Plankton
25011
223716373
2008-07-05T12:23:12Z
DorganBot
2844817
robot Adding: [[sh:Plankton]]
:''This article is about the marine organisms. For the SpongeBob SquarePants character, see [[Plankton (SpongeBob SquarePants)]]''
----
[[Image:plankton.jpg|thumb|right|200px|[[Photomontage]] of plankton organisms]]
'''Plankton''' consist of any drifting [[organism]]s ([[animal]]s, [[plant]]s, [[archaea]], or [[bacteria]]) that inhabit the [[pelagic zone]] of [[ocean]]s, [[sea]]s, or bodies of [[fresh water]]. Plankton are defined by their [[ecological niche]] rather than their [[genetic]] classification. They provide a crucial source of food to aquatic life.
==Definitions==
[[Image:Diatoms through the microscope.jpg|thumb|left|200px|Some marine [[diatom]]s - a key [[phytoplankton]] group]]The name '''plankton''' is derived from the [[Greek language|Greek]] word πλανκτος ("planktos"), meaning "wanderer" or "drifter".<ref>{{cite book
| last = Thurman
| first = H. V.
| year = 1997
| title = Introductory Oceanography
| publisher = Prentice Hall College
| location = New Jersey, USA
| isbn = 0132620723
}}</ref> While some forms of plankton are capable of independent movement and can swim up to several hundreds of [[meter]]s vertically in a single [[day]] (a behavior called [[diel vertical migration]]), their horizontal position is primarily determined by [[ocean current|currents]] in the body of water they inhabit. By definition, organisms classified as plankton are unable to resist ocean currents. This is in contrast to '''[[nekton]]''' organisms that can swim against the ambient flow of the water environment and control their position (e.g. [[squid]], [[fish]], and [[marine mammal]]s).
Within the plankton, itself, '''[[holoplankton]]''' are those organisms that spend their entire [[biological life cycle|life cycle]] as part of the plankton (e.g. most [[algae]], [[copepod]]s, [[salp]]s, and some [[jellyfish]]). By contrast, '''[[meroplankton]]''' are those organisms that are only planktonic for part of their lives (usually the [[Larva|larval]] stage), and then graduate to either the nekton or a [[benthos|benthic]] (sea floor) existence. Examples of meroplankton include the larvae of [[sea urchin]]s, [[starfish]], [[crustacean]]s, marine [[worm]]s, and most [[fish]].
Plankton abundance and distribution are strongly dependent on factors such as ambient [[nutrients]] concentrations, the physical state of the water column, and the abundance of other plankton.
The study of plankton is termed [[planktology]]. Individual plankton are referred to as '''plankters'''.
<br style="clear:both;">
Biologist Peter DeBoer describes plankton as "micro organisms, without which, nothing on earth would exist. Nothing."
==Functional groups==
[[Image:hyperia.jpg|thumb|right|200px|An [[amphipoda|amphipod]] (''Hyperia macrocephala'')]]
Plankton are primarily divided into broad functional (or [[trophic level]]) groups:
* '''[[Phytoplankton]]''' (from Greek ''phyton'', or plant), [[autotroph]]ic, [[prokaryote|prokaryotic]] or [[eukaryote|eukaryotic]] [[alga]]e that live near the water surface where there is sufficient [[light]] to support [[photosynthesis]]. Among the more important groups are the [[diatom]]s, [[cyanobacteria]] and [[dinoflagellate]]s.
* '''[[Zooplankton]]''' (from Greek ''zoon'', or animal), small [[protozoa]]ns or [[metazoa]]ns (e.g. [[crustacea]]ns and other [[animal]]s) that feed on other plankton and [[telonemia]]. Some of the [[egg (biology)|egg]]s and [[larva]]e of larger animals, such as fish, crustaceans, and [[annelid]]s, are included here.
* '''[[Bacterioplankton]]''', [[bacterium|bacteria]] and [[archaea]], which play an important role in [[remineralisation|remineralising]] organic material down the water column (note that the prokaryotic phytoplankton are also bacterioplankton).
This scheme divides the plankton community into broad '''producer''', '''consumer''' and '''recycler''' groups. In reality, the trophic level of some plankton is not straightforward. For example, although most dinoflagellates are either photosynthetic producers or heterotrophic consumers, many species are [[mixotrophic]] depending upon their circumstances.
<br style="clear:both;">
==Size groups==
[[Image:Ctenophora.jpg|thumb|left|200px|[[Siphonophora]] – the "conveyor belt" of the upgrowing larvae and the ovarium can be seen]]
Plankton are also often described in terms of size.<ref>{{cite book
| last = Omori
| first = M.
| coauthors = Ikeda, T.
| year = 1992
| title = Methods in Marine Zooplankton Ecology
| publisher = Krieger Publishing Company
| location = Malabar, USA
| isbn = 0-89464-653-2
}}</ref> Usually the following divisions are used:
<center>
{|
|width="95"| '''Group'''
|width="120"| '''Size range''' ([[Equivalent spherical diameter|ESD]])
|width="90"|
|width="350"| '''Major organisms'''
|-
| Megaplankton || > 2×10<sup>-2</sup> m || (20+ [[Millimetre|mm]]) || [[metazoa]]ns; ''e.g.'' [[jellyfish]]
|-
| Macroplankton || 2×10<sup>-3</sup>→2×10<sup>-2</sup> [[Metre|m]] || (2-20 [[Millimetre|mm]]) || metazoans; ''e.g.'' [[Pteropod]]s; [[Chaetognath]]s; Euphausiacea ([[krill]]); Medusae; Tunicata; Cephalopoda
|-
| Mesoplankton || 2×10<sup>-4</sup>→2×10<sup>-3</sup> m || (0.2 [[Millimetre|mm]]-2 [[Millimetre|mm]]) || metazoans; ''e.g.'' [[copepod]]s; Medusae; Cladocera; Ostracoda; [[Chaetognath]]s; [[Pteropod]]s; Tunicata; Heteropoda
|-
| Microplankton || 2×10<sup>-5</sup>→2×10<sup>-4</sup> m || (20-200 [[Micrometre|µm]]) || large [[eukaryote|eukaryotic]] [[protist]]s; most phytoplankton; Protozoa (Foraminifera); ciliates; Rotifera; juvenile metazoans - Crustacea ([[copepod]] nauplii)
|-
| Nanoplankton || 2×10<sup>-6</sup>→2×10<sup>-5</sup> m || (2-20 µm) || small eukaryotic protists; Small [[Diatoms]]; Small Flagellates; Pyrrophyta; Chrysophyta; Chlorophyta; Xanthophyta
|-
| [[Picoplankton]] || 2×10<sup>-7</sup>→2×10<sup>-6</sup> m || (0.2-2 µm) || small eukaryotic protists; [[bacterium|bacteria]]; Chrysophyta
|-
| Femtoplankton || < 2×10<sup>-7</sup> m || (< 0.2 µm) || marine [[virus]]es
|-
|}
</center>
However, some of these terms may be used with very different boundaries, especially on the larger end of the scale. The existence and importance of nano- and even smaller plankton was only discovered during the [[1980]]s, but they are thought to make up the largest proportion of all plankton in number and diversity.
<br style="clear:both;">
==Distribution==
[[Image:Amphipodredkils.jpg|thumb|right|200px|An [[amphipoda|amphipod]]]]
Plankton are found throughout the oceans, seas and lakes of Earth. However, the local abundance of plankton varies horizontally, vertically and seasonally. The primary source of this variability is the availability of light. All plankton ecosystems are driven by the input of solar energy (but see [[chemosynthesis]]), and this confines primary production to surface waters, and to geographical regions and seasons when light is abundant.
A secondary source of variability is that of nutrient availability. Although large areas of the [[tropics|tropical]] and [[sub-tropical]] oceans have abundant light, they experience relatively low primary production because of the poor availability of nutrients such as [[nitrate]], [[phosphate]] and [[silicate]]. This is a product of large-scale [[ocean current|ocean circulation]] and [[stratification]] of the water column. In such regions, primary production, still usually occurs at greater depth, although at a reduced level (because of reduced light).
Despite significant concentrations of [[macronutrient]]s, some regions of the ocean are unproductive (so-called [[HNLC|HNLC regions]])<ref>{{Cite journal
| last = Martin
| first = J. H.
| coauthors = 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
}}</ref>. Field studies have found that the mineral [[micronutrient]] [[iron]] is deficient in these regions, and that adding it can lead to the formation of [[algal bloom|blooms]] of many (though not all) kinds of phytoplankton<ref>{{Cite journal
| last = Boyd
| first = P.W., et al.
| year = 2000
| title = A mesoscale pytoplankton bloom in the polar Southern Ocean stimulated by fertilization
| journal = Nature
| volume = 407
| pages = 695–702
| doi = 10.1038/35037500
}}</ref>. Iron primarily reaches the ocean through the deposition of atmospheric dust on the sea surface. Paradoxically, oceanic areas adjacent to unproductive, [[arid]] regions of continents thus typically have abundant phytoplankton (e.g., the western [[Atlantic Ocean]], where [[trade winds]] bring dust from the [[Sahara Desert]] in north [[Africa]]). It has been suggested that large-scale "[[Iron fertilization|seeding]]" of the world's oceans with iron could generate blooms of phytoplankton large enough to draw down enough carbon dioxide out of the atmosphere to offset its anthropogenic emissions (responsible for [[global warming]]), although other researchers have disputed the scale of this effect<ref>{{Cite journal
| last = Aumont
| first = O.
| coauthors = Bopp, L.
| year = 2006
| url = http://www.agu.org/pubs/crossref/2006/2005GB002591.shtml
| title = Globalizing results from ocean ''in situ'' iron fertilization studies
| journal = Global Biogeochemical Cycles
| volume = 20
| issue = 2
| doi = 10.1029/2005GB002591
| pages = GB2017
}}</ref>.
While plankton are found in the greatest abundance in surface waters, they occur throughout the water column. At depths where no primary production occurs, zooplankton and bacterioplankton instead make use of organic material sinking from the more productive surface waters above. This flux of sinking material can be especially high following the termination of [[spring bloom]]s.
<br style="clear:both;">
==Biogeochemical significance==
[[Image:Copepodkils.jpg|thumb|left|200px|A [[copepod]] (''Calanoida'' sp.) ca. [[1 E-3 m|1-2 mm]] long]]
Aside from representing the bottom few levels of a [[food chain]] that leads up to [[Commerce|commercially]] important [[Fishery|fisheries]], plankton [[ecosystem]]s play a role in the [[biogeochemical cycle]]s of many important [[chemical element]]s. Of particular contemporary significance is their role in the ocean's [[carbon cycle]].
As stated, phytoplankton fix [[carbon]] in sunlit surface waters via photosynthesis. Through (primarily) zooplankton grazing, this carbon enters the planktonic foodweb, where it is either [[Cellular respiration|respired]] to provide [[metabolism|metabolic]] energy, or accumulates as [[Biomass (ecology)|biomass]] or [[detritus]]. As living or dead organic material is typically more [[density|dense]] than [[seawater]] it tends to sink, and in open ocean ecosystems away from the [[coast]]s this leads to the transport of carbon from surface waters to the deep. This process is known as the '''[[biological pump]]''', and is one of the reasons that the oceans constitute the largest (active) pool of carbon on [[Earth science|Earth]].
Some researchers have even proposed that it might be possible to increase the ocean's uptake of [[carbon dioxide#atmosphere|carbon dioxide]] generated through [[anthropogenic|human activities]] by increasing the production of plankton through [[fertilization]], primarily with the [[micronutrient]] [[iron]]. However, it is debatable whether this technique is practical at a large scale, and some researchers have drawn attention to possible drawbacks such as ocean [[Anoxic sea water|anoxia]] and resultant [[methanogen|methanogenesis]] (caused by the excess production [[remineralisation|remineralising]] at depth).<ref>{{Cite journal
| last = Chisholm
| first = S.W., ''et al.''
| year = 2001
| title = Dis-crediting ocean fertilization
| journal = Science
| volume = 294
| issue = 5541
| pages = 309–310
| doi = 10.1126/science.1065349
| pmid = 11598285
}}</ref>
<br style="clear:both;">
==Importance to fish==
[[Image:Plankton creates sea foam 2.jpg|[[Sea]] [[foam]] is produced by plankton|200px|thumb]]
Zooplankton are initially the sole prey item for almost all [[fish]] [[larva|larvae]] as they use up their yolk sacs and switch to external feeding for nutrition. Fish species rely on the density and distribution of zooplankton to coincide with first-feeding larvae for good survival of larvae, which can otherwise starve. Natural factors (e.g. variations in oceanic currents) and man-made factors (e.g. dams on rivers) can strongly affect zooplankton density and distribution, which can in turn strongly affect the larval survival, and therefore breeding success and stock strength, of fish species.
==See also==
* [[Algal bloom]]
* [[Biological pump]]
* [[Gelatinous zooplankton]]
* [[Iron fertilization]]
* [[Nekton]]
* [[Ocean acidification]]
* [[Paradox of the plankton]]
* [[Primary production]]
==References==
{{reflist}}
==External links==
* [http://planktonnet.sb-roscoff.fr/index.php Plankton*Net], [[taxonomy|taxonomic]] database of images of plankton species
[[Category:Biological oceanography]]
[[Category:Planktology]]
[[Category:Aquatic ecology]]
[[ar:بلانكتون]]
[[bg:Планктон]]
[[ca:Plàncton]]
[[cs:Plankton]]
[[cy:Plancton]]
[[da:Plankton]]
[[de:Plankton]]
[[et:Plankton]]
[[el:Πλαγκτόν]]
[[es:Plancton]]
[[eo:Planktono]]
[[fa:پلانکتون]]
[[fr:Plancton]]
[[gd:Meanbh-bheò]]
[[ko:플랑크톤]]
[[hr:Plankton]]
[[id:Plankton]]
[[ia:Plancton]]
[[is:Svif]]
[[it:Plancton]]
[[he:פלנקטון]]
[[la:Plancton]]
[[lt:Planktonas]]
[[hu:Plankton]]
[[ms:Plankton]]
[[nl:Plankton]]
[[ja:プランクトン]]
[[no:Plankton]]
[[nn:Plankton]]
[[pl:Plankton]]
[[pt:Plâncton]]
[[ro:Plancton]]
[[ru:Планктон]]
[[simple:Plankton]]
[[sr:Планктон]]
[[sh:Plankton]]
[[fi:Plankton]]
[[sv:Plankton]]
[[th:แพลงก์ตอน]]
[[vi:Sinh vật phù du]]
[[tr:Plankton]]
[[uk:Планктон]]
[[zh:浮游生物界]]