View source for Coccolith

{{Short description|Calcium carbonate scales covering some phytoplankton species}}
[[File:Coccolithus pelagicus.jpg|thumb|upright=1.2| {{center|[[Scanning electron micrograph]] of ''[[Coccolithus]] pelagicus'', plated with coccoliths}}]]

'''Coccoliths''' are individual plates or scales of [[calcium carbonate]] formed by [[coccolithophore]]s (single-celled [[phytoplankton]] such as ''[[Emiliania huxleyi]]'') and cover the cell surface arranged in the form of a spherical shell, called a ''[[coccosphere]]''.

==Overview==
Coccoliths, which are about 2 to 25 micrometres across, enclose coccolithophores, which are spherical cells about 5-100 micrometres across.<ref name=Moheimani2012>{{citation |journal=[[Algal Research]] |volume=1 |issue=2 |year=2012 |pages=120–133 |title=Bioremediation and other potential applications of coccolithophorid algae: A review. . Bioremediation and other potential applications of coccolithophorid algae: A review |first1=N.R. |last1=Moheimani |first2=J.P. |last2=Webb |first3= M.A. |last3=Borowitzka |doi=10.1016/j.algal.2012.06.002}}</ref>
Coccolithophores are an important group of about 200 marine phytoplankton species{{hsp}}<ref>{{cite journal |doi = 10.2113/gsmicropal.51.4.267|title = A review of selected aspects of coccolithophore biology with implications for paleobiodiversity estimation|year = 2005|last1 = Young|first1 = J. R.|last2 = Geisen|first2 = M.|last3 = Probert|first3 = I.|journal = Micropaleontology|volume = 51|issue = 4|pages = 267–288|url = https://epic.awi.de/id/eprint/11940/1/You2005a.pdf}}</ref>  which cover themselves with a [[calcium carbonate]] shell called a "coccosphere". They are ecologically and biogeochemically important but the reason why they [[calcify]] remains elusive. One key function may be that the coccosphere offers protection against [[microzooplankton]] predation, which is one of the main causes of phytoplankton death in the ocean.<ref name=Haunost2021>{{cite journal | last1=Haunost | first1=Mathias | last2=Riebesell | first2=Ulf | last3=D'Amore | first3=Francesco | last4=Kelting | first4=Ole | last5=Bach | first5=Lennart T. | title=Influence of the Calcium Carbonate Shell of Coccolithophores on Ingestion and Growth of a Dinoflagellate Predator | journal=Frontiers in Marine Science | publisher=Frontiers Media SA | volume=8 | date=30 June 2021 | issn=2296-7745 | doi=10.3389/fmars.2021.664269| doi-access=free }} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

<gallery mode="packed" style="float:right;" heights="200px">
File:Cross section of a coccolithophore with coccolith layer.png| Partial cross section of a coccolithophore with coccolith layer{{hsp}}<ref>{{cite journal | last1=Irie | first1=Takahiro | last2=Bessho | first2=Kazuhiro | last3=Findlay | first3=Helen S. | last4=Calosi | first4=Piero | title=Increasing Costs Due to Ocean Acidification Drives Phytoplankton to Be More Heavily Calcified: Optimal Growth Strategy of Coccolithophores | journal=PLOS ONE | publisher=Public Library of Science (PLoS) | volume=5 | issue=10 | date=2010-10-15 | issn=1932-6203 | doi=10.1371/journal.pone.0013436 | article-number=e13436 | doi-access=free }} [[File:CC-BY icon.svg|50px]] Modified material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>|alt=Partial cross section of a coccolithophore with coccolith layer
File:Diagram of a coccolithophore cell and its shield of coccoliths.png|Coccolithophore cell surrounded by its shield of coccoliths. The coccolith-bearing cell is called the [[#Coccolithophore shells|coccosphere]].<ref>{{cite journal | last=Aloisi | first=G. | title=Covariation of metabolic rates and cell size in coccolithophores | journal=Biogeosciences | publisher=Copernicus GmbH | volume=12 | issue=15 | date=6 August 2015 | issn=1726-4189 | doi=10.5194/bg-12-4665-2015 | pages=4665–4692| bibcode=2015BGeo...12.4665A | s2cid=6227548 | doi-access=free }}</ref><ref>{{cite journal | last=Henderiks | first=Jorijntje | title=Coccolithophore size rules — Reconstructing ancient cell geometry and cellular calcite quota from fossil coccoliths | journal=Marine Micropaleontology | publisher=Elsevier BV | volume=67 | issue=1–2 | year=2008 | issn=0377-8398 | doi=10.1016/j.marmicro.2008.01.005 | pages=143–154| bibcode=2008MarMP..67..143H }}</ref>
</gallery>

Coccolithophores have been an integral part of [[marine plankton]] communities since the [[Jurassic]].<ref>{{cite book |doi = 10.1007/978-3-662-06278-4_18|chapter = Calcareous nannoplankton evolution and diversity through time|title = Coccolithophores|year = 2004|last1 = Bown|first1 = Paul R.|last2 = Lees|first2 = Jackie A.|last3 = Young|first3 = Jeremy R.|pages = 481–508|isbn = 978-3-642-06016-8}}</ref><ref>{{cite book |doi = 10.1007/978-3-662-06278-4_19|chapter = Carbonate fluxes and calcareous nannoplankton|title = Coccolithophores|year = 2004|last1 = Hay|first1 = William W.|pages = 509–528|isbn = 978-3-642-06016-8}}</ref> Today, coccolithophores contribute ~1–10% to [[Marine primary production|primary production]] in the surface ocean{{hsp}}<ref>{{cite journal |doi = 10.1016/j.dsr2.2006.12.003|title = Relating coccolithophore calcification rates to phytoplankton community dynamics: Regional differences and implications for carbon export|year = 2007|last1 = Poulton|first1 = Alex J.|last2 = Adey|first2 = Tim R.|last3 = Balch|first3 = William M.|last4 = Holligan|first4 = Patrick M.|journal = Deep Sea Research Part II: Topical Studies in Oceanography|volume = 54|issue = 5–7|pages = 538–557|bibcode = 2007DSRII..54..538P}}</ref> and ~50% to pelagic CaCO<sub>3</sub> sediments.<ref>{{cite journal |doi = 10.1029/2009PA001731|title = Ratio of coccolith CaCO3to foraminifera CaCO3in late Holocene deep sea sediments|year = 2009|last1 = Broecker|first1 = Wallace|last2 = Clark|first2 = Elizabeth|journal = Paleoceanography|volume = 24|issue = 3|bibcode = 2009PalOc..24.3205B|doi-access = free}}</ref> Their calcareous shell increases the sinking velocity of photosynthetically fixed {{CO2}} into the deep ocean by [[Ballast minerals|ballasting]] organic matter.<ref>{{cite journal |doi = 10.1029/2001GB001765|title = Association of sinking organic matter with various types of mineral ballast in the deep sea: Implications for the rain ratio|year = 2002|last1 = Klaas|first1 = Christine|last2 = Archer|first2 = David E.|journal = Global Biogeochemical Cycles|volume = 16|issue = 4|page = 1116|bibcode = 2002GBioC..16.1116K| s2cid=34159028 |doi-access = free}}</ref><ref>{{cite journal |doi = 10.1016/j.pocean.2007.11.003|title = Particulate organic carbon fluxes to the ocean interior and factors controlling the biological pump: A synthesis of global sediment trap programs since 1983|year = 2008|last1 = Honjo|first1 = Susumu|last2 = Manganini|first2 = Steven J.|last3 = Krishfield|first3 = Richard A.|last4 = Francois|first4 = Roger|journal = Progress in Oceanography|volume = 76|issue = 3|pages = 217–285|bibcode = 2008PrOce..76..217H}}</ref> At the same time, the [[biogenic]] precipitation of calcium carbonate during coccolith formation reduces the total alkalinity of seawater and releases {{CO2}}.<ref>{{cite journal |doi = 10.4319/lo.1994.39.2.0458|title = Marine calcification as a source of carbon dioxide: Positive feedback of increasing atmospheric CO2|year = 1994|last1 = Frankignoulle|first1 = Michel|last2 = Canon|first2 = Christine|last3 = Gattuso|first3 = Jean-Pierre|journal = Limnology and Oceanography|volume = 39|issue = 2|pages = 458–462|bibcode = 1994LimOc..39..458F| hdl=2268/246251 |doi-access = free}}</ref><ref>{{cite book |doi = 10.1007/978-3-662-06278-4_5|chapter = Coccolithophores and the biological pump: Responses to environmental changes|title = Coccolithophores|year = 2004|last1 = Rost|first1 = Björn|last2 = Riebesell|first2 = Ulf|pages = 99–125|isbn = 978-3-642-06016-8}}</ref> Thus, coccolithophores play an important role in the [[marine carbon cycle]] by influencing the efficiency of the [[biological carbon pump]] and the oceanic uptake of atmospheric {{CO2}}.<ref name=Haunost2021 />

As of 2021, it is not known why coccolithophores calcify and how their ability to produce coccoliths is associated with their ecological success.<ref>Young, J. R. (1987). Possible Functional Interpretations of Coccolith Morphology. New York: Springer-Verlag, 305–313.</ref><ref>Young, J. R. (1994). "Functions of coccoliths," in Coccolithophores, eds A. Winter and W. G. Siesser (Cambridge: Cambridge University Press), 63–82.</ref><ref>{{cite journal |doi = 10.3354/meps09993|title = Environmental controls on coccolithophore calcification|year = 2012|last1 = Raven|first1 = JA|last2 = Crawfurd|first2 = K.|journal = Marine Ecology Progress Series|volume = 470|pages = 137–166|bibcode = 2012MEPS..470..137R|doi-access = free|hdl = 10453/114799|hdl-access = free}}</ref><ref name=Monteiro2016>{{cite journal |doi = 10.1126/sciadv.1501822|title = Why marine phytoplankton calcify|year = 2016|last1 = Monteiro|first1 = Fanny M.|last2 = Bach|first2 = Lennart T.|last3 = Brownlee|first3 = Colin|last4 = Bown|first4 = Paul|last5 = Rickaby|first5 = Rosalind E. M.|last6 = Poulton|first6 = Alex J.|last7 = Tyrrell|first7 = Toby|last8 = Beaufort|first8 = Luc|last9 = Dutkiewicz|first9 = Stephanie|last10 = Gibbs|first10 = Samantha|last11 = Gutowska|first11 = Magdalena A.|last12 = Lee|first12 = Renee|last13 = Riebesell|first13 = Ulf|last14 = Young|first14 = Jeremy|last15 = Ridgwell|first15 = Andy|journal = Science Advances|volume = 2|issue = 7|article-number = e1501822|pmid = 27453937|pmc = 4956192|bibcode = 2016SciA....2E1822M}}</ref><ref>{{cite journal |doi = 10.3389/fmars.2019.00049|doi-access = free|title = On the Genesis and Function of Coccolithophore Calcification|year = 2019|last1 = Müller|first1 = Marius N.|journal = Frontiers in Marine Science|volume = 6}}</ref> The most plausible benefit of having a coccosphere seems to be a protection against predators or viruses.<ref name="Evolution of Primary Producers in t">{{cite book |doi = 10.1016/B978-012370518-1/50015-1|chapter = Armor: Why, when, and How|title = Evolution of Primary Producers in the Sea|year = 2007|last1 = Hamm|first1 = Christian|last2 = Smetacek|first2 = Victor|pages = 311–332|isbn = 978-0-12-370518-1}}</ref><ref name=Monteiro2016 /> Viral infection is an important cause of phytoplankton death in the oceans,<ref>{{cite journal |doi = 10.1111/j.1550-7408.2004.tb00537.x|title = Viral Control of Phytoplankton Populations-a Review1|year = 2004|last1 = Brussaard|first1 = Corina P. D.|journal = The Journal of Eukaryotic Microbiology|volume = 51|issue = 2|pages = 125–138|pmid = 15134247|s2cid = 21017882}}</ref> and it has recently been shown that calcification can influence the interaction between a coccolithophore and its virus.<ref>{{cite journal |doi = 10.1111/1462-2920.14362|title = The mutual interplay between calcification and coccolithovirus infection|year = 2019|last1 = Johns|first1 = Christopher T.|last2 = Grubb|first2 = Austin R.|last3 = Nissimov|first3 = Jozef I.|last4 = Natale|first4 = Frank|last5 = Knapp|first5 = Viki|last6 = Mui|first6 = Alwin|last7 = Fredricks|first7 = Helen F.|last8 = Van Mooy|first8 = Benjamin A. S.|last9 = Bidle|first9 = Kay D.|journal = Environmental Microbiology|volume = 21|issue = 6|pages = 1896–1915|pmid = 30043404|pmc = 7379532}}</ref><ref>{{cite journal |doi = 10.3389/fmars.2020.530757|doi-access = free|title = The Calcium Carbonate Shell of Emiliania huxleyi Provides Limited Protection Against Viral Infection|year = 2020|last1 = Haunost|first1 = Mathias|last2 = Riebesell|first2 = Ulf|last3 = Bach|first3 = Lennart T.|journal = Frontiers in Marine Science|volume = 7}}</ref> The major predators of marine phytoplankton are [[microzooplankton]] like [[ciliate]]s and [[dinoflagellate]]s. These are estimated to consume about two-thirds of the primary production in the ocean{{hsp}}<ref>{{cite journal |doi = 10.4319/lo.2004.49.1.0051|title = Phytoplankton growth, microzooplankton grazing, and carbon cycling in marine systems|year = 2004|last1 = Calbet|first1 = Albert|last2 = Landry|first2 = Michael R.|journal = Limnology and Oceanography|volume = 49|issue = 1|pages = 51–57|bibcode = 2004LimOc..49...51C| hdl=10261/134985 | s2cid=22995996 |hdl-access = free}}</ref> and microzooplankton can exert a strong grazing pressure on coccolithophore populations.<ref>{{cite journal |doi = 10.1016/j.pocean.2018.02.024|title = Growth and mortality of coccolithophores during spring in a temperate Shelf Sea (Celtic Sea, April 2015)|year = 2019|last1 = Mayers|first1 = K.M.J.|last2 = Poulton|first2 = A.J.|last3 = Daniels|first3 = C.J.|last4 = Wells|first4 = S.R.|last5 = Woodward|first5 = E.M.S.|last6 = Tarran|first6 = G.A.|last7 = Widdicombe|first7 = C.E.|last8 = Mayor|first8 = D.J.|last9 = Atkinson|first9 = A.|last10 = Giering|first10 = S.L.C.|journal = Progress in Oceanography|volume = 177|page = 101928|bibcode = 2019PrOce.17701928M|s2cid = 135347218|doi-access = free}}</ref> Although calcification does not prevent predation, it has been argued that the coccosphere reduces the grazing efficiency by making it more difficult for the predator to utilise the organic content of coccolithophores.<ref>Young, J. R. (1994) "Functions of coccoliths". In: ''Coccolithophores'', Eds A. Winter and W. G. Siesser (Cambridge: Cambridge University Press), 63–82.</ref> [[Heterotrophic]] [[protist]]s are able to selectively choose prey on the basis of its size or shape and through chemical signals{{hsp}}<ref>{{cite journal |doi = 10.1111/j.1550-7408.2004.tb00540.x|title = Interactions between Planktonic Microalgae and Protozoan Grazers1|year = 2004|last1 = Tillmann|first1 = Urban|journal = The Journal of Eukaryotic Microbiology|volume = 51|issue = 2|pages = 156–168|pmid = 15134250|s2cid = 36526359}}</ref><ref>{{cite journal |doi = 10.1093/plankt/fbq114|title = The role of dissolved infochemicals in mediating predator-prey interactions in the heterotrophic dinoflagellate Oxyrrhis marina|year = 2011|last1 = Breckels|first1 = M. N.|last2 = Roberts|first2 = E. C.|last3 = Archer|first3 = S. D.|last4 = Malin|first4 = G.|last5 = Steinke|first5 = M.|journal = Journal of Plankton Research|volume = 33|issue = 4|pages = 629–639|doi-access = free}}</ref> and may thus favor other prey that is available and not protected by coccoliths.<ref name=Haunost2021 />

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== Formation and composition ==
{{biomineralization sidebar}}

Coccoliths are formed within the cell in [[Vesicle (biology and chemistry)|vesicle]]s derived from the [[golgi body]]. When the coccolith is complete these vesicles fuse with the cell wall and the coccolith is [[exocytosis|exocytosed]] and incorporated in the coccosphere.  The coccoliths are either dispersed following death and breakup of the coccosphere, or are shed continually by some species. They sink through the water column to form an important part of the deep-sea [[sediment]]s (depending on the water depth). [[Thomas Huxley]] was the first person to observe these forms in modern marine sediments and he gave them the name 'coccoliths' in a report published in 1858.<ref>{{ cite book | last=Huxley | first=Thomas Henry | author-link=Thomas Henry Huxley | year=1858 | chapter=Appendix A | title=Deep Sea Soundings in the North Atlantic Ocean between Ireland and Newfoundland, made in H.M.S. Cyclops, Lieut.-Commander Joseph Dayman, in June and July 1857 | location=London | publisher=British Admiralty | pages=63–68 [64] | chapter-url=http://access.bl.uk/item/viewer/ark:/81055/vdc_000000034E24#?c=0&m=0&s=0&cv=69&xywh=-1748%2C-1%2C4910%2C2575 }}</ref><ref>{{ cite journal | last=Huxley | first=Thomas Henry | author-link=Thomas Henry Huxley | year=1868 | title=On some organisms living at great depth in the North Atlantic Ocean | journal=Quarterly Journal of Microscopical Science | series=New series | volume=8 | pages=203–212 | url=https://biodiversitylibrary.org/page/27676855 }}</ref>
Coccoliths are composed of calcium carbonate as the mineral [[calcite]] and are the main constituent of [[chalk]] deposits such as the [[white cliffs of Dover]] (deposited in [[Cretaceous]] times), in which they were first described by [[Henry Clifton Sorby]] in 1861.<ref>{{ cite journal | last=Sorby  | first=Henry Clifton | author-link=Henry Clifton Sorby | year=1861 | title=On the organic origin of the so-called 'Crystalloids' of the chalk | journal=Annals and Magazine of Natural History | series=Ser. 3 | volume=8 | issue=45 | pages=193–200 | doi=10.1080/00222936108697404 | url=https://biodiversitylibrary.org/page/15602222 }}</ref>

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File:Collapsed coccosphere of Pleurochrysis carterae.jpg|Collapsed coccosphere of ''[[Pleurochrysis carterae]]''
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== Types ==
There are two main types of coccoliths, '''heterococcoliths''' and '''holococcoliths'''. Heterococcoliths are formed of a radial array of elaborately shaped crystal units. Holococcoliths are formed of minute (~0.1 micrometre) calcite [[Rhombohedral crystal system|rhombohedra]], arranged in continuous arrays. The two coccolith types were originally thought to be produced by different families of coccolithophores. Now, however, it is known through a mix of observations on field samples and laboratory cultures, that the two coccolith types are produced by the same species but at different life cycle phases. Heterococcoliths are produced in the diploid life-cycle phase and holococcoliths in the haploid phase. Both in field samples and laboratory cultures, there is the possibility of observing a cell covered by a combination of heterococcoliths and holococcoliths. This indicates the transition from the diploid to the haploid phase of the species. Such combination of coccoliths has been observed in field samples, with many of them coming from the Mediterranean.<ref>{{Cite journal|last1=Fortuño|first1=José Manuel|last2=Cros|first2=Lluïsa|date=2002-03-30|title=Atlas of Northwestern Mediterranean Coccolithophores|url=http://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/view/630|journal=Scientia Marina|language=en|volume=66|issue=S1|pages=1–182|doi=10.3989/scimar.2002.66s11|issn=1886-8134|doi-access=free|hdl=10261/5441|hdl-access=free}}</ref><ref>{{cite book |title=Coccolithophores of the Eastern Mediterranean sea: A look into the marine microworld |last1=Malinverno |first1=E |last2=Dimiza |first2=MD |last3=Triantaphyllou |first3=MV |last4=Dermitzakis |first4=MD |last5=Corselli |first5=C |publisher="ION" Publishing Group |year=2008 |isbn=978-960-411-660-7 |location=Athens }}</ref>

[[File:Cocolithtypes.jpg|thumb|upright=1.8| {{center|Types of coccoliths}}]]

===Shape===
Coccoliths are also classified depending on shape. Common shapes include:<ref name="WinterSiesser2006">{{cite book|author1=Amos Winter|author2=William G. Siesser|title=Coccolithophores|url=https://books.google.com/books?id=EivD3H27ulUC&pg=PA54|date= 2006|publisher=Cambridge University Press|isbn=978-0-521-03169-1|pages=54–58}}</ref><ref name="Tomas2012">{{cite book|author=Carmelo R Tomas|title=Marine Phytoplankton: A Guide to Naked Flagellates and Coccolithophorids|url=https://books.google.com/books?id=NwH2-w2qJgYC&pg=PA161|date=2012|publisher=Academic Press|isbn=978-0-323-13827-7|pages=161–165}}</ref>

* '''Calyptrolith''' – basket-shaped with openings near the base
* '''Caneolith''' – disc- or bowl-shaped
* '''Ceratolith''' – horseshoe or wishbone shaped
* '''Cribrilith''' – disc-shaped, with numerous perforations in the central area
* '''Cyrtolith''' – convex disc shaped, may with a projecting central process
* '''Discolith''' – ellipsoidal with a raised rim, in some cases the high rim forms a vase or cup-like structure
* '''Helicolith''' – a placolith with a spiral margin
* '''Lopadolith''' – basket or cup-shaped with a high rim, opening distally
* '''Pentalith''' – pentagonal shape composed of five four-sided crystals
* '''Placolith''' – rim composed of two plates stacked on top of one another
* '''Prismatolith''' – polygonal, may have perforations
* '''Rhabdolith''' – a single plate with a club-shaped central process
* '''Scapholith''' – rhombohedral, with parallel lines in center

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| caption1  = Helicoliths  of ''Helicosphaera carteri''

| image2    = Emiliania huxleyi coccolithophore (PLoS).png
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| caption2 =Coccosphere of ''Emiliania huxleyi'' consisting of overlapping placoliths

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<gallery mode="packed" style="float:left;" heights="500px">
File:Coccolith structures of representative Noelaerhabdaceae.jpg| Coccolith structures of representative [[Noelaerhabdaceae]].<ref name=Bendif2016>{{cite journal | last1=Bendif | first1=El Mahdi | last2=Probert | first2=Ian | last3=Díaz-Rosas | first3=Francisco | last4=Thomas | first4=Daniela | last5=van den Engh | first5=Ger | last6=Young | first6=Jeremy R. | last7=von Dassow | first7=Peter | title=Recent Reticulate Evolution in the Ecologically Dominant Lineage of Coccolithophores | journal=Frontiers in Microbiology | publisher=Frontiers Media SA | volume=7 | date=2016-05-24 | issn=1664-302X | doi=10.3389/fmicb.2016.00784 | doi-access=free }} [[File:CC-BY icon.svg|50px]] Modified material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref><br />Each [[morphospecies]] is associated with a SEM image in the next diagram
</gallery>

<gallery mode="packed" style="float:right;" heights="420px">
File:Images of representative Noelaerhabdaceae and other coccolithophores.jpg| SEM images correspond to coccolith drawings in the previous diagram<br /> (A) ''[[Gephyrocapsa]] ericsonii'' RCC4032 (B) ''Gephyrocapsa muellerae'' (C) ''[[Gephyrocapsa oceanica]]'' (D) ''[[Reticulofenestra]] parvular'' RCC4033; (E) Reticulofenestra parvular RCC4034; (F) Reticulofenestra parvular RCC4035; (G) Reticulofenestra parvular RCC4036; (H) ''[[Emiliania huxleyi]]'' morphotype R; (I) ''Emiliania huxleyi'' morphotype A; (J) ''Emiliania huxleyi'' morphotype B.
{{center|<small>Scale bar = 2 microns</small>}}
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== Function ==
Although coccoliths are remarkably elaborate structures whose formation is a complex product of cellular processes, their function is unclear. Hypotheses include defence against grazing by [[zooplankton]] or infection by [[bacteria]] or [[viruses]]; maintenance of [[buoyancy]]; release of [[carbon dioxide]] for [[photosynthesis]]; to filter out harmful [[UV]] light; or in deep-dwelling species, to concentrate light for photosynthesis.

== Fossil record ==
Because coccoliths are formed of low-Mg calcite, the most stable form of calcium carbonate, they are readily fossilised.  They are found in sediments together with similar microfossils of uncertain affinities (nanoliths) from the [[Upper Triassic]] to recent. They are widely used as biostratigraphic markers and as paleoclimatic proxies. Stable oxygen and carbon isotope data from coccoliths is used to reconstruct estimates of oceanic CO<sub>2</sub> concentrations in the geologic past.<ref>{{Cite journal |last=Hermoso |first=Michaël |date=1 April 2016 |title=Isotopic record of Pleistocene glacial/interglacial cycles in pelagic carbonates: Revisiting historical data from the Caribbean Sea |url=https://linkinghub.elsevier.com/retrieve/pii/S027737911630035X |journal=[[Quaternary Science Reviews]] |language=en |volume=137 |pages=69–78 |doi=10.1016/j.quascirev.2016.02.003 |access-date=17 September 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Coccoliths and related fossils are referred to as ''[[calcareous nanofossils]]'' or ''calcareous [[nanoplankton|nannoplankton (nanoplankton)]]''.


==References==
{{Reflist}}

== External links ==
{{commons category|Coccolith}}
*[http://www.soes.soton.ac.uk/staff/tt/eh/coccoliths.html The EHUX website] - site dedicated to ''Emiliania huxleyi'', containing essays on blooms, coccolith function, etc.
*[http://ina.tmsoc.org International Nannoplankton Association site] - includes an illustrated guide to coccolith terminology and several image galleries.
*[http://ina.tmsoc.org/Nannotax3/index.php?dir=Coccolithophores Nannotax] - illustrated guide to the taxonomy of coccolithophores and other nannofossils.
* [https://web.archive.org/web/20090310022540/http://bioinfo.csusm.edu/ Cocco Express - Coccolithophorids Expressed Sequence Tags (EST) & Microarray Database]
*[https://web.archive.org/web/20040529042518/http://www-ocean.tamu.edu/Quarterdeck/QD5.2/shatto-slowey2.html Possible functions of Coccoliths]

{{Protist structures}}
{{Authority control}}

[[Category:Calcium compounds]]