View source for Biology:Marine microorganism

{{short description|Any life form too small for the naked human eye to see that lives in a marine environment}}
[[File:Marine carbon cycle.jpg|thumb|360px| {{center|Role of the microbial community in the marine carbon cycle}}]]

'''Marine microorganisms''' are defined by their habitat as the [[Biology:Microorganism|microorganism]]s living in a [[Earth:Marine habitat|marine environment]], that is, in the [[Chemistry:Saline water|saltwater]] of a sea or ocean or the brackish water of a coastal [[Earth:Estuary|estuary]]. A microorganism (or '''microbe''' or '''microbial''') is any [[Engineering:Microscope|microscopic]] living organism, that is, any life form too small for the naked human eye to really see, needing a microscope. Microorganisms are very diverse. They can be [[Biology:Unicellular organism|single-celled]]<ref name=Brock>{{cite book | editor1=Madigan M |editor2=Martinko J | title=Brock Biology of Microorganisms | edition=13th | publisher=Pearson Education | year=2006 | isbn=978-0-321-73551-5 |page=1096}}</ref> or [[Biology:Multicellular organism|multicellular]] and include all [[Biology:Bacteria|bacteria]] and [[Biology:Archaea|archaea]] and most [[Biology:Protozoa|protozoa]], as well as some species of [[Biology:Fungi|fungi]], [[Biology:Algae|algae]], and certain microscopic animals, such as [[Biology:Rotifer|rotifer]]s and [[Biology:Copepod|copepod]]s. Many [[Physics:Macroscopic scale|macroscopic]] animals and [[Biology:Plant|plant]]s have microscopic [[Biology:Juvenile (organism)|juvenile stages]]. Some microbiologists also classify [[Biology:Virus|virus]]es (and viroids) as microorganisms, but others consider these as nonliving.<ref>{{Cite journal|author=Rybicki EP |title=The classification of organisms at the edge of life, or problems with virus systematics |journal=South African Journal of Science |volume=86 |pages=182–6 |year=1990 |issn=0038-2353}}</ref><ref name=pmid13481308>{{Cite journal |author=Lwoff A |title=The concept of virus |journal=Journal of General Microbiology |volume=17 |issue=2 |pages=239–53 |year=1956 |pmid=13481308

Marine microorganisms constitute about 70% of the biomass in the sea.<ref name="Bar-On2018">Bar-On YM, Phillips R and Milo R (2018) [https://www.pnas.org/content/115/25/6506 The biomass distribution on Earth] ''PNAS'', '''115''' (25): 6506–6511. {{doi|10.1073/pnas.1711842115}}</ref> They are crucial to nutrient recycling in [[Earth:Ecosystem|ecosystem]]s as they act as [[Biology:Decomposer|decomposer]]s. A small proportion of microorganisms are [[Biology:Pathogen|pathogen]]ic, causing disease and even death in plants and animals.<ref>[http://www.who.int/healthinfo/bodgbd2002revised/en/index.html 2002 WHO mortality data] Accessed 20 January 2007</ref> As inhabitants of the largest environment on Earth, microbial marine systems drive changes in every global system. Microbes are responsible for virtually all the [[Earth:Photosynthesis|photosynthesis]] that occurs in the ocean, as well as the cycling of [[Chemistry:Carbon|carbon]], [[Chemistry:Nitrogen|nitrogen]], [[Chemistry:Phosphorus|phosphorus]] and other nutrients and trace elements.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2015/12/151210181647.htm |title=Functions of global ocean microbiome key to understanding environmental changes |date=10 December 2015 |website=www.sciencedaily.com |publisher=University of Georgia |accessdate=11 December 2015}}</ref>

Despite its diversity, microscopic life in the oceans is still poorly understood. For example, the role of [[Biology:Virus|virus]]es in marine ecosystems has barely been explored even in the beginning of the 21st century.<ref>{{cite journal|last=Suttle
|first=C.A.|title=Viruses in the Sea|journal=Nature|year=2005|volume=437|issue=9|pages=356–361|doi=10.1038/nature04160|pmid=16163346}}</ref>

{{marine life sidebar}}

==Overview==
{{multiple image
 | align = right
 | direction = horizontal
 | width = 220
 | header = microbial mats
 | header_align = center
 | image1 = Cyanobacterial-algal mat.jpg
 | alt1 = 
 | caption1 = [[Biology:Microbial mat|Microbial mat]]s are the earliest form of life on Earth for which there is good [[Biology:Fossil|fossil]] evidence. The image shows a cyanobacterial-algal mat.
 | image2 = Stromatolites in Sharkbay.jpg
 | alt2 = 
 | caption2 = Stromatolites are formed from microbial mats as microbes slowly move upwards to avoid being smothered by sediment.
}}
[[File:Relative scale.svg|thumb|upright=1.3|The range of sizes shown by prokaryotes (bacteria and archaea) and viruses relative to those of other organisms and biomolecules]]

Microorganisms make up about 70% of the marine biomass.<ref name="Bar-On2018" /> A [[Biology:Microorganism|microorganism]], or microbe, is a [[Engineering:Microscope|microscopic]] organism too small to be recognised adequately with the naked eye. In practice, that includes organism smaller than about 0.1 mm.<ref name=Glöckner2012>Glöckner, F.O., Gasol, J.M., McDonough, N., Calewaert, J.B. et al. (2012) [http://archives.esf.org/fileadmin/Public_documents/Publications/MarineBoard_PP17_microcean.pdf Marine microbial diversity and its role in ecosystem functioning and environmental change]. European Science Foundation, Position Paper 17. {{isbn|978-2-918428-71-8}}</ref>{{rp|13}}

Such organisms can be [[Biology:Unicellular organism|single-celled]]<ref name="Brock" /> or [[Biology:Multicellular organism|multicellular]]. Microorganisms are diverse and include all [[Biology:Bacteria|bacteria]] and [[Biology:Archaea|archaea]], most [[Biology:Protist|protist]]s including [[Biology:Algae|algae]], [[Biology:Protozoa|protozoa]] and [[Biology:Fungi|fungal-like]] protists, as well as certain microscopic animals such as [[Biology:Rotifer|rotifer]]s. Many [[Physics:Macroscopic scale|macroscopic]] animals and [[Biology:Plant|plant]]s have microscopic [[Biology:Juvenile (organism)|juvenile stages]]. Some microbiologists also classify [[Biology:Virus|virus]]es (and viroids) as microorganisms, but others consider these as nonliving.<ref>{{Cite journal|author=Rybicki EP |title=The classification of organisms at the edge of life, or problems with virus systematics |journal=South African Journal of Science |volume=86 |pages=182–6 |year=1990 |issn=0038-2353}}</ref><ref name="pmid13481308" />

Microorganisms are crucial to nutrient recycling in [[Earth:Ecosystem|ecosystem]]s as they act as [[Biology:Decomposer|decomposer]]s. Some microorganisms are [[Biology:Pathogen|pathogen]]ic, causing disease and even death in plants and animals.<ref>[http://www.who.int/healthinfo/bodgbd2002revised/en/index.html 2002 WHO mortality data] Accessed 20 January 2007</ref> As inhabitants of the largest environment on Earth, microbial marine systems drive changes in every global system. Microbes are responsible for virtually all the [[Earth:Photosynthesis|photosynthesis]] that occurs in the ocean, as well as the cycling of [[Chemistry:Carbon|carbon]], [[Chemistry:Nitrogen|nitrogen]], [[Chemistry:Phosphorus|phosphorus]] and other nutrients and trace elements.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2015/12/151210181647.htm |title=Functions of global ocean microbiome key to understanding environmental changes |date=10 December 2015 |website=www.sciencedaily.com |publisher=University of Georgia |access-date=11 December 2015}}</ref>
{{clade
|label1='''[[Biology:Marine microorganisms|Marine microorganisms]]&nbsp;&nbsp;&nbsp;'''
|1={{clade
   |1 = Viruses [[File:Bacteriophage2.png|45 px]]
   |label2=<span style="color:black;">&nbsp; Prokaryotes &nbsp;</span>
   |2={{clade
      |1 = Bacteria [[File:Prokaryote cell.svg|45 px]]
      |2 = Archaea &nbsp; &nbsp; [[File:Haloquadratum walsbyi00 (cropped).png|25 px]]
      }}
   |label3=<span style="color:black;">Eukaryotes</span>
   |3={{clade
      |1 = Protists [[File:Diatomee - Diatom (fossile) - Stephanopyxis sp. - 630x (14117161428).jpg|55 px]]
      |2 = [[Biology:Microfungi|Microfungi]] &nbsp; [[File:S cerevisiae under DIC microscopy.jpg|25 px]]
      |4 = Microanimals &nbsp; [[File:SEM image of Milnesium tardigradum in active state - journal.pone.0045682.g001-2.png|45 px]]
      }}
   }}
}}

{{Quote box
 |title = 
 |quote = While recent technological developments and scientific discoveries have been substantial, we still lack a major understanding at all levels of the basic ecological questions in relation to the microorganisms in our seas and oceans. These fundamental questions are:<br />
1. What is out there? Which microorganisms are present in our seas and oceans and in what numbers
do they occur?<br />
2. What are they doing? What functions do each of these microorganisms perform in the marine environment and how do they contribute to the global cycles of energy and matter?<br />
3. What are the factors that determine the presence or absence of a microorganism and how do they influence biodiversity and function and vice versa?
 |source = – European Science Foundation, 2012<ref name=Glöckner2012 />{{rp|14}}
 |salign = right
 |width = 300px
}}
[[File:Marine critters.jpg|thumb|left|Under a magnifier, a splash of seawater teems with microscopic life]]
[[File:Microbial Loop.jpg|thumb|left| {{center|Marine [[Biology:Microbial loop|microbial loop]]}}]]
[[File:Ocean mist and spray 2.jpg|thumb|upright=1.3 |right| Sea spray containing marine microorganisms can be swept high into the atmosphere and may travel the globe before falling back to earth.]]

Microscopic life undersea is diverse and still poorly understood, such as for the role of [[Biology:Virus|virus]]es in marine ecosystems.<ref>{{cite journal|last=Suttle|first=C.A.|title=Viruses in the Sea|journal=Nature|year=2005|volume=437|issue=9|pages=356–361| doi=10.1038/nature04160|pmid=16163346|bibcode=2005Natur.437..356S}}</ref> Most marine viruses are [[Biology:Bacteriophage|bacteriophage]]s, which are harmless to plants and animals, but are essential to the regulation of saltwater and freshwater ecosystems.<ref name="Shors p. 5">Shors p. 5</ref> They infect and destroy bacteria in aquatic microbial communities, and are the most important mechanism of [[Earth:Carbon cycle|recycling carbon]] in the marine environment. The organic molecules released from the dead bacterial cells stimulate fresh bacterial and algal growth.<ref name="Shors p. 593">Shors p. 593</ref> Viral activity may also contribute to the [[Biology:Biological pump|biological pump]], the process whereby [[Chemistry:Carbon|carbon]] is [[Earth:Carbon sequestration|sequestered]] in the deep ocean.<ref name="pmid17853907">{{vcite journal |author=Suttle CA |title=Marine viruses—major players in the global ecosystem |journal=Nature Reviews Microbiology |volume=5 |issue=10 |pages=801–12 |year=2007 |pmid=17853907 |doi=10.1038/nrmicro1750}}</ref>

A stream of airborne microorganisms circles the planet above weather systems but below commercial air lanes.<ref>[https://www.smithsonianmag.com/science-nature/living-bacteria-are-riding-earths-air-currents-180957734/ Living Bacteria Are Riding Earth’s Air Currents] ''Smithsonian Magazine'', 11 January 2016.</ref> Some peripatetic microorganisms are swept up from terrestrial dust storms, but most originate from marine microorganisms in [[Earth:Sea spray|sea spray]]. In 2018, scientists reported that hundreds of millions of viruses and tens of millions of bacteria are deposited daily on every square meter around the planet.<ref>{{cite news |last=Robbins |first=Jim |title=Trillions Upon Trillions of Viruses Fall From the Sky Each Day |url=https://www.nytimes.com/2018/04/13/science/virosphere-evolution.html |date=13 April 2018 |work={{wipe|The New York Times}} |accessdate=14 April 2018}}</ref><ref name="ISME-2018">{{cite journal |last1=Reche |first1=Isabel |last2=D’Orta |first2=Gaetano |last3=Mladenov |first3=Natalie |last4=Winget |first4= Danielle M |last5=Suttle |first5= Curtis A |title=Deposition rates of viruses and bacteria above the atmospheric boundary layer |journal=ISME Journal |volume=12 |issue=4 |pages=1154–1162 |date=29 January 2018 |doi=10.1038/s41396-017-0042-4 |pmid=29379178 |pmc=5864199}}</ref>

Microscopic organisms live throughout the [[Biology:Biosphere|biosphere]]. The mass of [[Biology:Prokaryote|prokaryote]] microorganisms &mdash; which includes bacteria and archaea, but not the nucleated [[Biology:Microorganism#Eukaryotes|eukaryote microorganisms]] &mdash; may be as much as 0.8 trillion tons of carbon (of the total biosphere [[Earth:Biomass (ecology)|mass]], estimated at between 1 and 4 trillion tons).<ref name="AGCI-2014">{{cite web |author=Staff |title=The Biosphere |url=http://www.agci.org/classroom/biosphere/index.php |date=2014 |work=Aspen Global Change Institute |accessdate=10 November 2014}}</ref> Single-celled [[Biology:Piezophile|barophilic]] marine microbes have been found at a depth of {{convert|10900|m|ft|abbr=on}} in the Mariana Trench, the deepest spot in the Earth's oceans.<ref name="LS-20130317">{{cite web |last=Choi |first=Charles Q. |title=Microbes Thrive in Deepest Spot on Earth |url=http://www.livescience.com/27954-microbes-mariana-trench.html |date=17 March 2013 |publisher=LiveScience |accessdate=17 March 2013}}</ref><ref name="NG-20130317">{{cite journal |last1=Glud |first1=Ronnie |last2=Wenzhöfer |first2=Frank |last3=Middelboe |first3=Mathias |last4=Oguri |first4=Kazumasa |last5=Turnewitsch |first5=Robert |last6=Canfield |first6=Donald E. |last7=Kitazato |first7=Hiroshi |title=High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth |doi=10.1038/ngeo1773 |date=17 March 2013 |journal=[[Earth:Nature Geoscience|Nature Geoscience]] |volume=6 |issue=4 |pages=284–288 |bibcode = 2013NatGe...6..284G}}</ref> Microorganisms live inside rocks {{convert|580|m|ft|abbr=on}} below the sea floor under {{convert|2590|m|ft|abbr=on}} of ocean off the coast of the northwestern {{wipe|United States}},<ref name="LS-20130317" /><ref name="LS-20130314">{{cite web |last=Oskin |first=Becky |title=Intraterrestrials: Life Thrives in Ocean Floor |url=http://www.livescience.com/27899-ocean-subsurface-ecosystem-found.html |date=14 March 2013 |publisher=LiveScience |accessdate=17 March 2013}}</ref> as well as {{convert|2400|m|ft mi|abbr=on}} beneath the seabed off Japan.<ref name="BBC-20141215-RM">{{cite news |last=Morelle |first=Rebecca |title=Microbes discovered by deepest marine drill analysed |url=https://www.bbc.com/news/science-environment-30489814 |date=15 December 2014 |work=BBC News |accessdate=15 December 2014}}</ref> The greatest known temperature at which microbial life can exist is {{convert|122|°C|°F|abbr=on}} (''Methanopyrus kandleri'').<ref>{{cite journal | author = Takai K |author2=Nakamura K |author3=Toki T |author4=Tsunogai U |display-authors=4 |author5=Miyazaki M |author6=Miyazaki J |author7=Hirayama H |author8=Nakagawa S |author9=Nunoura T |author10=Horikoshi K | title = Cell proliferation at 122°C and isotopically heavy CH4 production by a hyperthermophilic methanogen under high-pressure cultivation | journal = Proceedings of the National Academy of Sciences of the United States of America | date = 2008 | volume = 105 | issue = 31| pages = 10949–54 | doi = 10.1073/pnas.0712334105 | pmid = 18664583 | pmc = 2490668|bibcode=2008PNAS..10510949T}}</ref> In 2014, scientists confirmed the existence of microorganisms living {{convert|800|m|ft|abbr=on}} below the ice of [[Earth:Antarctica|Antarctica]].<ref name="NAT-20140820">{{cite journal |last=Fox |first=Douglas |title=Lakes under the ice: Antarctica's secret garden |date=20 August 2014 |journal=Nature |volume=512 |issue=7514 |pages=244–246 |doi=10.1038/512244a |bibcode=2014Natur.512..244F |pmid=25143097}}</ref><ref name="FRB-20140820">{{cite web |last=Mack |first=Eric |title=Life Confirmed Under Antarctic Ice; Is Space Next? |url=https://www.forbes.com/sites/ericmack/2014/08/20/life-confirmed-under-antarctic-ice-is-space-next/ |date=20 August 2014 |work={{wipe|Forbes}} |accessdate=21 August 2014}}</ref> According to one researcher, "You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are."<ref name="LS-20130317" />

{{clear}}

==Marine viruses==
[[File:Marine virus-host interactions.jpg|thumb|400px|right| {{center|Virus-host interactions in the marine ecosystem,<br />including viral infection of bacteria, phytoplankton and fish <ref>Middelboe, M. and Brussaard, C. (2017) "Marine viruses: key players in marine ecosystems". ''Viruses''. '''9'''(10): 302. {{doi|10.3390/v9100302}}</ref>}}]]


A [[Biology:Virus|virus]] is a small [[Biology:Pathogen|infectious agent]] that [[Biology:Replicate|replicates]] only inside the living [[Biology:Cell|cells]] of other organisms. Viruses can infect all types of life forms, from [[Biology:Animal|animal]]s and [[Biology:Plant|plant]]s to [[Biology:Microorganism|microorganism]]s, including [[Biology:Bacteria|bacteria]] and [[Biology:Archaea|archaea]].<ref name="pmid16984643">{{vcite journal
|author=Koonin EV, Senkevich TG, Dolja VV
|title=The ancient Virus World and evolution of cells
|journal=Biology Direct
|volume=1
|page=29
|year=2006
|pmid=16984643
|pmc=1594570
|doi=10.1186/1745-6150-1-29
|pages=29}}</ref>

When not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles. These viral particles, also known as ''virions'', consist of two or three parts: (i) the genetic material made from either [[Biology:DNA|DNA]] or [[Biology:RNA|RNA]], long [[Physics:Molecule|molecule]]s that carry genetic information; (ii) a [[Biology:Protein|protein]] coat called the [[Biology:Capsid|capsid]], which surrounds and protects the genetic material; and in some cases (iii) an [[Biology:Viral envelope|envelope]] of [[Chemistry:Lipid|lipid]]s that surrounds the protein coat when they are outside a cell. The shapes of these virus particles range from simple [[Helix|helical]] and [[Icosahedron|icosahedral]] forms for some virus species to more complex structures for others. Most virus species have virions that are too small to be seen with an [[Engineering:Optical microscope|optical microscope]]. The average virion is about one one-hundredth the size of the average [[Biology:Bacterium|bacterium]].

The origins of viruses in the [[Biology:Evolutionary history of life|evolutionary history of life]] are unclear: some may have [[Biology:Evolution|evolved]] from [[Biology:Plasmid|plasmid]]s—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of [[Biology:Horizontal gene transfer|horizontal gene transfer]], which increases [[Biology:Genetic diversity|genetic diversity]].<ref name="Canchaya" /> Viruses are considered by some to be a life form, because they carry genetic material, reproduce, and evolve through [[Biology:Natural selection|natural selection]]. However, they lack key characteristics (such as cell structure) that are generally considered necessary to count as life. Because they possess some but not all such qualities, viruses have been described as "organisms at the edge of life"<ref name="ReferenceA">{{vcite journal|author = Rybicki, EP|year = 1990|title = The classification of organisms at the edge of life, or problems with virus systematics|journal = South African Journal of Science |volume = 86|pages = 182–186}}</ref> and as replicators.<ref name="Koonin and Starokadomskyy">{{cite journal |title=Are viruses alive? The replicator paradigm sheds decisive light on an old but misguided question |journal=Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences |date=October 2016 |volume=59 |last=Koonin |first=E. V. |last2=Starokadomskyy |first2=P. |pages=125–134 |doi=10.1016/j.shpsc.2016.02.016 |pmid=26965225 |pmc=5406846}}</ref>

{{multiple image
 | align = left
 | direction = horizontal
 | header            = Bacteriophages (phages)
 | header_align      = center
 | footer            = &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Phage injecting its genome into bacteria
 | footer_align      = center
 | image1    = Phage.jpg
 | width1    = 160
 | alt1      = 
 | caption1  = {{center|Multiple phages attached to a bacterial cell wall at 200,000x magnification}}
[[File:Phage injecting its genome into bacteria.svg|330px]]
 | image2    = Tailed phage.png
 | width2    = 166
 | alt2      = 
 | caption2  = {{center|Diagram of a typical [[Biology:Caudovirales|tailed phage]]}}
}}

Viruses are found wherever there is life and have probably existed since living cells first evolved.<ref name="pmid16494962">{{vcite journal
|author=Iyer LM, Balaji S, Koonin EV, Aravind L
|title=Evolutionary genomics of nucleo-cytoplasmic large DNA viruses
|journal=Virus Research
|volume=117
|issue=1
|pages=156–84
|year=2006
|pmid=16494962
|doi=10.1016/j.virusres.2006.01.009}}</ref> The origin of viruses is unclear because they do not form fossils, so [[Biology:Molecular biology|molecular techniques]] have been used to compare the DNA or RNA of viruses and are a useful means of investigating how they arose.<ref name="pmid20660197">{{vcite journal |author=Sanjuán R, Nebot MR, Chirico N, Mansky LM, Belshaw R |title=Viral mutation rates |journal=Journal of Virology |volume=84 |issue=19 |pages=9733–48 |year=2010 |month=October |pmid=20660197 |doi=10.1128/JVI.00694-10 |pmc=2937809}}</ref>

Viruses are now recognised as ancient and as having origins that pre-date the divergence of life into the [[Biology:Three-domain system|three domains]].<ref name="Mahy Gen 28">{{vcite book |author=Mahy WJ & Van Regenmortel MHV (eds) |title=Desk Encyclopedia of General Virology |publisher=Academic Press |location=Oxford |year=2009 |pages=28 |isbn=0-12-375146-2}}</ref>

Opinions differ on whether viruses are a form of life or organic structures that interact with living organisms.<ref name="pmid26965225">{{vcite journal |vauthors=Koonin EV, Starokadomskyy P |title=Are viruses alive? The replicator paradigm sheds decisive light on an old but misguided question |journal=Studies in History and Philosophy of Biological and Biomedical Sciences |year=2016 |pmid=26965225 |doi=10.1016/j.shpsc.2016.02.016 |pmc=5406846}}</ref> They are considered by some to be a life form, because they carry genetic material, reproduce by creating multiple copies of themselves through self-assembly, and evolve through [[Biology:Natural selection|natural selection]]. However they lack key characteristics such as a cellular structure generally considered necessary to count as life. Because they possess some but not all such qualities, viruses have been described as replicators<ref>{{cite journal |title=Are viruses alive? The replicator paradigm sheds decisive light on an old but misguided question. |journal=Studies in History and Philosophy of Biological and Biomedical Sciences |date=7 March 2016 |last=Koonin |first=E. V. |last2=Starokadomskyy |first2=P. |doi=10.1016/j.shpsc.2016.02.016 |pmid=26965225 |volume=59 |pmc=5406846 |pages=125–34}}</ref> and as "organisms at the edge of life".<ref name="ReferenceA" />

===Phages===
[[File:Caudovirales.svg|thumb|160px|right| {{center|In terms of individual counts, tailed phage are the most abundant biological entities in the sea.}}]]
[[File:Cyanophages.png|thumb|326px|right| {{center|These are cyanophages, viruses that infect cyanobacteria (scale bars indicate 100 nm)}}]]

[[Biology:Bacteriophage|Bacteriophage]]s, often just called ''phages'', are viruses that [[Biology:Parasite|parasite]] bacteria and archaea. [[Biology:Marine bacteriophage|Marine phages]] parasite marine bacteria and archaea, such as [[Biology:Cyanobacteria|cyanobacteria]].<ref name=Mann>{{cite journal | last = Mann | first = NH | title = The Third Age of Phage | journal = PLoS Biology | volume = 3 | issue = 5 | pages = 753–755 | date = 2005-05-17 | doi = 10.1371/journal.pbio.0030182 | pmid = 15884981 | pmc = 1110918}}</ref> They are a common and diverse group of viruses and are the most abundant biological entity in marine environments, because their hosts, bacteria, are typically the numerically dominant cellular life in the sea. Generally there are about 1 million to 10 million viruses in each mL of seawater, or about ten times more double-stranded DNA viruses than there are cellular organisms,<ref name="auto">{{vcite journal|author=Wommack KE, Colwell RR|title=Virioplankton: viruses in aquatic ecosystems|journal=Microbiology and Molecular Biology Reviews |volume=64|issue=1|pages=69–114|year=2000|pmid=10704475|pmc=98987|doi=10.1128/MMBR.64.1.69-114.2000}}</ref><ref name="auto1">{{vcite journal|author=Suttle CA|title=Viruses in the sea|journal=Nature |volume=437 |pages=356–361|year=2005|pmid=16163346 |doi=10.1038/nature04160}}</ref> although estimates of viral abundance in seawater can vary over a wide range.<ref>{{vcite journal|author=Bergh O, Børsheim KY, Bratbak G, Heldal M|title=High abundance of viruses found in aquatic environments|journal=Nature|volume=340|issue=6233|pages=467–8|year=1989|pmid=2755508|doi=10.1038/340467a0|bibcode = 1989Natur.340..467B}}</ref><ref>{{vcite journal|author=Wigington CH, Sonderegger D, Brussaard CPD, Buchan A, Finke JF, Fuhrman JA, Lennon JT, Middelboe M, Suttle CA, Stock C, Wilson WH, Wommack KE, Wilhelm SW, Weitz JS |title=Re-examination of the relationship between marine virus and microbial cell abundances|journal=Nature Microbiology |volume=1|pages=15024|year=2016 |pmid=27572161|doi=10.1038/nmicrobiol.2015.24}}</ref> [[Biology:Caudovirales|Tailed bacteriophages]] appear to dominate marine ecosystems in number and diversity of organisms.<ref name=Mann /> Bacteriophages belonging to the families [[Biology:Corticovirus|Corticoviridae]],<ref>{{cite journal|title=Putative prophages related to lytic tailless marine dsDNA phage PM2 are widespread in the genomes of aquatic bacteria|journal=BMC Genomics|year=2007|volume=8|pages=236|doi=10.1186/1471-2164-8-236|pmid=17634101|vauthors=Krupovic M, Bamford DH |pmc=1950889}}</ref> [[Biology:Inoviridae|Inoviridae]]<ref>{{cite journal|title=High frequency of a novel filamentous phage, VCY φ, within an environmental Vibrio cholerae population|journal=Applied and Environmental Microbiology |year=2012|volume=78|issue=1|pages=28–33|doi=10.1128/AEM.06297-11|pmid=22020507|vauthors=Xue H, Xu Y, Boucher Y, Polz MF |pmc=3255608}}</ref> and [[Biology:Microviridae|Microviridae]]<ref name=Roux>{{cite journal|title=Evolution and diversity of the Microviridae viral family through a collection of 81 new complete genomes assembled from virome reads|journal=PLOS ONE|year=2012|volume=7|issue=7|pages=e40418|doi=10.1371/journal.pone.0040418|pmid=22808158|vauthors=Roux S, Krupovic M, Poulet A, Debroas D, Enault F |pmc=3394797|bibcode=2012PLoSO...740418R}}</ref> are also known to infect diverse marine bacteria.

===Role of viruses===
Microorganisms make up about 70% of the marine biomass.<ref name="Bar-On2018"/> It is estimated viruses kill 20% of this biomass each day and that there are 15 times as many viruses in the oceans as there are bacteria and archaea. Viruses are the main agents responsible for the rapid destruction of harmful [[Biology:Algal bloom|algal bloom]]s,<ref name="pmid16163346">{{vcite journal |author=Suttle CA |title=Viruses in the sea |journal=Nature |volume=437 |issue=7057 |pages=356–61 |year=2005 |pmid=16163346 |doi=10.1038/nature04160|bibcode = 2005Natur.437..356S}}</ref> which often kill other marine life.<ref name="cdc.gov">{{vcite web
|url=https://www.cdc.gov/hab/redtide/
|title=Harmful Algal Blooms: Red Tide: Home|CDC HSB
|publisher=www.cdc.gov
|accessdate=2014-12-19
}}</ref>
The number of viruses in the oceans decreases further offshore and deeper into the water, where there are fewer host organisms.<ref name="pmid17853907" />

There are also archaean viruses which replicate within [[Biology:Archaea|archaea]]: these are double-stranded DNA viruses with unusual and sometimes unique shapes.<ref name="Lawrence">{{vcite journal|author=Lawrence CM, Menon S, Eilers BJ, ''et al.''|title=Structural and functional studies of archaeal viruses|journal=Journal of Biological Chemistry |volume=284|issue=19|pages=12599–603|year=2009|pmid=19158076|doi=10.1074/jbc.R800078200|pmc=2675988}}</ref><ref name=Prangishvili>{{vcite journal |author=Prangishvili D, Forterre P, Garrett RA |title=Viruses of the Archaea: a unifying view |journal=Nature Reviews Microbiology |volume=4 |issue=11 |pages=837–48 |year=2006 |pmid=17041631 |doi=10.1038/nrmicro1527}}</ref> These viruses have been studied in most detail in the [[Earth:Thermophile|thermophilic]] archaea, particularly the orders [[Biology:Sulfolobales|Sulfolobales]] and [[Biology:Thermoproteales|Thermoproteales]].<ref>{{vcite journal|author=Prangishvili D, Garrett RA|title=Exceptionally diverse morphotypes and genomes of crenarchaeal hyperthermophilic viruses|journal=Biochemical Society Transactions|volume=32|issue=Pt 2|pages=204–8|year=2004|pmid=15046572|doi=10.1042/BST0320204}}</ref>

Viruses are an important natural means of [[Biology:Horizontal gene transfer|transferring genes]] between different species, which increases [[Biology:Genetic diversity|genetic diversity]] and drives evolution.<ref name="Canchaya">{{vcite journal|author=Canchaya C, Fournous G, Chibani-Chennoufi S, Dillmann ML, Brüssow H|title=Phage as agents of lateral gene transfer|journal=Current Opinion in Microbiology |volume=6 |issue=4 |pages=417–24 |year=2003 |pmid=12941415|doi=10.1016/S1369-5274(03)00086-9}}</ref> It is thought that viruses played a central role in the early evolution, before the diversification of bacteria, archaea and eukaryotes, at the time of the last universal common ancestor of life on Earth.<ref name="pmid11536914">{{vcite journal |author=Forterre P, Philippe H |title=The last universal common ancestor (LUCA), simple or complex? |journal=The Biological Bulletin |volume=196 |issue=3 |pages=373–5; discussion 375–7 |year=1999 |pmid=11536914 |doi= 10.2307/1542973}}</ref> Viruses are still one of the largest reservoirs of unexplored genetic diversity on Earth.<ref name="pmid17853907" />

{{clear}}

===Giant viruses===
[[File:Electron microscopic image of a mimivirus - journal.ppat.1000087.g007 crop.png|thumb|160px|left|The giant [[Biology:Mimivirus|mimivirus]]]]
[[File:Tupanvirus.jpeg|thumb| Largest known virus, Tupanvirus, named after ''Tupã'', the Guarani supreme god of creation]]

Viruses normally range in length from about 20 to 300 nanometers. This can be contrasted with the length of bacteria, which starts at about 400 nanometers. There are also [[Biology:Giant virus|giant virus]]es, typically about 1000 nanometers (one micron) in length. The largest known of these is ''[[Biology:Tupanvirus|Tupanvirus]]''. This genus of giant virus was discovered in 2018 in the deep ocean as well as a soda lake, and can reach up to 2.3 microns in total length.<ref>{{cite journal|title=Tailed giant Tupanvirus possesses the most complete translational apparatus of the known virosphere| first1=Jônatas| last1=Abrahão|first2=Lorena|last2=Silva|first3=Ludmila Santos|last3=Silva|first4=Jacques Yaacoub Bou| last4=Khalil| first5=Rodrigo| last5=Rodrigues|first6=Thalita|last6=Arantes|first7=Felipe|last7=Assis|first8=Paulo|last8=Boratto|first9=Miguel|last9=Andrade|first10=Erna Geessien|last10=Kroon|first11=Bergmann|last11=Ribeiro|first12=Ivan|last12=Bergier|first13=Herve|last13=Seligmann|first14=Eric|last14=Ghigo|first15=Philippe|last15=Colson|first16=Anthony|last16=Levasseur|first17=Guido|last17=Kroemer|first18=Didier|last18=Raoult|first19=Bernard La|last19=Scola|date=27 February 2018| journal=Nature Communications| volume=9|issue=1| pages=749|doi=10.1038/s41467-018-03168-1|pmid = 29487281| pmc=5829246| bibcode=2018NatCo...9..749A}}</ref>

The discovery and subsequent characterization of giant viruses has triggered some debate concerning their evolutionary origins. The two main hypotheses for their origin are that either they evolved from small viruses, picking up DNA from host organisms, or that they evolved from very complicated organisms into the current form which is not self-sufficient for reproduction.<ref>{{cite web | first = Rae Ellen | last = Bichell | name-list-format = vanc | title = In Giant Virus Genes, Hints About Their Mysterious Origin | url = https://www.npr.org/sections/health-shots/2017/04/06/522478901/in-giant-virus-genes-hints-about-their-mysterious-origin | work = All Things Considered}}</ref> What sort of complicated organism giant viruses might have diverged from is also a topic of debate. One proposal is that the origin point actually represents a fourth [[Biology:Three-domain system|domain]] of life,<ref name=AmSci-099-4>{{cite journal |journal=American Scientist |title=Giant Viruses |first=James L. |last=Van Etten | name-list-format = vanc |date=July–August 2011 |volume=99 |issue=4 |pages=304–311 |doi=10.1511/2011.91.304 |url=http://www.americanscientist.org/issues/feature/2011/4/giant-viruses}}</ref><ref name=Comm-005-1>{{cite journal | vauthors = Legendre M, Arslan D, Abergel C, Claverie JM | title = Genomics of Megavirus and the elusive fourth domain of Life | journal = Communicative & Integrative Biology | volume = 5 | issue = 1 | pages = 102–6 | date = January 2012 | pmid = 22482024 | pmc = 3291303 | doi = 10.4161/cib.18624}}</ref> but this has been largely discounted.<ref>{{cite journal | vauthors = Schulz F, Yutin N, Ivanova NN, Ortega DR, Lee TK, Vierheilig J, Daims H, Horn M, Wagner M, Jensen GJ, Kyrpides NC, Koonin EV, Woyke T | title = Giant viruses with an expanded complement of translation system components | journal = Science | volume = 356 | issue = 6333 | pages = 82–85 | date = April 2017 | pmid = 28386012 | doi = 10.1126/science.aal4657 | bibcode = 2017Sci...356...82S | url = https://escholarship.org/content/qt0kf9t6gn/qt0kf9t6gn.pdf?t=oruwia}}</ref><ref>{{cite journal | vauthors = Bäckström D, Yutin N, Jørgensen SL, Dharamshi J, Homa F, Zaremba-Niedwiedzka K, Spang A, Wolf YI, Koonin EV, Ettema TJ | title = Virus Genomes from Deep Sea Sediments Expand the Ocean Megavirome and Support Independent Origins of Viral Gigantism | journal = mBio | volume = 10 | issue = 2 |pages=e02497-02418 | date = March 2019 | doi = 10.1128/mBio.02497-18 | pmid = 30837339 | pmc = 6401483}}</ref>
{{clear}}

==Prokaryotes==


===Marine bacteria===
[[File:Vibrio vulnificus 01.png|thumb|right|''[[Biology:Vibrio vulnificus|Vibrio vulnificus]]'', a virulent bacterium found in estuaries and along coastal areas]]
[[File:Synechococcus elongatus PCC 7942 electron micrograph showing carboxysomes.jpeg|thumb| Electron micrograph showing a species of the widespread cyanobacteria ''[[Biology:Synechococcus|Synechococcus]]''. Carboxysomes appear as polyhedral dark structures.]]

[[Biology:Bacteria|Bacteria]] constitute a large domain of prokaryotic [[Biology:Microorganism|microorganism]]s. Typically a few [[Micrometre|micrometre]]s in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on [[Astronomy:Earth|Earth]], and are present in most of its [[Earth:Habitat|habitat]]s. Bacteria inhabit soil, water, [[Earth:Hot spring|acidic hot springs]], [[Physics:Radioactive waste|radioactive waste]],<ref>{{cite journal |vauthors=Fredrickson JK, Zachara JM, Balkwill DL, Kennedy D, Li SM, Kostandarithes HM, Daly MJ, Romine MF, Brockman FJ | title = Geomicrobiology of high-level nuclear waste-contaminated vadose sediments at the Hanford site, Washington state | journal = Applied and Environmental Microbiology | volume = 70 | issue = 7 | pages = 4230–41 | year = 2004 | pmid = 15240306 | pmc = 444790 | doi = 10.1128/AEM.70.7.4230-4241.2004}}</ref> and the deep portions of [[Earth:Crust (geology)|Earth's crust]]. Bacteria also live in symbiotic and parasitic relationships with plants and animals.

Once regarded as [[Biology:Plant|plant]]s constituting the class ''Schizomycetes'', bacteria are now classified as prokaryotes. Unlike cells of animals and other [[Biology:Eukaryote|eukaryote]]s, bacterial cells do not contain a [[Biology:Cell nucleus|nucleus]] and rarely harbour [[Biology:Cell membrane|membrane-bound]] [[Biology:Organelle|organelle]]s. Although the term ''bacteria'' traditionally included all prokaryotes, the [[Scientific classification|scientific classification]] changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that [[Biology:Evolution|evolved]] from an ancient common ancestor. These evolutionary domains are called ''Bacteria'' and ''[[Biology:Archaea|Archaea]]''.<ref name="Woese">{{cite journal |vauthors=Woese CR, Kandler O, Wheelis ML | title = Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 87 | issue = 12 | pages = 4576–9 | year = 1990 | pmid = 2112744 | pmc = 54159 | doi = 10.1073/pnas.87.12.4576 | bibcode = 1990PNAS...87.4576W}}</ref>

The ancestors of modern bacteria were unicellular microorganisms that were the [[Biology:Abiogenesis|first forms of life]] to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life.<ref>{{cite journal | vauthors = Schopf JW | title = Disparate rates, differing fates: tempo and mode of evolution changed from the Precambrian to the Phanerozoic | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 91 | issue = 15 | pages = 6735–42 | year = 1994 | pmid = 8041691 | pmc = 44277 | doi = 10.1073/pnas.91.15.6735 | bibcode = 1994PNAS...91.6735S}}</ref><ref>{{cite journal |vauthors=DeLong EF, Pace NR | title = Environmental diversity of bacteria and archaea | journal = Systematic Biology | volume = 50 | issue = 4 | pages = 470–8 | year = 2001 | pmid = 12116647 | doi = 10.1080/106351501750435040 | citeseerx = 10.1.1.321.8828}}</ref> Although bacterial [[Biology:Fossil|fossil]]s exist, such as [[Earth:Stromatolite|stromatolite]]s, their lack of distinctive [[Biology:Morphology|morphology]] prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species. However, gene sequences can be used to reconstruct the bacterial [[Biology:Phylogenetics|phylogeny]], and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage.<ref>{{cite journal |vauthors=Brown JR, Doolittle WF | title = Archaea and the prokaryote-to-eukaryote transition | journal = Microbiology and Molecular Biology Reviews | volume = 61 | issue = 4 | pages = 456–502 | year = 1997 | pmid = 9409149 | pmc = 232621}}</ref> <!-- The [[Biology:Most recent common ancestor|most recent common ancestor]] of bacteria and archaea was probably a [[Earth:Thermophile|hyperthermophile]] that lived about 2.5 billion–3.2 billion years ago.<ref>{{cite journal |vauthors=Di Giulio M |title=The universal ancestor and the ancestor of bacteria were hyperthermophiles |journal=Journal of Molecular Evolution |volume=57 |issue=6 |pages=721–30 |year=2003 |pmid=14745541 |doi=10.1007/s00239-003-2522-6}}</ref><ref>{{cite journal |vauthors=Battistuzzi FU, Feijao A, Hedges SB |title=A genomic timescale of prokaryote evolution: insights into the origin of methanogenesis, phototrophy, and the colonization of land |journal=BMC Evolutionary Biology |volume=4 |pages=44 |year=2004 |pmid=15535883 |pmc=533871 |doi=10.1186/1471-2148-4-44}}</ref> -->
Bacteria were also involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into [[Biology:Endosymbiont|endosymbiotic]] associations with the ancestors of eukaryotic cells, which were themselves possibly related to the [[Biology:Archaea|Archaea]].<ref name=Dyall>{{cite journal |last1=Dyall |first1=Sabrina D. |last2=Brown |first2=Mark T. |last3=Johnson |first3=Patricia J. |date=9 April 2004 |title=Ancient Invasions: From Endosymbionts to Organelles |journal=Science |volume=304 |issue=5668 |pages=253–257 |bibcode=2004Sci...304..253D |doi=10.1126/science.1094884 |issn=0036-8075 |pmid=15073369|url=https://semanticscholar.org/paper/5e0ed5bd35f68ca5ebae1aed41b93d279e9ecc88 }}</ref><ref>{{cite journal |vauthors=Poole AM, Penny D | title = Evaluating hypotheses for the origin of eukaryotes | journal = BioEssays | volume = 29 | issue = 1 | pages = 74–84 | year = 2007 | pmid = 17187354 | doi = 10.1002/bies.20516| url = https://semanticscholar.org/paper/dda2734ae60b55ce556a3889d5842734ffb15ad7 }}</ref> This involved the engulfment by proto-eukaryotic cells of [[Biology:Alphaproteobacteria|alphaproteobacteria]]l symbionts to form either [[Biology:Mitochondrion|mitochondria]] or [[Biology:Hydrogenosome|hydrogenosome]]s, which are still found in all known Eukarya. Later on, some eukaryotes that already contained mitochondria also engulfed cyanobacterial-like organisms. This led to the formation of [[Biology:Chloroplast|chloroplast]]s in algae and plants. There are also some algae that originated from even later endosymbiotic events. Here, eukaryotes engulfed a eukaryotic algae that developed into a "second-generation" plastid.<ref>{{cite journal |vauthors=Lang BF, Gray MW, Burger G | title = Mitochondrial genome evolution and the origin of eukaryotes | journal = Annual Review of Genetics | volume = 33 | pages = 351–97 | year = 1999 | pmid = 10690412 | doi = 10.1146/annurev.genet.33.1.351}}</ref><ref>{{cite journal | vauthors = McFadden GI | title = Endosymbiosis and evolution of the plant cell | journal = Current Opinion in Plant Biology | volume = 2 | issue = 6 | pages = 513–9 | year = 1999 | pmid = 10607659 | doi = 10.1016/S1369-5266(99)00025-4}}</ref> This is known as secondary endosymbiosis.

<gallery mode=packed heights=140px style=float:left;>
File:Sulphide bacteria crop2.jpg|The marine ''[[Biology:Thiomargarita namibiensis|Thiomargarita namibiensis]]'', largest known bacterium
File:Potomac river eutro.jpg|[[Biology:Cyanobacteria|Cyanobacteria]] [[Biology:Algal bloom|blooms]] can contain lethal [[Chemistry:Cyanotoxin|cyanotoxin]]s
File:Glaucocystis sp.jpg|The [[Biology:Chloroplast|chloroplast]]s of [[Biology:Glaucophyte|glaucophyte]]s have a [[Biology:Peptidoglycan|peptidoglycan]] layer, evidence suggesting their endosymbiotic origin from [[Biology:Cyanobacteria|cyanobacteria]].<ref name="keeling">{{cite journal|journal =American Journal of Botany|year = 2004|volume = 91|pages = 1481–1493|title = Diversity and evolutionary history of plastids and their hosts|author = Patrick J. Keeling|url = http://www.amjbot.org/cgi/content/full/91/10/1481|doi = 10.3732/ajb.91.10.1481|issue=10|pmid=21652304}}</ref>
</gallery>

{{clear}}

The largest known bacterium, the marine ''[[Biology:Thiomargarita namibiensis|Thiomargarita namibiensis]]'', can be visible to the naked eye and sometimes attains {{convert|0.75|mm|µm|abbr=on}}.<ref>{{Citation|work=Max Planck Institute for Marine Microbiology |date=8 April 1999 |title=The largest Bacterium: Scientist discovers new bacterial life form off the African coast |url=http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/1999/news17_99.htm |url-status=dead |archiveurl=https://web.archive.org/web/20100120043846/http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/1999/news17_99.htm |archivedate=20 January 2010}}</ref><ref>{{Citation |title=List of Prokaryotic names with Standing in Nomenclature - Genus Thiomargarita |url=http://www.bacterio.cict.fr/t/thiomargarita.html |url-status=dead |archiveurl=https://web.archive.org/web/20090828190032/http://www.bacterio.cict.fr/t/thiomargarita.html |archivedate=28 August 2009 |df=dmy-all}}</ref>

===Marine archaea===
[[File:Morning-Glory Hotspring.jpg|thumb|right|Archaea were initially viewed as extremophiles living in harsh environments, such as the yellow archaea pictured here in a hot spring, but they have since been found in a much broader range of habitats.<ref name=Bang2015>{{cite journal |vauthors=Bang C, Schmitz RA |title=Archaea associated with human surfaces: not to be underestimated |journal=FEMS Microbiology Reviews |volume= 39|issue= 5|pages= 631–48|date=2015 |pmid=25907112 |doi=10.1093/femsre/fuv010}}</ref>]]

The [[Biology:Archaea|archaea]] (Greek for ''ancient''<ref>[http://www.etymonline.com/index.php?l=a&p=41 Archaea] ''Online Etymology Dictionary''. Retrieved 17 August 2016.</ref>) constitute a domain and [[Biology:Kingdom|kingdom]] of [[Biology:Unicellular organism|single-celled]] [[Biology:Microorganism|microorganism]]s. These microbes are prokaryotes, meaning they have no [[Biology:Cell nucleus|cell nucleus]] or any other membrane-bound [[Biology:Organelle|organelle]]s in their cells.

Archaea were initially classified as [[Biology:Bacteria|bacteria]], but this classification is outdated.<ref>{{cite journal |author=Pace NR |title=Time for a change |journal=Nature |volume=441 |issue=7091 |page=289 |date=May 2006 |pmid=16710401 |doi=10.1038/441289a|bibcode = 2006Natur.441..289P}}</ref> Archaeal cells have unique properties separating them from the other two domains of life, [[Biology:Bacteria|Bacteria]] and Eukaryota. The Archaea are further divided into multiple recognized [[Biology:Phylum|phyla]]. Classification is difficult because the majority have not been isolated in the laboratory and have only been detected by analysis of their [[Biology:Nucleic acid|nucleic acid]]s in samples from their environment.

Archaea and bacteria are generally similar in size and shape, although a few archaea have very strange shapes, such as the flat and square-shaped cells of ''[[Biology:Haloquadratum|Haloquadratum walsbyi]]''.<ref>{{cite journal |author=Stoeckenius W |title=Walsby's square bacterium: fine structure of an orthogonal procaryote |journal=Journal of Bacteriology |volume=148 |issue=1 |pages=352–60 |date=1 October 1981|pmid=7287626 |url=http://jb.asm.org/content/148/1/352.long |pmc=216199}}</ref> Despite this morphological similarity to bacteria, archaea possess [[Biology:Gene|gene]]s and several [[Biology:Metabolic pathway|metabolic pathway]]s that are more closely related to those of eukaryotes, notably the [[Biology:Enzyme|enzyme]]s involved in transcription and [[Biology:Translation|translation]]. Other aspects of archaeal biochemistry are unique, such as their reliance on [[Chemistry:Ether lipid|ether lipid]]s in their [[Biology:Cell membrane|cell membrane]]s, such as [[Chemistry:Archaeol|archaeol]]s. Archaea use more energy sources than eukaryotes: these range from organic compounds, such as sugars, to [[Chemistry:Ammonia|ammonia]], [[Physics:Ion|metal ions]] or even [[Chemistry:Hydrogen|hydrogen gas]]. Salt-tolerant archaea (the [[Biology:Haloarchaea|Haloarchaea]]) use sunlight as an energy source, and other species of archaea [[Earth:Carbon fixation|fix carbon]]; however, unlike plants and [[Biology:Cyanobacteria|cyanobacteria]], no known species of archaea does both. Archaea reproduce asexually by [[Binary fission|binary fission]], [[Medicine:Fragmentation (reproduction)|fragmentation]], or [[Biology:Budding|budding]]; unlike bacteria and eukaryotes, no known species forms [[Biology:Spore|spore]]s.

Archaea are particularly numerous in the oceans, and the archaea in [[Earth:Plankton|plankton]] may be one of the most abundant groups of organisms on the planet. Archaea are a major part of Earth's life and may play roles in both the [[Earth:Carbon cycle|carbon cycle]] and the [[Biology:Nitrogen cycle|nitrogen cycle]].

<gallery mode=packed heights=150px style=float:left;>
File:Halobacteria with scale.jpg|Halobacteria, found in water near saturated with salt, are now recognised as archaea.
File:Haloquadratum walsbyi00.jpg|Flat, square-shaped cells of the archaea ''[[Biology:Haloquadratum|Haloquadratum walsbyi]]''
File:Methanosarcina barkeri fusaro.gif|''[[Biology:Methanosarcina|Methanosarcina barkeri]]'', a marine archaea that produces [[Chemistry:Methane|methane]]
File:Thermophile bacteria2.jpg| [[Earth:Thermophile|Thermophile]]s, such as ''[[Biology:Pyrolobus fumarii|Pyrolobus fumarii]]'', survive well over 100&nbsp;°C
File:Pyrococcus furiosus.png| Drawing of another marine thermophile, ''[[Biology:Pyrococcus furiosus|Pyrococcus furiosus]]''
</gallery>

{{clear}}

==Eukaryotes==
[[File:Parakaryon myojinensis drawing.svg|thumb| ''Parakaryon myojinensis'', a possible transitional form between a prokaryote and a eukaryote]]

All living organisms can be grouped as either [[Biology:Prokaryote|prokaryote]]s or [[Biology:Eukaryote|eukaryote]]s. Life originated as [[Biology:Unicellular organism|single-celled]] prokaryotes and later evolved into the more complex eukaryotes. In contrast to prokaryotic cells, eukaryotic cells are highly organised. Prokaryotes are the bacteria and archaea, while eukaryotes are the other life forms — [[Biology:Protist|protist]]s, plants, fungi and animals. Protists are usually single-celled, while plants, fungi and animals are usually [[Biology:Multicellular organism|multi-celled]].

A possible transitional form of microorganism between a prokaryote and a eukaryote was discovered in 2012 by Japanese scientists. ''[[Biology:Parakaryon myojinensis|Parakaryon myojinensis]]'' is a unique microorganism larger than a typical prokaryote, but with nuclear material enclosed in a membrane as in a eukaryote, and the presence of [[Biology:Endosymbiont|endosymbiont]]s. This is seen to be the first plausible evolutionary form of microorganism, showing a stage of development from the prokaryote to the eukaryote.<ref name="Parakaryon">{{cite web |title=Deep sea microorganisms and the origin of the eukaryotic cell |url=http://protistology.jp/journal/jjp47/JJP47YAMAGUCHI.pdf |accessdate=24 October 2017}}</ref><ref name="Yamaguchi">{{cite journal|last1=Yamaguchi |display-authors=et al|first1=Masashi |title=Prokaryote or eukaryote? A unique microorganism from the deep sea |issue=6 |journal=Journal of Electron Microscopy |volume=61 |pages=423–431 |doi=10.1093/jmicro/dfs062 |pmid=23024290 |date=1 December 2012}}</ref>
 
===Marine protists===

[[Biology:Protist|Protist]]s are eukaryotes that cannot be classified as plants, fungi or animals. They are usually single-celled and microscopic. Life originated as [[Biology:Prokaryote|single-celled prokaryotes]] (bacteria and archaea) and later evolved into [[Biology:Eukaryote|more complex eukaryotes]]. Eukaryotes are the more developed life forms known as plants, animals, fungi and protists. The term protist came into use historically as a term of convenience for eukaryotes that cannot be strictly classified as plants, animals or fungi. They are not a part of modern cladistics, because they are paraphyletic (lacking a common ancestor). 

====By trophic mode====
Protists can be broadly divided into four groups depending on whether their nutrition is plant-like, animal-like, fungal-like,<ref>Whittaker, R.H. and Margulis, L. (1978) "Protist classification and the kingdoms of organisms". ''Biosystems'', '''10'''(1–2): 3–18. {{doi|10.1016/0303-2647(78)90023-0}}</ref> or a mixture of these.<ref>Faure E, Not F, Benoiston AS, Labadie K, Bittner L and Ayata SD (2019) "Mixotrophic protists display contrasted biogeographies in the global ocean". ''ISME Journal'', '''13'''(4): 1072–1083. {{doi|10.1038/s41396-018-0340-5}}</ref>

{|class="wikitable"
! colspan=8 |{{centre|Protists according to how they get food}}
|-
! colspan=2 |Type of protist
! Description
! colspan=2 | Example
! Some other examples
|-
! width=90px | Plant-like
| width=90px | {{center|[[Biology:Algae|Algae]]<br />(see below)}}
| [[Biology:Autotroph|Autotroph]]ic protists that make their own food without needing to consume other organisms, usually by using photosynthesis
| [[File:Pyramimonas sp.jpg|100px]]
| Green algae, ''[[Biology:Pyramimonas|Pyramimonas]]''
| [[Biology:Red algae|Red]] and [[Biology:Brown algae|brown algae]], [[Biology:Diatom|diatom]]s and some [[Biology:Dinoflagellate|dinoflagellate]]s. Plant-like protists are important components of phytoplankton discussed below.
|-
! Animal-like
| {{center|Protozoans}}
| [[Biology:Heterotroph|Heterotroph]]ic protists that get their food consuming other organisms (bacteria, archaea and small algae) 
| [[File:Haeckel Spumellaria detail.png|100px]]
| Radiolarian protist as drawn by [[Biography:Ernst Haeckel|Haeckel]]
| Foraminiferans, and some marine amoebae, ciliates and [[Biology:Flagellate|flagellate]]s.
|-
! Fungal-like
| {{center|Slime moulds<br />and<br />slime nets}}
| Saprotrophic protists that get their food from the remains of organisms that have broken down and decayed 
| [[File:Aplanonet3.jpg|100px]]
| Marine slime nets form labyrinthine networks of tubes in which amoeba without pseudopods can travel
| Marine lichen
|-
! Mixotropes 
| {{center|Various}}
| Mixotrophic and osmotrophic protists that get their food from a combination of the above 
| [[File:Euglena mutabilis - 400x - 1 (10388739803) (cropped).jpg|100px]]
| ''[[Biology:Euglena|Euglena mutabilis]]'', a photosynthetic [[Biology:Flagellate|flagellate]]
| Many marine mixotropes are found among protists, including among ciliates, [[Biology:Rhizaria|Rhizaria]] and dinoflagellates<ref name="Leles2017" />
|-
|}

{{multiple image
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 | footer            = [[Biology:Choanoflagellate|Choanoflagellate]]s, unicellular "collared" [[Biology:Flagellate|flagellate]] protists, are thought to be the closest living relatives of the [[Biology:Animal|animal]]s.<ref name="Budd2015">{{cite journal |doi=10.1111/brv.12239 |pmid=26588818 |title=The origin of the animals and a 'Savannah' hypothesis for early bilaterian evolution |journal=Biological Reviews |volume=92 |issue=1 |pages=446–473 |year=2017 |last1=Budd |first1=Graham E |last2=Jensen |first2=Sören}}</ref>
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 | caption2  = {{center|cell schematic}}
}}

Protists are highly diverse organisms currently organised into 18 phyla, but are not easy to classify.<ref>{{Cite journal|author=Cavalier-Smith T |title=Kingdom protozoa and its 18 phyla |journal=Microbiological Reviews |volume=57 |issue=4 |pages=953–94 |date=December 1993 |pmid=8302218 |url=http://mmbr.asm.org/cgi/pmidlookup?view=long&pmid=8302218 |pmc=372943}}</ref><ref>{{Cite journal|author=Corliss JO |title=Should there be a separate code of nomenclature for the protists? |journal=BioSystems |volume=28 |issue=1–3 |pages=1–14 |year=1992 |pmid=1292654 | doi=10.1016/0303-2647(92)90003-H}}</ref> Studies have shown high protist diversity exists in oceans, deep sea-vents and river sediments, suggesting a large number of eukaryotic microbial communities have yet to be discovered.<ref>{{Cite journal|vauthors=Slapeta J, Moreira D, López-García P |title=The extent of protist diversity: insights from molecular ecology of freshwater eukaryotes |journal=Proceedings of the Royal Society B: Biological Sciences |volume=272 |issue=1576 |pages=2073–81 |year=2005 |pmid=16191619 |doi=10.1098/rspb.2005.3195 |pmc=1559898}}</ref><ref>{{Cite journal|vauthors=Moreira D, López-García P |title=The molecular ecology of microbial eukaryotes unveils a hidden world |journal=Trends in Microbiology |volume=10 |issue=1 |pages=31–8 |year=2002 |pmid=11755083 | url=http://download.bioon.com.cn/view/upload/month_0803/20080326_daa08a6fdb5d38e3a0d8VBrocN3WtOdR.attach.pdf | doi=10.1016/S0966-842X(01)02257-0}}</ref> There has been little research on mixotrophic protists, but recent studies in marine environments found mixotrophic protests contribute a significant part of the protist [[Earth:Biomass (ecology)|biomass]].<ref name="Leles2017">Leles, S.G., Mitra, A., Flynn, K.J., Stoecker, D.K., Hansen, P.J., Calbet, A., McManus, G.B., Sanders, R.W., Caron, D.A., Not, F. and Hallegraeff, G.M. (2017) "Oceanic protists with different forms of acquired phototrophy display contrasting biogeographies and abundance". ''Proceedings of the Royal Society B: Biological Sciences'', '''284'''(1860):20170664. {{doi|10.1098/rspb.2017.0664}}</ref> 

<gallery caption="Single-celled and microscopic protists" mode=packed heights=130px style=float:left;>
File:Diatoms through the microscope.jpg| [[Biology:Diatom|Diatom]]s are a major algae group generating about 20% of world oxygen production.<ref>[https://www.livescience.com/46250-teasing-apart-the-diatom-genome.html The Air You're Breathing? A Diatom Made That]</ref>
File:Diatom algae Amphora sp.jpg| Diatoms have glass like cell walls made of [[Chemistry:Silica|silica]] and called [[Biology:Frustule|frustule]]s.<ref>{{cite web | title=More on Diatoms | website=University of California Museum of Paleontology | url = http://www.ucmp.berkeley.edu/chromista/diatoms/diatommm.html}}</ref>
File:Triceratium morlandii var. morlandii.jpg|Fossil diatom frustule from 32-40 [[Physics:Mya (unit)|mya]]
File:Podocyrtis papalis Ehrenberg - Radiolarian (30448963206).jpg| Radiolarian
File:Gephyrocapsa oceanica color (lightened).jpg| Single-celled alga, ''Gephyrocapsa oceanica''
File:CSIRO ScienceImage 7609 SEM dinoflagellate.jpg| Two [[Biology:Dinoflagellate|dinoflagellate]]s
File:Zooxanthellae.jpg| [[Biology:Zooxanthellae|Zooxanthellae]] is a photosynthetic algae that lives inside hosts like [[Biology:Coral|coral]]
File:Paramecium bursaria.jpg| A single-celled ciliate with green zoochlorellae living inside endosymbiotically
File:Euglenoid movement.jpg| Euglenoid
File:The ciliate Frontonia sp.jpg| This ciliate is digesting [[Biology:Cyanobacteria|cyanobacteria]]. The [[Biology:Cytostome|cytostome]] or mouth is at the bottom right.
</gallery>
{{clear}}
[[File:Frontonia ingesting a diatom.ogg|thumb| Video of a ciliate ingesting a diatom]]

In contrast to the cells of prokaryotes, the cells of eukaryotes are highly organised. Plants, animals and fungi are usually [[Biology:Multicellular organism|multi-celled]] and are typically [[Physics:Macroscopic|macroscopic]]. Most protists are single-celled and microscopic. But there are exceptions. Some single-celled marine protists are macroscopic. Some marine slime molds have unique life cycles that involve switching between unicellular, [[Biology:Colony|colonial]], and multicellular forms.<ref>{{Cite journal|author=Devreotes P |title=Dictyostelium discoideum: a model system for cell-cell interactions in development |journal=Science |volume=245 |issue=4922 |pages=1054–8 |year=1989 |pmid=2672337 | doi=10.1126/science.2672337|bibcode=1989Sci...245.1054D}}</ref> Other marine protist are neither single-celled nor microscopic, such as [[Biology:Seaweed|seaweed]]. 

{{anchor|Macroscopic protists}}
<gallery caption="Macroscopic protists (see also unicellular macroalgae&nbsp;→&nbsp;)" mode=packed heights=130px style=float:left;>
File:Chaos carolinensis Wilson 1900.jpg| The single-celled ''giant amoeba'' has up to 1000 [[Biology:Cell nucleus|nuclei]] and reaches lengths of 5&nbsp;mm
File:Gromia in situ closeup.png| ''[[Biology:Gromia sphaerica|Gromia sphaerica]]'' is a large spherical testate amoeba which makes mud trails. Its diameter is up to 3.8 cm.<ref name="Matz2008">{{cite journal| last = Matz | first = Mikhail V. |  author2 = Tamara M. Frank | author3 = N. Justin Marshall | author4 = Edith A. Widder | author5 = Sonke Johnsen | title = Giant Deep-Sea Protist Produces Bilaterian-like Traces | journal = Current Biology | volume = 18| issue = 23 | pages = 1849–1854 | publisher = Elsevier Ltd | date = 2008-12-09 | url = http://www.biology.duke.edu/johnsenlab/pdfs/pubs/sea%20grapes%202008.pdf | doi = 10.1016/j.cub.2008.10.028 | accessdate = | pmid = 19026540}}</ref>
File:Spiculosiphon oceana AB.png| ''[[Biology:Spiculosiphon oceana|Spiculosiphon oceana]]'', a unicellular foraminiferan with an appearance and lifestyle that mimics a [[Biology:Sponge|sponge]], grows to 5 cm long.
File:Xenophyophore.jpg| The [[Biology:Xenophyophore|xenophyophore]], another single-celled foraminiferan, lives in [[Earth:Abyssal zone|abyssal zone]]s. It has a giant shell up to 20&nbsp;cm across.<ref>{{Cite journal|last=Gooday|first=A. J.|last2=Aranda da Silva|first2=A.|last3=Pawlowski|first3=J.|date=2011-12-01|title=Xenophyophores (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)|journal=Deep-Sea Research Part II: Topical Studies in Oceanography|series=The Geology, Geochemistry, and Biology of Submarine Canyons West of Portugal|volume=58|issue=23–24|pages=2401–2419|doi=10.1016/j.dsr2.2011.04.005|bibcode=2011DSRII..58.2401G}}</ref> 
File:Giant Kelp.jpg| Giant kelp, a [[Biology:Brown algae|brown algae]], is not a true plant, yet it is multicellular and can grow to 50m 
</gallery>
{{clear}}

Protists have been described as a taxonomic grab bag where anything that doesn't fit into one of the main [[Biology:Kingdom|biological kingdoms]] can be placed.<ref>Neil A C, Reece J B, Simon E J (2004) [https://books.google.com/books?id=lRhFAQAAIAAJ&q=protists+%22taxonomic+grab+bag%22&dq=protists+%22taxonomic+grab+bag%22&hl=en&sa=X&ved=0ahUKEwiKnMmIkrTkAhWe7HMBHTI-A-sQ6AEIMzAB ''Essential biology with physiology''] Pearson/Benjamin Cummings, Page 291. {{ISBN|9780805375039}}</ref> Some modern authors prefer to exclude multicellular organisms from the traditional definition of a protist, restricting protists to unicellular organisms.<ref name="O'Malley">{{Cite journal | doi = 10.1007/s10539-012-9354-y| title = The other eukaryotes in light of evolutionary protistology| journal = Biology & Philosophy| volume = 28| issue = 2| pages = 299–330| year = 2012| vauthors = O'Malley MA, Simpson AG, Roger AJ}}</ref><ref name="Adl 05">{{cite journal | vauthors = Adl SM, Simpson AG, Farmer MA, Andersen RA, Anderson OR, Barta JR, Bowser SS, Brugerolle G, Fensome RA, Fredericq S, James TY, Karpov S, Kugrens P, Krug J, Lane CE, Lewis LA, Lodge J, Lynn DH, Mann DG, McCourt RM, Mendoza L, Moestrup O, Mozley-Standridge SE, Nerad TA, Shearer CA, Smirnov AV, Spiegel FW, Taylor MF | title = The new higher level classification of eukaryotes with emphasis on the taxonomy of protists | journal = The Journal of Eukaryotic Microbiology | volume = 52 | issue = 5 | pages = 399–451 | year = 2005 | pmid = 16248873 | doi = 10.1111/j.1550-7408.2005.00053.x| url = https://semanticscholar.org/paper/a283651b716e32dfe1c51189317f41daf93110a7 }}</ref> This more constrained definition excludes many [[Biology:Brown algae|brown]], multicellular [[Biology:Red algae|red]] and [[Biology:Green algae|green algae]], and [[Biology:Slime mold|slime mold]]s.<ref>{{Cite book | url = https://books.google.com/books?id=9IWaqAOGyt4C | title = Kingdoms and Domains: An Illustrated Guide to the Phyla of Life on Earth | last = Margulis | first = Lynn | last2 = Chapman | first2 = Michael J. | name-list-format = vanc | date = 2009-03-19 | publisher = Academic Press | isbn = 9780080920146}}</ref>

====By locomotion====
Another way of categorising protists is according to their mode of locomotion. Many unicellular protists, particularly protozoans, are motile and can [[Biology:Aquatic locomotion#Micro-organisms|generate movement]] using flagella, cilia or pseudopods. Cells which use flagella for movement are usually referred to as [[Biology:Flagellate|flagellate]]s, cells which use cilia are usually referred to as ciliates, and cells which use pseudopods are usually referred to as [[Biology:Amoeba|amoeba]] or amoeboids. Other protists are [[Biology:Sessility (motility)|not motile]], and consequently have no movement mechanism.

{|class="wikitable"
! colspan=9 | {{centre|Protists according to their motility}}
|-
! colspan=2 | Type of protist
! style="background:rgb(255,255,255)"| Movement mechanism
! width=30% | Description
! colspan=2 | Example
! width=30% | Other examples
|-
! rowspan=3 style="background:rgb(110,110,170)" |[[Biology:Motility|<span style="color:white;">Motile</span>]]
! width=90px | [[Biology:Flagellate|Flagellate]]s
| style="background:rgb(255,255,255)"| [[File:Locomotion by flagellum.jpg|120px|]]
| A [[Biology:Flagellum|flagellum]] (Latin for ''whip'') is a lash-like appendage that protrudes from the cell body of some protists (as well as some bacteria). Flagellates use from one to several flagella for locomotion and sometimes as feeding and sensory [[Biology:Organelle|organelle]].
| [[File:CSIRO ScienceImage 6743 SEM Cryptophyte.jpg|100px]]
| Cryptophytes
| All [[Biology:Dinoflagellate|dinoflagellate]]s and nanoflagellates ([[Biology:Choanoflagellate|choanoflagellate]]s, silicoflagellates, most [[Biology:Green algae|green algae]]) <ref name=Dawson2013>{{cite journal|last1=Dawson|first1=Scott C|last2=Paredez|first2=Alexander R|title=Alternative cytoskeletal landscapes: cytoskeletal novelty and evolution in basal excavate protists|journal=Current Opinion in Cell Biology|year=2013|volume=25|issue=1|pages=134–141|doi=10.1016/j.ceb.2012.11.005|pmid=23312067|pmc=4927265}}</ref><ref name=Atkinson2018 /><br />{{center|<small>(Other protists go through a phase as [[Biology:Gamete|gamete]]s when they have temporary flagellum – some radiolarians, foraminiferans and [[Biology:Apicomplexa|Apicomplexa]])</small>}}
|-
! Ciliates
| style="background:rgb(255,255,255)"| [[File:Locomotion by cilia.jpg|120px]]
| A [[Biology:Cilium|cilium]] (Latin for ''eyelash'') is a tiny flagellum. Ciliates use multiple cilia, which can number in many hundreds, to power themselves through the water.
| [[File:Stichotricha secunda - 400x (14974779356).jpg|100px]]
| ''[[Biology:Paramecium bursaria|Paramecium bursaria]]''<br /><small>click to see cillia</small>
| Foraminiferans, and some marine amoebae, ciliates and [[Biology:Flagellate|flagellate]]s.
|-
! [[Biology:Amoeba|Amoeba]]s<br /><small>(amoeboids)</small>
| style="background:rgb(255,255,255)"| [[File:Locomotion by pseudopod.jpg|120px]]
| [[Biology:Amoeba|Amoeba]] have the ability to alter shape by extending and retracting [[Biology:Pseudopodia|pseudopods]] (Greek for ''false feet'').<ref>{{Cite book|title = Dictionary of Microbiology and Molecular Biology, 3rd Edition, revised|last = Singleton|first = Paul|publisher = John Wiley & Sons|year = 2006|isbn = 978-0-470-03545-0 |location = Chichester, UK|pages = 32}}</ref> 
| [[File:Amoeba proteus from Leidy.jpg|center|70px]]
| ''[[Biology:Amoeba|Amoeba]]''
| Found in every major protist [[Biology:Lineage (evolution)|lineage]]. Amoeboid cells occur among the protozoans, but also in the [[Biology:Algae|algae]] and the [[Biology:Fungi|fungi]].<ref>{{cite web|url=http://tolweb.org/notes/?note_id=51|title=Amoebae: Protists Which Move and Feed Using Pseudopodia|author=David J. Patterson|publisher=Tree of Life web project}}</ref><ref>{{cite web|url=http://www.bms.ed.ac.uk/research/others/smaciver/amoebae.htm |title=The Amoebae |publisher=The University of Edinburgh |url-status=dead |archiveurl=https://web.archive.org/web/20090610035748/http://www.bms.ed.ac.uk/research/others/smaciver/amoebae.htm |archivedate=10 June 2009}}</ref>
|-
! colspan=2 style="background:rgb(150,80,150)" | [[Biology:Sessility (motility)|<span style="color:white;">Not motile</span>]]
| style="background:rgb(255,255,255)"| {{center|none}}
| 
| [[File:Diatom - Triceratium favus.jpg|center|70px]]
| [[Biology:Diatom|Diatom]]
| [[Biology:Diatom|Diatom]]s, [[Biology:Coccolithophore|coccolithophore]]s, and non‐motile species of ''[[Biology:Phaeocystis|Phaeocystis]]'' <ref name=Atkinson2018>Atkinson, A., Polimene, L., Fileman, E.S., Widdicombe, C.E., McEvoy, A.J., Smyth, T.J., Djeghri, N., Sailley, S.F. and Cornwell, L.E. (2018) "Comment. What drives plankton seasonality in a stratifying shelf sea? Some competing and complementary theories"] ''Limnology and Oceanography'', '''63'''(6): 2877–2884. {{doi|10.1002/lno.11036}}</ref> Among protozoans the parasitic [[Biology:Apicomplexa|Apicomplexa]] are non‐motile.
|}

[[Biology:Flagellate|Flagellate]]s include bacteria as well as protists. The rotary motor model used by bacteria uses the protons of an [[Biology:Electrochemical gradient|electrochemical gradient]] in order to move their flagella. [[Physics:Torque|Torque]] in the flagella of bacteria is created by particles that conduct protons around the base of the flagellum. The direction of rotation of the flagella in bacteria comes from the occupancy of the proton channels along the perimeter of the flagellar motor.<ref>{{cite journal |author = Brady, Richard M. |title= Torque and switching in the bacterial flagellar motor. An electrostatic model|journal= Biophysical Journal |volume= 64 |issue= 4| year = 1993 | pages = 961–973|bibcode = 1993BpJ....64..961B |doi = 10.1016/S0006-3495(93)81462-0 |pmid= 7684268|pmc= 1262414}}</ref>

Ciliates generally have hundreds to thousands of cilia that are densely packed together in arrays. During movement, an individual cilium deforms using a high-friction power stroke followed by a low-friction recovery stroke. Since there are multiple cilia packed together on an individual organism, they display collective behavior in a [[Metachronal rhythm|metachronal rhythm]]. This means the deformation of one cilium is in phase with the deformation of its neighbor, causing deformation waves that propagate along the surface of the organism. These propagating waves of cilia are what allow the organism to use the cilia in a coordinated manner to move. A typical example of a ciliated microorganism is the ''[[Biology:Paramecium|Paramecium]]'', a one-celled, ciliated protozoan covered by thousands of cilia. The cilia beating together allow the ''Paramecium'' to propel through the water at speeds of 500 micrometers per second.<ref>{{cite journal|last=Lauga|first=Eric|author2=Thomas R Powers|title=The hydrodynamics of swimming microorganisms|journal=Reports on Progress in Physics|date=25 August 2009|volume=72|issue=9}}</ref>

[[File:Amoeba engulfing diatom.ogv|thumb|Amoeba engulfing a diatom]]

<gallery caption="Flagellate, ciliates and amoeba" mode=packed heights=140px style=float:left;>
File:Flagellum base diagram-en.svg| Bacterial flagellum rotated by a [[Physics:Molecular motor|molecular motor]] at its base
File:PSM V61 D203 Salmon spermatozoa for artificial propagation.png|thumb|70px|Salmon spermatozoa
File:Инфузория туфелька поедает бактерии!.gif| [[Biology:Paramecium|Paramecium]] feeding on bacteria
File:Oxytricha trifallax.jpg| The ciliate ''[[Biology:Oxytricha trifallax|Oxytricha trifallax]]'' with cilia clearly visible
File:Collection Penard MHNG Specimen 05bis-1-1 Amoeba proteus.tif| Amoeba with ingested diatoms
</gallery>
{{clear}}

===Marine fungi===
[[File:Lichen rock.jpeg|thumb|right|Lichen on a rock in a marine splash zone. Lichens are mutualistic associations between a fungus and an alga or cyanobacterium.]]
[[File:Littoraria irrorata.jpg|thumb| A sea snail, ''Littoraria irrorata'', covered in lichen. This snail farms intertidal ascomycetous fungi]]

Over 1500 species of [[Biology:Fungi|fungi]] are known from marine environments.<ref>{{cite journal|last=Hyde|first=K.D. |author2=E.B.J. Jones |author3=E. Leaño |author4=S.B. Pointing |author5=A.D. Poonyth |author6=L.L.P. Vrijmoed|title=Role of fungi in marine ecosystems|journal=Biodiversity and Conservation|year=1998|volume=7|issue=9|pages=1147–1161|doi=10.1023/A:1008823515157}}</ref> These are parasitic on marine algae or animals, or are saprobes feeding on dead organic matter from algae, corals, protozoan cysts, sea grasses, and other substrata.<ref>Kirk, P.M., Cannon, P.F., Minter, D.W. and Stalpers, J. "Dictionary of the Fungi". Edn 10. CABI, 2008</ref> Spores of many species have special appendages which facilitate attachment to the substratum.<ref>{{cite journal|last=Hyde|first=K.D.|author2=E.B.J. Jones|title=Spore attachment in marine fungi|journal=Botanica Marina|year=1989|volume=32|issue=3|pages=205–218|doi=10.1515/botm.1989.32.3.205}}</ref> Marine fungi can also be found in [[Earth:Sea foam|sea foam]] and around hydrothermal areas of the ocean.<ref name=LeCalvez2009>{{cite journal | vauthors=Le Calvez T, Burgaud G, Mahé S, Barbier G, Vandenkoornhuyse P | title=Fungal diversity in deep-sea hydrothermal ecosystems | journal=Applied and Environmental Microbiology | volume=75 | issue=20 | pages=6415–21 | date=October 2009 | pmid=19633124 | pmc=2765129 | doi=10.1128/AEM.00653-09}}</ref> A diverse range of unusual secondary [[Biology:Metabolite|metabolite]]s is produced by marine fungi.<ref>{{cite journal|last=San-Martín|first=A. |author2=S. Orejanera |author3=C. Gallardo |author4=M. Silva |author5=J. Becerra |author6=R. Reinoso |author7=M.C. Chamy |author8=K. Vergara |author9=J. Rovirosa|title=Steroids from the marine fungus Geotrichum sp|journal=Journal of the Chilean Chemical Society|year=2008|volume=53|issue=1|pages=1377–1378}}</ref>

[[Earth:Mycoplankton|Mycoplankton]] are [[Biology:Saprotrophic nutrition|saprotropic]] members of the [[Earth:Plankton|plankton]] communities of [[Biology:Marine biology|marine]] and [[Earth:Limnology|freshwater]] [[Earth:Aquatic ecosystem|ecosystems]].<ref>Jones, E.B.G., Hyde, K.D., & Pang, K.-L., eds. (2014). ''[https://books.google.com/books?id=mXfnBQAAQBAJ Freshwater fungi: and fungal-like organisms]''. Berlin/Boston: De Gruyter.</ref><ref>{{cite book |year=2012 |editor1-last=Jones |editor1-first=E.B.G. |editor2-last=Pang |editor2-first=K.-L. |display-editors= |title=Marine Fungi, and Fungal-like Organisms |url=http://www.degruyter.com/view/product/177990 |type= |series=Marine and Freshwater Botany |edition= |location=Berlin, Boston |publisher=De Gruyter |publication-date=August 2012 |isbn=978-3-11-026406-7 |access-date=3 September 2015 |ref=jones2012 |doi=10.1515/9783110264067}}</ref> They are composed of filamentous free-living [[Biology:Fungus|fungi]] and yeasts associated with planktonic particles or [[Earth:Phytoplankton|phytoplankton]].<ref>{{Cite journal|title = Distribution and Diversity of Planktonic Fungi in the West Pacific Warm Pool|journal = PLOS ONE|volume = 9|issue = 7|pages = e101523|doi = 10.1371/journal.pone.0101523.s001|pmid = 24992154|pmc = 4081592|bibcode = 2014PLoSO...9j1523W|last1 = Wang|first1 = Xin|last2 = Singh|first2 = Purnima|last3 = Gao|first3 = Zheng|last4 = Zhang|first4 = Xiaobo|last5 = Johnson|first5 = Zackary I.|last6 = Wang|first6 = Guangyi|year = 2014}}</ref> Similar to [[Biology:Bacterioplankton|bacterioplankton]], these aquatic fungi play a significant role in [[Biology:Heterotroph|heterotroph]]ic [[Chemistry:Mineralization (soil science)|mineralization]] and nutrient cycling.<ref>{{cite book |last1=Wang |first1=G. |last2=Wang |first2=X. |last3=Liu |first3=X. |last4=Li |first4=Q. |editor-last=Raghukumar |editor-first=C. |title=Biology of marine fungi |location=Berlin, Heidelberg |publisher=Springer-Verlag |year=2012 |pages=71–88 |chapter=Diversity and biogeochemical function of planktonic fungi in the ocean |isbn=978-3-642-23341-8 |chapter-url=https://www.springer.com/us/book/9783642233418 |access-date=3 September 2015 |doi=10.1007/978-3-642-23342-5}}</ref> While mostly microscopic, some mycoplankton can be up to 20&nbsp;mm in diameter and over 50&nbsp;mm in length.<ref>{{Cite journal|title = Fungi and Macroaggregation in Deep-Sea Sediments|journal = Microbial Ecology|date = 2007-11-11|issn = 0095-3628|pages = 168–177|volume = 56|issue = 1|doi = 10.1007/s00248-007-9334-y|pmid = 17994287|first = Samir|last = Damare|first2 = Chandralata|last2 = Raghukumar}}</ref>

A typical milliliter of seawater contains about 10<sup>3</sup> to 10<sup>4</sup> fungal cells.<ref>{{Cite journal|title = Seaweed resistance to microbial attack: A targeted chemical defense against marine fungi|journal = Proceedings of the National Academy of Sciences|date = 2003-06-10|issn = 0027-8424|pmc = 165804|pmid = 12756301|pages = 6916–6921|volume = 100|issue = 12|doi = 10.1073/pnas.1131855100|first = Julia|last = Kubanek|first2 = Paul R.|last2 = Jensen|first3 = Paul A.|last3 = Keifer|first4 = M. Cameron|last4 = Sullards|first5 = Dwight O.|last5 = Collins|first6 = William|last6 = Fenical|bibcode = 2003PNAS..100.6916K}}</ref> This number is greater in coastal ecosystems and [[Earth:Estuary|estuaries]] due to nutritional runoff from terrestrial communities. A higher diversity of mycoplankton is found around coasts and in surface waters down to 1000 metres, with a [[Earth:Water column|vertical profile]] that depends on how abundant [[Earth:Phytoplankton|phytoplankton]] is.<ref name="HIdiversity">{{Cite journal|title = Molecular characterization of the spatial diversity and novel lineages of mycoplankton in Hawaiian coastal waters|journal = The ISME Journal|date = 2009-07-30|issn = 1751-7362|pages = 111–120|volume = 4|issue = 1|doi = 10.1038/ismej.2009.87|pmid = 19641535|first = Zheng|last = Gao|first2 = Zackary I.|last2 = Johnson|first3 = Guangyi|last3 = Wang}}</ref><ref>{{Cite journal|title = Identification of Habitat-Specific Biomes of Aquatic Fungal Communities Using a Comprehensive Nearly Full-Length 18S rRNA Dataset Enriched with Contextual Data|journal = PLoS ONE|date = 2015-07-30|pmc = 4520555|pmid = 26226014|pages = e0134377|volume = 10|issue = 7|doi = 10.1371/journal.pone.0134377|first = Katrin|last = Panzer|first2 = Pelin|last2 = Yilmaz|first3 = Michael|last3 = Weiß|first4 = Lothar|last4 = Reich|first5 = Michael|last5 = Richter|first6 = Jutta|last6 = Wiese|first7 = Rolf|last7 = Schmaljohann|first8 = Antje|last8 = Labes|first9 = Johannes F.|last9 = Imhoff|bibcode = 2015PLoSO..1034377P}}</ref> This profile changes between seasons due to changes in nutrient availability.<ref name=":3">Gutierrez, Marcelo H; Pantoja, Silvio; Quinones, Renato a and Gonzalez, Rodrigo R. First record of flamentous fungi in the coastal upwelling ecosystem off central Chile. ''Gayana (Concepc.)'' [online]. 2010, vol.74, n.1, pp. 66-73. {{ISSN|0717-6538}}.
</ref> Marine fungi survive in a constant oxygen deficient environment, and therefore depend on oxygen diffusion by [[Physics:Turbulence|turbulence]] and oxygen generated by [[Biology:Phototroph|photosynthetic organisms]].<ref name="Sridhar2009">{{Cite book|title = Plankton Dynamics of Indian Waters|last = Sridhar|first = K.R.|publisher = Pratiksha Publications|year = 2009|isbn = |location = Jaipur, India|pages = 133–148|chapter = 10. Aquatic fungi – Are they planktonic?}}</ref>

Marine fungi can be classified as:<ref name="Sridhar2009" />
* Lower fungi - adapted to marine habitats ([[Biology:Zoospore|zoosporic]] fungi, including mastigomycetes: oomycetes and [[Biology:Chytridiomycetes|chytridiomycetes]])
* Higher fungi - filamentous, modified to planktonic lifestyle ([[Biology:Hyphomycetes|hyphomycetes]], [[Biology:Ascomycota|ascomycetes]], [[Biology:Basidiomycota|basidiomycetes]]). Most mycoplankton species are higher fungi.<ref name="HIdiversity" />

[[Biology:Lichen|Lichen]]s are [[Biology:Mutualism|mutualistic]] associations between a fungus, usually an ascomycete, and an alga or a [[Biology:Cyanobacteria|cyanobacterium]]. Several lichens are found in marine environments.<ref>[http://ocean.otr.usm.edu/~w529014/index_files/Page2025.htm Species of Higher Marine Fungi] {{webarchive|url=https://web.archive.org/web/20130422084649/http://ocean.otr.usm.edu/~w529014/index_files/Page2025.htm |date=22 April 2013}} University of Mississippi. Retrieved 2012-02-05.</ref> Many more occur in the splash zone, where they occupy different vertical zones depending on how tolerant they are to submersion.<ref>[http://www.fungaldiversity.org/fdp/sfdp/FD_5_1-7.pdf Freshwater and marine lichen-forming fungi] Retrieved 2012-02-06.</ref> Some lichens live a long time; one species has been dated at 8,600 years.<ref>{{cite web |url=https://www.nps.gov/glac/learn/nature/lichens.htm |title=Lichens|publisher=National Park Service, US Department of the Interior, Government of the United States|date=22 May 2016|accessdate=4 April 2018}}</ref> However their lifespan is difficult to measure because what defines the same lichen is not precise.<ref name=ELNGDL>{{cite web|url=http://www.earthlife.net/lichens/growth.html|title=The Earth Life Web, Growth and Development in Lichens|publisher=earthlife.net}}</ref> Lichens grow by vegetatively breaking off a piece, which may or may not be defined as the same lichen, and two lichens of different ages can merge, raising the issue of whether it is the same lichen.<ref name=ELNGDL/>

The [[Biology:Sea snail|sea snail]] ''[[Biology:Littoraria irrorata|Littoraria irrorata]]'' damages plants of ''[[Biology:Spartina|Spartina]]'' in the sea marshes where it lives, which enables spores of intertidal ascomycetous fungi to colonise the plant. The snail then eats the fungal growth in preference to the grass itself.<ref>{{cite journal |author1=Silliman B. R. |author2=S. Y. Newell |lastauthoramp=yes |year=2003 |title=Fungal farming in a snail |journal=PNAS |volume=100 |issue= 26|pages=15643–15648 |doi=10.1073/pnas.2535227100 |pmid=14657360 |pmc=307621}}</ref>

According to fossil records, fungi date back to the late [[Earth:Proterozoic|Proterozoic]] era 900-570 million years ago. Fossil marine lichens 600 million years old have been discovered in China.<ref>{{cite journal |vauthors=Yuan X, Xiao S |lastauthoramp=yes |year=2005 |title=Lichen-Like Symbiosis 600 Million Years Ago |journal=Science |volume=308 |issue=5724 |pages=1017–1020 |doi=10.1126/science.1111347 |url= https://semanticscholar.org/paper/fbd0ac941f7263144e394cb201491c25b963e66b|pmid=15890881|bibcode=2005Sci...308.1017Y}}</ref> It has been hypothesized that mycoplankton evolved from terrestrial fungi, likely in the [[Earth:Paleozoic|Paleozoic]] era (390 million years ago).<ref>{{Cite book|title = Marine Fungi: and Fungal-like Organisms|url = https://books.google.com/books?id=RcF97cHppPsC|publisher = Walter de Gruyter|date = 2012-08-31|isbn = 9783110264067|first = E. B. Gareth|last = Jones|first2 = Ka-Lai|last2 = Pang}}</ref>

===Marine microanimals===

As juveniles, animals develop from microscopic stages, which can include [[Biology:Spore|spore]]s, [[Biology:Egg|egg]]s and [[Biology:Larva|larva]]e. At least one microscopic animal group, the [[Biology:Parasite|parasitic]] [[Biology:Cnidaria|cnidaria]]n [[Biology:Myxozoa|Myxozoa]], is unicellular in its adult form, and includes marine species. Other adult marine microanimals are multicellular. Microscopic adult [[Biology:Arthropod|arthropod]]s are more commonly found inland in freshwater, but there are marine species as well. Microscopic adult marine [[Biology:Crustacean|crustacean]]s include some [[Biology:Copepod|copepod]]s, [[Biology:Cladocera|cladocera]] and [[Biology:Tardigrade|tardigrade]]s (water bears). Some marine [[Biology:Nematode|nematode]]s and [[Biology:Rotifer|rotifer]]s are also too small to be recognised with the naked eye, as are many [[Biology:Loricifera|loricifera]], including the recently discovered [[Biology:Anaerobic organism|anaerobic]] species that spend their lives in an [[Earth:Anoxic waters|anoxic]] environment.<ref>{{cite journal |author=Janet Fang |date=6 April 2010 |title=Animals thrive without oxygen at sea bottom |journal=Nature |volume=464 |doi=10.1038/464825b |pmid=20376121 |pages=825 |issue=7290}}</ref><ref>{{cite web|url=http://www.sciencenews.org/view/generic/id/58154/description/Multicelled_animals_may_live_oxygen-free|title=Briny deep basin may be home to animals thriving without oxygen|work=Science News|date=2013-09-23}}</ref> Copepods contribute more to the secondary productivity and [[Physics:Carbon sink|carbon sink]] of the world oceans than any other group of organisms.

<gallery mode=packed heights=150px style=float:left; caption="Marine microanimals">
File:Copepod 2.jpg| Over 10,000 marine species are [[Biology:Copepod|copepod]]s, small, often microscopic [[Biology:Crustacean|crustacean]]s
File:Gastrotrich.jpg| Darkfield photo of a [[Biology:Gastrotrich|gastrotrich]], 0.06-3.0 mm long, a worm-like animal living between sediment particles
File:Pliciloricus enigmatus.jpg|Armoured ''[[Biology:Pliciloricus enigmaticus|Pliciloricus enigmaticus]]'', about 0.2 mm long, live in spaces between marine gravel
File:Squatinella sp. (Rädertierchen - Rotifera) - 160x (13402418244).jpg| [[Biology:Rotifer|Rotifer]]s, usually 0.1–0.5 mm long, may look like protists but are multicellular and belong to the Animalia 
File:SEM image of Milnesium tardigradum in active state - journal.pone.0045682.g001-2.png| [[Biology:Tardigrade|Tardigrade]]s (water bears), about 0.5 mm long, are among the most resilient animals known
</gallery>
{{clear}}

==Primary producers==
[[File:Seawifs global biosphere.jpg|400 px|thumb|right|Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation. Dark red and blue-green indicate regions of high photosynthetic activity in the ocean and on land, respectively.]]
{{main|Biology:Algae}}

[[Earth:Primary producer|Primary producer]]s are the [[Biology:Autotroph|autotroph]] organisms that make their own food instead of eating other organisms. This means primary producers become the starting point in the food chain for [[Biology:Heterotroph|heterotroph]] organisms that do eat other organisms. Some marine primary producers are specialised bacteria and archaea which are [[Biology:Chemotroph|chemotroph]]s, making their own food by gathering around hydrothermal vents and cold seeps and using [[Earth:Chemosynthesis|chemosynthesis]]. However most marine [[Earth:Primary production|primary production]] comes from organisms which use [[Earth:Photosynthesis|photosynthesis]] on the carbon dioxide dissolved in the water. This process uses energy from sunlight to convert water and [[Chemistry:Carbon dioxide|carbon dioxide]]<ref name=Campbell2008>{{cite book| ref = harv |last1=Campbell|first1=Neil A.|last2=Reece|first2=Jane B.|last3=Urry|first3=Lisa Andrea|last4=Cain|first4=Michael L.|last5=Wasserman |first5 =Steven Alexander | last6 = Minorsky | first6 =Peter V. | last7 = Jackson | first7 =Robert Bradley
|title=Biology|edition=8|year=2008|publisher=Pearson – Benjamin Cummings|location=San Francisco|isbn=978-0-321-54325-7}}</ref>{{rp|186–187}} into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells.<ref name=Campbell2008 />{{rp|1242}} Marine primary producers are important because they underpin almost all marine animal life by generating most of the [[Chemistry:Oxygen|oxygen]] and food that provide other organisms with the chemical energy they need to exist. 

The principal marine primary producers are [[Biology:Cyanobacteria|cyanobacteria]], [[Biology:Algae|algae]] and marine plants. The [[Chemistry:Oxygen|oxygen]] released as a by-product of photosynthesis is needed by [[Biology:Anaerobic organism|nearly]] all living things to carry out [[Biology:Cellular respiration|cellular respiration]]. In addition, primary producers are influential in the global [[Earth:Carbon cycle|carbon]] and [[Physics:Water cycle|water]] cycles. They stabilize coastal areas and can provide habitats for marine animals. The term [[Biology:Division|division]] has been traditionally used instead of [[Biology:Phylum|phylum]] when discussing primary producers, but the International Code of Nomenclature for algae, fungi, and plants now accepts both terms as equivalents.<ref name="ICN">{{Cite book |year=2012 |editor-last=McNeill |editor-first=J. |displayeditors=etal|title=International Code of Nomenclature for algae, fungi, and plants (Melbourne Code), Adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011 |edition=electronic |publisher=International Association for Plant Taxonomy |url=http://www.iapt-taxon.org/nomen/main.php?page=art3 |accessdate=2017-05-14}}</ref>

===Cyanobacteria===
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 | caption3  = {{center| NASA image of a large [[Biology:Algal bloom|bloom]] of ''[[Biology:Nodularia|Nodularia]]'' cyanobacteria swirling in the Baltic Sea <ref>[https://phys.org/news/2019-11-oxygen-ocean-disrupt-fundamental-biological.html Changes in oxygen concentrations in our ocean can disrupt fundamental biological cycles] ''Phys.org'', 25 November 2019.</ref>}}
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Cyanobacteria are a phylum (division) of bacteria which range from unicellular to [[Biology:Protein filament|filamentous]] and include [[Biology:Colony#Microbial colonies|colonial species]]. They are found almost everywhere on earth: in damp soil, in both freshwater and marine environments, and even on Antarctic rocks.<ref name="WalshSmith2011">{{cite book|editor-last1=Walsh|editor-first1=Patrick J.|editor-last2=Smith|editor-first2=Sharon|editor-last3=Fleming|editor-first3=Lora|editor-first4=Helena |editor-last4=Solo-Gabriele |editor-first5=William H.|editor-last5= Gerwick| name-list-format = vanc |title=Oceans and Human Health: Risks and Remedies from the Seas|chapter-url={{google books |plainurl=y |id=LMZPqW-PmFYC|page=271}}|date=2 September 2011|chapter=Cyanobacteria and cyanobacterial toxins|pp=271–296|publisher=Academic Press|isbn=978-0-08-087782-2}}</ref> In particular, some species occur as drifting cells floating in the ocean, and as such were amongst the first of the [[Earth:Phytoplankton|phytoplankton]].

The first primary producers that used photosynthesis were oceanic [[Biology:Cyanobacteria|cyanobacteria]] about 2.3&nbsp;billion years ago.<ref>{{Cite web|url= http://www.astrobio.net/news-exclusive/the-rise-of-oxygen/|title= The Rise of Oxygen - Astrobiology Magazine|website= Astrobiology Magazine|language= en-US|access-date= 2016-04-06}}</ref><ref>{{cite journal|last= Flannery|first= D. T.|author2= R.M. Walter|title= Archean tufted microbial mats and the Great Oxidation Event: new insights into an ancient problem|journal= Australian Journal of Earth Sciences|date= 2012|volume= 59|issue= 1|pages= 1–11|doi= 10.1080/08120099.2011.607849 |bibcode = 2012AuJES..59....1F|url= https://semanticscholar.org/paper/8e2fb3f5ab865aed8faceee53c45558724c13c6c}}</ref> The release of molecular [[Chemistry:Oxygen|oxygen]] by [[Biology:Cyanobacteria|cyanobacteria]] as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this led to the near-extinction of [[Biology:Anaerobic organism|oxygen-intolerant organisms]], a dramatic change which redirected the evolution of the major animal and plant species.<ref name=astrobiology>{{cite web |url=http://astrobiology.arc.nasa.gov/roadmap/g5.html |archiveurl=https://www.webcitation.org/664nY11q7?url=http://astrobiology.arc.nasa.gov/roadmap/g5.html |archivedate=11 March 2012 |title=Understand the evolutionary mechanisms and environmental limits of life |accessdate=13 July 2009 |last=Rothschild |first=Lynn |date=September 2003 |publisher=NASA}}</ref>

The tiny (0.6 µm) marine cyanobacterium ''[[Biology:Prochlorococcus|Prochlorococcus]]'', discovered in 1986, forms today an important part of the base of the ocean food chain and accounts for much of the photosynthesis of the open ocean<ref>{{cite journal | vauthors = Nadis S | title = The cells that rule the seas | journal = Scientific American | volume = 289 | issue = 6 | pages = 52–3 | date = December 2003 | pmid = 14631732 | doi = 10.1038/scientificamerican1203-52 | url = http://guowei.ccps.tp.edu.tw/nc/UploadDocument/255_02%20The%20Cells%20that%20Rules%20the%20Sea.pdf | bibcode = 2003SciAm.289f..52N | accessdate = 2 June 2019 | archive-url = https://web.archive.org/web/20140419222251/http://guowei.ccps.tp.edu.tw/nc/UploadDocument/255_02%20The%20Cells%20that%20Rules%20the%20Sea.pdf | archive-date = 19 April 2014 | url-status = dead}}</ref> and an estimated 20% of the oxygen in the Earth's atmosphere.<ref name="npr">{{cite web|url=https://www.npr.org/templates/story/story.php?storyId=91448837|title=The Most Important Microbe You've Never Heard Of|author=|date=|website=npr.org}}</ref> It is possibly the most plentiful genus on Earth: a single millilitre of surface seawater may contain 100,000 cells or more.<ref>{{Cite journal | last1 = Flombaum | first1 = P. | last2 = Gallegos | first2 = J. L. | last3 = Gordillo | first3 = R. A. | last4 = Rincon | first4 = J. | last5 = Zabala | first5 = L. L. | last6 = Jiao | first6 = N. | last7 = Karl | first7 = D. M. | last8 = Li | first8 = W. K. W. | last9 = Lomas | first9 = M. W. | doi = 10.1073/pnas.1307701110 | last10 = Veneziano | first10 = D. | last11 = Vera | first11 = C. S. | last12 = Vrugt | first12 = J. A. | last13 = Martiny | first13 = A. C. | title = Present and future global distributions of the marine Cyanobacteria Prochlorococcus and Synechococcus | journal = Proceedings of the National Academy of Sciences | volume = 110 | issue = 24 | pages = 9824–9829 | year = 2013 | pmid = 23703908| pmc = 3683724| bibcode = 2013PNAS..110.9824F}}</ref>

Originally, biologists thought [[Biology:Cyanobacteria|cyanobacteria]] was algae, and referred to it as "blue-green algae". The more recent view is that cyanobacteria is a bacteria, and hence is not even in the same [[Biology:Kingdom|Kingdom]] as algae. Most authorities exclude all prokaryotes, and hence cyanobacteria from the definition of algae.<ref name="IntroBot">{{cite book |last=Nabors |first=Murray W. |title=Introduction to Botany |year=2004 |publisher=Pearson Education, Inc |location=San Francisco, CA |isbn=978-0-8053-4416-5}}</ref><ref name="Allaby 92">{{cite encyclopedia |editor1-last=Allaby |editor1-first=M. |year=1992 |encyclopedia=The Concise Dictionary of Botany |publisher=Oxford University Press |location=Oxford |title=Algae}}</ref>
{{clear left}}

===Algae===
[[Biology:Algae|Algae]] is an informal term for a widespread and diverse group of photosynthetic protists which are not necessarily closely related and are thus polyphyletic. Marine algae can be divided into six groups: [[Biology:Green algae|green]], [[Biology:Red algae|red]] and [[Biology:Brown algae|brown algae]], euglenophytes, [[Biology:Dinoflagellate|dinoflagellate]]s and [[Biology:Diatom|diatom]]s.

Dinoflagellates and diatoms are important components of marine algae and have their own sections below. Euglenophytes are a phylum of unicellular flagellates with only a few marine members.

Not all algae are microscopic. Green, red and brown algae all have multicellular macroscopic forms that make up the familiar [[Biology:Seaweed|seaweed]]s. [[Biology:Green algae|Green algae]], an informal group, contains about 8,000 recognised species.<ref>{{cite journal | vauthors = Guiry MD | title = How many species of algae are there? | journal = Journal of Phycology | volume = 48 | issue = 5 | pages = 1057–63 | date = October 2012 | pmid = 27011267 | doi = 10.1111/j.1529-8817.2012.01222.x| url = https://semanticscholar.org/paper/27efb217aa66823b850686a2016c68cb69fdd584 }}</ref> Many species live most of their lives as single cells or are filamentous, while others form [[Biology:Colony|colonies]] made up from long chains of cells, or are highly differentiated macroscopic seaweeds. [[Biology:Red algae|Red algae]], a (disputed) phylum contains about 7,000 recognised species,<ref name="algaetaxo">{{Cite web|url=http://www.algaebase.org/browse/taxonomy/?id=97240|title=Algaebase|last=Guiry|first=M.D.|last2=Guiry|first2=G.M.|date=2016|website=www.algaebase.org|publisher=|access-date=November 20, 2016}}</ref> mostly multicellular and including many notable seaweeds.<ref name="algaetaxo" /><ref name="Thomas 02">{{cite book|title=Seaweeds|publisher=Life Series. [[Biology:Natural History Museum, London|Natural History Museum]], London|year=2002|isbn=978-0-565-09175-0|author=D. Thomas}}</ref> [[Biology:Brown algae|Brown algae]] form a [[Biology:Class|class]] containing about 2,000 recognised species,<ref>{{Cite book|url=https://books.google.com/books?id=s1P855ZWc0kC&pg=166|title=Algae : an introduction to phycology|last1=Hoek|first1=Christiaan|last2=den Hoeck|first2=Hoeck Van|last3=Mann|first3=David|last4=Jahns|first4=H.M.|date=1995|publisher=Cambridge University Press|isbn=9780521316873|oclc=443576944|page=166}}</ref> mostly multicellular and including many seaweeds such as [[Biology:Kelp|kelp]].
Unlike higher plants, algae lack roots, stems, or leaves. They can be classified by size as ''[[Biology:Microalgae|microalgae]]'' or ''macroalgae''.

[[Biology:Microalgae|Microalgae]] are the microscopic types of algae, not visible to the naked eye. They are mostly unicellular species which exist as individuals or in chains or groups, though some are multicellular. Microalgae are important components of the marine protists discussed above, as well as the phytoplankton discussed below. They are very [[Biology:Biodiversity|diverse]]. It has been estimated there are 200,000-800,000 species of which about 50,000 species have been described.<ref name = Flanders>Starckx, Senne (31 October 2012) [http://www.flanderstoday.eu/current-affairs/place-sun A place in the sun - Algae is the crop of the future, according to researchers in Geel] Flanders Today, Retrieved 8 December 2012</ref> Depending on the species, their sizes range from a few micrometers (µm) to a few hundred micrometers. They are specially adapted to an environment dominated by viscous forces.

<gallery mode=packed heights=130px style=float:left;>
File:Chlamydomonas globosa - 400x (13263097835).jpg|''Chlamydomonas globosa'', a unicellular green alga with two flagella just visible at bottom left
File:Инфузории Ophridium versatile.jpg| ''[[Biology:Chlorella vulgaris|Chlorella vulgaris]]'', a common green [[Biology:Microalgae|microalgae]], in endosymbiosis with a ciliate <ref>Duval, B. and Margulis, L. (1995) "The microbial community of ''Ophrydium versatile'' colonies: endosymbionts, residents, and tenants". ''Symbiosis'', '''18''':181–210. {{PMID|11539474}}</ref>
File:Centric diatom.jpg| Centric diatom
File:Dinoflagellates.jpg| Dinoflagellates
</gallery>
{{clear}}

Macroalgae are the larger, multicellular and more visible types of algae, commonly called [[Biology:Seaweed|seaweed]]s. Seaweeds usually grow in shallow coastal waters where they are anchored to the seafloor by a [[Biology:Holdfast|holdfast]]. Like microalgae, macroalgae (seaweeds) can be regarded as marine protists since they are not true plants. But they are not microorganisms, so they are not within the scope of this article. 

Unicellular organisms are usually microscopic, less than one tenth of a millimeter long. There are exceptions. Mermaid's wineglass, a genus of subtropical [[Biology:Green algae|green algae]], is single-celled but remarkably large and complex in form with a single large nucleus, making it a model organism for studying [[Biology:Cell biology|cell biology]].<ref>{{cite journal|last=Mandoli|first=DF|year=1998|title=Elaboration of Body Plan and Phase Change during Development of Acetabularia: How Is the Complex Architecture of a Giant Unicell Built?|journal=Annual Review of Plant Physiology and Plant Molecular Biology|volume=49|pages=173–198|pmid=15012232|doi=10.1146/annurev.arplant.49.1.173|url=https://semanticscholar.org/paper/8b5da31980927cc126fcbd52e38826121fa20bbe}}</ref> Another single-celled algae, ''[[Biology:Caulerpa taxifolia|Caulerpa taxifolia]]'', has the appearance of a vascular plant including "leaves" arranged neatly up stalks like a fern. Selective breeding in aquariums to produce hardier strains resulted in an accidental release into the Mediterranean where it has become an [[Earth:Invasive species|invasive species]] known colloquially as ''killer algae''.<ref>{{cite journal|author1=Pierre Madl |author2=Maricela Yip | title = Literature Review of Caulerpa taxifolia| journal = BUFUS-Info | volume = 19 | issue = 31 | year = 2004 | url = http://biophysics.sbg.ac.at/ct/caulerpa.htm |doi= |id= | accessdate=}}</ref>

==Marine microplankton==
[[File:Plankton collage.jpg|thumb|upright=1.1|right| Plankton are drifting or floating organisms that cannot swim against a current, and include organisms from most areas of life: bacteria, archaea, algae, protozoa and animals.|alt=Six relatively large variously-shaped organisms with dozens of small light-colored dots all against a dark background. Some of the organisms have antennae that are longer than their bodies.]]
[[File:Super Blooms.ogv|thumb|upright=1.1| Red, orange, yellow and green represent areas where algal blooms abound. Blue areas represent nutrient-poor zones where phytoplankton exist in lower concentrations.]]
{{further|Biology:Bacterioplankton|Biology:Ichthyoplankton|Earth:Mycoplankton}}

[[Earth:Plankton|Plankton]] (from Greek for ''wanderers'') are a diverse group of organisms that live in the [[Earth:Water column|water column]] of large bodies of water but cannot swim against a current. As a result, they wander or drift with the currents.<ref>{{cite book
| last = Lalli
| first = C.
|author2=Parsons, T.
 | year = 1993
| title = Biological Oceanography: An Introduction
| publisher = Butterworth-Heinemann
| isbn = 0-7506-3384-0}}</ref> Plankton are defined by their [[Biology:Ecological niche|ecological niche]], not by any [[Biology:Phylogenetics|phylogenetic]] or [[Biology:Taxonomy|taxonomic]] classification. They are a crucial source of food for many marine animals, from [[Biology:Forage fish|forage fish]] to [[Biology:Whale|whale]]s. Plankton can be divided into a plant-like component and an animal component.

===Phytoplankton===
[[Earth:Phytoplankton|Phytoplankton]] are the plant-like components of the plankton community ("phyto" comes from the Greek for ''plant''). They are autotrophic (self-feeding), meaning they generate their own food and do not need to consume other organisms.

Phytoplankton perform three crucial functions: they generate nearly half of the world atmospheric oxygen, they regulate ocean and atmospheric carbon dioxide levels, and they form the base of the marine [[Biology:Food web|food web]]. When conditions are right, [[Biology:Algal bloom|blooms]] of phytoplankton algae can occur in surface waters. Phytoplankton are r-strategists which grow rapidly and can double their population every day. The blooms can become toxic and deplete the water of oxygen. However, phytoplankton numbers are usually kept in check by the phytoplankton exhausting available nutrients and by grazing zooplankton.<ref name=Wassilieff2006>Wassilieff, Maggy (2006) [https://teara.govt.nz/en/plankton/page-1 "Plankton - Plant plankton"], ''Te Ara - the Encyclopedia of New Zealand''. Accessed: 2 November 2019.</ref>

Phytoplankton consist mainly of microscopic photosynthetic [[Biology:Eukaryote|eukaryote]]s which inhabit the upper sunlit layer in all oceans. They need sunlight so they can photosynthesize. Most phytoplankton are single-celled algae, but other phytoplankton are bacteria and some are [[Biology:Protist|protist]]s.<ref>Lindsey, R., Scott, M. and Simmon, R. (2010) [https://earthobservatory.nasa.gov/features/Phytoplankton "What are phytoplankton"]. ''NASA Earth Observatory''.</ref> Phytoplankton include cyanobacteria (above), [[Biology:Diatom|diatom]]s, various other types of [[Biology:Algae|algae]] (red, green, brown, and yellow-green), [[Biology:Dinoflagellate|dinoflagellate]]s, [[Biology:Euglenid|euglenoids]], coccolithophorids, cryptomonads, chlorophytes, [[Biology:Prasinophyte|prasinophyte]]s, and silicoflagellates. They form the base of the [[Earth:Primary production|primary production]] that drives the ocean [[Biology:Food web|food web]], and account for half of the current global primary production, more than the terrestrial forests.<ref>Field, C. B., Behrenfeld, M. J., Randerson, J. T., and Falwoski, P. G. (1998) [https://science.sciencemag.org/content/281/5374/237 "Primary production of the biosphere: Integrating terrestrial and oceanic components"]. ''Science'', '''281'''(5374): 237–240. {{doi|10.1126/science.281.5374.237}}</ref>

<gallery caption=Phytoplankton mode=packed heights=130px style=float:left;>
File:Phytoplankton Lake Chuzenji.jpg| Phytoplankton are the foundation of the ocean food chain
File:Phytopla.jpg|They come in many shapes and sizes.
File:Phytoplankton - the foundation of the oceanic food chain.jpg| [[Biology:Colony|Colonial]] phytoplankton
File:Prochlorococcus marinus 2.jpg| The cyanobacterium ''[[Biology:Prochlorococcus|Prochlorococcus]]'' accounts for much of the ocean's primary production
File:Cyanobacterial Scum.JPG|Green [[Biology:Cyanobacteria|cyanobacteria]] scum washed up on a rock in California
</gallery>
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====Diatoms====
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[[Biology:Diatom|Diatom]]s form a (disputed) phylum containing about 100,000 recognised species of mainly unicellular algae. Diatoms generate about 20 percent of the oxygen produced on the planet each year,<ref>[https://www.livescience.com/46250-teasing-apart-the-diatom-genome.html The Air You're Breathing? A Diatom Made That]</ref> take in over 6.7 billion metric tons of [[Chemistry:Silicon|silicon]] each year from the waters in which they live,<ref>Treguer, P.; Nelson, D. M.; Van Bennekom, A. J.; Demaster, D. J.; Leynaert, A.; Queguiner, B. (1995). "The Silica Balance in the World Ocean: A Reestimate". Science. 268 (5209): 375–9. Bibcode:1995Sci...268..375T. doi:10.1126/science.268.5209.375. {{PMID|17746543}}</ref> and contribute nearly half of the organic material found in the oceans. 

<gallery mode=packed heights=130px style=float:left;>
File:Diatoms (248 05) Various diatoms.jpg|[[Biology:Diatom|Diatom]]s are one of the most common types of phytoplankton
File:Diatom2.jpg| They come in many shapes
File:Diatom Helipelta metil.jpg| Their protective shells (frustles) are made of silicon
File:Diatom - Triceratium favus.jpg
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Diatoms are enclosed in protective silica (glass) shells called [[Biology:Frustule|frustule]]s. Each frustule is made from two interlocking parts covered with tiny holes through which the diatom exchanges nutrients and wastes.<ref name=Wassilieff2006/> The frustules of dead diatoms drift to the ocean floor where, over millions of years, they can build up as much as half a mile deep.<ref>{{Cite web|url=https://www.kcl.ac.uk/sspp/departments/geography/people/academic/drake/Research/The-Sahara-Megalakes-Project/Lake-Megachad.aspx|title=King's College London - Lake Megachad|website=www.kcl.ac.uk|language=en-GB|access-date=2018-05-05}}</ref>

<gallery mode=packed heights=130px style=float:left;>
File:Diatom algae Amphora sp.jpg| Silicified frustule of a pennate diatom with two overlapping halves
File:Fjouenne sbrmvr012w 20070924163039 small.jpg| ''Guinardia delicatula'', a diatom responsible for [[Biology:Algal bloom|algal bloom]]s in the North Sea and the English Channel <ref>Arsenieff, L., Simon, N., Rigaut-Jalabert, F., Le Gall, F., Chaffron, S., Corre, E., Com, E., Bigeard, E. and Baudoux, A.C. (2018) "First Viruses Infecting the Marine Diatom Guinardia delicatula". ''Frontiers in microbiology'', '''9''': 3235. {{doi|10.3389/fmicb.2018.03235}}</ref>
File:Ископаемая диатомовая водоросль.jpg| Fossil diatom
File:Pinnularia major.jpg| There are over 100,000 species of [[Biology:Diatom|diatom]]s which account for 50% of the ocean's primary production
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====Coccolithophores====
[[Biology:Coccolithophore|Coccolithophore]]s are minute unicellular photosynthetic protists with two flagella for locomotion. Most of them are protected by a shell covered with ornate circular plates or scales called [[Chemistry:Coccolith|coccolith]]s. The coccoliths are made from calcium carbonate. The term coccolithophore derives from the Greek for a ''seed carrying stone'', referring to their small size and the coccolith stones they carry. Under the right conditions they bloom, like other phytoplankton, and can turn the ocean milky white.<ref>Wassilieff, Maggy (2006) [https://teara.govt.nz/en/photograph/5130/a-coccolithophore "A coccolithophore"], ''Te Ara - the Encyclopedia of New Zealand''. Accessed: 2 November 2019.</ref>

{{multiple image
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File:Coccolithus pelagicus.jpg
File:JRYSEM-247-05-azurapl.jpg| {{center|Coccolithophores named after the BBC documentary series<br />''The Blue Planet''}}
File:Emiliania huxleyi coccolithophore (PLoS).png| The [[Biology:Coccolithophore|coccolithophore]] ''Emiliania huxleyi''
File:Cwall99 lg.jpg| [[Biology:Algae bloom|Algae bloom]] of ''Emiliania huxleyi'' off the southern coast of England
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====Redfield and f- ratios====
During the 1930s Alfred C. Redfield found similarities between the composition of elements in phytoplankton and the major dissolved nutrients in the deep ocean.<ref>{{cite book |last1=Redfield |first1=Alfred C. |year=1934 |chapter=On the Proportions of Organic Derivatives in Sea Water and their Relation to the Composition of Plankton |pages=176–92 |editor1-last=Johnstone |editor1-first=James |editor2-last=Daniel |editor2-first=Richard Jellicoe |title=James Johnstone Memorial Volume |location=Liverpool |publisher=University Press of Liverpool |oclc=13993674}}</ref> Redfield proposed that the ratio of carbon to nitrogen to phosphorus (106:16:1) in the ocean was controlled by the phytoplankton’s requirements, as phytoplankton subsequently release nitrogen and phosphorus as they remineralize. This ratio has become known as the [[Redfield ratio]], and is used as a fundamental principle in describing the [[Chemistry:Stoichiometry|stoichiometry]] of seawater and phytoplankton evolution.<ref name="Arrigo2005">{{cite journal |last1=Arrigo |first1=Kevin R. |title=Marine microorganisms and global nutrient cycles |journal=Nature |volume=437 |issue=7057 |pages=349–55 |year=2005 |pmid=16163345 |doi=10.1038/nature04159 |bibcode=2005Natur.437..349A}}</ref> 

However, the Redfield ratio is not a universal value and can change with things like geographical latitude.<ref>Martiny, A.C., Pham, C.T., Primeau, F.W., Vrugt, J.A., Moore, J.K., Levin, S.A. and Lomas, M.W. (2013) "Strong latitudinal patterns in the elemental ratios of marine plankton and organic matter". ''Nature Geoscience'', '''6'''(4): 279–283. {{doi|10.1038/ngeo1757}}</ref> Based on allocation of resources, phytoplankton can be classified into three different growth strategies: survivalist, bloomer and generalist. Survivalist phytoplankton has a high N:P ratio (>30) and contains an abundance of resource-acquisition machinery to sustain growth under scarce resources. Bloomer phytoplankton has a low N:P ratio (<10), contains a high proportion of growth machinery and is adapted to exponential growth. Generalist phytoplankton has similar N:P to the Redfield ratio and contain relatively equal resource-acquisition and growth machinery.<ref name="Arrigo2005"/>

The [[Earth:F-ratio|f-ratio]] is the fraction of total [[Earth:Primary production|primary production]] fuelled by [[Chemistry:Nitrate|nitrate]] (as opposed to that fuelled by other [[Chemistry:Nitrogen|nitrogen]] [[Chemistry:Chemical compound|compounds]] such as [[Chemistry:Ammonium|ammonium]]). The ratio was originally defined by Richard Eppley and Bruce Peterson in one of the first [[Academic publishing#Academic paper|papers]] estimating global oceanic production.<ref name=eppley>{{cite journal | doi=10.1038/282677a0 | last1=Eppley | first1=R.W. |last2=Peterson |first2=B.J. | year=1979 | title=Particulate organic matter flux and planktonic new production in the deep ocean | journal=Nature | volume=282 | pages=677–680 | issue=5740|bibcode = 1979Natur.282..677E }}</ref>

===Zooplankton===
[[Earth:Zooplankton|Zooplankton]] are the animal component of the planktonic community ("zoo" comes from the Greek for ''animal''). They are heterotrophic (other-feeding), meaning they cannot produce their own own food and must consume instead other plants or animals as food. In particular, this means they eat phytoplankton.

Zooplankton are generally larger than phytoplankton, mostly still microscopic but some can be seen with the naked eye. Many protozoans (single-celled protists that prey on other microscopic life) are zooplankton, including zooflagellates, [[Biology:Foraminifera|foraminifera]]ns, radiolarians, some [[Biology:Dinoflagellate|dinoflagellate]]s and marine microanimals. Macroscopic zooplankton (not covered further here) include pelagic cnidarians, ctenophores, [[Biology:Mollusc|mollusc]]s, [[Biology:Arthropod|arthropod]]s and [[Biology:Tunicate|tunicate]]s, as well as planktonic [[Biology:Chaetognatha|arrow worms]] and [[Biology:Polychaete|bristle worms]].

'''Microzooplankton: major grazers of the plankton...'''
<gallery mode=packed heights=144px style=float:left;>
File:Copepod 2 with eggs.jpg|[[Biology:Copepod|Copepod]]s eat phytoplankton. This one is carrying eggs.
File:Tintinnid ciliate Favella.jpg| [[Biology:Tintinnid|Tintinnid]] ciliate ''Favella''
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====Radiolarians====
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Radiolarians are unicellular predatory protists encased in elaborate globular shells usually made of silica and pierced with holes. Their name comes from the Latin for "radius". They catch prey by extending parts of their body through the holes. As with the silica frustules of diatoms, radiolarian shells can sink to the ocean floor when radiolarians die and become preserved as part of the ocean sediment. These remains, as microfossils, provide valuable information about past oceanic conditions.<ref name=Wassilieff2006b>Wassilieff, Maggy (2006) [http://www.TeAra.govt.nz/en/photograph/5138/radiolarian-fossils "Plankton - Animal plankton"], ''Te Ara - the Encyclopedia of New Zealand''. Accessed: 2 November 2019.</ref>

<gallery mode=packed heights=150px style=float:left;>
File:Mikrofoto.de-Radiolarien 6.jpg| Like diatoms, radiolarians come in many shapes
File:Theocotylissa ficus Ehrenberg - Radiolarian (34638920262).jpg| Also like diatoms, radiolarian shells are usually made of silicate
File:Acantharian radiolarian Xiphacantha (Haeckel).jpg| However acantharian radiolarians have shells made from [[Chemistry:Strontium sulfate|strontium sulfate]] crystals
File:Spherical radiolarian 2.jpg|thumb|Cutaway schematic diagram of a spherical radiolarian shell
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{{multiple image
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  | footer            = {{center|Computer simulations of [[Turing pattern]]s on a sphere<br />closely replicate some radiolarian shell patterns <ref>Varea, C., Aragon, J.L. and Barrio, R.A. (1999) "Turing patterns on a sphere". ''Physical Review E'', '''60'''(4): 4588. {{doi|10.1103/PhysRevE.60.4588}}</ref>}}
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====Foraminiferans====
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Like radiolarians, [[Biology:Foraminifera|foraminifera]]ns (''forams'' for short) are single-celled predatory protists, also protected with shells that have holes in them. Their name comes from the Latin for "hole bearers". Their shells, often called [[Biology:Test|tests]], are chambered (forams add more chambers as they grow). The shells are usually made of calcite, but are sometimes made of [[Medicine:Agglutination|agglutinated]] sediment particles or [[Biology:Chiton|chiton]], and (rarely) of silica. Most forams are benthic, but about 40 species are planktic.<ref name=Hemleben>{{cite book |first=C. |last=Hemleben |first2=O.R. |last2=Anderson |first3=M. |last3=Spindler |title=Modern Planktonic Foraminifera |url=https://books.google.com/books?id=NaHOmAEACAAJ |year=1989 |publisher=Springer-Verlag |isbn=978-3-540-96815-3}}</ref> They are widely researched with well established fossil records which allow scientists to infer a lot about past environments and climates.<ref name=Wassilieff2006b />

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<gallery mode=packed heights=144px style=float:left;>
File:EB1911 Foraminifera - Section of Rotalia beccarii.jpg| section showing chambers of a spiral foram
File:Live Ammonia tepida.jpg| Live ''[[Biology:Ammonia tepida|Ammonia tepida]]'' streaming granular ectoplasm for catching food
File:Planktic Foraminifera of the northern Gulf of Mexico.jpg| Group of planktonic forams
File:Nummulitids.jpg| Fossil [[Biology:Nummulite|nummulitid]] forams of various sizes from the [[Earth:Eocene|Eocene]]
File:All Gizah Pyramids.jpg| The Egyptian pyramids were constructed from limestone that contained [[Biology:Nummulite|nummulite]]s.<ref>[http://www.ucl.ac.uk/GeolSci/micropal/foram.html#histofstudy Foraminifera: History of Study], [[Organization:University College London|University College London]]. Retrieved: 18 November 2019.</ref>
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A number of forams are [[Biology:Mixotroph|mixotroph]]ic (see below). These have unicellular [[Biology:Algae|algae]] as [[Biology:Endosymbiont|endosymbiont]]s, from diverse lineages such as the [[Biology:Green algae|green algae]], [[Biology:Red algae|red algae]], [[Biology:Golden algae|golden algae]], [[Biology:Diatom|diatom]]s, and [[Biology:Dinoflagellate|dinoflagellate]]s.<ref name=Hemleben/> Mixotrophic foraminifers are particularly common in nutrient-poor oceanic waters.<ref>[https://books.google.no/books?id=QvvlBwAAQBAJ&pg=PA22&dq=%22The+symbiont-bearing+foraminifera+are+particularly+common+in+nutrient-poor+oceanic+waters%22&hl=no&sa=X&ved=0ahUKEwj24brB_sviAhXJ4KYKHfuvAB0Q6AEIKTAA#v=onepage&q=%22The%20symbiont-bearing%20foraminifera%20are%20particularly%20common%20in%20nutrient-poor%20oceanic%20waters%22&f=false Advances in Microbial Ecology, Volum 11]</ref> Some forams are [[Earth:Kleptoplasty|kleptoplastic]], retaining [[Biology:Chloroplast|chloroplast]]s from ingested algae to conduct [[Earth:Photosynthesis|photosynthesis]].<ref>{{Cite journal|title = Benthic Foraminifera of dysoxic sediments: chloroplast sequestration and functional morphology|year = 1999|last= Bernhard|first=J. M.|author2=Bowser, S.M.|journal = Earth-Science Reviews|volume = 46|issue = 1|pages = 149–165|doi = 10.1016/S0012-8252(99)00017-3|bibcode=1999ESRv...46..149B}}</ref>
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====Amoeba====
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File:Amoeba proteus 2.jpg| Naked amoeba showing food vacuoles and ingested diatom
File:Arcella sp.jpg| Shell or test of a testate amoeba, ''[[Biology:Arcella|Arcella]]'' sp.
File:Collection Penard MHNG Specimen 533-2-1 Pamphagus granulatus.tif| Xenogenic testate amoeba covered in diatoms (from [https://commons.wikimedia.org/wiki/Commons:P%C3%A9nard_project Penard's Amoeba Collection])
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[[File:Amoeba engulfing diatom.ogv|thumb|left|{{center|Amoeba engulfing a diatom}}]]
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====Ciliates====
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File:Faure FremietTspCamp.jpg| ''Tintinnopsis campanula''
File:Oxytricha chlorelligera - 400x (10403483023).jpg| ''[[Biology:Oxytricha|Oxytricha chlorelligera]]''
File:Stylonychia putrina - 160x - II (13215594964).jpg| ''[[Biology:Stylonychia|Stylonychia putrina]]''
File:Holophyra ovum - 400x (9836710085).jpg| ''Holophyra'' ovum
File:Mikrofoto.de-Blepharisma japonicum 15.jpg| ''[[Biology:Blepharisma japonicum|Blepharisma japonicum]]''
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File:Из жизни инфузорий.webm| Several taxa of ciliates interacting
File:Blepharisma americana.ogg| ''[[Chemistry:Blepharisma|Blepharisma americanum]]'' swimming in a drop of pond water with other microorganisms
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===Mixotrophs===
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A [[Biology:Mixotroph|mixotroph]] is an organism that can use a mix of different [[Biology:Primary nutritional groups|sources of energy and carbon]], instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. It is estimated that mixotrophs comprise more than half of all microscopic plankton.<ref>[https://www.irishexaminer.com/lifestyle/outdoors/richard-collins/beware-the-mixotrophs--they-can-destroy-entire-ecosystems-in-a-matter-of-hours-430358.html Beware the mixotrophs - they can destroy entire ecosystems 'in a matter of hours']</ref> There are two types of eukaryotic mixotrophs: those with their own [[Biology:Chloroplast|chloroplast]]s, and those with [[Biology:Endosymbiont|endosymbiont]]s—and others that acquire them through [[Earth:Kleptoplasty|kleptoplasty]] or by enslaving the entire phototrophic cell.<ref>[https://phys.org/news/2017-08-microscopic-body-snatchers-infest-oceans.html Microscopic body snatchers infest our oceans - Phys.org]</ref>

The distinction between plants and animals often breaks down in very small organisms. Possible combinations are [[Biology:Phototroph|photo-]] and [[Biology:Chemotroph|chemotroph]]y, [[Biology:Lithotroph|litho-]] and [[Biology:Organotroph|organotroph]]y, [[Biology:Autotroph|auto-]] and [[Biology:Heterotroph|heterotroph]]y or other combinations of these. Mixotrophs can be either [[Biology:Eukaryote|eukaryotic]] or [[Biology:Prokaryote|prokaryotic]].<ref name='Eiler'>{{cite journal |author= Eiler A |title= Evidence for the Ubiquity of Mixotrophic Bacteria in the Upper Ocean: Implications and Consequences |journal=Appl Environ Microbiol |volume=72 |issue=12 |pages= 7431–7|date=December 2006|pmid=17028233 |doi=10.1128/AEM.01559-06|pmc=1694265}}</ref> They can take advantage of different environmental conditions.<ref>{{cite journal |vauthors=Katechakis A, Stibor H |title=The mixotroph ''Ochromonas tuberculata'' may invade and suppress specialist phago- and phototroph plankton communities depending on nutrient conditions |journal= Oecologia|volume= 148 |issue= 4|pages=692–701 |date=July 2006|pmid=16568278 |doi= 10.1007/s00442-006-0413-4}}</ref>

Recent studies of marine microzooplankton found 30–45% of the ciliate abundance was mixotrophic, and up to 65% of the amoeboid, foram and radiolarian [[Earth:Biomass (ecology)|biomass]] was mixotrophic.<ref name="Leles2017" />

''[[Biology:Phaeocystis|Phaeocystis]]'' is an important algal genus found as part of the marine [[Earth:Phytoplankton|phytoplankton]] around the world. It has a [[Biology:Polymorphism|polymorphic]] life cycle, ranging from free-living cells to large colonies.<ref name=":0">{{Cite journal|title = Phaeocystis blooms in the global ocean and their controlling mechanisms: a review|journal = Journal of Sea Research|date = 2005-01-01|pages = 43–66|volume = 53|series = Iron Resources and Oceanic Nutrients - Advancement of Global Environmental Simulations|issue = 1–2|doi = 10.1016/j.seares.2004.01.008|first = Véronique|last = Schoemann|first2 = Sylvie|last2 = Becquevort|first3 = Jacqueline|last3 = Stefels|first4 = Véronique|last4 = Rousseau|first5 = Christiane|last5 = Lancelot|citeseerx = 10.1.1.319.9563}}</ref> It has the ability to form floating colonies, where hundreds of cells are embedded in a gel matrix, which can increase massively in size during [[Biology:Algal bloom|blooms]].<ref>{{cite web |url= http://www.phaeocystis.org/|title = Welcome to the Phaeocystis antarctica genome sequencing project homepage |date= |accessdate= |website= |last= |first=}}</ref> As a result, ''Phaeocystis'' is an important contributor to the marine [[Earth:Carbon cycle|carbon]]<ref>{{cite journal |title=Rapid and early export of Phaeocystis antarctica blooms in the Ross Sea, Antarctica <!--http://www.nature.com/doifinder/10.1038/35007061-->|journal = Nature|pages = 595–598|volume = 404|issue = 6778|doi = 10.1038/35007061|pmid = 10766240|first = G. R.|last = DiTullio|first2 = J. M.|last2 = Grebmeier|first3 = K. R.|last3 = Arrigo|first4 = M. P.|last4 = Lizotte|first5 = D. H.|last5 = Robinson|first6 = A.|last6 = Leventer|first7 = J. P.|last7 = Barry|first8 = M. L.|last8 = VanWoert|first9 = R. B.|last9 = Dunbar|year = 2000}}</ref> and [[Biology:Sulfur cycle|sulfur cycle]]s.<ref>{{Cite journal|title = DMSP-lyase activity in a spring phytoplankton bloom off the Dutch coast, related to Phaeocystis sp. abundance|journal = Marine Ecology Progress Series|date = 1995-07-20|pages = 235–243|volume = 123|doi = 10.3354/meps123235|first = Stefels|last = J|first2 = Dijkhuizen|last2 = L|first3 = Gieskes|last3 = WWC|url = https://pure.rug.nl/ws/files/62552225/DMSP_lyase_activity_in_a_spring_phytoplankton_bloom_off_the_Dutch_coast.pdf}}</ref> ''Phaeocystis'' species are endosymbionts to [[Biology:Acantharea|acantharian]] radiolarians.<ref name=":4">{{cite journal|last=Decelle|first=Johan|last2=Simó|first2=Rafel|last3=Galí|first3=Martí|last4=Vargas|first4=Colomban de|last5=Colin|first5=Sébastien|last6=Desdevises|first6=Yves|last7=Bittner|first7=Lucie|last8=Probert|first8=Ian|last9=Not|first9=Fabrice|date=2012-10-30|title=An original mode of symbiosis in open ocean plankton|journal=Proceedings of the National Academy of Sciences|language=en|volume=109|issue=44|pages=18000–18005|doi=10.1073/pnas.1212303109|issn=0027-8424|pmid=23071304|pmc=3497740}}</ref><ref name=":5">{{Cite journal|last=Mars Brisbin|first=Margaret|last2=Grossmann|first2=Mary M.|last3=Mesrop|first3=Lisa Y.|last4=Mitarai|first4=Satoshi|date=2018|title=Intra-host Symbiont Diversity and Extended Symbiont Maintenance in Photosymbiotic Acantharea (Clade F)|journal=Frontiers in Microbiology|language=English|volume=9|pages=1998|doi=10.3389/fmicb.2018.01998|pmid=30210473|pmc=6120437|issn=1664-302X}}</ref>

<gallery caption="Mixoplankton" mode=packed heights=144px style=float:left;>
File:Tintinnid ciliate Favella.jpg| [[Biology:Tintinnid|Tintinnid]] ciliate ''Favella''
File:Euglena mutabilis - 400x - 1 (10388739803) (cropped).jpg|''[[Biology:Euglena|Euglena mutabilis]]'', a photosynthetic [[Biology:Flagellate|flagellate]]
File:Stichotricha secunda - 400x (14974779356).jpg| Zoochlorellae (green) living inside the ciliate ''Stichotricha secunda''
</gallery>
{{clear}}

====Dinoflagellates====

{{multiple image
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  | caption1  = Unarmored dinoflagellates Kofoid (1921)
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  | caption2  = Haeckel Peridinea (1904)
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[[Biology:Dinoflagellate|Dinoflagellate]]s are part of the algae group, and form a phylum of unicellular flagellates with about 2,000 marine species.<ref name="Gómez12">{{cite journal|author=Gómez F |title=A checklist and classification of living dinoflagellates (Dinoflagellata, Alveolata) |journal=CICIMAR Océanides |volume=27 |issue=1 |pages=65–140 |year=2012 |url=http://www.cicimar.ipn.mx/oacis/Medios/oceanides/P%20065%20Fernando%20Gomez.pdf |url-status=dead |archive-url=https://web.archive.org/web/20131127104918/http://www.cicimar.ipn.mx/oacis/Medios/oceanides/P%20065%20Fernando%20Gomez.pdf |archive-date=2013-11-27}}</ref> The name comes from the Greek "dinos" meaning ''whirling'' and the Latin "flagellum" meaning a ''whip'' or ''lash''. This refers to the two whip-like attachments (flagella) used for forward movement. Most dinoflagellates are protected with red-brown, cellulose armour. Like other phytoplankton, dinoflagellates are r-strategists which under right conditions can [[Biology:Algal bloom|bloom]] and create [[Biology:Red tide|red tide]]s. [[Biology:Excavata|Excavates]] may be the most basal flagellate lineage.<ref name=Dawson2013 />

By trophic orientation dinoflagellates are all over the place. Some dinoflagellates are known to be [[Earth:Photosynthesis|photosynthetic]], but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy).<ref>{{Cite journal | last1 = Stoecker | first1 = D. K. | title = Mixotrophy among Dinoflagellates | doi = 10.1111/j.1550-7408.1999.tb04619.x | journal = The Journal of Eukaryotic Microbiology | volume = 46 | issue = 4 | pages = 397–401 | year = 1999 | pmid = | pmc = | name-list-format = vanc}}</ref> Some species are [[Biology:Endosymbiont|endosymbiont]]s of marine animals and other protists, and play an important part in the biology of [[Earth:Coral reef|coral reef]]s. Others predate other protozoa, and a few forms are parasitic. Many dinoflagellates are mixotrophic and could also be classified as phytoplankton. 

<gallery mode=packed heights=144px style=float:left;>
File:Gyrodinium dinoflagellate.jpg| ''[[Biology:Gymnodinium|Gyrodinium]]'', one of the few naked dinoflagellates which lack armour
File:Protoperidinium dinoflagellate.jpg| The dinoflagellate, ''Protoperidinium'' extrudes a large feeding veil to capture prey
File:Radiolarian - Podocyrtis (Lampterium) mitra Ehrenberg - 160x.jpg| Nassellarian radiolarians can be in symbiosis with dinoflagellates
</gallery>

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 | caption1  = {{center|A surf wave at night sparkles with blue light due to the presence of a bioluminescent dinoflagellate, such as ''Lingulodinium polyedrum''}}
 | image2    = Potential Mechanism for Dazzling Blue Flashes of Light in Oceans Identified (6300345394).jpg
 | alt2      = 
 | caption2  = {{center|Suggested explanation for glowing seas<ref>[https://www.nsf.gov/news/news_summ.jsp?org=NSF&cntn_id=122037 Suggested Explanation for Glowing Seas--Including Currently Glowing California Seas] ''National Science Foundation'', 18 October 2011.</ref>}}
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{{clear left}}

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 | image1    = Peridinium digitale.jpg
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 | caption1  = &nbsp; &nbsp; &nbsp; &nbsp; Armoured
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 | caption2  = &nbsp; &nbsp; &nbsp; &nbsp; Unarmoured
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Dinoflagellates often live in [[Earth:Symbiosis|symbiosis]] with other organisms. Many nassellarian radiolarians house [[Biology:Dinoflagellate|dinoflagellate]] [[Earth:Symbiosis|symbionts]] within their tests.<ref>{{Cite book|title=Handbook of the Protists|last=Boltovskoy|first=Demetrio|last2=Anderson|first2=O. Roger|last3=Correa|first3=Nancy M.|date=2017|publisher=Springer, Cham|isbn=9783319281476|pages=731–763|language=en|doi=10.1007/978-3-319-28149-0_19}}</ref> The nassellarian provides [[Chemistry:Ammonium|ammonium]] and [[Chemistry:Carbon dioxide|carbon dioxide]] for the dinoflagellate, while the dinoflagellate provides the nassellarian with a mucous membrane useful for hunting and protection against harmful invaders.<ref>{{Cite book|title=Radiolaria|last=Anderson|first=O. R.|publisher=Springer Science & Business Media|year=1983|isbn=|location=|pages=}}</ref> There is evidence from [[Biology:DNA|DNA]] analysis that dinoflagellate symbiosis with radiolarians evolved independently from other dinoflagellate symbioses, such as with [[Biology:Foraminifera|foraminifera]].<ref>{{Cite journal|last=Gast|first=R. J.|last2=Caron|first2=D. A.|date=1996-11-01|title=Molecular phylogeny of symbiotic dinoflagellates from planktonic foraminifera and radiolaria|journal=Molecular Biology and Evolution|language=en|volume=13|issue=9|pages=1192–1197|doi=10.1093/oxfordjournals.molbev.a025684|pmid=8896371|issn=0737-4038}}</ref>

Some dinoflagellates are [[Biology:Dinoflagellate#Bioluminescence|bioluminescent]]. At night, ocean water can light up internally and [[Biology:Dinoflagellate#Bioluminescence|sparkle with blue light]] because of these dinoflagellates.<ref>{{cite book |last=Castro |first=Peter |first2=Michael E. |last2=Huber |title=Marine Biology |publisher=McGraw Hill |year=2010 |isbn=978-0071113021 |pages=95 |edition=8th | name-list-format = vanc}}</ref><ref>{{cite journal | vauthors = Hastings JW | title = Chemistries and colors of bioluminescent reactions: a review | journal = Gene | volume = 173 | issue = 1 Spec No | pages = 5–11 | year = 1996 | pmid = 8707056 | doi = 10.1016/0378-1119(95)00676-1}}</ref> Bioluminescent dinoflagellates possess [[Biology:Scintillons|scintillons]], individual cytoplasmic bodies which contain [[Biology:Dinoflagellate luciferase|dinoflagellate luciferase]], the main enzyme involved in the luminescence. The luminescence, sometimes called ''the phosphorescence of the sea'', occurs as brief (0.1 sec) blue flashes or sparks when individual scintillons are stimulated, usually by mechanical disturbances from, for example, a boat or a swimmer or surf.<ref name="haddock">{{cite journal | vauthors = Haddock SH, Moline MA, Case JF | title = Bioluminescence in the sea | journal = Annual Review of Marine Science | volume = 2 | pages = 443–93 | date = 2009 | pmid = 21141672 | doi = 10.1146/annurev-marine-120308-081028 | bibcode = 2010ARMS....2..443H| url = https://semanticscholar.org/paper/2889f76ba6e892c4dfd7177d9b6d58f6e42e8f9b }}</ref>

<gallery mode=packed heights=144px style=float:left;>
File:Noctiluca scintillans unica.jpg| ''[[Biology:Noctiluca scintillans|Noctiluca scintillans]]'', a bioluminescent dinoflagellate <ref>Buskey, E.J. (1995) "Growth and bioluminescence of ''Noctiluca scintillans'' on varying algal diets". ''Journal of Plankton Research'', '''17'''(1): 29–40. {{doi|10.1093/plankt/17.1.29}}</ref>

File:Archives de zoologie expérimentale et générale (1920) (20299351186).jpg| ''[[Biology:Oodinium|Oodinium]]'', a genus of parasitic dinoflagellates, causes velvet disease in fish <ref>{{cite web|title=Protozoa Infecting Gills and Skin|url=http://www.merckvetmanual.com:80/mvm/index.jsp?cfile=htm/bc/170410.htm|publisher=The Merck Veterinary Manual|accessdate= 4 November 2019|archiveurl=https://web.archive.org/web/20160303221140/http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm%2Fbc%2F170410.htm |archivedate=3 March 2016|url-status=dead |df=dmy-all}}</ref>
File:Karenia brevis.jpg| ''[[Biology:Karenia brevis|Karenia brevis]]'' produces red tides highly toxic to humans <ref>{{Cite journal|last=Brand|first=Larry E.|last2=Campbell|first2=Lisa|last3=Bresnan|first3=Eileen|title=''Karenia'': The biology and ecology of a toxic genus|journal=Harmful Algae|volume=14|pages=156–178|doi=10.1016/j.hal.2011.10.020|year=2012}}</ref>
File:Algal bloom(akasio) by Noctiluca in Nagasaki.jpg| [[Biology:Red tide|Red tide]]
</gallery>
{{clear}}

==Marine microbenthos==
[[File:Archaea rock.jpg|thumb| Archaea rock - this deep ocean rock harboured worms that consumed methane-eating archaea]]

Marine microbenthos are microorganisms that live in the [[Earth:Benthic zone|benthic zone]] of the ocean – that live near or on the seafloor, or within or on surface seafloor sediments. The word ''benthos'' comes from Greek, meaning "depth of the sea". Microbenthos are found everywhere on or about the seafloor of continental shelves, as well as in deeper waters, with greater diversity in or on seafloor sediments. In shallow waters, seagrass meadows, coral reefs and kelp forests provide particularly rich habitats. In [[Earth:Photic zone|photic zone]]s benthic diatoms dominate as photosynthetic organisms. In [[Earth:Intertidal zone|intertidal zone]]s changing [[Astronomy:Tide|tide]]s strongly control opportunities for microbenthos.

<gallery mode=packed heights=180px style="float:left;">
File:Elphidium-incertum hg.jpg| ''[[Biology:Elphidium|Elphidium]]'' a widespread abundant genus of benthic forams
File:FMIB 50025 Textilaria.jpeg| ''[[Biology:Heterohelix|Heterohelix]]'', an extinct genus of benthic forams
</gallery>
{{clear}}

==Marine microfossils==
[[File:Marine sediment thickness (cropped).jpg|thumb|upright=1.4| {{center|Thickness of marine sediments}}]]

Sediments at the bottom of the ocean have two main origins, terrigenous and biogenous. [[Earth:Terrigenous sediment|Terrigenous sediment]]s account for about 45% of the total marine sediment, and originate in the erosion of [[Earth:Rock (geology)|rocks]] on land, transported by rivers and land runoff, windborne dust, volcanoes, or grinding by glaciers. 

Biogenous sediments account for the other 55% of the total sediment, and originate in the skeletal remains of marine protists (single-celled plankton and benthos microorganisms). Much smaller amounts of precipitated minerals and meteoric dust can also be present. ''Ooze'', in the context of a marine sediment, does not refer to the consistency of the sediment but to its biological origin. The term ooze was originally used by John Murray, the "father of modern oceanography", who proposed the term ''radiolarian ooze'' for the silica deposits of radiolarian shells brought to the surface during the Challenger Expedition.<ref>Thomson, Charles Wyville (2014) [https://books.google.co.nz/books?id=zcFkAwAAQBAJ&printsec=frontcover&dq=%22Voyage+of+the+Challenger+:+The+Atlantic%22&hl=en&sa=X&ved=0ahUKEwjsi8aKzejkAhWOfysKHf6MB10Q6AEINTAC#v=onepage&q=radiolarian%20ooze&f=false ''Voyage of the Challenger : The Atlantic''] Cambridge University Press, page235. 
{{ISBN|9781108074759}}.</ref> A ''biogenic ooze'' is a [[Earth:Pelagic sediment|pelagic sediment]] containing at least 30 percent from the skeletal remains of marine organisms.

{{clear}}

{|class="wikitable"
! colspan=9 |{{centre|Main types of biogenic ooze}}
|-
! type
! mineral<br />forms
! protist<br />involved
!
! name of skeleton
! width=100px | typical size<br /><small>(mm)</small>
! colspan=2 |
|-
! width=90px rowspan=2 | [[Earth:Siliceous ooze|Siliceous ooze]]
| rowspan=2 align=center | SiO<sub>2</sub><br />[[Chemistry:Silica|silica]]<br />[[Chemistry:Quartz|quartz]]<br />[[Chemistry:Glass|glass]]<br />[[Chemistry:Opal|opal]]<br />[[Earth:Chert|chert]]
| [[Biology:Diatom|diatom]]
| style="background:#000000;"| [[File:Lyrella hennedy 1600x contrast invertion.jpg|90px]]
| [[Biology:Frustule|frustule]]
| 0.002 to 0.2<ref name="HasleSyvertsen1996">{{cite book|author1=Grethe R. Hasle|author2=Erik E. Syvertsen |author3=Karen A. Steidinger |author4=Karl Tangen|editor=Carmelo R. Tomas|title=Identifying Marine Diatoms and Dinoflagellates|chapter-url=https://books.google.com/books?id=KQxPtwonlqoC|accessdate=2013-11-13|date=1996-01-25|publisher=Academic Press|isbn=978-0-08-053441-1|pages=5–385|chapter=Marine Diatoms}}</ref>
| [[File:Stephanopyxis grunowii.jpg|100px]] 
| diatom microfossil from 40 million years ago
|-
| radiolarian
| style="background:#000000;"| [[File:Calocycloma sp. - Radiolarian (32163186535).jpg|90px]]
| [[Biology:Test|test]] or shell
| 0.1 to 0.2
| [[File:Radiolarian - Heliodiscus umbonatus (Ehr.), Haeckel (28187768550).jpg|100px]]
| elaborate silica shell of a radiolarian
|-
! rowspan=3 | Calcareous ooze
| rowspan=3 align=center | [[Chemistry:Calcium carbonate|CaCO<sub>3</sub>]]<br />[[Chemistry:Calcite|calcite]]<br />[[Chemistry:Aragonite|aragonite]]<br />[[Earth:Limestone|limestone]]<br />[[Chemistry:Marble|marble]]<br />[[Earth:Chalk|chalk]]
| foraminiferan
| style="background:#000000;"| [[File:Foram-globigerina hg.jpg|90px]]
| test or shell
| under 1
| [[File:Globigerina.png|100px]]
| Calcified [[Biology:Test|test]] of a planktic foraminiferan. There are about 10,000 living species of foraminiferans <ref name="adl2007">Ald, S.M. ''et al.'' (2007) [http://wayback.archive-it.org/all/20110331223739/http://myweb.dal.ca/jmarchib/2007.Adl.Syst.biol.pdf Diversity, Nomenclature, and Taxonomy of Protists], ''Syst. Biol.'' 56(4), 684–689, DOI: 10.1080/10635150701494127.</ref>
|-
| [[Biology:Coccolithophore|coccolithophore]]
| style="background:#000000;"| [[File:Coccolithus pelagicus 2.jpg|90px]]
| [[Chemistry:Coccolith|coccolith]]s
| under 0.1 <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>
| [[File:CSIRO ScienceImage 7202 SEM Coccolithophorid.jpg|100px]] 
| Coccolithophores are the largest global source of biogenic calcium carbonate, and significantly contribute to the global carbon cycle.<ref>Taylor, A.R., Chrachri, A., Wheeler, G., Goddard, H. and Brownlee, C. (2011) "A voltage-gated H+ channel underlying pH homeostasis in calcifying coccolithophores". ''PLoS biology'', '''9'''(6): p.e1001085 {{doi|10.1371/journal.pbio.1001085}}</ref> They are the main constituent of chalk deposits such as the white cliffs of Dover.
|-
|}

<gallery mode=packed heights=160px style=float:left;>
File:Diatomaceous Earth BrightField.jpg|[[Earth:Diatomaceous earth|Diatomaceous earth]] is a soft, siliceous, [[Earth:Sedimentary rock|sedimentary rock]] made up of microfossils in the form of the [[Biology:Frustule|frustule]]s (shells) of single cell diatoms (click to magnify)
File:PSM V44 D483 Globigerina ooze.jpg| Illustration of a ''[[Biology:Globigerina|Globigerina]]'' ooze
</gallery>

[[File:Marinesediments.jpg|thumb|upright=1.4| {{center|'''Distribution of pelagic sediments'''<br /> Yellow: calcareous sediments<br />Green: siliceous sediments<br />Brown: pelagic clay<br />White: sediments of the continental margin<br />Blue: glacial sediments<br />Orange: land-formed sediments<br /><small>For further information, [https://en.wikibooks.org/wiki/Historical_Geology/Marine_sediments see here]</small>}}]]

<gallery mode=packed heights=160px style=float:left;>
File:FMIB 47660 Shells from Globigerina Ooze.jpeg| Shells ([[Biology:Test|tests]]), usually made of calcium carbonate, from a [[Biology:Foraminifera|foraminifera]]l ooze on the deep ocean floor
File:Carbonate-Silicate Cycle (Carbon Cycle focus).jpg| Carbonate-silicate cycle
</gallery>
{{clear}}

==Marine food web==
[[File:Viral shunt.jpg|thumb|320px| The viral shunt pathway facilitates the flow of dissolved organic matter (DOM) and particulate organic matter (POM) through the marine food web]]

Marine microorganisms play central roles in the [[Biology:Marine food web|marine food web]].

The viral shunt pathway is a mechanism that prevents marine microbial [[Earth:Particulate organic matter|particulate organic matter]] (POM) from migrating up [[Earth:Trophic level|trophic level]]s by recycling them into dissolved organic matter (DOM), which can be readily taken up by microorganisms.<ref>{{Cite journal|last=Wilhelm|first=Steven W.|last2=Suttle|first2=Curtis A.|date=1999|title=Viruses and Nutrient Cycles in the Sea|journal=BioScience|volume=49|issue=10|pages=781–788|doi=10.2307/1313569|issn=1525-3244|jstor=1313569}}</ref> Viral shunting helps maintain diversity within the microbial ecosystem by preventing a single species of marine microbe from dominating the micro-environment.<ref>Weinbauer, Markus G., et al. "Synergistic and antagonistic effects of viral lysis and protistan grazing on bacterial biomass, production and diversity." ''Environmental Microbiology'' 9.3 (2007): 777-788.</ref> The DOM recycled by the viral shunt pathway is comparable to the amount generated by the other main sources of marine DOM.<ref>Robinson, Carol, and Nagappa Ramaiah. "Microbial heterotrophic metabolic rates constrain the microbial carbon pump." The American Association for the Advancement of Science, 2011.</ref>

{{clear}}

==Niche communities==
[[File:Thurber_snow.jpg|thumb|260px|right| Algal and bacterial community beneath Antarctic sea ice]]
{{multiple image
 | align = right
 | direction = horizontal
 | image1    = High Rise black smoker.jpg
 | width1    = 170
 | alt1      = 
 | caption1  = Black smoker in the High Rise portion of the [[Earth:Endeavour Hydrothermal Vents|Endeavour Hydrothermal Vents]].
 | image2    = Alvinella pompejana01.jpg
 | width2    = 250
 | alt2      = 
 | caption2  = Bacteria can be beneficial. This Pompeii worm, an [[Earth:Extremophile|extremophile]] found only at [[Earth:Hydrothermal vent|hydrothermal vent]]s, has a protective cover of [[Biology:Symbiotic bacteria|symbiotic bacteria]].
}}

[[Earth:Sea ice microbial communities|Sea ice microbial communities]] (SIMCO) refer to groups of [[Biology:Microorganism|microorganism]]s living within and at the interfaces of [[Earth:Sea ice|sea ice]] at the poles. The ice matrix they inhabit has strong vertical gradients of salinity, light, temperature and nutrients. Sea ice chemistry is most influenced by the salinity of the brine which affects the [[Chemistry:PH|pH]] and the concentration of dissolved nutrients and gases. The [[Earth:Brine|brine]] formed during the melting sea ice creates pores and channels in the sea ice in which these microbes can live.  As a result of these gradients and dynamic conditions, a higher abundance of microbes are found in the lower layer of the ice, although some are found in the middle and upper layers.<ref name="Boetius 2015">{{cite journal|last=Boetius|first=Antje|last2=Anesio|first2=Alexandre M.|last3=Deming|first3=Jody W.|last4=Mikucki|first4=Jill A.|last5=Rapp|first5=Josephine Z.|date=November 1, 2015|title=Microbial ecology of the cryosphere: sea ice and glacial habitats|journal=Nature Reviews Microbiology|volume=13|issue=11|pages=677–690|doi=10.1038/nrmicro3522|pmid=26344407}}</ref>

[[Earth:Hydrothermal vent|Hydrothermal vent]]s are located where the tectonic plates are moving apart and spreading. This allows water from the ocean to enter into the crust of the earth where it is heated by the magma. The increasing pressure and temperature forces the water back out of these openings, on the way out, the water accumulates dissolved minerals and chemicals from the rocks that it encounters. Vents can be characterized by temperature and chemical composition as ''diffuse vents'' which release clear relatively cool water usually below 30&nbsp;°C, as ''white smokers'' which emit milky coloured water at warmer temperatures, about 200-330&nbsp;°C, and as ''black smokers'' which emit water darkened by accumulated precipitates of sulfide at hot temperatures, about 300-400&nbsp;°C.<ref>{{Cite journal|last=Lutz|first=Richard A.|last2=Kennish|first2=Michael J.|date=1993|title=Ecology of deep-sea hydrothermal vent communities: A review|journal=Reviews of Geophysics|language=en|volume=31|issue=3|pages=211|doi=10.1029/93rg01280|issn=8755-1209|bibcode=1993RvGeo..31..211L}}</ref>

[[Biology:Hydrothermal vent microbial communities|Hydrothermal vent microbial communities]] are microscopic unicellular organisms that live and reproduce in the chemically distinct area around hydrothermal vents. These include organisms in [[Biology:Microbial mat|microbial mat]]s, free floating cells, and bacteria in [[Biology:Endosymbiont|endosymbiotic]] relationships with animals. Because there is no sunlight at these depths, energy is provided by [[Earth:Chemosynthesis|chemosynthesis]] where symbiotic bacteria and archaea form the bottom of the food chain and are able to support a variety of organisms such as [[Biology:Riftia pachyptila|giant tube worms]] and [[Biology:Alvinella pompejana|Pompeii worms]]. These organisms utilize this symbiotic relationship in order to utilize and obtain the chemical energy that is released at these hydrothermal vent areas.<ref>{{Cite journal|last=Kádár|first=Enikõ|last2=Costa|first2=Valentina|last3=Santos|first3=Ricardo S.|last4=Powell|first4=Jonathan J.|date=July 2006|title=Tissue partitioning of micro-essential metals in the vent bivalve Bathymodiolus azoricus and associated organisms (endosymbiont bacteria and a parasite polychaete) from geochemically distinct vents of the Mid-Atlantic Ridge|journal=Journal of Sea Research|volume=56|issue=1|pages=45–52|doi=10.1016/j.seares.2006.01.002|issn=1385-1101|bibcode=2006JSR....56...45K}}</ref> Chemolithoautotrophic bacteria derive nutrients and energy from the geological activity at a hydrothermal vent to fix carbon into organic forms. 

[[Biology:Virus|Virus]]es are also a part of the hydrothermal vent microbial community and their influence on the microbial ecology in these ecosystems is a burgeoning field of research.<ref>{{Cite journal|last=Anderson|first=Rika E.|last2=Brazelton|first2=William J.|last3=Baross|first3=John A.|date=2011|title=Is the genetic landscape of the deep subsurface biosphere affected by viruses?|journal=Frontiers in Microbiology|volume=2|pages=219|doi=10.3389/fmicb.2011.00219|issn=1664-302X|pmc=3211056|pmid=22084639}}</ref> Viruses are the most abundant life in the ocean, harboring the greatest reservoir of genetic diversity.<ref>{{Cite journal|last=Suttle|first=Curtis A.|date=September 2005|title=Viruses in the sea|journal=Nature|volume=437|issue=7057|pages=356–361|doi=10.1038/nature04160|pmid=16163346|issn=0028-0836|bibcode=2005Natur.437..356S}}</ref> As their infections are often fatal, they constitute a significant source of mortality and thus have widespread influence on biological oceanographic processes, [[Biology:Evolution|evolution]] and [[Chemistry:Geochemical cycle#Differentiating biogeochemical cycles|biogeochemical cycling]] within the ocean.<ref>{{Cite journal|last=Suttle|first=Curtis A.|date=October 2007|title=Marine viruses — major players in the global ecosystem|journal=Nature Reviews Microbiology|language=En|volume=5|issue=10|pages=801–812|doi=10.1038/nrmicro1750|pmid=17853907|issn=1740-1526}}</ref> Evidence has been found however to indicate that viruses found in vent habitats have adopted a more [[Biology:Mutualism|mutualistic]] than [[Earth:Parasitism|parasitic]] evolutionary strategy in order to survive the extreme and volatile environment they exist in.<ref name=":17">{{Cite journal|last=Anderson|first=Rika E.|last2=Sogin|first2=Mitchell L.|last3=Baross|first3=John A.|date=2014-10-03|title=Evolutionary Strategies of Viruses, Bacteria and Archaea in Hydrothermal Vent Ecosystems Revealed through Metagenomics|journal=PLoS ONE|volume=9|issue=10|pages=e109696|doi=10.1371/journal.pone.0109696|issn=1932-6203|pmc=4184897|pmid=25279954|bibcode=2014PLoSO...9j9696A}}</ref> Deep-sea hydrothermal vents were found to have high numbers of viruses indicating high viral production.<ref name=":18">{{Cite journal|last=Ortmann|first=Alice C.|last2=Suttle|first2=Curtis A.|date=August 2005|title=High abundances of viruses in a deep-sea hydrothermal vent system indicates viral mediated microbial mortality|journal=Deep Sea Research Part I: Oceanographic Research Papers|volume=52|issue=8|pages=1515–1527|doi=10.1016/j.dsr.2005.04.002|issn=0967-0637|bibcode=2005DSRI...52.1515O}}</ref> Like in other marine environments, deep-sea hydrothermal viruses affect abundance and diversity of [[Biology:Prokaryote|prokaryote]]s and therefore impact microbial biogeochemical cycling by [[Biology:Lysis|lysing]] their hosts to replicate.<ref>{{Cite journal|last=Breitbart|first=Mya|date=2012-01-15|title=Marine Viruses: Truth or Dare|journal=Annual Review of Marine Science|language=en|volume=4|issue=1|pages=425–448|doi=10.1146/annurev-marine-120709-142805|pmid=22457982|issn=1941-1405|bibcode=2012ARMS....4..425B}}</ref> However, in contrast to their role as a source of mortality and population control, viruses have also been postulated to enhance survival of prokaryotes in extreme environments, acting as reservoirs of genetic information. The interactions of the virosphere with microorganisms under environmental stresses is therefore thought to aide microorganism survival through dispersal of host genes through [[Biology:Horizontal gene transfer in evolution|horizontal gene transfer]].<ref>{{Cite journal|last=Goldenfeld|first=Nigel|last2=Woese|first2=Carl|date=January 2007|title=Biology's next revolution|journal=Nature|volume=445|issue=7126|pages=369|doi=10.1038/445369a|pmid=17251963|issn=0028-0836|arxiv=q-bio/0702015|bibcode=2007Natur.445..369G}}</ref>

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==Deep biosphere and dark matter==
[[File:Picoplancton fluorescence Pacific.jpg|thumb|320px| {{center|Fluorescence microscopy of various [[Biology:Picoplankton|picoplankton]] in the ocean, much of which cannot be effectively studied because they resist attempts at laboratory culture}}]]

The [[Biology:Deep biosphere|deep biosphere]] is that part of the [[Biology:Biosphere|biosphere]] that resides below the first few meters of the surface. It extends at least 5&nbsp;kilometers below the continental surface and 10.5&nbsp;kilometers below the sea surface, with temperatures that may exceed 100°C. 

Above the surface living organisms consume organic matter and oxygen. Lower down, these are not available, so they make use of "edibles" ([[Chemistry:Electron acceptor|electron acceptor]]s) such as hydrogen released from rocks by various chemical processes, methane, reduced sulfur compounds and ammonium. They "breathe" [[Chemistry:Electron donor|electron donor]]s such as nitrates and nitrites, manganese and iron oxides, oxidized sulfur compounds and carbon dioxide.

There is very little energy at greater depths, and metabolism can be up to a million times slower than at the surface. Cells may live for thousands of years before dividing and there is no known limit to their age. The subsurface accounts for about 90% of the [[Earth:Biomass (ecology)|biomass]] in bacteria and archaea, and 15% of the total biomass for the biosphere. Eukaryotes are also found, mostly microscopic, but including some multicellular life. Viruses are also present and infect the microbes.

[[File:Unidentified spherical algal microorganism.jpg|thumb|left| Unidentified spherical algal microorganism, part of the microbial dark matter]]

In 2018, researchers from the [[Organization:Deep Carbon Observatory|Deep Carbon Observatory]] announced that life forms, including 70% of the bacteria and archaea on Earth, totaling a biomass of 23&nbsp;billion tonnes [[Chemistry:Carbon|carbon]], live up to {{nowrap|{{convert|4.8|km|mi|abbr=on}}}} deep underground, including {{nowrap|{{convert|2.5|km|mi|abbr=on}}}} below the seabed.<ref name="EA-20181211">{{cite news |author=Deep Carbon Observatory |title=Life in deep Earth totals 15 to 23&nbsp;billion tons of carbon – hundreds of times more than humans |url=https://www.eurekalert.org/pub_releases/2018-12/tca-lid120318.php |date=10 December 2018 |work=EurekAlert! |accessdate=11 December 2018 |df=dmy-all}}</ref><ref name="SA-20181211">{{cite news |last=Dockrill |first=Peter |title=Scientists Reveal a Massive Biosphere of Life Hidden Under Earth's Surface |url=https://www.sciencealert.com/scientists-lift-lid-on-massive-biosphere-of-life-hidden-under-earth-s-surface |date=11 December 2018 |work=Science Alert |accessdate=11 December 2018 |df=dmy-all}}</ref><ref name="TI-20181211">{{cite news |last=Gabbatiss |first=Josh |title=Massive 'deep life' study reveals billions of tonnes of microbes living far beneath Earth's surface |url=https://www.independent.co.uk/news/science/deep-life-microbes-underground-bacteria-earth-surface-carbon-observatory-science-study-a8677521.html |date=11 December 2018 |work=The Independent |accessdate=11 December 2018 |df=dmy-all}}</ref> In 2019 microbial organisms were discovered living {{Convert|7900|ft}} below the surface, [[Earth:Sulfate-reducing microorganisms|breathing sulfur]] and eating rocks such as [[Chemistry:Pyrite|pyrite]] as their regular food source.<ref>[https://www.tandfonline.com/doi/abs/10.1080/01490451.2019.1641770?journalCode=ugmb20 ‘Follow the Water’: Hydrogeochemical Constraints on Microbial Investigations 2.4 km Below Surface at the Kidd Creek Deep Fluid and Deep Life Observatory], Garnet S. Lollar, Oliver Warr, Jon Telling, Magdalena R. Osburn & Barbara Sherwood Lollar, Received 15 Jan 2019, Accepted 01 Jul 2019, Published online: 18 Jul 2019.</ref><ref>[https://deepcarbon.net/worlds-oldest-groundwater-supports-life-through-water-rock-chemistry World’s Oldest Groundwater Supports Life Through Water-Rock Chemistry], July 29, 2019, deepcarbon.net.</ref><ref>[https://www.nbcnews.com/mach/science/strange-life-forms-found-deep-mine-point-vast-underground-galapagos-ncna1050906 Strange life-forms found deep in a mine point to vast 'underground Galapagos'], By Corey S. Powell, Sept. 7, 2019, nbcnews.com.</ref> This discovery occurred in the oldest known water on Earth.<ref>[http://thescienceexplorer.com/nature/oldest-water-earth-found-deep-within-canadian-shield Oldest Water on Earth Found Deep Within the Canadian Shield], December 14, 2016, Maggie Romuld</ref>

To date biologists have been unable to [[Biology:Microbiological culture|culture]] in the laboratory the vast majority of microorganisms. This applies particularly to bacteria and archaea, and is due to a lack of knowledge or ability to supply the required growth conditions.<ref name="FileeTetart2005">{{cite journal|last1=Filee|first1=J.|last2=Tetart|first2=F.|last3=Suttle|first3=C. A.|last4=Krisch|first4=H. M.|title=Marine T4-type bacteriophages, a ubiquitous component of the dark matter of the biosphere|journal=Proceedings of the National Academy of Sciences|volume=102|issue=35|year=2005|pages=12471–12476|issn=0027-8424|doi=10.1073/pnas.0503404102|pmid=16116082|pmc=1194919}}</ref><ref name="EA-20180925">{{cite news |author=University of Tennessee at Knoxville |title=Study: Microbial dark matter dominates Earth's environments |url=https://www.eurekalert.org/pub_releases/2018-09/uota-smd092518.php |date=25 September 2018 |work=Eurekalert! |accessdate=26 September 2018|author-link=University of Tennessee at Knoxville }}</ref> The term ''[[Biology:Microbial dark matter|microbial dark matter]]'' has come to be used to describe microorganisms scientists know are there but have been unable to culture, and whose properties therefore remain elusive.<ref name="FileeTetart2005"/> Microbial dark matter is unrelated to the [[Astronomy:Dark matter|dark matter]] of physics and cosmology, but is so-called for the difficulty in effectively studying it. It is hard to estimate its relative magnitude, but the accepted gross estimate is that less than one percent of microbial species in a given ecological niche is culturable. In recent years effort is being put to decipher more of the microbial dark matter by means of learning their [[Biology:Genome|genome]] [[Biology:DNA|DNA]] sequence from environmental samples<ref name="HedlundDodsworth2014">{{cite journal|last1=Hedlund|first1=Brian P.|last2=Dodsworth|first2=Jeremy A.|last3=Murugapiran|first3=Senthil K.|last4=Rinke|first4=Christian|last5=Woyke|first5=Tanja|title=Impact of single-cell genomics and metagenomics on the emerging view of extremophile "microbial dark matter"|journal=Extremophiles|volume=18|issue=5|year=2014|pages=865–875|issn=1431-0651|doi=10.1007/s00792-014-0664-7|pmid=25113821}}</ref> and then by gaining insights to their metabolism from their sequenced genome, promoting the knowledge required for their cultivation.

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==Anthropogenic impacts==
[[File:Microorganisms and climate change.png|thumb|right|upright=2.2| {{center|Microorganisms and climate change in marine and terrestrial biomes <ref name=Cavicchioli2019 />}}]]

In marine environments, microbial [[Earth:Primary production|primary production]] contributes substantially to [[Earth:Carbon sequestration|CO<sub>2</sub> sequestration]]. Marine microorganisms also recycle nutrients for use in the [[Biology:Marine food web|marine food web]] and in the process release CO<sub>2</sub> to the atmosphere. Microbial biomass and other organic matter (remnants of plants and animals) are converted to fossil fuels over millions of years. By contrast, burning of fossil fuels liberates greenhouse gases in a small fraction of that time. As a result, the [[Earth:Carbon cycle|carbon cycle]] is out of balance, and atmospheric CO<sub>2</sub> levels will continue to rise as long as fossil fuels continue to be burnt.<ref name=Cavicchioli2019>Cavicchioli, R., Ripple, W.J., Timmis, K.N., Azam, F., Bakken, L.R., Baylis, M., Behrenfeld, M.J., Boetius, A., Boyd, P.W., Classen, A.T. and Crowther, T.W. (2019) "Scientists’ warning to humanity: microorganisms and climate change". ''Nature Reviews Microbiology'', '''17''': 569–586. {{doi|10.1038/s41579-019-0222-5}}</ref>
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==See also==
{{div col|colwidth=20em}}
* [[Biology:Marine life|Marine life]]
* [[Earth:Deep chlorophyll maximum|Deep chlorophyll maximum]]
* [[Earth:Hawaii Ocean Time-series|Hawaii Ocean Time-series]]
* [[Organization:International Census of Marine Microbes|International Census of Marine Microbes]]
* [[Biology:Marine microbial symbiosis|Marine microbial symbiosis]]
* [[Biology:Microbial biogeography|Microbial biogeography]]
* Microbial communities
* [[Earth:Microbial ecology|Microbial ecology]]
* [[Biology:Microbial food web|Microbial food web]]
* [[Biology:Microbial loop|Microbial loop]]
* [[Biology:Microbial oxidation of sulfur|Microbial oxidation of sulfur]]
** [[Earth:Sulfate-reducing microorganisms|Sulfate-reducing microorganisms]]
* Microbially induced sedimentary structure
* [[Biology:Microbiology of oxygen minimum zones|Microbiology of oxygen minimum zones]]
* [[Earth:Oceanic carbon cycle|Oceanic carbon cycle]]
* [[Earth:Ooid|Ooid]]
* [[Biology:Picoeukaryote|Picoeukaryote]]
* [[Biology:Roseobacter|Roseobacter]]
{{div col end}}

==References==
{{reflist}}

==Other references==
* [http://www.radiolaria.org/arts.htm Radiolarian art]

{{microorganisms|state=expanded}}
{{marine pollution}}

[[Category:Microorganisms]]
[[Category:Marine organisms]]
[[Category:Planktology]]
[[Category:Biological oceanography]]
[[Category:Marine biology]]

{{Sourceattribution|Marine microorganism|1}}