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=== Formation ===
Coccoliths are produced by a [[biomineralization]] process known as coccolithogenesis.<ref name=Moheimani2012 /> Generally, calcification of coccoliths occurs in the presence of light, and these scales are produced much more during the exponential phase of growth than the stationary phase.<ref name=Linschooten1991>{{citation |journal=Journal of Phycology |volume=27 |issue=1 |year=1991 |pages=82–86 |title=Role of the light-dark cycle and medium composition on the production of coccoliths by Emiliania huxleyi (haptophyceae) |first=Cornelis |last=Linschooten |doi=10.1111/j.0022-3646.1991.00082.x |s2cid=84368830 |display-authors=etal }}</ref> Although not yet entirely understood, the biomineralization process is tightly regulated by [[calcium signaling]]. [[Calcite]] formation begins in the [[golgi complex]] where protein templates nucleate the formation of CaCO<sub>3</sub> crystals and complex acidic [[polysaccharides]] control the shape and growth of these crystals.<ref name=deVargas2007>{{cite book |last1=de Vargas |first1=C. |last2=Aubrey |first2=M.P. |last3=Probert |first3=I. |last4=Young |first4=J. |editor1-last=Falkowski |editor1-first=P.G.|editor2-last=Knoll |editor2-first=A.H. |title=Origin and Evolution of Coccolithophores |chapter=From coastal hunters to oceanic farmers. |pages=251–285 |year=2007 |publisher=Elsevier |location=Boston}}</ref> As each scale is produced, it is exported in a Golgi-derived [[vesicle (biology)|vesicle]] and added to the inner surface of the coccosphere. This means that the most recently produced coccoliths may lie beneath older coccoliths.<ref name=Young2003>{{cite book |last1= Young |first1= J.R. |last2=Karen |first2=H. |editor1-last=Dove |editor1-first=P.M. |editor-link1=Patricia M. Dove |editor2-last=Yoreo |editor2-first= J.J. |editor3-last=Weiner |editor3-first=S. |title=Reviews in Mineralogy and Geochemistry |chapter=Biomineralization Within Vesicles: The Calcite of Coccoliths |pages=189–216 |publisher=Mineralogical Society of America |year=2003 |location=Washington, D.C.}}</ref>
Depending upon the phytoplankton's stage in the life cycle, two different types of coccoliths may be formed. Holococcoliths are produced only in the haploid phase, lack radial symmetry, and are composed of anywhere from hundreds to thousands of similar minute (ca 0.1 μm) rhombic [[calcite]] crystals. These crystals are thought to form at least partially outside the cell. Heterococcoliths occur only in the diploid phase, have radial symmetry, and are composed of relatively few complex crystal units (fewer than 100). Although they are rare, combination coccospheres, which contain both holococcoliths and heterococcoliths, have been observed in the plankton recording coccolithophore life cycle transitions. Finally, the coccospheres of some species are highly modified with various appendages made of specialized coccoliths.<ref name=Young2009>{{citation |journal=Journal of Phycology |volume=45 |issue=1 |year=2009 |pages=213–226 |title=Coccolith function and morphogenesis: insights from appendage-bearing coccolithophores of the family syracosphaeraceae (haptophyta) |first= J.R. |last=Young |doi=10.1111/j.1529-8817.2008.00643.x |pmid=27033659 |display-authors=etal |doi-access=
<!-- Deleted image removed: [[File:Figure 1.jpg|frame|alt=Figure 1|Figure 1: Main types of coccoliths produced. Adapted from Figure 1 of Figure 1 of (Young, et al., 2003)<ref name=Young2009 />]] -->
<!-- Deleted image removed: [[File:Figure 2.jpg|frame|alt=Figure 2|Figure 2: Specialized coccolith structures, adapted from Figure 1 of (Young, et al., 2009).<ref name=Jordan1997 />]] -->
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===Evolutionary responses to ocean acidification===
Research also suggests that [[ocean acidification]] due to increasing concentrations of CO<sub>2</sub> in the atmosphere may affect the calcification machinery of coccolithophores. This may not only affect immediate events such as increases in population or coccolith production, but also may induce [[evolutionary adaptation]] of coccolithophore species over longer periods of time. For example, coccolithophores use H<sup>+</sup> [[ion channels]] in to constantly pump H<sup>+</sup> ions out of the cell during coccolith production. This allows them to avoid [[acidosis]], as coccolith production would otherwise produce a toxic excess of H<sup>+</sup> ions. When the function of these ion channels is disrupted, the coccolithophores stop the calcification process to avoid acidosis, thus forming a [[feedback loop]].<ref name=Beaufort2011>{{citation |journal=Nature |volume=476 |issue=7358 |year=2011 |pages=80–3 |title=Sensitivity of coccolithophores to carbonate chemistry and ocean acidification |first=L. |last=Beaufort |doi=10.1038/nature10295|pmid=21814280 |s2cid=4417285 |display-authors=etal }}</ref> Low ocean [[alkalinity]], impairs ion channel function and therefore places evolutionary selective pressure on coccolithophores and makes them (and other ocean calcifiers) vulnerable to ocean acidification.<ref name=Tyrell1999>{{citation |journal=Journal of Geophysical Research |volume=104 |issue=C2 |year=1999 |pages=3223–3241 |title=Optical impacts of oceanic coccolithophore blooms |first1=T. |last1=Tyrell |doi=10.1029/1998jc900052 |display-authors=1 |last2=Mobley |first2=C. D. |bibcode=1999JGR...104.3223T|doi-access=
Decreasing coccolith mass is related to both the increasing concentrations of CO<sub>2</sub> and decreasing concentrations of CO<sub>3</sub><sup>2−</sup> in the world's oceans. This lower calcification is assumed to put coccolithophores at ecological disadvantage. Some species like ''Calcidiscus'' ''leptoporus'', however, are not affected in this way, while the most abundant coccolithophore species, ''E. huxleyi'' might be (study results are mixed).<ref name="Beaufort2011"/><ref name=Rodriguez2008>{{cite web |url=https://www.independent.co.uk/news/science/can-seashells-save-the-world-813915.html |title=Can seashells save the world?|website=[[Independent.co.uk]] |date=22 April 2008 }}</ref> Also, highly calcified coccolithophorids have been found in conditions of low CaCO<sub>3</sub> saturation contrary to predictions.<ref name="Smith2012"/> Understanding the effects of increasing ocean acidification on coccolithophore species is absolutely essential to predicting the future chemical composition of the ocean, particularly its carbonate chemistry. Viable conservation and management measures will come from future research in this area. Groups like the European-based [[CALMARO]]<ref name=Calmaro>{{cite web |url=http://www.calmaro.eu |title=cal.mar.o |access-date=2021-04-24 |archive-date=2020-12-30 |archive-url=https://web.archive.org/web/20201230012133/https://www.calmaro.eu/ |url-status=dead }}</ref> are monitoring the responses of coccolithophore populations to varying pH's and working to determine environmentally sound measures of control.
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{{See also|CLAW hypothesis}}
The coccolithophorids help in regulating the temperature of the oceans. They thrive in warm seas and release [[dimethyl sulphide|dimethyl sulfide]] (DMS) into the air whose [[nucleation|nuclei]] help to produce thicker clouds to block the sun.<ref>{{cite journal |doi = 10.1038/326655a0|title = Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate|year = 1987|last1 = Charlson|first1 = Robert J.|last2 = Lovelock|first2 = James E.|last3 = Andreae|first3 = Meinrat O.|last4 = Warren|first4 = Stephen G.|journal = Nature|volume = 326|issue = 6114|pages = 655–661|bibcode = 1987Natur.326..655C|s2cid = 4321239}}</ref> When the oceans cool, the number of coccolithophorids decrease and the amount of clouds also decrease. When there are fewer clouds blocking the sun, the temperature also rises. This, therefore, maintains the balance and equilibrium of nature.<ref>{{cite book | author=Lovelock, James | title=The Revenge of Gaia | publisher=Penguin | year=2007 | isbn=978-0-14-102597-1| title-link=The Revenge of Gaia }}</ref><ref>{{cite journal |doi = 10.1029/2004GB002333|title = Solar variability, dimethyl sulphide, clouds, and climate|year = 2005|last1 = Larsen|first1 = S. H.|journal = Global Biogeochemical Cycles|volume = 19|issue = 1|pages = GB1014|bibcode = 2005GBioC..19.1014L|doi-access =
== See also ==
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