Editing Diatom (section)

== Ecology ==
{{plankton sidebar|taxonomy}}
[[File:Diatoms+Abundance.png|thumb|upright=1.7|right| {{center|Regions of high abundance of diatoms in the ocean}}]]
[[File:Diatoms Egge and Aksnes 1992 plot.png|thumb|upright=1.7|right| {{center|Diatom dominance (as a percentage of total cell
counts)<br />versus silicate concentration <ref name="Egge 92">{{cite journal |last1=Egge |first1=J. K. |last2=Aksnes |first2=D. L. |year=1992 |title=Silicate as regulating nutrient in phytoplankton competition |journal=Mar. Ecol. Prog. Ser. |volume=83 |pages=281–289 |doi=10.3354/meps083281 |bibcode=1992MEPS...83..281E |doi-access=free}}</ref>}}]]

===Distribution===

Diatoms are a widespread group and can be found in the [[ocean]]s, in [[fresh water]], in [[soil]]s, and on damp surfaces. They are one of the dominant components of [[phytoplankton]] in nutrient-rich coastal waters and during oceanic spring blooms, since they can divide more rapidly than other groups of phytoplankton.<ref name="Furnas 1990" /> Most live [[pelagic]]ally in open water, although some live as surface films at the water-sediment interface ([[benthos|benthic]]), or even under damp atmospheric conditions. They are especially important in oceans, where a 2003 study found that they contribute an estimated 45% of the total oceanic [[primary production]] of organic material.<ref name="BGCC1">{{cite journal |doi=10.1029/2002GB002018 |title=Role of diatoms in regulating the ocean's silicon cycle |journal=Global Biogeochemical Cycles |volume=17 |issue=4 |year=2003 |last1=Yool |first1=Andrew |last2=Tyrrell |first2=Toby |pages=n/a |bibcode=2003GBioC..17.1103Y |citeseerx=10.1.1.394.3912 |s2cid=16849373 }}</ref> However, a more recent 2016 study estimates that the number is closer to 20%.<ref>{{Cite journal |last1=Malviya |first1=Shruti |last2=Scalco |first2=Eleonora |last3=Audic |first3=Stéphane |last4=Vincent |first4=Flora |last5=Veluchamy |first5=Alaguraj |last6=Poulain |first6=Julie |last7=Wincker |first7=Patrick |last8=Iudicone |first8=Daniele |last9=de Vargas |first9=Colomban |last10=Bittner |first10=Lucie |last11=Zingone |first11=Adriana |last12=Bowler |first12=Chris |date=2016-02-29 |title=Insights into global diatom distribution and diversity in the world's ocean |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=11 |pages=E1516–E1525 |doi=10.1073/pnas.1509523113 |doi-access=free |pmid=26929361 |issn=0027-8424|pmc=4801293 |bibcode=2016PNAS..113E1516M }}</ref> Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically.<ref>{{cite journal |doi=10.2307/2406711 |pmid=28563010 |jstor=2406711 |title=Plankton Evolution |journal=Evolution |volume=24 |issue=1 |pages=1–22 |year=1970 |last1=Lipps |first1=Jere H. }}</ref><ref name="Horner2002">{{cite book|author=Rita A. Horner|title=A taxonomic guide to some common marine phytoplankton|url=https://books.google.com/books?id=JU8VAQAAIAAJ|access-date=13 November 2013|year=2002|publisher=Biopress|isbn=978-0-948737-65-7|pages=25–30|archive-date=1 August 2020|archive-url=https://web.archive.org/web/20200801020312/https://books.google.com/books?id=JU8VAQAAIAAJ|url-status=live}}</ref>

===Growth===
[[Plankton]]ic diatoms in freshwater and marine environments typically exhibit a "[[boom and bust]]" (or "''bloom'' and bust") lifestyle. When conditions in the upper mixed layer (nutrients and light) are favourable (as at the [[Spring (season)|spring]]), their competitive edge and rapid growth rate<ref name="Furnas 1990">{{cite journal |doi=10.1093/plankt/12.6.1117 |id={{INIST|5474600}} |title=In situ growth rates of marine phytoplankton: Approaches to measurement, community and species growth rates |journal=Journal of Plankton Research |volume=12 |issue=6 |pages=1117–51 |year=1990 |last1=Furnas |first1=Miles J. }}</ref> enables them to dominate phytoplankton communities ("boom" or "bloom"). As such they are often classed as opportunistic [[r-selection|r-strategists]] (i.e. those organisms whose ecology is defined by a high growth rate, ''r'').

===Impact===
The freshwater diatom ''[[Didymosphenia geminata]]'', commonly known as ''Didymo,'' causes severe [[environmental degradation]] in water-courses where it blooms, producing large quantities of a brown jelly-like material called "brown snot" or "rock snot". This diatom is native to Europe and is an [[invasive species]] both in the [[antipodes]] and in parts of [[North America]].<ref>[http://alienspecies.royalbcmuseum.bc.ca/eng/species/didymo-rock-snot "Didymo, Aliens Among Us"]. {{webarchive|url=https://web.archive.org/web/20151007110108/http://alienspecies.royalbcmuseum.bc.ca/eng/species/didymo-rock-snot |date=7 October 2015 }} Virtual Exhibit of the [[Virtual Museum of Canada]]</ref><ref>{{Cite web |url=http://www.ct.gov/deep/cwp/view.asp?A=4013&Q=476204 |title=DEP Reports Didymo Discovered in the West Branch Farmington River |access-date=27 April 2015 |archive-url=https://web.archive.org/web/20150216015753/http://www.ct.gov/deep/cwp/view.asp?A=4013&Q=476204 |archive-date=16 February 2015 |url-status=dead }}</ref> The problem is most frequently recorded from [[Australia]] and [[Didymo in New Zealand|New Zealand]].<ref>{{cite web |title=Didymo Stakeholder Update – 31 October 2008 |url=http://www.biosecurity.govt.nz/pests/didymo/update-31-10-08 |url-status=dead |archive-url=https://web.archive.org/web/20130212200059/http://www.biosecurity.govt.nz/pests/didymo/update-31-10-08 |archive-date=12 February 2013 |access-date=1 December 2013 |publisher=MAF Biosecurity New Zealand}}</ref>

When conditions turn unfavourable, usually upon depletion of nutrients, diatom cells typically increase in sinking rate and exit the upper mixed layer ("bust"). This sinking is induced by either a loss of buoyancy control, the synthesis of mucilage that sticks diatoms cells together, or the production of heavy ''resting spores''. Sinking out of the upper mixed layer removes diatoms from conditions unfavourable to growth, including grazer populations and higher temperatures (which would otherwise increase cell [[metabolism]]). Cells reaching deeper water or the shallow seafloor can then rest until conditions become more favourable again. In the open ocean, many sinking cells are lost to the deep, but refuge populations can persist near the [[thermocline]].

Ultimately, diatom cells in these resting populations re-enter the upper mixed layer when vertical mixing entrains them. In most circumstances, this mixing also replenishes nutrients in the upper mixed layer, setting the scene for the next round of diatom blooms. In the open ocean (away from areas of continuous [[upwelling]]<ref name="Dugdale 1998">{{cite journal | last1=Dugdale | first1=R. C. | last2=Wilkerson | first2=F. P. | year=1998 | title=Silicate regulation of new production in the equatorial Pacific upwelling | journal=Nature | volume=391 | issue=6664| pages=270–273 | doi=10.1038/34630|bibcode=1998Natur.391..270D | s2cid=4394149 }}</ref>), this cycle of bloom, bust, then return to pre-bloom conditions typically occurs over an annual cycle, with diatoms only being prevalent during the spring and early summer. In some locations, however, an autumn bloom may occur, caused by the breakdown of summer stratification and the entrainment of nutrients while light levels are still sufficient for growth. Since vertical mixing is increasing, and light levels are falling as winter approaches, these blooms are smaller and shorter-lived than their spring equivalents.

In the open ocean, the diatom (spring) bloom is typically ended by a shortage of silicon. Unlike other minerals, the requirement for silicon is unique to diatoms and it is not regenerated in the plankton ecosystem as efficiently as, for instance, [[nitrogen]] or [[phosphorus]] nutrients. This can be seen in maps of surface nutrient concentrations – as nutrients decline along gradients, silicon is usually the first to be exhausted (followed normally by nitrogen then phosphorus).

Because of this bloom-and-bust cycle, diatoms are believed to play a disproportionately important role in the export of carbon from oceanic surface waters<ref name="Dugdale 1998" /><ref name="Smetacek 1985">{{cite journal | last1=Smetacek | first1=V. S. | year=1985 | title=Role of sinking in diatom life-history cycles: Ecological, evolutionary and geological significance | journal=Mar. Biol. | volume=84 | issue=3| pages=239–251 | doi=10.1007/BF00392493 | bibcode=1985MarBi..84..239S | s2cid=85054779 }}</ref> (see also the [[biological pump]]). Significantly, they also play a key role in the regulation of the [[biogeochemical cycle]] of [[silicon]] in the modern ocean.<ref name="BGCC1" /><ref name="AAAS1" />

===Reason for success===
Diatoms are ecologically successful, and occur in virtually every environment that contains water – not only oceans, seas, lakes, and streams, but also soil and wetlands.{{Citation needed|date=February 2016}} The use of silicon by diatoms is believed by many researchers to be the key to this ecological success. Raven (1983)<ref name="Raven 1983">{{cite journal | last1=Raven | first1=J. A. | year=1983 | title=The transport and function of silicon in plants | journal=Biol. Rev. | volume=58 | issue=2| pages=179–207 | doi=10.1111/j.1469-185X.1983.tb00385.x| s2cid=86067386 }}</ref> noted that, relative to organic [[cell wall]]s, silica frustules require less energy to synthesize (approximately 8% of a comparable organic wall), potentially a significant saving on the overall cell energy budget. In a now classic study, Egge and Aksnes (1992)<ref name="Egge 92" /> found that diatom [[ecological dominance|dominance]] of [[mesocosm]] communities was directly related to the availability of silicic acid – when concentrations were greater than 2 [[Mole (unit)|μmol]] m<sup>−3</sup>, they found that diatoms typically represented more than 70% of the phytoplankton community. Other researchers<ref name="milligan 2002">{{cite journal | last1=Milligan | first1=A. J. | last2=Morel | first2=F. M. M. | year=2002 | title=A proton buffering role for silica in diatoms | journal=Science | volume=297 | issue=5588| pages=1848–1850 | doi=10.1126/science.1074958 | pmid=12228711|bibcode=2002Sci...297.1848M | s2cid=206507070 }}</ref> have suggested that the biogenic silica in diatom cell walls acts as an effective [[pH]] [[buffering agent]], facilitating the conversion of [[bicarbonate]] to dissolved CO<sub>2</sub> (which is more readily assimilated). More generally, notwithstanding these possible advantages conferred by their use of silicon, diatoms typically have higher growth rates than other algae of the same corresponding size.<ref name="Furnas 1990" />

===Sources for collection===
{{Further|topic=the genus of filamentous diatoms|Oscillaria}}
Diatoms can be obtained from multiple sources.<ref name="Chamberlain 1901">Chamberlain, C. J. (1901) ''Methods in Plant Histology'', University of Chicago Press.</ref> Marine diatoms can be collected by direct water sampling, and benthic forms can be secured by scraping [[barnacle]]s, [[oyster]] and other shells. Diatoms are frequently present as a brown, slippery coating on submerged stones and sticks, and may be seen to "stream" with river current. The surface mud of a pond, ditch, or lagoon will almost always yield some diatoms. Living diatoms are often found clinging in great numbers to filamentous algae, or forming gelatinous masses on various submerged plants. ''[[Cladophora]]'' is frequently covered with ''[[Cocconeis]]'', an elliptically shaped diatom; ''[[Vaucheria]]'' is often covered with small forms. Since diatoms form an important part of the food of [[mollusc]]s, [[tunicate]]s, and [[fish]]es, the [[alimentary tract]]s of these animals often yield forms that are not easily secured in other ways. Diatoms can be made to emerge by filling a jar with water and mud, wrapping it in black paper and letting direct sunlight fall on the surface of the water. Within a day, the diatoms will come to the top in a scum and can be isolated.<ref name="Chamberlain 1901" />