Marine prokaryotes

Parts of a prokaryote

Diagram above contains clickable links

Cellular life forms can be divided into prokaryotes and eukaryotes. Prokaryotes are bacteria or archaea, and the diagram shows some (clickable) parts shared by both. But bacteria and archaea also have fundamental differences, as indicated by their placement in different domains.

Marine prokaryotes are marine bacteria and marine archaea. They are defined by their habitat as prokaryotes that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. All cellular life forms can be divided into prokaryotes and eukaryotes. Eukaryotes are organisms whose cells have a nucleus enclosed within membranes, whereas prokaryotes are the organisms that do not have a nucleus enclosed within a membrane.^[1]^[2]^[3] The three-domain system of classifying life adds another division: the prokaryotes are divided into two domains of life, the microscopic bacteria and the microscopic archaea, while everything else, the eukaryotes, become the third domain.^[4]

Prokaryotes play important roles in ecosystems as decomposers recycling nutrients. Some prokaryotes are pathogenic, causing disease and even death in plants and animals.^[5] Marine prokaryotes are responsible for significant levels of the photosynthesis that occurs in the ocean, as well as significant cycling of carbon and other nutrients.^[6]

Prokaryotes live throughout the biosphere. In 2018 it was estimated the total biomass of all prokaryotes on the planet was equivalent to 77 billion tonnes of carbon (77 Gt C). This is made up of 7 Gt C for archaea and 70 Gt C for bacteria. These figures can be contrasted with the estimate for the total biomass for animals on the planet, which is about 2 Gt C, and the total biomass of humans, which is 0.06 Gt C.^[7] This means archaea collectively have over 100 times the collective biomass of humans, and bacteria over 1000 times.

There is no clear evidence of life on Earth during the first 600 million years of its existence. When life did arrive, it was dominated for 3,200 million years by the marine prokaryotes. More complex life, in the form of crown eukaryotes, didn't appear until the Cambrian explosion a mere 500 million years ago.^[8]

^ Youngson RM (2006). Collins Dictionary of Human Biology. Glasgow: HarperCollins. ISBN 978-0-00-722134-9.
^ Nelson DL, Cox MM (2005). Lehninger Principles of Biochemistry (4th ed.). New York: W.H. Freeman. ISBN 978-0-7167-4339-2.
^ Martin EA, ed. (1983). Macmillan Dictionary of Life Sciences (2nd ed.). London: Macmillan Press. ISBN 978-0-333-34867-3.
^ Fuerst JA (2010). "Beyond Prokaryotes and Eukaryotes: Planctomycetes and Cell Organization". Nature Education. 3 (9): 44.
^ 2002 WHO mortality data Accessed 20 January 2007
^ University of Georgia (10 December 2015). "Functions of global ocean microbiome key to understanding environmental changes". www.sciencedaily.com. Retrieved 11 December 2015.
^ Bar-On YM, Phillips R, Milo R (2018). "The biomass distribution on Earth" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 115 (25): 6506–6511. Bibcode:1998PNAS...95.6578W. doi:10.1073/pnas.1711842115. PMC 6016768. PMID 29784790.
^ Doglioni C, Pignatti J, Coleman M (2016). "Why did life develop on the surface of the Earth in the Cambrian?". Geoscience Frontiers. 7 (6): 865–873. Bibcode:2016GeoFr...7..865D. doi:10.1016/j.gsf.2016.02.001. hdl:11573/925124.

[Youngson-1] Youngson RM (2006). Collins Dictionary of Human Biology. Glasgow: HarperCollins. ISBN 978-0-00-722134-9.

[Nelson&Cox-2] Nelson DL, Cox MM (2005). Lehninger Principles of Biochemistry (4th ed.). New York: W.H. Freeman. ISBN 978-0-7167-4339-2.

[Martin-3] Martin EA, ed. (1983). Macmillan Dictionary of Life Sciences (2nd ed.). London: Macmillan Press. ISBN 978-0-333-34867-3.

[4] Fuerst JA (2010). "Beyond Prokaryotes and Eukaryotes: Planctomycetes and Cell Organization". Nature Education. 3 (9): 44.

[2002_WHO_mortality_data-5] 2002 WHO mortality data Accessed 20 January 2007

[6] University of Georgia (10 December 2015). "Functions of global ocean microbiome key to understanding environmental changes". www.sciencedaily.com. Retrieved 11 December 2015.

[Bar-On2018-7] Bar-On YM, Phillips R, Milo R (2018). "The biomass distribution on Earth" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 115 (25): 6506–6511. Bibcode:1998PNAS...95.6578W. doi:10.1073/pnas.1711842115. PMC 6016768. PMID 29784790.

[Doglioni2016-8] Doglioni C, Pignatti J, Coleman M (2016). "Why did life develop on the surface of the Earth in the Cambrian?". Geoscience Frontiers. 7 (6): 865–873. Bibcode:2016GeoFr...7..865D. doi:10.1016/j.gsf.2016.02.001. hdl:11573/925124.

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