it sinks into open ocean ecosystems away from the coastlines, transporting carbon along with it. This process, called the [[biological pump]], is one reason that oceans constitute the largest [[carbon sink]] on [[Earth science|Earth]]. However, it has been shown to be influenced by increments of temperature.<ref>{{cite journal |last1= Sarmento |first1= H. |last2= Montoya |first2= JM. |last3= Vázquez-Domínguez |first3= E. |last4= Vaqué |first4= D.|last5= Gasol |first5= JM. |year= 2010 |title= Warming effects on marine microbial food web processes: how far can we go when it comes to predictions? |pmc= 2880134 |journal= Philosophical Transactions of the Royal Society B: Biological Sciences |volume= 365 |issue=1549 |pages= 2137–2149 |doi= 10.1098/rstb.2010.0045 |pmid= 20513721 }}</ref><ref>{{cite journal |last1= Vázquez-Domínguez |first1= E. |last2= Vaqué |first2= D. |last3= Gasol |first3= JM. |year=2007 |title= Ocean warming enhances respiration and carbon demand of coastal microbial plankton. |journal= Global Change Biology |volume= 13 |issue=7 |pages= 1327–1334 |doi= 10.1111/j.1365-2486.2007.01377.x |bibcode= 2007GCBio..13.1327V |hdl= 10261/15731 |s2cid= 8721854 |hdl-access= free }}</ref><ref>{{cite journal |last1= Vázquez-Domínguez |first1= E. |last2= Vaqué |first2= D. |last3= Gasol |first3= JM. |year= 2012 |title= Temperature effects on the heterotrophic bacteria, heterotrophic nanoflagellates, and microbial top predators of NW Mediterranean. |journal= Aquatic Microbial Ecology |volume= 67 |issue=2 |pages= 107–121 |doi= 10.3354/ame01583 |doi-access= free |hdl= 10261/95626 |hdl-access= free }}</ref><ref>{{cite journal |last1= Mazuecos |first1= E. |last2= Arístegui |first2=J. |last3= Vázquez-Domínguez |first3= E. |last4= Ortega-Retuerta |first4= E. |last5= Gasol |first5= JM. |last6= Reche |first6= I. |year=2012 |title= Temperature control of microbial respiration and growth efficiency in the mesopelagic zone of the South Atlantic and Indian Oceans. |journal= Deep Sea Research Part I: Oceanographic Research Papers  |volume= 95 |issue=2 |pages= 131–138 |doi= 10.3354/ame01583 |doi-access= free |hdl= 10261/95626 |hdl-access= free }}</ref> In 2019, a study indicated that at ongoing rates of [[Ocean acidification|seawater acidification]], Antarctic phytoplanktons could become smaller and less effective at storing carbon before the end of the century.<ref>{{Cite web|url=https://phys.org/news/2019-08-acid-oceans-plankton-fueling-faster.html|title=Acid oceans are shrinking plankton, fueling faster climate change|last1=Petrou|first1=Katherina|last2=Nielsen|first2=Daniel|date=2019-08-27|website=phys.org|language=en-us|access-date=2019-09-07}}</ref>

It might be possible to increase the ocean's uptake of [[Carbon dioxide#In the Earth.27s atmosphere|carbon dioxide]] ({{chem|C|O|2}}) generated through [[Human impact on the environment|human activities]] by increasing plankton production through [[iron fertilization]] – introducing amounts of [[iron]] into the ocean. However, this technique may not be practical at a large scale. Ocean [[Anoxic sea water|oxygen depletion]] and resultant [[methanogen|methane production]] (caused by the excess production [[remineralisation|remineralising]] at depth) is one potential drawback.<ref>{{Cite journal   
| last1 = Chisholm |first1 = S.W. | year=2001   
| title = Dis-crediting ocean fertilization
| journal= Science | volume=294 | issue= 5541
| pages= 309–310 |doi= 10.1126/science.1065349
| pmid = 11598285
| last2 = Falkowski | first2 = PG   
| last3 = Cullen | first3 = JJ
|s2cid = 130687109 | display-authors = 1   
}}</ref><ref>{{Cite journal
 |last         = Aumont
 |first        = O.
 |author2      = Bopp, L.
 |year         = 2006
 |title        = Globalizing results from ocean ''in situ'' iron fertilization studies
 |journal      = Global Biogeochemical Cycles
 |volume       = 20
 |issue        = 2
 |doi          = 10.1029/2005GB002591
 |page         = GB2017
 |bibcode      = 2006GBioC..20.2017A
 |doi-access   = free
 }}</ref>

===Oxygen production===
{{see also|oxygen cycle}}

[[Phytoplankton]] absorb energy from the Sun and nutrients from the water to produce their own nourishment or energy. In the process of [[photosynthesis]], phytoplankton release molecular [[oxygen]] ({{chem|O|2}}) into the water as a waste byproduct. It is estimated that about 50% of the world's oxygen is produced via phytoplankton photosynthesis.<ref name="NalGeo">{{cite news |last=Roach |first=John |url= http://news.nationalgeographic.com/news/2004/06/0607_040607_phytoplankton.html |archive-url= https://web.archive.org/web/20040608065449/http://news.nationalgeographic.com/news/2004/06/0607_040607_phytoplankton.html |url-status= dead |archive-date= June 8, 2004 |title=Source of Half Earth's Oxygen Gets Little Credit |work=National Geographic News |date=June 7, 2004 |access-date=2016-04-04 }}</ref> The rest is produced via photosynthesis on land by [[plant]]s.<ref name="NalGeo"/> Furthermore, phytoplankton photosynthesis has controlled the atmospheric [[Carbon dioxide in Earth's atmosphere|{{chem|C|O|2}}]]/[[Oxygen#Build-up in the atmosphere|{{chem|O|2}}]] balance since the early [[Precambrian]] Eon.<ref name="Tappan">{{cite journal |title=Primary production, isotopes, extinctions and the atmosphere |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=April 1968 |last=Tappan |first=Helen |volume=4 |issue=3 |pages=187–210 |doi=10.1016/0031-0182(68)90047-3 |bibcode= 1968PPP.....4..187T }}</ref>

===Absorption efficiency===
{{see also|biological pump}}

The ''absorption efficiency'' (AE) of plankton is the proportion of food absorbed by the plankton that determines how available the consumed organic materials are in meeting the required physiological demands.<ref name=Steinberg12017>{{cite journal |doi = 10.1146/annurev-marine-010814-015924|title = Zooplankton and the Ocean Carbon Cycle|year = 2017|last1 = Steinberg|first1 = Deborah K.|last2 = Landry|first2 = Michael R.|journal = Annual Review of Marine Science|volume = 9|pages = 413–444|pmid = 27814033|bibcode = 2017ARMS....9..413S}}</ref> Depending on the feeding rate and prey composition, variations in absorption efficiency may lead to variations in [[fecal pellet]] production, and thus regulates how much organic material is recycled back to the marine environment. Low feeding rates typically lead to high absorption efficiency and small, dense pellets, while high feeding rates typically lead to low absorption efficiency and larger pellets with more organic content. Another contributing factor to [[dissolved organic matter]] (DOM) release is respiration rate. Physical factors such as oxygen availability, pH, and light conditions may affect overall oxygen consumption and how much carbon is loss from zooplankton in the form of respired {{CO2}}. The relative sizes of zooplankton and prey also mediate how much carbon is released via [[sloppy feeding]]. Smaller prey are ingested whole, whereas larger prey may be fed on more "sloppily", that is more biomatter is released through inefficient consumption.<ref name="Møller2005">{{cite journal |doi = 10.1093/plankt/fbh147|title = Sloppy feeding in marine copepods: Prey-size-dependent production of dissolved organic carbon|year = 2004|last1 = Moller|first1 = E. F.|journal = Journal of Plankton Research|volume = 27|pages = 27–35|doi-access = free}}</ref><ref name="Møller2007">{{cite journal |doi = 10.4319/lo.2007.52.1.0079|title = Production of dissolved organic carbon by sloppy feeding in the copepods Acartia tonsa, Centropages typicus, and Temora longicornis|year = 2007|last1 = Møller|first1 = Eva Friis|journal = Limnology and Oceanography|volume = 52|issue = 1|pages = 79–84|bibcode = 2007LimOc..52...79M|doi-access = free}}</ref> There is also evidence that diet composition can impact nutrient release, with carnivorous diets releasing more [[dissolved organic carbon]] (DOC) and ammonium than omnivorous diets.<ref name=Thor2003>{{cite journal |doi = 10.3354/ame033279|title = Fate of organic carbon released from decomposing copepod fecal pellets in relation to bacterial production and ectoenzymatic activity|year = 2003|last1 = Thor|first1 = P.|last2 = Dam|first2 = HG|last3 = Rogers|first3 = DR|journal = Aquatic Microbial Ecology|volume = 33|pages = 279–288|doi-access = free}}</ref>

==Biomass variability==
The growth of phytoplankton populations is dependent on light levels and nutrient availability. The chief factor limiting growth varies from region to region in the world's oceans. On a broad scale, growth of phytoplankton in the oligotrophic tropical and subtropical gyres is generally limited by nutrient supply, while light often limits phytoplankton growth in subarctic gyres. Environmental variability at multiple scales influences the nutrient and light available for phytoplankton, and as these organisms form the base of the marine food web, this variability in phytoplankton growth influences higher trophic levels. For example, at interannual scales phytoplankton levels temporarily plummet during [[El Niño]] periods, influencing populations of zooplankton, fishes, sea birds, and [[marine mammal]]s.

The effects of anthropogenic warming on the global population of phytoplankton is an area of active research. Changes in the vertical stratification of the water column, the rate of temperature-dependent biological reactions, and the atmospheric supply of nutrients are expected to have important impacts on future phytoplankton productivity.<ref>{{cite journal | last1 = Steinacher | first1 = M. | display-authors = etal | year = 2010 | title = Projected 21st century decrease in marine productivity: a multi-model analysis | journal = Biogeosciences | volume = 7 | issue = 3| pages = 979–1005 | doi = 10.5194/bg-7-979-2010 | bibcode = 2010BGeo....7..979S | doi-access = free | hdl = 11858/00-001M-0000-0011-F69E-5 | hdl-access = free }}</ref> Additionally, changes in the mortality of phytoplankton due to rates of zooplankton grazing may be significant.

[[File:Cycling of marine phytoplankton.png|thumb|upright=1.8|left| {{center|Marine phytoplankton cycling throughout water column}}]]
[[File:Amphipodredkils.jpg|thumb|upright=1.2| [[Amphipoda|Amphipod]] with curved [[exoskeleton]] and two long and two short antennae]]
{{clear}}

==Plankton diversity==
<gallery mode="packed" caption="Some of the diversity found in plankton">
File: Pelagibacter.jpg|''[[Pelagibacter ubique]]'', the most common bacteria in the ocean, plays a major role in global [[carbon cycle]]s
File:Prochlorococcus marinus (cropped).jpg|The tiny [[cyanobacterium]] ''[[Prochlorococcus]]'' is a major contributor to atmospheric oxygen
File:Noctiluca scintillans varias.jpg|The [[Noctiluca scintillans|sea sparkle]] [[dinoflagellate]] glows in the night to produce the [[milky seas effect]]
File:Copepodkils.jpg|[[Copepod]] from Antarctica, a translucent ovoid animal with two long antennae
File:Clupeaharenguslarvaeinsitukils.jpg|Herring larva imaged with the remains of the [[yolk]] and the long gut visible in the transparent animal
File:Icefishuk.jpg|[[Notothenioidei|Icefish]] larvae from Antarctica have no haemoglobin
File:Mnemiopsis leidyi 2.jpg|The [[sea walnut]] [[ctenophore]] has a transient anus which forms only when it needs to defecate<ref>{{cite magazine| title=Animal with an anus that comes and goes could reveal how ours evolved| author=Michael Le Page| magazine=New Scientist| url=https://www.newscientist.com/article/2195656-animal-with-an-anus-that-comes-and-goes-could-reveal-how-ours-evolved/|  date=March 2019}}</ref>
File:LeptocephalusConger.jpg|Eel larva drifting with the gulf stream
File:Krill666.jpg|[[Antarctic krill]], probably the largest biomass of a single species on the planet
File:Dinoflagellates and a tintinnid ciliate.jpg|Microzooplankton are major grazers of the plankton: two [[dinoflagellate]]s and a [[tintinnid]] ciliate.
File:Sargassum on the beach, Cuba.JPG|[[Sargassum]] seaweed drifts with currents using air bladders to stay afloat
File:Plankton creates sea foam 2.jpg|Planktonic [[sea foam]] bubbles with image of photographer
File:Janthina.jpg|Macroplankton: a ''[[Janthina janthina]]'' snail (with bubble float) cast up onto a beach in [[Maui]]
</gallery>
{{clear}}

== Planktonic relationships ==
===Fish and plankton===

[[Zooplankton]] are the initial prey item for almost all [[fish larva]]e as they switch from their [[yolk sac]]s to external feeding. Fish rely on the density and distribution of zooplankton to match that of new larvae, which can otherwise starve. Natural factors (e.g., current variations, temperature changes) and man-made factors (e.g. river dams, [[ocean acidification]], rising temperatures) can strongly affect zooplankton populations, which can in turn strongly affect fish larval survival, and therefore breeding success.

It has been shown that plankton can be patchy in marine environments where there aren't significant fish populations and additionally, where fish are abundant, zooplankton dynamics are influenced by the fish predation rate in their environment. Depending on the predation rate, they could express regular or chaotic behavior.<ref>{{Cite journal |last1=Medvinsky |first1=Alexander B. |last2=Tikhonova |first2=Irene A. |last3=Aliev |first3=Rubin R. |last4=Li |first4=Bai-Lian |last5=Lin |first5=Zhen-Shan |last6=Malchow |first6=Horst |date=2001-07-26 |title=Patchy environment as a factor of complex plankton dynamics |url=https://link.aps.org/doi/10.1103/PhysRevE.64.021915 |journal=Physical Review E |language=en |volume=64 |issue=2 |pages=021915 |doi=10.1103/PhysRevE.64.021915 |pmid=11497628 |bibcode=2001PhRvE..64b1915M |issn=1063-651X|url-access=subscription }}</ref>

A negative effect that fish larvae can have on planktonic algal blooms is that the larvae will prolong the blooming event by diminishing available zooplankton numbers; this in turn permits excessive phytoplankton growth allowing the bloom to flourish .<ref name="sciencedirect.com"/>

The importance of both phytoplankton and zooplankton is also well-recognized in extensive and semi-intensive pond fish farming. Plankton population-based pond management strategies for fish rearing have been practiced by traditional fish farmers for decades, illustrating the importance of plankton even in man-made environments.

===Whales and plankton===
Of all animal fecal matter, it is whale feces that is the 'trophy' in terms of increasing nutrient availability. Phytoplankton are the powerhouse of open ocean primary production and they can acquire many nutrients from whale feces.<ref>{{Cite web |title=whale poop and phytoplankton, fighting climate change |url=https://www.ifaw.org/journal/whale-poop-phytoplankton-climate-change |access-date=2022-03-29 |website=IFAW |language=en-US}}</ref> In the marine food web, phytoplankton are at the base of the food web and are consumed by zooplankton & krill, which are preyed upon by larger and larger marine organisms, including whales, so it can be said that whale feces fuels the entire food web.

=== Humans and plankton ===
Plankton have many direct and indirect effects on humans.

Around 70% of the oxygen in the atmosphere is produced in the oceans from [[phytoplankton]] performing photosynthesis, meaning that the majority of the oxygen available for us and other organisms that [[Cellular respiration#Aerobic respiration|respire aerobically]] is produced by plankton.<ref>{{Cite journal |last1=Sekerci |first1=Yadigar |last2=Petrovskii |first2=Sergei |date=2015-12-01 |title=Mathematical Modelling of Plankton–Oxygen Dynamics Under the Climate Change |url=https://doi.org/10.1007/s11538-015-0126-0 |journal=Bulletin of Mathematical Biology |language=en |volume=77 |issue=12 |pages=2325–2353 |doi=10.1007/s11538-015-0126-0 |pmid=26607949 |s2cid=8637912 |issn=1522-9602|hdl=2381/36058 |hdl-access=free }}</ref>

Plankton also make up the base of the marine food web, providing food for all the trophic levels above. Recent studies have analyzed the marine food web to see if the system runs on a [[Top-down and bottom-up design|top-down or bottom-up approach]]. Essentially, this research is focused on understanding whether changes in the food web are driven by nutrients at the bottom of the food web or predators at the top. The general conclusion is that the bottom-up approach seemed to be more predictive of food web behavior.<ref>{{Cite journal |last1=Frederiksen |first1=Morten |last2=Edwards |first2=Martin |last3=Richardson |first3=Anthony J. |last4=Halliday |first4=Nicholas C. |last5=Wanless |first5=Sarah |date=November 2006 |title=From plankton to top predators: bottom-up control of a marine food web across four trophic levels |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2656.2006.01148.x |journal=Journal of Animal Ecology |language=en |volume=75 |issue=6 |pages=1259–1268 |doi=10.1111/j.1365-2656.2006.01148.x |pmid=17032358 |bibcode=2006JAnEc..75.1259F |issn=0021-8790|url-access=subscription }}</ref> This indicates that plankton have more sway in determining the success of the primary consumer species that prey on them than do the secondary consumers that prey on the primary consumers.

In some cases, plankton act as an intermediate [[Host (biology)|host]] for deadly parasites in humans. One such&nbsp;case is that of [[cholera]], an infection caused by several pathogenic strains of ''[[Vibrio cholerae]]''. These species have been shown to have a symbiotic relationship with chitinous zooplankton species like [[copepod]]s. These bacteria benefit not only from the food provided by the chiton from the zooplankton, but also from the protection from acidic environments. Once the copepods have been ingested by a human host, the chitinous exterior protects the bacteria from the stomach acids in the stomach and proceed to the intestines. Once there, the bacteria bind with the surface of the small intestine and the host will start developing symptoms, including extreme diarrhea, within five days.<ref>{{Cite journal |last1=Lipp |first1=Erin K. |author-link1 = Erin Lipp|last2=Huq |first2=Anwar |last3=Colwell |first3=Rita R. |date=October 2002 |title=Effects of Global Climate on Infectious Disease: the Cholera Model |journal=Clinical Microbiology Reviews |language=en |volume=15 |issue=4 |pages=757–770 |doi=10.1128/CMR.15.4.757-770.2002 |issn=0893-8512 |pmc=126864 |pmid=12364378 }}</ref>

== See also ==
* [[Aeroplankton]]
* [[Gelatinous zooplankton]]
* [[Ichthyoplankton]]
* [[Nekton]]
* [[Paradox of the plankton]]
* [[Seston]]
* [[Veliger]]

== References ==
{{reflist}}

==Further reading==
*Kirby, Richard R. (2010). ''Ocean Drifters: A Secret World Beneath the Waves''. Studio Cactus Ltd, UK. {{ISBN|978-1-904239-10-9}}.
*Dusenbery, David B. (2009). ''Living at Micro Scale: The Unexpected Physics of Being Small''. Harvard University Press, Cambridge, Massachusetts {{ISBN|978-0-674-03116-6}}.
*Kiørboe, Thomas (2008). ''A Mechanistic Approach to Plankton Ecology''. Princeton University Press, Princeton, N.J. {{ISBN|978-0-691-13422-2}}.
*Dolan, J.R., Agatha, S., Coats, D.W., Montagnes, D.J.S., Stocker, D.K., eds. (2013).''Biology and Ecology of Tintinnid Ciliates: Models for Marine Plankton''. Wiley-Blackwell, Oxford, UK {{ISBN|978-0-470-67151-1}}.

== External links ==
{{wiktionary}}
{{commons|Plankton}}
{{EB1911 poster|Plankton}}
{{wikiquote}}
* [http://vimeo.com/84872751/ Ocean Drifters] – Short film narrated by David Attenborough about the varied roles of plankton
* [http://www.planktonchronicles.org/ Plankton Chronicles] {{Webarchive|url=https://web.archive.org/web/20200728100833/http://planktonchronicles.org/en/ |date=2020-07-28 }} – Short documentary films and photos
* [http://www.st.nmfs.noaa.gov/plankton/ COPEPOD: The Global Plankton Database] – Global coverage database of zooplankton biomass and abundance data
* [http://planktonnet.awi.de/ Plankton*Net] {{Webarchive|url=https://web.archive.org/web/20060821183345/http://planktonnet.awi.de/ |date=2006-08-21 }} – [[Taxonomy (biology)|Taxonomic]] database of images of plankton species
* [https://web.archive.org/web/20080530005405/http://www.tafi.org.au/zooplankton/ Guide to the marine zooplankton of south-eastern Australia] – Tasmanian Aquaculture and Fisheries Institute
* [https://web.archive.org/web/20090725052255/http://www.sahfos.ac.uk/ Sir Alister Hardy Foundation for Ocean Science] – Continuous Plankton Recorder Survey
* [https://web.archive.org/web/20081201125235/http://imos.org.au/auscpr.html Australian Continuous Plankton Recorder Project] – Integrated Marine Observing System
* [http://news.bbc.co.uk/1/hi/sci/tech/8498786.stm Sea Drifters] – BBC Audio slideshow
* [http://gallery.obs-vlfr.fr/gallery2/v/Aquaparadox/ Aquaparadox: the diversity of planktonic microorganisms] – Images of planktonic microorganisms
* [https://web.archive.org/web/20170327115015/https://aslo.org/lo/toc/vol_19/issue_2/0360b.pdf Plankton, planktic, planktonic] – Essays on nomenclature
* [http://www.oxfordjournals.org/our_journals/plankt Journal of Plankton Research]{{dead link|date=January 2025|bot=medic}}{{cbignore|bot=medic}} – Scientific periodical devoted to plankton
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[[Category:Plankton| ]]
[[Category:Biological oceanography]]
[[Category:Planktology| ]]
[[Category:Aquatic ecology]]
[[Category:Oceanographical terminology]]