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Plankton
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{{About|the marine organisms|other uses}}{{pp-pc1}}{{short description|Organisms that live in the water column and are incapable of swimming against a current}}File:Plankton collage.jpg|thumb|right|300px|alt=Six relatively large variously-shaped organisms with dozens of small light-colored dots all against a dark background. Some of the organisms have antennae that are longer than their bodies.Plankton are the diverse collection of organisms that live in large bodies of water and are unable to swim against a current."MEMBERWIDE"> FIRST = C. YEAR=1993, Biological Oceanography: An Introduction, Butterworth-HeinemannWEBSITE=AMERICAN HERITAGE DICTIONARY ACCESSDATE=9 NOVEMBER 2018, They provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish and whales.Planktonic organisms include bacteria, archaea, algae, protozoa and drifting or floating animals that inhabit—for example—the pelagic zone of oceans, seas, or bodies of fresh water. Essentially, plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification.Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish.WEB,weblink Microzooplankton: the microscopic (micro) animals (zoo) of the plankton, John Dolan, November 2012, Technically the term does not include organisms on the surface of the water, which are called pleuston—or those that swim actively in the water, which are called nekton.

Terminology

File:Diatoms through the microscope.jpg |thumb |left|Some marine diatoms—a key (phytoplankton]] group|alt=Photo of mostly transparent diatoms of varying shapes: one resembles a bagel, another a short length of tape, others look like tiny kayaks)The name plankton is derived from the Greek adjective πλαγκτός (), meaning errant, and by extension, wanderer or drifter,THURMAN > FIRST = H.V., 1997, Introductory Oceanography, Prentice Hall College, New Jersey, USA, 978-0-13-262072-7, and was coined by Victor Hensen in 1887.Hensen, V. 1887. Uber die Bestimmung des Planktons oder des im Meere treibenden Materials an Pflanzen und Thieren. V. Bericht der Commission zur Wissenschaftlichen Untersuchung der Deutschen Meere, Jahrgang 12-16, p. 1-108, weblink.WEB,weblink Online Etymology Dictionary, etymonline.com, 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 currents. This is in contrast to nekton organisms, such as fish, squid and marine mammals, which can swim against the ambient flow and control their position in the environment.Within the plankton, holoplankton spend their entire life cycle as plankton (e.g. most algae, copepods, salps, and some jellyfish). By contrast, meroplankton are only planktic for part of their lives (usually the larval stage), and then graduate to either a nektic (swimming) or benthic (sea floor) existence. Examples of meroplankton include the larvae of sea urchins, starfish, crustaceans, marine worms, and most fish.BOOK, Karleskint, George, Turner, Richard, Small, James, Introduction to Marine Biology, 4th, Brooks/Cole, 2013, Chapter 17: The Open Sea, 978-1-133-36446-7, The amount and distribution of plankton depends on available nutrients, the state of water and a large amount of other plankton.BOOK, Agrawai, Anju, Gopnal, Krishna, Biomonitoring of Water and Waste Water, 34,weblink 2013, Springer India 2013, April 2, 2018, 978-8-132-20864-8, The study of plankton is termed planktology and a planktonic individual is referred to as a plankter.WEB,weblink plankter - marine biology, Encyclopædia Britannica, 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.JOURNAL, Emiliani, C., 1991, Planktic/Planktonic, Nektic/Nektonic, Benthic/Benthonic, Journal of Paleontology, 65, 329, 1305769, 2, 10.1017/S0022336000020576,

Trophic groups

File:hyperia.jpg |thumb|An amphipodamphipodPlankton are primarily divided into broad functional (or trophic level) groups:
  • Phytoplankton (from Greek phyton, or plant), are autotrophic prokaryotic or eukaryotic algae that live near the water surface where there is sufficient light to support photosynthesis. Among the more important groups are the diatoms, cyanobacteria, dinoflagellates and coccolithophores.
  • Zooplankton (from Greek zoon, or animal), are small protozoans or metazoans (e.g. crustaceans and other animals) that feed on other plankton. Some of the eggs and larvae of larger nektonic animals, such as fish, crustaceans, and annelids, are included here.
  • 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).
  • Mycoplankton, include fungi and fungus-like organisms, which, like bacterioplankton, are also significant in remineralisation and nutrient cycling.Wang, G., Wang, X., Liu, X., & Li, Q. (2012). "Diversity and biogeochemical function of planktonic fungi in the ocean". In: C. Raghukumar (ed.), Biology of Marine Fungi. Springer Berlin Heidelberg, p. 71-88, weblink.
  • Mixotrophs. Plankton have traditionally been categorized as producer, 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 switching to eat 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 benefit from its photosynthesis, or they digest their prey except for the plastids which continues to perform photosynthesis (kleptoplasty).Modelling mixotrophic functional diversity and implications for ecosystem function - Oxford Journals
Recognition of the importance of mixotrophy as an ecological strategy is increasing,JOURNAL, Hartmann, M., Grob, C., Tarran, G.A., Martin, A.P., Burkill, P.H., Scanlan, D.J., Zubkov, M.V., 2012, Mixotrophic basis of Atlantic oligotrophic ecosystems, Proc. Natl. Acad. Sci. USA, 109, 15, 5756–5760, 10.1073/pnas.1118179109, 22451938, 3326507, 2012PNAS..109.5756H, as well as the wider role this may play in marine biogeochemistry.JOURNAL, Ward, B.A., Follows, M.J., 2016, Marine mixotrophy increases trophic transfer efficiency, mean organism size, and vertical carbon flux, Proc. Natl. Acad. Sci. USA, 113, 11, 2958–2963, 10.1073/pnas.1517118113, 26831076, 4801304, 2016PNAS..113.2958W, Studies have shown that mixotrophs are much more important for the marine ecology than previously assumed, and comprise more than half of all microscopic plankton.Mixing It Up in the Web of Life | The Scientist MagazineUncovered: the mysterious killer triffids that dominate life in our oceans

Size groups

File:Janthina.jpg|thumb|Macroplankton: a Janthina janthina snail (with bubble float) cast up onto a beach in MauiMauiPlankton are also often described in terms of size.OMORI > FIRST = M. YEAR=1992, Methods in Marine Zooplankton Ecology, Krieger Publishing Company, Malabar, USA, 978-0-89464-653-9, Usually the following divisions are used:
{|
Group Size range    (ESD) Examples 20 cm >metazoans; e.g. jellyfish; Ctenophora (phylum)>ctenophores; salps and pyrosomes (pelagic Tunicata); Cephalopoda; Amphipodametazoans; e.g. Pteropods; Chaetognaths; Euphausiacea (krill); Medusae; Ctenophora (phylum)>ctenophores; salps, doliolids and pyrosomes (pelagic Tunicata); Cephalopoda; Janthinidae (one family of gastropods); Amphipoda| metazoans; e.g. copepods; Medusae; Cladocera; Ostracoda; Chaetognaths; Pteropods; TunicataMicrometre>µm large eukaryote protists; most phytoplankton; Protozoa Foraminifera; tintinnids; other ciliates; Rotifera; juvenile metazoans - crustacean>Crustacea (copepod nauplii)| small eukaryotic protists; Small Diatoms; Small Flagellates; Pyrrophyta; Chrysophyta; Chlorophyta; XanthophytaPicoplankton >eukaryotic protists; bacterium>bacteria; ChrysophytaMarine bacteriophage>marine viruses
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 microorganisms and operate at low Reynolds numbers, where the viscosity of water is much more important than its mass or inertia.BOOK, Dusenbery, David B., Living at micro scale: the unexpected physics of being small, Harvard University Press, Cambridge, 2009, 978-0-674-03116-6,

Distribution

(File:Plankton satellite image.jpg|thumb|400px|right|thumb| {{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.}})Plankton inhabit oceans, seas, lakes, 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 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 circulation and water column 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 regions).MARTIN > FIRST = J.H. YEAR=1988, Iron-deficiency limits phytoplankton growth in the Northeast Pacific Subarctic volume=331, 341–343 issue=6154, 1988Natur.331..341M, The micronutrient iron is deficient in these regions, and adding it can lead to the formation of phytoplankton blooms.BOYD > FIRST = P.W., 2000, A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by fertilization volume=407, 695–702 pmid = 11048709 first2 = AJ first3 = CS first4 = ER first5 = T first6 = R first7 = DC first8 = AR first9 = KO, 6805weblink 1, 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 blooms.

Ecological significance

Food chain

Aside from representing the bottom few levels of a food chain that supports commercially important fisheries, plankton ecosystems play a role in the biogeochemical cycles of many important chemical elements, including the ocean's carbon cycle.JOURNAL, Falkowski, Paul G., 1994,weblink The role of phytoplankton photosynthesis in global biogeochemical cycles, Photosyntheis Research, 39, 3, 235–258, 10.1007/BF00014586, 24311124, {{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }}

Carbon cycle

Primarily by grazing on phytoplankton, zooplankton provide carbon to the planktic foodweb, either respiring it to provide metabolic energy, or upon death as biomass or detritus. Organic material tends to be 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. However, it has been shown to be influenced by increments of temperature.JOURNAL, Sarmento, H., Montoya, JM., Vázquez-Domínguez, E., Vaqué, D., Gasol, JM., 2010, Warming effects on marine microbial food web processes: how far can we go when it comes to predictions?, 2880134, Philosophical Transactions of the Royal Society B: Biological Sciences, 365, 1549, 2137–2149, 10.1098/rstb.2010.0045, 20513721, JOURNAL, Vázquez-Domínguez, E., Vaqué, D., Gasol, JM., 2007, Ocean warming enhances respiration and carbon demand of coastal microbial plankton., Global Change Biology, 13, 7, 1327–1334, 10.1111/j.1365-2486.2007.01377.x, 2007GCBio..13.1327V, 10261/15731, JOURNAL, Vázquez-Domínguez, E., Vaqué, D., Gasol, JM., 2012, Temperature effects on the heterotrophic bacteria, heterotrophic nanoflagellates, and microbial top predators of NW Mediterranean., Aquatic Microbial Ecology, 67, 2, 107–121, 10.3354/ame01583, JOURNAL, Mazuecos, E., Arístegui, J., Vázquez-Domínguez, E., Ortega-Retuerta, E., Gasol, JM., Reche, I., 2012, Temperature control of microbial respiration and growth efficiency in the mesopelagic zone of the South Atlantic and Indian Oceans., Deep Sea Research Part I: Oceanographic Research Papers, 95, 2, 131–138, 10.3354/ame01583, It might be possible to increase the ocean's uptake of carbon dioxide ({{chem|C|O|2}}) generated through human activities by increasing plankton production through seeding, primarily with the micronutrient iron. However, this technique may not be practical at a large scale. Ocean oxygen depletion and resultant methane production (caused by the excess production remineralising at depth) is one potential drawback.CHISHOLM >FIRST = S.W., 2001, Dis-crediting ocean fertilization volume=294, 5541doi= 10.1126/science.1065349, 11598285 first2 = PG first3 = JJ, 1, AUMONT > FIRST = O. YEAR=2006,weblink Globalizing results from ocean in situ iron fertilization studies, Global Biogeochemical Cycles issue=2 page= GB2017, 2006GBioC..20.2017A,

Oxygen production

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 biproduct. It is estimated that about 50% of the world's oxygen is produced via phytoplankton photosynthesis.NEWS, Roach, John,weblink Source of Half Earth's Oxygen Gets Little Credit, National Geographic News, June 7, 2004, 2016-04-04, The rest is produced via photosynthesis on land by plants. Furthermore, phytoplankton photosynthesis has controlled the atmospheric {{chem|C|O|2}}/{{chem|O|2}} balance since the early Precambrian Eon.JOURNAL, Primary production, isotopes, extinctions and the atmosphere, Palaeogeography, Palaeoclimatology, Palaeoecology, April 1968, Tappan, Helen, 4, 3, 187–210, 10.1016/0031-0182(68)90047-3, 1968PPP.....4..187T,

Biomass variability

File:Amphipodredkils.jpg|thumb| Amphipod with curved exoskeletonexoskeletonThe 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 Ni̱o periods, influencing populations of zooplankton, fishes, sea birds, and marine mammals.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.Steinacher, M., et al. (2010). "Projected 21st century decrease in marine productivity: a multi-model analysis". Biogeosciences, 7, 979-1005. Additionally, changes in the mortality of phytoplankton due to rates of zooplankton grazing may be significant.Freshly hatched fish larvae are also plankton for a few days, as long as it takes before they can swim against currents.{{clear}}File:Copepodkils.jpg| Copepod from Antarctica, a translucent ovoid animal with two long antennaeFile:Clupeaharenguslarvaeinsitukils.jpg|Herring larva imaged in situ in the typical oblique swimming position with the remains of the yolk and the long gut visible in the transparent animalFile:Icefishuk.jpg|Icefish larvae from Antarctica have no haemoglobinFile:Ctenophora.jpg|Siphonophora Рthe "conveyor belt" of the upgrowing larvae and the ovarium can be seen File:LeptocephalusConger.jpg|Eel larva drifting with the gulf stream{{clear}}File:Antarctic_krill_(Euphausia_superba).jpg|Antarctic krill, probably the largest biomass of a single species on the planetFile:Meganyctiphanes norvegica.jpg|Northern krill: the mid gut is red. It feeds on zooplanktonFile:Tomopteriskils.jpg|Tomopteris is a genus of marine planktonic polychaeteFile:Dinoflagellates and a tintinnid ciliate.jpg|Microzooplankton, the major grazers of the plankton: two dinoflagellates and a tintinnid ciliate).File:Plankton creates sea foam 2.jpg|Sea foam can be produced by plankton, photo of many, differently sized bubbles with image of photographer{{clear}}

Importance to fish

Zooplankton are the initial prey item for almost all fish larvae as they switch from their yolk sacs 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) and man-made factors (e.g. river dams) can strongly affect zooplankton, which can in turn strongly affect larval survival, and therefore breeding success.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 practised by traditional fish farmers for decades, illustrating the importance of plankton even in man-made environments.

See also

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References

{{reflist|30em}}

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}} {{plankton|state=expanded}}{{aquatic ecosystem topics|expanded=none}}{{Authority control}}

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