View source for Coccolithophore

{{Short description|Unicellular algae responsible for the formation of chalk}}
{{Paraphyletic group
| auto = yes
| subheader = [[Paraphyletic]] grouping of algae
| fossil_range = {{fossilrange|Rhaetian|Recent}}
| image = Coccolithus pelagicus.jpg
| image_caption = ''[[Coccolithus]] pelagicus''
| parent = Prymnesiophyceae
| includes =
*''[[Isochrysidales]]''
*''[[Coccolithales]]''
}}
[[File:Coccolithophores.png|thumb|upright=1.1|Coccolithophore cells are covered with protective calcified (chalk) scales called [[coccolith]]s]]

'''Coccolithophores''', or '''coccolithophorids''', are [[single-celled organisms]] which are part of the [[phytoplankton]], the [[autotrophic]] (self-feeding) component of the [[plankton]] community. They form a group of about 200 species, and belong either to the kingdom [[Protista]], according to [[Robert Whittaker (ecologist)|Robert Whittaker]]'s [[five-kingdom system]], or clade [[Hacrobia]], according to a newer biological classification system. Within the Hacrobia, the coccolithophores are in the [[phylum]] or [[division (botany)|division]] [[Haptophyta]], class [[Prymnesiophyceae]] (or [[Coccolithophyceae]]). Coccolithophores are almost exclusively [[Marine (ocean)|marine]], are [[photosynthesis|photosynthetic]] and [[Mixotroph|mixotrophic]], and exist in large numbers throughout the [[Photic zone|sunlight zone]] of the [[ocean]].

Coccolithophores are the most productive [[calcifying organism]]s on the planet, covering themselves with a [[calcium carbonate]] shell called a ''[[coccosphere]]''. However, the reasons they [[calcify]] remain 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>

Coccolithophores are ecologically important, and biogeochemically they play significant roles in the marine [[biological pump]] and the [[Oceanic carbon cycle|carbon cycle]].<ref>{{cite book | last1=Rost | first1=Björn | last2=Riebesell | first2=Ulf | chapter=Coccolithophores and the biological pump: Responses to environmental changes | title=Coccolithophores | publisher=Springer Berlin Heidelberg | publication-place=Berlin, Heidelberg | year=2004 | pages=99–125 | isbn=978-3-642-06016-8 | doi=10.1007/978-3-662-06278-4_5}}</ref><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> Depending on habitat, they can produce up to 40 percent of the local [[marine primary production]].<ref name="de Vries2021" /> They are of particular interest to those studying global [[climate change]] because, as [[Ocean acidification|ocean acidity]] increases, their coccoliths may become even more important as a [[carbon sink]].<ref name=Smith2012>{{citation |journal=Proceedings of the National Academy of Sciences  |volume=109 |issue=23 |year=2012 |pages=8845–8849 |title=Predominance of heavily calcified coccolithophores at low CaCO3 saturation during winter in the Bay of Biscay |first=H.E.K. |last=Smith |doi=10.1073/pnas.1117508109 |display-authors=etal  |bibcode = 2012PNAS..109.8845S |pmid=22615387 |pmc=3384182|doi-access=free }}</ref> Management strategies are being employed to prevent [[eutrophication]]-related coccolithophore blooms, as these blooms lead to a decrease in nutrient flow to lower levels of the ocean.<ref name=Yunev2007>{{citation |journal=Estuarine, Coastal and Shelf Science |volume=74 |issue=1–2 |year=2007 |pages=63–67 |title=Nutrient and phytoplankton trends on the western Black Sea shelf in response to cultural eutrophication and climate changes |first1=O.A. |last1=Yunev |doi=10.1016/j.ecss.2007.03.030 |display-authors=1 |last2=Moncheva |first2=Snejana |last3=Khaliulin |first3=Aleksey |last4=Ærtebjerg |first4=Gunni |last5=Nixon |first5=Scott |bibcode = 2007ECSS...74...63Y }}</ref>

The most abundant species of coccolithophore, ''[[Emiliania huxleyi]]'', belongs to the order [[Isochrysidales]] and family [[Noëlaerhabdaceae]].<ref name=Hay1967 /> It is found in [[temperate]], [[subtropical]], and [[tropical]] oceans.<ref name=Foissner2006>{{citation |journal=Acta Protozoologica |volume=45 |issue=2 |pages=111–136 |year=2005 |title=Biogeography and dispersal of micro-organisms: a review emphasizing protists}}</ref> This makes ''E. huxleyi'' an important part of the [[planktonic]] base of a large proportion of [[marine food webs]]. It is also the fastest growing coccolithophore in laboratory cultures.<ref name=Buitenhuis2008>{{citation |journal=Limnology and Oceanography |volume=53 |issue=3 |year=2008 |pages=1181–1185 |title=Growth Rates of Six Coccolithoripd Strains as a Function of Temperature |doi=10.4319/lo.2008.53.3.1181|last1=Buitenhuis |first1=Erik T. |last2=Pangerc |first2=Tanja |last3=Franklin |first3=Daniel J. |last4=Le Quéré |first4=Corinne |last5=Malin |first5=Gill |s2cid=16601834 |bibcode=2008LimOc..53.1181B |doi-access=free }}</ref> It is studied for the extensive [[Phytoplankton bloom|blooms]] it forms in nutrient depleted waters after the reformation of the summer [[thermocline]].<ref name=Egge1992>{{citation |journal=Marine Ecology Progress Series |volume=83 |issue=2 |year=1992 |pages=281–289 |title=Silicate as regulating nutrient in phytoplankton competition |doi=10.3354/meps083281|last1=Egge |first1=JK |last2=Aksnes |first2=DL |bibcode=1992MEPS...83..281E |doi-access=free }}</ref><ref name="hup.harvard.edu">{{Cite web|url=http://www.hup.harvard.edu/catalog.php?isbn=9780674975910|title=Life at the Edge of Sight — Scott Chimileski, Roberto Kolter {{!}} Harvard University Press|website=www.hup.harvard.edu|language=en|access-date=2018-01-26}}</ref> and for its production of molecules known as [[alkenone]]s that are commonly used by [[Earth science|earth scientists]] as a means to estimate past [[sea surface temperature]]s.<ref name=Betaleb1999>{{citation |journal=Marine Chemistry |volume=64 |issue=4 |year=1999 |pages=301–313 |title=Silicate as regulating nutrient in phytoplankton competition |first=I. |last= Bentaleb |display-authors=etal  |doi=10.1016/S0304-4203(98)00079-6 }}.</ref>

==Overview==
Coccolithophores (or coccolithophorids, from the adjective<ref>{{cite web| url = http://ina.tmsoc.org/terminology/1general.htm| title = International Nanoplankton Association}}</ref>) form a group of about 200 phytoplankton species.<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| bibcode=2005MiPal..51..267Y |url = https://epic.awi.de/id/eprint/11940/1/You2005a.pdf}}</ref> They belong either to the kingdom [[Protista]], according to [[Robert Whittaker (ecologist)|Robert Whittaker]]'s [[Kingdom (biology)|Five kingdom classification]], or clade [[Hacrobia]], according to the newer biological classification system. Within the Hacrobia, the coccolithophores are in the [[phylum]] or [[division (botany)|division]] [[Haptophyta]], class [[Prymnesiophyceae]] (or [[Coccolithophyceae]]).<ref name=Hay1967>{{citation |journal=Transactions of the Gulf Coast Association of Geological Societies |volume=17 |year=1967 |pages=428–480 |title=Calcareous nannoplankton zonation of the Cenozoic of the Gulf Coast and Caribbean-Antillean area, and transoceanic correlation |first1=W.W. |last1= Hay |first2=H.P. |last2=Mohler |first3=P.H. |last3=Roth |first4=R.R. |last4=Schmidt |first5=J.E. |last5=Boudreaux}}.</ref> Coccolithophores are distinguished by special [[calcium carbonate]] plates (or scales) of uncertain function called ''[[coccolith]]s'', which are also important [[Micropaleontology|microfossils]]. However, there are Prymnesiophyceae species lacking coccoliths (e.g. in genus ''[[Prymnesium]]''), so not every member of Prymnesiophyceae is a coccolithophore.<ref>{{cite book|last1=Schaechter|first1=Moselio|title=Eukaryotic Microbes|date=2012|publisher=Academic Press|isbn=978-0-12-383876-6|page=239|url=https://books.google.com/books?id=DJLIhDnqMk0C|access-date=30 January 2015}}</ref>

Coccolithophores are single-celled [[phytoplankton]] that produce small [[calcium carbonate]] (CaCO<sub>3</sub>) scales ([[coccolith]]s) which cover the cell surface in the form of a spherical coating, called a [[coccosphere]]. Many species are also [[mixotrophs]], and are able to photosynthesise as well as ingest prey.<ref>{{Cite journal |last=Avrahami |first=Yoav |last2=Frada |first2=Miguel J. |date=31 March 2020 |year=2020 |editor-last=Mock |editor-first=T. |title=Detection of Phagotrophy in the Marine Phytoplankton Group of the Coccolithophores (Calcihaptophycidae, Haptophyta) During Nutrient‐replete and Phosphate‐limited Growth |url=https://onlinelibrary.wiley.com/doi/10.1111/jpy.12997 |journal=Journal of Phycology |language=en |volume=56 |issue=4 |pages=1103–1108 |doi=10.1111/jpy.12997 |issn=0022-3646}}</ref>

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 inorganic carbon fixation (calcification) to total carbon fixation (calcification plus photosynthesis) in the surface ocean<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|pages = 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 = 9780123705181}}</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| bibcode=2019EnvMi..21.1896J }}</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<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<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 />

==Structure==
[[File:Diagram of a coccolithophore cell and its shield of coccoliths.png|thumb|upright=1.1|Coccolithophore cell surrounded by its shield of [[coccolith]]s. 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>]]

Coccolithophores are spherical cells about 5–100 micrometres across, enclosed by calcareous plates called [[coccoliths]], which are about 2–25 micrometres across. Each cell contains two brown [[chloroplasts]] which surround the [[Cell nucleus|nucleus]].<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>

Enclosed in each coccosphere is a single cell with [[membrane]] bound [[organelles]].  Two large [[chloroplasts]] with brown [[pigment]] are located on either side of the cell and surround the [[Cell nucleus|nucleus]], [[mitochondria]], [[golgi apparatus]], [[endoplasmic reticulum]], and other organelles.  Each cell also has two [[flagella]]r structures, which are involved not only in motility, but also in [[mitosis]] and formation of the [[cytoskeleton]].<ref name=Billard2004>{{cite book |last1=Billard |first1=Chantal |last2=Inouye |first2=Isoa |editor1-first= Hans R. |editor1-last=Thierstein |editor2-first= Jeremy R. |editor2-last=Young |title=Coccolithophores-from molecular processes to global impact |publisher=Springler |date=August 17, 2004 |location=Berlin |chapter=What is new in coccolithophore biology? |isbn=9783540219286 |pages=1–29}}.</ref>  In some species, a functional or [[vestigial]] [[haptonema]] is also present.<ref name=Jordan2012 /> This structure, which is unique to [[haptophytes]], coils and uncoils in response to environmental stimuli.  Although poorly understood, it has been proposed to be involved in prey capture.<ref name=Billard2004 /> 
<!-- Deleted image removed: [[File:Figure 3coccoliths.jpg|frame|alt=Figure 3|Detailed cellular structure of coccolithophore.  Scale bar 1um.  Adapted from Figure 1 of (Jordan, 2012).<ref name=Rost2004 />]] -->

==Ecology==
===Life history strategy===
[[File:Life cycle strategies of phytoplankton.png|thumb|upright=1.7| {{center|Life cycle strategies of phytoplankton}}  (a) [[dinoflagellate]]s tend to utilize a [[haplontic]] (asexual) life cycle, (b) [[diatom]]s tend to utilize a [[diplontic]] (sexual) life cycle, and (c) coccolithophores tend to utilize a haplo-diplontic life cycle. Note that not all coccolithophores calcify in their haploid phase.<ref name="de Vries2021">{{cite journal | last1=de Vries | first1=Joost | last2=Monteiro | first2=Fanny | last3=Wheeler | first3=Glen | last4=Poulton | first4=Alex | last5=Godrijan | first5=Jelena | last6=Cerino | first6=Federica | last7=Malinverno | first7=Elisa | last8=Langer | first8=Gerald | last9=Brownlee | first9=Colin | title=Haplo-diplontic life cycle expands coccolithophore niche | journal=Biogeosciences | publisher=Copernicus GmbH | volume=18 | issue=3 | date=2021-02-16 | issn=1726-4189 | doi=10.5194/bg-18-1161-2021 | pages=1161–1184| bibcode=2021BGeo...18.1161D | s2cid=233976784 | 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>]]

The complex life cycle of coccolithophores is known as a [[Biological life cycle#Haplodiplontic life cycle|haplodiplontic life cycle]], and is characterized by an alternation of both asexual and sexual phases. The asexual phase is known as the [[haploid]] phase, while the sexual phase is known as the [[diploid]] phase. During the haploid phase, coccolithophores produce haploid cells through [[mitosis]]. These haploid cells can then divide further through mitosis or undergo sexual reproduction with other haploid cells. The resulting diploid cell goes through [[meiosis]] to produce haploid cells again, starting the cycle over. With coccolithophores, asexual reproduction by mitosis is possible in both phases of the life cycle, which is a contrast with most other organisms that have alternating life cycles.<ref name="Young2003"/> Both [[abiotic]] and [[biotic factors]] may affect the frequency with which each phase occurs.<ref name=Vardi2012>{{citation |journal=Proceedings of the National Academy of Sciences |volume=109 |issue=47 |year=2012 |pages=19327–19332 |title=Host–virus dynamics and subcellular controls of cell fate in a natural coccolithophore population |first=A. |last=Vardi |doi=10.1073/pnas.1208895109 |pmid=23134731 |display-authors=etal  |bibcode = 2012PNAS..10919327V |pmc=3511156 |doi-access=free }}</ref>

Coccolithophores [[asexual reproduction|reproduce asexually]] through [[Fission (biology)|binary fission.]] In this process the coccoliths from the parent cell are divided between the two daughter cells. There have been suggestions stating the possible presence of a sexual reproduction process due to the diploid stages of the coccolithophores, but this process has never been observed.<ref name=Houdan2006>{{citation |journal=Aquatic Microbial Ecology |volume=44 |year=2006 |pages=291–301 |title=. Ecology of oceanic coccolithophores. I. Nutritional preferences of the two stages in the life cycle of Coccolithus braarudii and Calcidiscus leptoporus |last1=Houdan |doi=10.3354/ame044291|last2=Probert |first2=I |last3=Zatylny |first3=C |last4=Véron |first4=B |last5=Billard |first5=C |display-authors=etal|doi-access=free }}</ref>

[[R/K selection theory|K or r- selected strategies]] of coccolithophores depend on their life cycle stage. When coccolithophores are diploid, they are r-selected. In this phase they tolerate a wider range of nutrient compositions.  When they are haploid they are K- selected and are often more competitive in stable low nutrient environments.<ref name=Houdan2006 /> Most coccolithophores are K strategist and are usually found on nutrient-poor surface waters. They are poor competitors when compared to other phytoplankton and thrive in habitats where other phytoplankton would not survive.<ref name=Hogan2009 /> These two stages in the life cycle of coccolithophores occur seasonally, where more nutrition is available in warmer seasons and less is available in cooler seasons. This type of life cycle is known as a complex heteromorphic life cycle.<ref name=Houdan2006 />

===Global distribution===
[[File:Coccolithophore+Abundance.png|thumb|upright=1.7| Global distribution of coccolithophores in the ocean]]

Coccolithophores occur throughout the world's oceans. Their distribution varies vertically by stratified layers in the ocean and geographically by different temporal zones.<ref name=Geisen2004>{{cite book |last1=Geisen |first1=M. |editor1-first= Hans R. |editor1-last=Thierstein |editor2-first= Jeremy R. |editor2-last=Young |title=Coccolithophores-from molecular processes to global impact |publisher=Springler |date=August 17, 2004 |location=Berlin |chapter=Species level variation in coccolithophores= |isbn=9783540219286 |pages=1–29 |display-authors=etal  }}.</ref> While most modern coccolithophores can be located in their associated stratified [[oligotrophic]] conditions, the most abundant areas of coccolithophores where there is the highest species diversity are located in subtropical zones with a temperate climate.<ref name=Jordan1997>{{citation |journal=Biodiversity & Conservation |volume=6 |issue=1 |year=1997 |pages=131–152 |title=Biodiversity among haptophyte algae |first1=R. W. |last1=Jordan |first2=A.H.L. |last2=Chamberlain|doi=10.1023/A:1018383817777 |s2cid=9564456 }}</ref> While water temperature and the amount of light intensity entering the water's surface are the more influential factors in determining where species are located, the ocean currents also can determine the location where certain species of coccolithophores are found.<ref name=Boeckel2006>{{citation |journal=Deep-Sea Research Part I: Oceanographic Research Papers |volume=53 |issue=6 |year=2006 |pages=1073–1099 |title=Coccolith distribution patterns in South Atlantic and Southern Ocean surface sediments in relation to environmental gradients |last1=Boeckel |doi=10.1016/j.dsr.2005.11.006|last2=Baumann |first2=Karl-Heinz |last3=Henrich |first3=Rüdiger |last4=Kinkel |first4=Hanno |bibcode = 2006DSRI...53.1073B |display-authors=etal}}</ref>

Although motility and colony formation vary according to the life cycle of different coccolithophore species, there is often alternation between a motile, haploid phase, and a non-motile diploid phase.  In both phases, the organism's dispersal is largely due to ocean [[current (ocean)|current]]s and circulation patterns.<ref name=deVargas2007 />

Within the Pacific Ocean, approximately 90 species have been identified with six separate zones relating to different Pacific currents that contain unique groupings of different species of coccolithophores.<ref name=Okada1973>{{citation |journal=Deep-Sea Research and Oceanographic Abstracts  |volume=20 |issue=4 |year=1973 |pages=355–374 |title=The distribution of oceanic coccolithophores in the Pacific |last1=Okada |doi=10.1016/0011-7471(73)90059-4|last2=Honjo |first2=Susumu |bibcode = 1973DSRA...20..355O |display-authors=etal}}</ref> The highest diversity of coccolithophores in the Pacific Ocean was in an area of the ocean considered the Central North Zone which is an area between 30 <sup>o</sup>N and 5 <sup>o</sup>N, composed of the North Equatorial Current and the Equatorial Countercurrent. These two currents move in opposite directions, east and west, allowing for a strong mixing of waters and allowing a large variety of species to populate the area.<ref name=Okada1973 />

In the Atlantic Ocean, the most abundant species are ''[[emiliania huxleyi|E. huxleyi]]'' and ''Florisphaera profunda'' with smaller concentrations of the species ''Umbellosphaera'' ''irregularis'', ''Umbellosphaera tenuis'' and different species of ''Gephyrocapsa''.<ref name=Okada1973 /> Deep-dwelling coccolithophore [[species abundance]] is greatly affected by [[nutricline]] and [[thermocline]] depths. These coccolithophores increase in abundance when the nutricline and thermocline are deep and decrease when they are shallow.<ref name=Kinkel2000>{{citation |journal=Marine Micropaleontology |volume=39 |issue=1–4 |year=2000 |pages=87–112 |title=Coccolithophores in the equatorial Atlantic Ocean: response to seasonal and Late Quaternary surface water variability |first=H. |last=Kinkel |doi=10.1016/s0377-8398(00)00016-5 |display-authors=etal  |bibcode=2000MarMP..39...87K }}</ref>

[[File:Comparative coccolithophore sizes.png|thumb|right|280px|Size comparison between the relatively large coccolithophore ''Scyphosphaera apsteinii'' and the relatively small but ubiquitous coccolithophore ''[[Emiliania huxleyi]]''<ref>Gafar, N. A., Eyre, B. D. and Schulz, K. G. (2019). "A comparison of species specific sensitivities to changing light and carbonate chemistry in calcifying marine phytoplankton". ''Scientific Reports'', '''9'''(1): 1–12. {{doi|10.1038/s41598-019-38661-0}}. [[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>]]

The complete distribution of coccolithophores is currently not known and some regions, such as the Indian Ocean, are not as well studied as other locations in the Pacific and Atlantic Oceans. It is also very hard to explain distributions due to multiple constantly changing factors involving the ocean's properties, such as coastal and equatorial [[upwelling]], frontal systems, [[benthic]] environments, unique oceanic topography, and pockets of isolated high or low water temperatures.<ref name="Young2009"/>
<!-- Deleted image removed: [[File:Table 1Cocco.jpg|frame|alt=Table 1|Table 1. Biogeographic coccolithophorid assemblages; adapted from Jordan, et Al., 1997.<ref name=Jordan1997 />]]
  -- Deleted image removed: [[File:Table 2Cocco.jpg|frame|alt=Table 1|Table 2. Depth-related coccolithophorid assemblages in subtropic waters; adapted from Jordan, et Al., 1997.<ref name=Jordan1997 /> The upper photic zone is low in nutrient concentration, high in light intensity and penetration, and usually higher in temperature. The lower photic zone is high in nutrient concentration, low in light intensity and penetration and relatively cool. The middle photic zone is an area that contains the same values in between that of the lower and upper photic zones.]] -->

The upper photic zone is low in nutrient concentration, high in light intensity and penetration, and usually higher in temperature. The lower photic zone is high in nutrient concentration, low in light intensity and penetration and relatively cool. The middle photic zone is an area that contains the same values in between that of the lower and upper photic zones.<ref name=Jordan1997 />

{{multiple image
 | align     = left
 | direction = horizontal
 | footer    = Larger coccolithophores such as the species above are less numerous than the smaller but ubiquitous ''[[Emiliania huxleyi]]'', but they are heavily calcified and make important contributions to global calcification.<ref>Daniels, C.J., Sheward, R.M. and Poulton, A.J. (2014) "Biogeochemical implications of comparative growth rates of ''Emiliania huxleyi'' and ''Coccolithus'' species". ''Biogeosciences'', '''11'''(23): 6915–6925. {{doi|10.5194/bg-11-6915-2014}}.</ref><ref>Durak, G.M., Taylor, A.R., Walker, C.E., Probert, I., De Vargas, C., Audic, S., Schroeder, D., Brownlee, C. and Wheeler, G.L. (2016) "A role for diatom-like silicon transporters in calcifying coccolithophores". ''Nature communications'', '''7''': 10543. {{doi|10.1038/ncomms10543}}. [[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> Unmarked scale bars 5&nbsp;μm.
 | width1    = 200
 | image1    = Calcidiscus leptoporus.png
 | caption1  = ''Calcidiscus leptoporus''
 | width2    = 188
 | image2    = Coccolithus braarudii.png
 | caption2  = ''[[Coccolithus|Coccolithus braarudii]]''
 | width3    = 212
 | image3    = Scyphosphaera apsteinii.png
 | caption3  = ''Scyphosphaera apsteinii''
}}

{{clear}}

====Great Calcite Belt====
[[File:Great Calcite Belt of the Southern Ocean.webm|thumb|upright=2|Yearly cycle of the [[Great Calcite Belt]] in the Southern Ocean]]
{{Main|Great Calcite Belt}}

The [[Great Calcite Belt]] of the [[Southern Ocean]] is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its [[diatom]] predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region provides an ideal setting to study environmental
influences on the distribution of different species within these taxonomic groups.<ref name=Smith2017>{{cite journal |doi = 10.5194/bg-14-4905-2017|title = The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt|year = 2017|last1 = Smith|first1 = Helen E. K.|last2 = Poulton|first2 = Alex J.|last3 = Garley|first3 = Rebecca|last4 = Hopkins|first4 = Jason|last5 = Lubelczyk|first5 = Laura C.|last6 = Drapeau|first6 = Dave T.|last7 = Rauschenberg|first7 = Sara|last8 = Twining|first8 = Ben S.|last9 = Bates|first9 = Nicholas R.|last10 = Balch|first10 = William M.|journal = Biogeosciences|volume = 14|issue = 21|pages = 4905–4925|bibcode = 2017BGeo...14.4905S|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>

The Great Calcite Belt, defined as an elevated [[particulate inorganic carbon]] (PIC) feature occurring alongside seasonally elevated [[chlorophyll a]] in [[Wiktionary:austral|austral]] spring and summer in the Southern Ocean,<ref name=Balch2005>{{cite journal |doi = 10.1029/2004JC002560|title = Calcium carbonate measurements in the surface global ocean based on Moderate-Resolution Imaging Spectroradiometer data|year = 2005|last1 = Balch|first1 = W. M.|last2 = Gordon|first2 = Howard R.|last3 = Bowler|first3 = B. C.|last4 = Drapeau|first4 = D. T.|last5 = Booth|first5 = E. S.|journal = Journal of Geophysical Research|volume = 110|issue = C7|pages = C07001|bibcode = 2005JGRC..110.7001B|doi-access = free}}</ref> plays an important role in climate fluctuations,<ref>{{cite journal |doi = 10.1038/30455|title = Simulated response of the ocean carbon cycle to anthropogenic climate warming|year = 1998|last1 = Sarmiento|first1 = Jorge L.|last2 = Hughes|first2 = Tertia M. C.|last3 = Stouffer|first3 = Ronald J.|last4 = Manabe|first4 = Syukuro|journal = Nature|volume = 393|issue = 6682|pages = 245–249|bibcode = 1998Natur.393..245S|s2cid = 4317429}}</ref><ref>{{cite journal |doi = 10.1029/2003GB002134|title = Response of ocean ecosystems to climate warming|year = 2004|last1 = Sarmiento|first1 = J. L.|last2 = Slater|first2 = R.|last3 = Barber|first3 = R.|last4 = Bopp|first4 = L.|last5 = Doney|first5 = S. C.|last6 = Hirst|first6 = A. C.|last7 = Kleypas|first7 = J.|last8 = Matear|first8 = R.|last9 = Mikolajewicz|first9 = U.|last10 = Monfray|first10 = P.|last11 = Soldatov|first11 = V.|last12 = Spall|first12 = S. A.|last13 = Stouffer|first13 = R.|journal = Global Biogeochemical Cycles|volume = 18|issue = 3|pages = n/a|bibcode = 2004GBioC..18.3003S|hdl = 1912/3392| s2cid=15482539 | url=https://hal.archives-ouvertes.fr/hal-03129787/file/2003GB002134.pdf |hdl-access = free}}</ref> accounting for over 60% of the Southern Ocean area (30–60° S).<ref name=Balch2011>{{cite journal |doi = 10.1029/2011JC006941|title = The contribution of coccolithophores to the optical and inorganic carbon budgets during the Southern Ocean Gas Exchange Experiment: New evidence in support of the "Great Calcite Belt" hypothesis|year = 2011|last1 = Balch|first1 = W. M.|last2 = Drapeau|first2 = D. T.|last3 = Bowler|first3 = B. C.|last4 = Lyczskowski|first4 = E.|last5 = Booth|first5 = E. S.|last6 = Alley|first6 = D.|journal = Journal of Geophysical Research|volume = 116|issue = C4|pages = C00F06|bibcode = 2011JGRC..116.0F06B}}</ref> The region between 30° and 50° S has the highest uptake of anthropogenic carbon dioxide (CO<sub>2</sub>) alongside the North Atlantic and North Pacific oceans.<ref>{{cite journal |doi = 10.1126/science.1097403|title = The Oceanic Sink for Anthropogenic CO2|year = 2004|last1 = Sabine|first1 = C. L.|last2 = Feely|first2 = R. A.|last3 = Gruber|first3 = N.|last4 = Key|first4 = R. M.|last5 = Lee|first5 = K.|last6 = Bullister|first6 = J. L.|last7 = Wanninkhof|first7 = R.|last8 = Wong|first8 = C. S.|last9 = Wallace|first9 = D. W.|last10 = Tilbrook|first10 = B.|last11 = Millero|first11 = F. J.|last12 = Peng|first12 = T. H.|last13 = Kozyr|first13 = A.|last14 = Ono|first14 = T.|last15 = Rios|first15 = A. F.|journal = Science|volume = 305|issue = 5682|pages = 367–371|pmid = 15256665|bibcode = 2004Sci...305..367S|s2cid = 5607281|url = http://oceanrep.geomar.de/46251/1/1193.full.pdf}}</ref>

====Effect of global climate change on distribution====
Recent studies show that climate change has direct and indirect impacts on Coccolithophore distribution and productivity. They will inevitably be affected by the increasing temperatures and thermal stratification of the top layer of the ocean, since these are prime controls on their ecology, although it is not clear whether global warming would result in net increase or decrease of coccolithophores. As they are calcifying organisms, it has been suggested that [[ocean acidification]] due to increasing carbon dioxide could severely affect coccolithophores.<ref name="Kinkel2000"/> Recent {{CO2}} increases have seen a sharp increase in the population of coccolithophores.<ref>{{cite news |url=http://www.csmonitor.com/Science/2015/1128/What-s-fueling-the-rise-of-coccolithophores-in-the-oceans |title=What's fueling the rise of coccolithophores in the oceans? |last1=Gitau |first1=Beatrice |date=28 November 2015 |website=www.csmonitor.com |publisher=The Christian Science Monitor |access-date=30 November 2015}}</ref>

===Role in the food web===
[[File:Bloom in the Barents Sea.jpg|thumb|upright=1.4| Satellite photograph: The milky blue colour of this [[phytoplankton]] bloom in [[Barents Sea]] strongly suggests it contains coccolithophores]]
[[File:Virus cocco 2.jpg|thumb|upright=1.4| A [[coccolithovirus]], ''[[Emiliania huxleyi virus 86]]'' (arrowed), infecting an ''[[Emiliania huxleyi]]'' coccolithophore.<ref name=ViralZone>{{cite web|title=Viral Zone|url=http://viralzone.expasy.org/all_by_species/589.html|publisher=ExPASy|access-date=15 June 2015}}</ref><ref name=ICTV>{{cite web|last1=ICTV|title=Virus Taxonomy: 2014 Release|url=http://ictvonline.org/virusTaxonomy.asp|access-date=15 June 2015}}</ref> This [[giant marine virus]] has one of the largest known [[virus genome]]s.<ref>[http://www.giantvirus.org/top.html Largest known viral genomes] ''Giantviruses.org''. Accessed: 11 June 2020.</ref>]]

Coccolithophores are one of the more abundant primary producers in the ocean.  As such, they are a large contributor to the [[Marine primary production|primary productivity]] of the tropical and subtropical oceans, however, exactly how much has yet to have been recorded.<ref name=Rost2004>{{citation |journal=Coccolithophores |volume=2 |year=2004 |pages=99–125 |title=Coccolithophores and the biological pump: responses to environmental changes |first1=B. |last1=Rost |first2=U. |last2=Riebesell |doi=10.1007/978-3-662-06278-4_5|isbn=978-3-642-06016-8 |url=http://epic.awi.de/11394/1/Ros2004a.pdf |archive-url=https://web.archive.org/web/20121110122119/http://epic.awi.de/11394/1/Ros2004a.pdf |archive-date=2012-11-10 |url-status=live |citeseerx=10.1.1.455.2864 }}</ref>

====Dependence on nutrients====
The ratio between the concentrations of [[nitrogen]], [[phosphorus]] and [[silicate]] in particular areas of the ocean dictates [[Dominance hierarchy|competitive dominance]] within phytoplankton communities. Each ratio essentially tips the odds in favor of either [[diatom]]s or other groups of phytoplankton, such as coccolithophores. A low silicate to nitrogen and phosphorus ratio allows coccolithophores to outcompete other phytoplankton species; however, when silicate to phosphorus to nitrogen ratios are high coccolithophores are outcompeted by diatoms. The increase in agricultural processes lead to [[eutrophication]] of waters and thus, coccolithophore blooms in these high nitrogen and phosphorus, low silicate environments.<ref name="Yunev2007"/>

====Impact on water column productivity====
The [[calcite]] in calcium carbonate allows coccoliths to scatter more light than they absorb. This has two important consequences: 1) Surface waters become brighter, meaning they have a higher [[albedo]], and 2) there is induced [[photoinhibition]], meaning photosythetic production is diminished due to an excess of light.  In case 1), a high concentration of coccoliths leads to a simultaneous increase in surface water temperature and decrease in the temperature of deeper waters. This results in more [[stratification (water)|stratification]] in the water column and a decrease in the vertical mixing of nutrients. However, a 2012 study estimated that the overall effect of coccolithophores on the increase in [[radiative forcing]] of the ocean is less than that from anthropogenic factors.<ref name="Morrissey2012">{{cite book |last1=Morrissey |first1=J.F. |last2=Sumich |first2=J.L. |year=2012 |pages=67 |title=Introduction to the Biology of Marine Life}}</ref> Therefore, the overall result of large blooms of coccolithophores is a decrease in water column productivity, rather than a contribution to global warming.

====Predator-prey interactions====
Their predators include the common predators of all phytoplankton including small fish, zooplankton, and shellfish larvae.<ref name=Hogan2009 /><ref name=Houdan2004>{{citation |journal=Journal of Plankton Research |volume=26 |issue=8 |year=2004 |pages=875–883 |title=Toxicity of coastal coccolithophores (Prymnesiophyceae, Haptophyta)  |first=A. |last=Houdan |doi=10.1093/plankt/fbh079 |display-authors=etal  |doi-access=free }}</ref> Viruses specific to this species have been isolated from several locations worldwide and appear to play a major role in spring bloom dynamics.

=====Toxicity=====
No environmental evidence of coccolithophore toxicity has been reported, but they belong to the class Prymnesiophyceae which contain orders with toxic species. Toxic species have been found in the genera ''Prymnesium'' Massart and ''Chrysochromulina'' Lackey. Members of the genus ''Prymnesium'' have been found to produce haemolytic compounds, the agent responsible for toxicity.  Some of these toxic species are responsible for large fish kills and can be accumulated in organisms such as shellfish; transferring it through the food chain. In laboratory tests for toxicity members of the oceanic coccolithophore genera ''Emiliania, Gephyrocapsa, Calcidiscus'' and ''Coccolithus'' were shown to be non-toxic as were species of the coastal genus ''Hymenomonas'', however several species of ''Pleurochrysis'' and ''Jomonlithus'', both coastal genera were toxic to ''Artemia''.<ref name="Houdan2004"/>

===Community interactions===
Coccolithophorids are predominantly found as single, free-floating haploid or diploid cells.<ref name="Geisen2004"/>

====Competition====
Most [[phytoplankton]] need sunlight and nutrients from the ocean to survive, so they thrive in areas with large inputs of nutrient rich water upwelling from the lower levels of the ocean. Most coccolithophores require sunlight only for energy production, and have a higher ratio of nitrate uptake over ammonium uptake (nitrogen is required for growth and can be used directly from nitrate but not ammonium). Because of this they thrive in still, nutrient-poor environments where other phytoplankton are starving.<ref name=Litchman2007>{{citation |journal=Ecology Letters |volume=10 |issue=12 |year=2007 |pages=1170–1181 |title=The role of functional traits and trade-offs in structuring phytoplankton communities: scaling from cellular to ecosystem level |first= E. |last=Litchman |doi=10.1111/j.1461-0248.2007.01117.x|pmid=17927770  |bibcode=2007EcolL..10.1170L |display-authors=etal  }}</ref> [[Trade-off]]s associated with these faster growth rates include a smaller cell radius and lower cell volume than other types of phytoplankton.

===Viral infection and coevolution===
Giant [[DNA virus|DNA-containing viruses]] are known to [[Lytic Cycle|lytically]] infect coccolithophores, particularly ''E. huxleyi''.  These viruses, known as E. huxleyi viruses (EhVs), appear to infect the coccosphere coated diploid phase of the life cycle almost exclusively.  It has been proposed that as the haploid organism is not infected and therefore not affected by the virus, the co-evolutionary "[[arms race]]" between coccolithophores and these viruses does not follow the classic [[Red Queen's Hypothesis|Red Queen]] evolutionary framework, but instead a "Cheshire Cat" ecological dynamic.<ref name=Frada2008>{{citation |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=41 |year=2008 |pages=15944–15949 |title=The "Cheshire Cat" escape strategy of the coccolithophore ''Emiliania huxleyi'' in response to viral infection |first=M. |last=Frada |doi=10.1073/pnas.0807707105 |display-authors=etal  |bibcode = 2008PNAS..10515944F |pmid=18824682 |pmc=2572935|doi-access=free }}</ref>  More recent work has suggested that viral synthesis of [[sphingolipids]] and induction of [[programmed cell death]] provides a more direct link to study a Red Queen-like [[coevolution]]ary arms race at least between the coccolithoviruses and diploid organism.<ref name="Vardi2012"/>

==Evolution and diversity==
Coccolithophores are members of the clade [[Haptophyta]], which is a sister clade to [[Centrohelida]], which are both in [[Haptista]].<ref name="Taylor-et-al-2017">{{cite journal | last1=Taylor | first1=Alison R. | last2=Brownlee | first2=Colin | last3=Wheeler | first3=Glen | title=Coccolithophore Cell Biology: Chalking Up Progress | journal=[[Annual Review of Marine Science]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=9 | issue=1 | date=2017-01-03 | issn=1941-1405 | doi=10.1146/annurev-marine-122414-034032 | pages=283–310| pmid=27814031 | bibcode=2017ARMS....9..283T | url=http://plymsea.ac.uk/id/eprint/9134/1/Taylor%20et%20al%20Ann%20Rev%20Mar%20Sci%202017.pdf |archive-url=https://web.archive.org/web/20210716073801/http://plymsea.ac.uk/id/eprint/9134/1/Taylor%20et%20al%20Ann%20Rev%20Mar%20Sci%202017.pdf |archive-date=2021-07-16 |url-status=live }}</ref> The oldest known coccolithophores are known from the Late Triassic, around the [[Norian]]-[[Rhaetian]] boundary.<ref>{{Cite journal|last1=Gardin|first1=Silvia|last2=Krystyn|first2=Leopold|last3=Richoz|first3=Sylvain|last4=Bartolini|first4=Annachiara|last5=Galbrun|first5=Bruno|date=October 2012|title=Where and when the earliest coccolithophores?: Where and when the earliest coccolithophores?|url=https://onlinelibrary.wiley.com/doi/10.1111/j.1502-3931.2012.00311.x|journal=Lethaia|language=en|volume=45|issue=4|pages=507–523|doi=10.1111/j.1502-3931.2012.00311.x}}</ref> Diversity steadily increased over the course of the Mesozoic, reaching its apex during the [[Late Cretaceous]]. However, there was a sharp drop during the [[Cretaceous-Paleogene extinction event]], when more than 90% of coccolithophore species became extinct. Coccoliths reached another, lower apex of diversity during the [[Paleocene–Eocene Thermal Maximum|Paleocene-Eocene thermal maximum]], but have subsequently declined since the [[Oligocene]] due to decreasing global temperatures, with species that produced large and heavily calcified coccoliths most heavily affected.<ref name="Monteiro2016" />
{{Multiple image
| image1            = Evolutionary history of coccolithophores.jpg
| caption1          = Evolutionary history of coccolithophores:<ref name="Monteiro2016" /> (A) Coccolithophore species richness over time; (B) The fossil record of major coccolithophore [[biomineralization]] innovations and morphogroups.
| image2            = Diversity of coccolithophores.jpg
| caption2          = Coccolithophore diversity. ''[[Emiliania huxleyi]]'' (E), the reference species for coccolithophore studies, is contrasted with a range of other species spanning the biodiversity of modern coccolithophores. All images are scanning electron micrographs of cells collected by seawater filtration from the open ocean. Species illustrated: (A) ''[[Coccolithus]] pelagicus'', (B) ''Calcidiscus leptoporus'', (C) ''[[Braarudosphaera bigelowii]]'', (D) ''[[Gephyrocapsa oceanica]]'', (E) ''[[Emiliania huxleyi]]'', (F) ''[[Discosphaera tubifera]]'', (G) ''[[Rhabdosphaera clavigera]]'', (H) ''Calciosolenia murrayi'', (I) ''Umbellosphaera irregularis'', (J) ''Gladiolithus flabellatus'', (K and L) ''Florisphaera profunda'', (M) ''[[Syracosphaera]] pulchra'', and (N) ''Helicosphaera carteri''. Scale bar is 5 μm.
| align             = center
| total_width       = 600
}}
{{clear}}

==Coccolithophore shells==
{{biomineralization sidebar|exoskeletons}}
{{See also|Protist shell|coccolith}}

* Exoskeleton: coccospheres and coccoliths

Each coccolithophore encloses itself in a protective shell of [[coccoliths]], calcified scales which make up its [[exoskeleton]] or '''coccosphere'''.<ref name=Falkowski2007>{{cite book |last1=Falkowski |first1=P.G.|last2=Knoll |first2=A.H. |title=Evolution of Primary Producers in the Sea |publisher=Elsevier Academic Press |date=August 29, 2007 |location=Amsterdam, Boston |isbn=9780123705181}}</ref> The coccoliths are created inside the coccolithophore cell and while some species maintain a single layer throughout life only producing new coccoliths as the cell grows, others continually produce and shed coccoliths.

=== Composition ===
The primary constituent of coccoliths is calcium carbonate, or [[chalk]]. Calcium carbonate is transparent, so the organisms' photosynthetic activity is not compromised by encapsulation in a coccosphere.<ref name=Hogan2009>{{cite book |last=Hogan |first= M.C. |editor-first=Cutler J. |editor-last=Cleveland |title=Encyclopedia of Earth |chapter="Coccolithophores" |publisher=Environmental Information Coalition, National Council for Science and the Environment |location= Washington, D.C.}}</ref>

=== 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&nbsp;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 |s2cid=27901484 |display-authors=etal  |doi-access= }}</ref>
<!-- 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 />]] -->

=== Function ===
While the exact function of the coccosphere is unclear, many potential functions have been proposed.  Most obviously coccoliths may protect the phytoplankton from predators. It also appears that it helps them to create a more stable [[pH]]. During photosynthesis carbon dioxide is removed from the water, making it more basic. Also calcification removes carbon dioxide, but chemistry behind it leads to the opposite pH reaction; it makes the water more acidic. The combination of photosynthesis and calcification therefore even out each other regarding pH changes.<ref>{{cite web| url = https://theconversation.com/microscopic-marine-plants-bioengineer-their-environment-to-enhance-their-own-growth-63355| title = Microscopic marine plants bioengineer their environment to enhance their own growth - The Conversation| date = 2 August 2016}}</ref> In addition, these exoskeletons may confer an advantage in energy production, as coccolithogenesis seems highly coupled with photosynthesis. Organic precipitation of calcium carbonate from bicarbonate solution produces free carbon dioxide directly within the cellular body of the alga, this additional source of gas is then available to the Coccolithophore for photosynthesis.  It has been suggested that they may provide a cell-wall like barrier to isolate intracellular chemistry from the marine environment.<ref name=Westbroek1983>{{citation |journal=Ecological Bulletins |year=1983 |pages= 291–299 |title=Calcification in Coccolithophoridae: Wasteful or Functional? |first=P.|last=Westbroek|display-authors=etal}}</ref> More specific, defensive properties of coccoliths may include protection from osmotic changes, chemical or mechanical shock, and short-wavelength light.<ref name=Jordan2012>{{citation |journal=eLS |year=2012|title=Haptophyta |last=Jordan |first=R.W. |doi=10.1002/9780470015902.a0001981.pub2 |isbn=978-0470016176}}</ref> It has also been proposed that the added weight of multiple layers of coccoliths allows the organism to sink to lower, more nutrient rich layers of the water and conversely, that coccoliths add buoyancy, stopping the cell from sinking to dangerous depths.<ref name=Irie2010>{{citation |journal=PLOS ONE |volume=5 |issue=10 |pages=e13436 |year=2010 |title=Increasing costs due to ocean acidification drives phytoplankton to be more heavily calcified: optimal growth strategy of coccolithophores |first=Takahiro|last=Irie |doi=10.1371/journal.pone.0013436|display-authors=etal|bibcode = 2010PLoSO...513436I |pmid=20976167 |pmc=2955539|doi-access=free }}</ref> Coccolith appendages have also been proposed to serve several functions, such as inhibiting grazing by zooplankton.<ref name=Young2009 />

=== Uses ===
Coccoliths are the main component of [[Chalk Group|the Chalk]], a Late Cretaceous rock formation which outcrops widely in southern England and forms the [[White Cliffs of Dover]], and of other similar rocks in many other parts of the world.<ref name="hup.harvard.edu"/> At the present day sedimented coccoliths are a major component of the [[Pelagic sediment#Oozes|calcareous oozes]] that cover up to 35% of the ocean floor and is kilometres thick in places.<ref name=deVargas2007 />  Because of their abundance and wide geographic ranges, the coccoliths which make up the layers of this ooze and the chalky sediment formed as it is compacted serve as valuable [[microfossils]].
[[File:Calcification and energetic costs of a coccolithophore cell.jpg|thumb|right|360px|Energetic costs of coccolithophore calcification.<ref name=Monteiro2016 /> Energetic costs reported as a percentage of total [[photosynthetic]] budget.]]

[[Calcification]], the biological production of [[calcium carbonate]] (CaCO<sub>3</sub>), is a key process in the [[marine carbon cycle]]. Coccolithophores are the major planktonic group responsible for pelagic CaCO<sub>3</sub> production.<ref>{{cite journal |doi = 10.1016/j.pocean.2017.10.007|title = Coccolithophore growth and calcification in a changing ocean|year = 2017|last1 = Krumhardt|first1 = Kristen M.|last2 = Lovenduski|first2 = Nicole S.|last3 = Iglesias-Rodriguez|first3 = M. Debora|last4 = Kleypas|first4 = Joan A.|author-link4=Joan Kleypas|journal = Progress in Oceanography|volume = 159|pages = 276–295| bibcode=2017PrOce.159..276K |doi-access = free}}</ref><ref>{{cite journal |doi = 10.5194/essd-10-1859-2018|title = A global compilation of coccolithophore calcification rates|year = 2018|last1 = Daniels|first1 = Chris J.|last2 = Poulton|first2 = Alex J.|last3 = Balch|first3 = William M.|last4 = Marañón|first4 = Emilio|last5 = Adey|first5 = Tim|last6 = Bowler|first6 = Bruce C.|last7 = Cermeño|first7 = Pedro|last8 = Charalampopoulou|first8 = Anastasia|last9 = Crawford|first9 = David W.|last10 = Drapeau|first10 = Dave|last11 = Feng|first11 = Yuanyuan|last12 = Fernández|first12 = Ana|last13 = Fernández|first13 = Emilio|last14 = Fragoso|first14 = Glaucia M.|last15 = González|first15 = Natalia|last16 = Graziano|first16 = Lisa M.|last17 = Heslop|first17 = Rachel|last18 = Holligan|first18 = Patrick M.|last19 = Hopkins|first19 = Jason|last20 = Huete-Ortega|first20 = María|last21 = Hutchins|first21 = David A.|last22 = Lam|first22 = Phoebe J.|last23 = Lipsen|first23 = Michael S.|last24 = López-Sandoval|first24 = Daffne C.|last25 = Loucaides|first25 = Socratis|last26 = Marchetti|first26 = Adrian|last27 = Mayers|first27 = Kyle M. J.|last28 = Rees|first28 = Andrew P.|last29 = Sobrino|first29 = Cristina|last30 = Tynan|first30 = Eithne|journal = Earth System Science Data|volume = 10|issue = 4|pages = 1859–1876| bibcode=2018ESSD...10.1859D |display-authors = 29|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> The diagram on the right shows the energetic costs of coccolithophore calcification:

: (A) Transport processes include the transport into the cell from the surrounding seawater of primary calcification substrates [[Ca2+|Ca<sub>2+</sub>]] and [[HCO3-|HCO<sub>3</sub><sup>−</sup>]] (black arrows) and the removal of the end product H<sup>+</sup> from the cell (gray arrow). The transport of Ca<sub>2+</sub> through the [[cytoplasm]] to the CV is the dominant cost associated with calcification.<ref name=Monteiro2016 />

: (B) [[Metabolic process]]es include the synthesis of CAPs (gray rectangles) by the [[Golgi complex]] (white rectangles) that regulate the [[nucleation]] and geometry of CaCO<sub>3</sub> crystals. The completed coccolith (gray plate) is a complex structure of intricately arranged CAPs and CaCO<sub>3</sub> crystals.<ref name=Monteiro2016 />

: (C) Mechanical and structural processes account for the secretion of the completed coccoliths that are transported from their original position adjacent to the nucleus to the cell periphery, where they are transferred to the surface of the cell. The costs associated with these processes are likely to be comparable to organic-scale [[exocytosis]] in noncalcifying [[haptophyte]] algae.<ref name=Monteiro2016 />

{{clear}}

[[File:Benefits of calcification in coccolithophores.jpg|thumb|left|500px|Benefits of coccolithophore calcification<ref name=Monteiro2016 />]]

The diagram on the left shows the benefits of coccolithophore calcification. (A) Accelerated photosynthesis includes CCM (1) and enhanced light uptake via scattering of scarce photons for deep-dwelling species (2). (B) Protection from photodamage includes sunshade protection from ultraviolet (UV) light and photosynthetic active radiation (PAR) (1) and energy dissipation under high-light conditions (2). (C) Armor protection includes protection against viral/bacterial infections (1) and grazing by selective (2) and nonselective (3) grazers.<ref name=Monteiro2016 />

The degree by which calcification can adapt to [[ocean acidification]] is presently unknown. Cell physiological examinations found the essential [[Efflux (microbiology)|H<sup>+</sup> efflux]] (stemming from the use of HCO<sub>3</sub><sup>−</sup> for intra-cellular calcification) to become more costly with ongoing ocean acidification as the electrochemical H<sup>+</sup> inside-out gradient is reduced and passive proton outflow impeded.<ref name="A Voltage-Gated H+ Channel Underlyi">{{cite journal |doi = 10.1371/journal.pbio.1001085|title = A Voltage-Gated H<sup>+</sup> Channel Underlying pH Homeostasis in Calcifying Coccolithophores|year = 2011|last1 = Taylor|first1 = Alison R.|last2 = Chrachri|first2 = Abdul|last3 = Wheeler|first3 = Glen|last4 = Goddard|first4 = Helen|last5 = Brownlee|first5 = Colin|journal = PLOS Biology|volume = 9|issue = 6|pages = e1001085|pmid = 21713028|pmc = 3119654 | doi-access=free }}</ref> Adapted cells would have to activate [[proton channel]]s more frequently, adjust their [[membrane potential]], and/or lower their internal [[pH]].<ref>{{cite journal |doi = 10.1016/j.tplants.2012.06.009|title = Proton channels in algae: Reasons to be excited|year = 2012|last1 = Taylor|first1 = Alison R.|last2 = Brownlee|first2 = Colin|last3 = Wheeler|first3 = Glen L.|journal = Trends in Plant Science|volume = 17|issue = 11|pages = 675–684|pmid = 22819465}}</ref> Reduced intra-cellular pH would severely affect the entire cellular machinery and require other processes (e.g. [[photosynthesis]]) to co-adapt in order to keep H<sup>+</sup> efflux alive.<ref>{{cite journal |doi = 10.1098/rstb.2013.0049|title = Emiliania huxleyi increases calcification but not expression of calcification-related genes in long-term exposure to elevated temperature and p CO 2|year = 2013|last1 = Benner|first1 = Ina|last2 = Diner|first2 = Rachel E.|last3 = Lefebvre|first3 = Stephane C.|last4 = Li|first4 = Dian|last5 = Komada|first5 = Tomoko|last6 = Carpenter|first6 = Edward J.|last7 = Stillman|first7 = Jonathon H.|journal = Philosophical Transactions of the Royal Society B: Biological Sciences|volume = 368|issue = 1627|pmid = 23980248|pmc = 3758179}}</ref><ref>{{cite journal |doi = 10.1026/1612-5010/a000109|title = Das physische Selbstkonzept, die individuell präferierte Bezugsnormorientierung und die Zielorientierung bei Grundschulkindern der zweiten und vierten Jahrgangsstufe|year = 2014|last1 = Lohbeck|first1 = Annette|last2 = Tietjens|first2 = Maike|last3 = Bund|first3 = Andreas|journal = Zeitschrift für Sportpsychologie|volume = 21|pages = 1–12}}</ref> The obligatory H<sup>+</sup> efflux associated with calcification may therefore pose a fundamental constraint on adaptation which may potentially explain why "calcification crisis" were possible during long-lasting (thousands of years) CO<sub>2</sub> perturbation events<ref name="Nannofossil carbonate fluxes during">{{cite journal |doi = 10.1029/2003PA000884|title = Nannofossil carbonate fluxes during the Early Cretaceous: Phytoplankton response to nutrification episodes, atmospheric CO2, and anoxia|year = 2004|last1 = Erba|first1 = Elisabetta|last2 = Tremolada|first2 = Fabrizio|journal = Paleoceanography|volume = 19|issue = 1|pages = n/a|bibcode = 2004PalOc..19.1008E|doi-access = free}}</ref><ref name="The first 150 million years history">{{cite journal |doi = 10.1016/j.palaeo.2005.09.013|title = The first 150 million years history of calcareous nannoplankton: Biosphere–geosphere interactions|year = 2006|last1 = Erba|first1 = Elisabetta|journal = Palaeogeography, Palaeoclimatology, Palaeoecology|volume = 232|issue = 2–4|pages = 237–250|bibcode = 2006PPP...232..237E}}</ref> even though evolutionary adaption to changing [[carbonate]] chemistry conditions is possible within one year.<ref name="Nannofossil carbonate fluxes during"/><ref name="The first 150 million years history"/> Unraveling these fundamental constraints and the limits of adaptation should be a focus in future coccolithophore studies because knowing them is the key information required to understand to what extent the calcification response to carbonate chemistry perturbations can be compensated by evolution.<ref name=Bach2015 />

Silicate- or cellulose-armored functional groups such as [[diatom]]s and [[dinoflagellate]]s do not need to sustain the calcification-related H<sup>+</sup> efflux. Thus, they probably do not need to adapt in order to keep costs for the production of structural elements low. On the contrary, dinoflagellates (except for calcifying species;<ref>{{cite journal |doi = 10.1371/journal.pone.0065987|title = Ocean Acidification Reduces Growth and Calcification in a Marine Dinoflagellate|year = 2013|last1 = Van De Waal|first1 = Dedmer B.|last2 = John|first2 = Uwe|last3 = Ziveri|first3 = Patrizia|last4 = Reichart|first4 = Gert-Jan|last5 = Hoins|first5 = Mirja|last6 = Sluijs|first6 = Appy|last7 = Rost|first7 = Björn|journal = PLOS ONE|volume = 8|issue = 6|pages = e65987|pmid = 23776586|pmc = 3679017|bibcode = 2013PLoSO...865987V| doi-access=free }}</ref> with generally inefficient CO<sub>2</sub>-fixing [[RuBisCO|RuBisCO enzymes]]<ref>{{cite journal |doi = 10.4319/lo.2000.45.3.0744|title = Evolutionary and ecological perspectives on carbon acquisition in phytoplankton|year = 2000|last1 = Tortell|first1 = Philippe D.|journal = Limnology and Oceanography|volume = 45|issue = 3|pages = 744–750|bibcode = 2000LimOc..45..744T|doi-access = free}}</ref> may even profit from chemical changes since photosynthetic [[carbon fixation]] as their source of structural elements in the form of cellulose should be facilitated by the ocean acidification-associated CO<sub>2</sub> fertilization.<ref>{{cite journal |doi = 10.1016/j.hal.2007.05.006|title = A comparison of future increased CO2 and temperature effects on sympatric Heterosigma akashiwo and Prorocentrum minimum|year = 2008|last1 = Fu|first1 = Fei-Xue|last2 = Zhang|first2 = Yaohong|last3 = Warner|first3 = Mark E.|last4 = Feng|first4 = Yuanyuan|last5 = Sun|first5 = Jun|last6 = Hutchins|first6 = David A.|journal = Harmful Algae|volume = 7|pages = 76–90}}</ref><ref>{{cite journal |doi = 10.1146/annurev-marine-120709-142720|title = Carbon Concentrating Mechanisms in Eukaryotic Marine Phytoplankton|year = 2011|last1 = Reinfelder|first1 = John R.|journal = Annual Review of Marine Science|volume = 3|pages = 291–315|pmid = 21329207|bibcode = 2011ARMS....3..291R}}</ref> Under the assumption that any form of shell/exoskeleton protects phytoplankton against predation<ref name="Evolution of Primary Producers in t"/> non-calcareous armors may be the preferable solution to realize protection in a future ocean.<ref name=Bach2015 />

[[File:Energetic effort for armor construction in shell-forming phytoplankton.jpg|thumb|upright=2|right|Representation of comparative energetic effort for armor construction in three major shell-forming phytoplankton taxa as a function of [[carbonate]] chemistry conditions<ref name=Bach2015 />]]

The diagram on the right is a representation of how the comparative energetic effort for armor construction in diatoms, dinoflagellates and coccolithophores appear to operate. The [[frustule]] (diatom shell) seems to be the most inexpensive armor under all circumstances because diatoms typically outcompete all other groups when silicate is available. The coccosphere is relatively inexpensive under sufficient [CO<sub>2</sub>], high [HCO<sub>3</sub><sup>−</sup>], and low [H<sup>+</sup>] because the substrate is saturating and protons are easily released into seawater.<ref name="A Voltage-Gated H+ Channel Underlyi"/> In contrast, the construction of [[Dinoflagellate#Morphology|thecal]] elements, which are organic ([[cellulose]]) plates that constitute the dinoflagellate shell, should rather be favored at high H<sup>+</sup> concentrations because these usually coincide with high [CO<sub>2</sub>]. Under these conditions dinoflagellates could down-regulate the energy-consuming operation of carbon concentrating mechanisms to fuel the production of organic source material for their shell. Therefore, a shift in carbonate chemistry conditions toward high [CO<sub>2</sub>] may promote their competitiveness relative to coccolithophores. However, such a hypothetical gain in competitiveness due to altered carbonate chemistry conditions would not automatically lead to dinoflagellate dominance because a huge number of factors other than carbonate chemistry have an influence on [[species composition]] as well.<ref name=Bach2015>{{cite journal |doi = 10.1016/j.pocean.2015.04.012|title = A unifying concept of coccolithophore sensitivity to changing carbonate chemistry embedded in an ecological framework|year = 2015|last1 = Bach|first1 = Lennart Thomas|last2 = Riebesell|first2 = Ulf|last3 = Gutowska|first3 = Magdalena A.|last4 = Federwisch|first4 = Luisa|last5 = Schulz|first5 = Kai Georg|journal = Progress in Oceanography|volume = 135|pages = 125–138|bibcode = 2015PrOce.135..125B|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><ref>{{Cite Q|Q52718666|author1=Xu, K. |author2=Hutchins, D.|author3=Gao, K.|doi-access=free}}</ref>

===Defence against predation===

Currently, the evidence supporting or refuting a protective function of the coccosphere against predation is limited. Some researchers found that overall microzooplankton predation rates were reduced during blooms of the coccolithophore ''[[Emiliania huxleyi]]'',<ref>{{cite journal |doi = 10.1017/S0025315402005593|title = Microplankton community structure and the impact of microzooplankton grazing during an Emiliania huxleyi bloom, off the Devon coast|year = 2002|last1 = Fileman|first1 = E.S.|last2 = Cummings|first2 = D.G.|last3 = Llewellyn|first3 = C.A.|journal = Journal of the Marine Biological Association of the United Kingdom|volume = 82|issue = 3|pages = 359–368| bibcode=2002JMBUK..82..359F |s2cid = 85890446}}</ref><ref>{{cite journal |doi = 10.1016/S0967-0645(02)00329-6|title = Phytoplankton growth, microzooplankton herbivory and community structure in the southeast Bering Sea: Insight into the formation and temporal persistence of an Emiliania huxleyi bloom|year = 2002|last1 = Olson|first1 = M.Brady|last2 = Strom|first2 = Suzanne L.|journal = Deep Sea Research Part II: Topical Studies in Oceanography|volume = 49|issue = 26|pages = 5969–5990|bibcode = 2002DSRII..49.5969O}}</ref> while others found high microzooplankton grazing rates on natural coccolithophore communities.<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> In 2020, researchers found that ''in situ'' ingestion rates of microzooplankton on ''E. huxleyi'' did not differ significantly from those on similar sized non-calcifying phytoplankton.<ref>{{cite journal |doi = 10.3389/fmars.2020.569896|doi-access = free|title = The Possession of Coccoliths Fails to Deter Microzooplankton Grazers|year = 2020|last1 = Mayers|first1 = Kyle M. J.|last2 = Poulton|first2 = Alex J.|last3 = Bidle|first3 = Kay|last4 = Thamatrakoln|first4 = Kimberlee|last5 = Schieler|first5 = Brittany|last6 = Giering|first6 = Sarah L. C.|last7 = Wells|first7 = Seona R.|last8 = Tarran|first8 = Glen A.|last9 = Mayor|first9 = Dan|last10 = Johnson|first10 = Matthew|last11 = Riebesell|first11 = Ulf|last12 = Larsen|first12 = Aud|last13 = Vardi|first13 = Assaf|last14 = Harvey|first14 = Elizabeth L.|journal = Frontiers in Marine Science|volume = 7|hdl = 1912/26802|hdl-access = free}}</ref> In laboratory experiments the heterotrophic dinoflagellate ''[[Oxyrrhis marina]]'' preferred calcified over non-calcified cells of ''E. huxleyi'', which was hypothesised to be due to size selective feeding behaviour, since calcified cells are larger than non-calcified ''E. huxleyi''.<ref>{{cite journal |doi = 10.3354/ame010307|title = Grazing in the heterotrophic dinoflagellate Oxyrrhis marina: Size selectivity and preference for calcified Emiliania huxleyi cells|year = 1996|last1 = Hansen|first1 = FC|last2 = Witte|first2 = HJ|last3 = Passarge|first3 = J.|journal = Aquatic Microbial Ecology|volume = 10|pages = 307–313|doi-access = free}}</ref> In 2015, Harvey et al. investigated predation by the dinoflagellate ''O. marina'' on different genotypes of non-calcifying ''E. huxleyi'' as well as calcified strains that differed in the degree of calcification.<ref name=Harvey2015>{{cite journal |doi = 10.1093/plankt/fbv081|title = Consequences of strain variability and calcification in ''Emiliania'' huxleyion microzooplankton grazing|year = 2015|last1 = Harvey|first1 = Elizabeth L.|last2 = Bidle|first2 = Kay D.|last3 = Johnson|first3 = Matthew D.|journal = Journal of Plankton Research|pages = fbv081|doi-access = free|hdl = 1912/7739|hdl-access = free}}</ref> They found that the ingestion rate of ''O. marina'' was dependent on the genotype of ''E. huxleyi'' that was offered, rather than on their degree of calcification. In the same study, however, the authors found that predators which preyed on non-calcifying [[genotype]]s grew faster than those fed with calcified cells.<ref name=Harvey2015 /> In 2018, Strom et al. compared predation rates of the dinoflagellate ''[[Amphidinium|Amphidinium longum]]'' on calcified relative to naked ''E. huxleyi'' prey and found no evidence that the coccosphere prevents ingestion by the grazer.<ref name=Strom2018>{{cite journal |doi = 10.1002/lno.10655|title = Phytoplankton defenses: Do Emiliania huxleyi coccoliths protect against microzooplankton predators?|year = 2018|last1 = Strom|first1 = Suzanne L.|last2 = Bright|first2 = Kelley J.|last3 = Fredrickson|first3 = Kerri A.|last4 = Cooney|first4 = Elizabeth C.|journal = Limnology and Oceanography|volume = 63|issue = 2|pages = 617–627|bibcode = 2018LimOc..63..617S| s2cid=90415703 |doi-access = free}}</ref> Instead, ingestion rates were dependent on the offered genotype of E. huxleyi.<ref name=Strom2018 /> Altogether, these two studies suggest that the genotype has a strong influence on ingestion by the microzooplankton species, but if and how calcification protects coccolithophores from microzooplankton predation could not be fully clarified.<ref name=Haunost2021 />

==Importance in global climate change==
{{Plankton sidebar|taxonomy}}

===Impact on the carbon cycle===
Coccolithophores have both long and short term effects on the [[carbon cycle]]. The production of coccoliths requires the uptake of [[dissolved inorganic carbon]] and calcium. [[Calcium carbonate]] and [[carbon dioxide]] are produced from calcium and [[bicarbonate]] by the following chemical reaction:<ref name=Mejia2011>{{citation |journal=PLOS Biology  |volume=9 |issue=6 |year=2011 |pages=e1001087 |title=Will Ion Channels Help Coccolithophores Adapt to Ocean Acidification? |first=R. |last=Mejia |doi=10.1371/journal.pbio.1001087|pmid=21713029 |pmc=3119655 |doi-access=free }}</ref>
: {{chem2|Ca(2+) + 2HCO3− <-> CaCO3 + CO2 + H2O}}

Because coccolithophores are photosynthetic organisms, they are able to use some of the {{CO2}} released in the calcification reaction for [[photosynthesis]].<ref name=Mackinder2010>{{citation |journal=Geomicrobiology Journal |volume=27 |issue=6–7 |year=2010 |pages=585–595 |title=Molecular Mechanisms Underlying Calcification in Coccolithophores |last1=Mackinder |doi=10.1080/01490451003703014|last2=Wheeler |first2=Glen |last3=Schroeder |first3=Declan |last4=Riebesell |first4=Ulf |last5=Brownlee |first5=Colin |bibcode=2010GmbJ...27..585M |s2cid=85403507 |display-authors=etal}}</ref>

However, the production of calcium carbonate drives surface alkalinity down, and in conditions of low alkalinity the {{CO2}} is instead released back into the atmosphere.<ref name=Bates1996>{{citation |journal=Marine Chemistry |volume=51 |issue=4 |year=1996 |pages=347–358 |title=Alkalinity changes in the Sargasso Sea; geochemical evidence of calfication? |last1=Bates |doi=10.1016/0304-4203(95)00068-2|last2=Michaels |first2=Anthony F. |last3=Knap |first3=Anthony H. |bibcode=1996MarCh..51..347B |display-authors=etal}}</ref>
As a result of this, researchers have postulated that large blooms of coccolithophores may contribute to global warming in the short term.<ref name=Marsh2003>{{citation |journal=Comparative Biochemistry and Physiology B |volume=136 |issue=4 |year=2003 |pages=743–754 |title=Regulation of CaCO3 formation in coccolithophores |first=M.E. |last=Marsh |doi=10.1016/s1096-4959(03)00180-5|pmid=14662299 }}</ref> A more widely accepted idea, however, is that over the long term coccolithophores contribute to an overall decrease in atmospheric {{CO2}} concentrations.  During calcification two carbon atoms are taken up and one of them becomes trapped as calcium carbonate.  This calcium carbonate sinks to the bottom of the ocean in the form of coccoliths and becomes part of sediment; thus, coccolithophores provide a sink for emitted carbon, mediating the effects of greenhouse gas emissions.<ref name=Marsh2003 />

===Evolutionary responses to ocean acidification===
Research also suggests that [[ocean acidification]] due to increasing concentrations of {{CO2}} 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= }}</ref> In 2008, field evidence indicating an increase in calcification of newly formed ocean sediments containing coccolithophores bolstered the first ever experimental data showing that an increase in ocean {{CO2}} concentration results in an increase in calcification of these organisms.
Decreasing coccolith mass is related to both the increasing concentrations of {{CO2}} and decreasing concentrations of {{chem2|CO3(2−)}} 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.

<gallery mode="packed" style="float:left" heights="200px">
File:Gephyrocapsa oceanica.jpg| ''[[Gephyrocapsa oceanica]]'' (scale bar is 1&nbsp;μm)
File:Diversity of coccolithophores (cropped) (Rhabdosphaera clavigera).jpg| ''[[Rhabdosphaera clavigera]]''
File:Diversity of coccolithophores (cropped).(Discosphaera tubifera).jpg| ''[[Discosphaera tubifera]]''
</gallery>

{{clear}}

===Impact on microfossil record===
{{See also|Protists in the fossil record}}

Coccolith fossils are prominent and valuable [[Microfossil#Calcareous|calcareous]] [[microfossil]]s. They are the largest global source of biogenic calcium carbonate, and significantly contribute to the global [[carbon cycle]].<ref>{{cite journal | last1 = Taylor | first1 = A.R. | last2 = Chrachri | first2 = A. | last3 = Wheeler | first3 = G. | last4 = Goddard | first4 = H. | last5 = Brownlee | first5 = C. | year = 2011 | title = A voltage-gated H<sup>+</sup> channel underlying pH homeostasis in calcifying coccolithophores | journal = PLOS Biology | volume = 9 | issue = 6| page = e1001085 | doi = 10.1371/journal.pbio.1001085 | pmid = 21713028 | pmc = 3119654 | doi-access = free }}</ref> They are the main constituent of chalk deposits such as the [[white cliffs of Dover]].

Of particular interest are fossils dating back to the [[Palaeocene-Eocene Thermal Maximum]] 55 million years ago.  This period is thought to correspond most directly to the current levels of {{CO2}} in the ocean.<ref name=Self-Trail2012>{{citation |journal=Marine Micropaleontology |volume=92–93 |year=2012 |pages=61–80 |title=Calcareous Nannofossil Assemblage Changes Across the Paleocene-Eocene Thermal Maximum: Evidence from a Shelf Setting |first1=J.M. |last1=Self-Trail |doi=10.1016/j.marmicro.2012.05.003 |display-authors=1 |last2=Watkins |first2=David K. |last3=Wandless |first3=Gregory A. |bibcode=2012MarMP..92...61S |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1466&context=geosciencefacpub }}</ref>  Finally, field evidence of coccolithophore fossils in rock were used to show that the deep-sea fossil record bears a [[megabias|rock record bias]] similar to the one that is widely accepted to affect the land-based [[fossil record]].<ref name=Lloyd2011>{{citation |journal=Geological Society, London, Special Publications |volume=358 |issue=1 |year=2011 |pages=167–177 |title=Quantifying the deep-sea rock and fossil record bias using coccolithophores |first=G.T. |last=Lloyd |doi=10.1144/sp358.11 |display-authors=etal  |bibcode = 2011GSLSP.358..167L |s2cid=129049029 }}</ref>

===Impact on the oceans===
{{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| s2cid=128504924 |doi-access = }}</ref>

== See also ==
* [[CLAW hypothesis]]
* [[Dimethyl sulfide]]
* [[Dimethylsulfoniopropionate]]
* [[Coccolithovirus|''Emiliania huxleyi'' virus 86]]
* ''[[Pleurochrysis carterae]]''

==References==
{{Reflist}}

== External links ==
Sources of detailed information
*[http://ina.tmsoc.org/Nannotax3 Nannotax3] – illustrated guide to the taxonomy of coccolithophores and other nannofossils.
*[http://ina.tmsoc.org INA&nbsp;&mdash; International Nannoplankton Association]
*[http://www.noc.soton.ac.uk/soes/staff/tt/eh/ ''Emiliania huxleyi'' Home Page]

Introductions to coccolithophores
*[http://www.ucmp.berkeley.edu/chromista/prymnesiophyta.html University of California, Berkeley.  Museum of Paleontology:  "Introduction to the Prymnesiophyta".]
*[http://www.paleoportal.org/index.php?globalnav=fossil_gallery&sectionnav=taxon&taxon_id=104 The Paleontology Portal:  Calcareous Nanoplankton]
*[http://www.radiolab.org/blogs/radiolab-blog/2012/mar/05/war-we-need/ RadioLab] – podcast on coccolithophores

{{Plankton}}
{{Cryptophyta and haptophyta}}
{{Taxonbar|from=Q1647990}}
{{Authority control}}

[[Category:Haptophytes]]
[[Category:Microfossils]]
[[Category:Extant Late Triassic first appearances]]
[[Category:Planktology]]
[[Category:Sedimentology]]

[[de:Haptophyta]]