Editing Cold seep (section)

== Formation and ecological succession ==

Cold seeps occur over fissures on the seafloor caused by [[tectonic]] activity. [[Oil]] and [[methane]] "seep" out of those fissures, get diffused by sediment, and emerge over an area several hundred meters wide.<ref name="Hsing 2010" />

Methane ({{chem|CH|4}}) is the main component of [[natural gas]].<ref name="Hsing 2010" /> But in addition to being an important energy source for humans, methane also forms the basis of a cold seep [[ecosystem]].<ref name="Hsing 2010" /> Cold seep [[Biota (ecology)|biota]] below {{convert|200|m|ft|abbr=on}} typically exhibit much greater systematic specialization and reliance on [[chemoautotrophy]] than those from shelf depths.<ref name="Bernardino 2012" /> Deep-sea seeps sediments are highly heterogeneous.<ref name="Bernardino 2012" /> They sustain different [[Geochemistry|geochemical]] and microbial processes that are reflected in a complex mosaic of habitats inhabited by a mixture of specialist ([[heterotrophic]] and [[Symbiosis|symbiont]]-associated) and background fauna.<ref name="Bernardino 2012" />
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They are remarkable in that they utilize a [[carbon]] source independent of [[photosynthesis]] and the sun-dependent photosynthetic food chain that supports all other life on Earth.<ref name="MMS 2006" /> Although the process of chemosynthesis is entirely microbial, chemosynthetic bacteria and their production can support thriving assemblages of higher organisms through [[symbiosis]].<ref name="MMS 2006" />

These prokaryotes, both [[Archaea]] and [[Bacteria]], process sulfides and methane through [[chemosynthesis]] into chemical energy. More complex organisms, such as [[Vesicomyidae|vesicomyid clams]] and [[Siboglinidae|siboglinid]] [[tube worm (body plan)|tube worms]] use this energy to power their own life processes.  In exchange, the microbes are provided with both safety and a reliable source of food. Other microbes form mats that blanket sizable areas.
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=== Chemosynthetic communities ===

[[File:bacterial mat.jpg|thumb|[[Bacterial mat]] consisting of sulfide-oxidizing bacteria ''[[Beggiatoa]]'' spp. at a seep on [[Blake Ridge]], off South Carolina. The red dots are range-finding laser beams.]]

Biological research in cold seeps and hydrothermal vents has been mostly focused on the [[microbiology]] and the prominent  macro-invertebrates thriving on [[Chemosynthesis|chemosynthetic]] microorganisms.<ref name="Vanreusel 2010" /> Much less research has been done on the smaller [[benthic]] fraction at the size of the [[meiofauna]] (<1&nbsp;mm).<ref name="Vanreusel 2010" />

A community composition's orderly shift from one set of species to another is called [[ecological succession]].<ref name="Hsing 2010" />

The first type of organism to take advantage of this deep-sea energy source is [[bacteria]].<ref name="Hsing 2010" /> Aggregating into [[bacterial mat]]s at cold seeps, these bacteria metabolize methane and [[hydrogen sulfide]] (another gas that emerges from seeps) for energy.<ref name="Hsing 2010" /> This process of obtaining energy from chemicals is known as [[chemosynthesis]].<ref name="Hsing 2010" />

[[File:Noaamussels 600A musselNearBrinePoolExpLophelia II 2010.jpg|left|thumb|A mussel bed at the edge of the brine pool]]

During this initial stage, when methane is relatively abundant, dense [[mussel]] beds also form near the cold seep.<ref name="Hsing 2010" /> Mostly composed of species in the genus ''[[Bathymodiolus]]'', these mussels do not directly consume food;<ref name="Hsing 2010" /> Instead, they are nourished by [[symbiotic]] bacteria that also produce energy from methane, similar to their relatives that form mats.<ref name="Hsing 2010" /> Chemosynthetic bivalves are prominent constituents of the fauna of cold seeps and are represented in that setting by five families: [[Solemyidae]], [[Lucinidae]], [[Vesicomyidae]], [[Thyasiridae]], and [[Mytilidae]].<ref name="Oliver 2011" />

This microbial activity produces [[calcium carbonate]], which is deposited on the [[seafloor]] and forms a layer of rock.<ref name="Hsing 2010" /> During a period lasting up to several decades, these rock formations attract [[siboglinidae|siboglinid]] [[Lamellibrachia|tubeworms]], which settle and grow along with the mussels.<ref name="Hsing 2010" /> Like the mussels, tubeworms rely on chemosynthetic bacteria (in this case, a type that needs [[hydrogen sulfide]] instead of methane) for survival.<ref name="Hsing 2010" /> True to any symbiotic relationship, a tubeworm also provides for its bacteria by appropriating hydrogen sulfide from the environment.<ref name="Hsing 2010" /> The sulfide not only comes from the water, but is also mined from the sediment through an extensive "root" system that a tubeworm "bush" establishes in the hard, carbonate substrate.<ref name="Hsing 2010" /> A tubeworm bush can contain hundreds of individual worms, which can grow a meter or more above the sediment.<ref name="Hsing 2010" />

Cold seeps do not last indefinitely. As the rate of gas seepage slowly decreases, the shorter-lived, methane-hungry mussels (or more precisely, their methane-hungry bacterial symbionts) start to die off.<ref name="Hsing 2010" /> At this stage, tubeworms become the dominant organism in a seep community.<ref name="Hsing 2010" /> As long as there is some sulfide in the sediment, the sulfide-mining tubeworms can persist.<ref name="Hsing 2010" /> Individuals of one tubeworm species ''[[Lamellibrachia luymesi]]'' have been estimated to live for over 250 years in such conditions.<ref name="Hsing 2010" />

{|
|-
||[[File:Siboglinidae.jpg|thumb|"Roots" of tubeworms also provide a supply of hydrogen sulfide from the sediment to the bacteria inside these tubeworms.]]
||[[File:Lamellibrachia luymesi.png|left|thumb|Symbiotic vestimentiferan tubeworm ''[[Lamellibrachia luymesi]]'' from a cold seep at 550&nbsp;m depth in the Gulf of Mexico. In the sediments around the base are orange bacterial mats of the sulfide-oxidizing bacteria ''[[Beggiatoa]]'' spp. and empty shells of various clams and snails, which are also common inhabitants of the seeps.<ref name="Boetius 2005" />]]
||[[File:cold seep community.jpg|left|thumb|[[Lamellibrachia|Tubeworms]], soft [[coral]]s, and chemosynthetic mussels at a seep located {{convert|3000|m|ft|abbr=on}} down on the Florida Escarpment. [[Eelpout]]s,  a [[Galatheidae|Galatheid]] crab, and an [[Alvinocarididae|alvinocarid]] shrimp feed on mussels damaged during a sampling exercise.]]
|}

=== The Benthic Filter ===
The organisms living at cold seeps have a large impact on the carbon cycle and on climate. Chemosynthetic organisms, specifically methanogenic (methane-consuming) organisms, prohibit the methane seeping up from beneath the seafloor from being released into the water above. Since methane is such a potent greenhouse gas, methane release could cause global warming when gas hydrate reservoirs destabilized.<ref name=":1">{{Cite journal|last1=Sommer|first1=S.|last2=Pfannkuche|first2=O.|last3=Linke|first3=P.|last4=Luff|first4=R.|last5=Greinert|first5=J.|last6=Drews|first6=M.|last7=Gubsch|first7=S.|last8=Pieper|first8=M.|last9=Poser|first9=M.|last10=Viergutz|first10=T.|date=June 2006|title=Efficiency of the benthic filter: Biological control of the emission of dissolved methane from sediments containing shallow gas hydrates at Hydrate Ridge: BIOLOGICAL CONTROL OF EMISSION OF DISSOLVED METHANE|journal=Global Biogeochemical Cycles|language=en|volume=20|issue=2|pages=n/a|doi=10.1029/2004GB002389|s2cid=54695808 |doi-access=free|hdl=1956/1315|hdl-access=free}}</ref> The consumption of methane by aerobic and anaerobic seafloor life is called "the benthic filter".<ref name=":2">{{Cite journal|last1=Boetius|first1=Antje|last2=Wenzhöfer|first2=Frank|date=September 2013|title=Seafloor oxygen consumption fuelled by methane from cold seeps|url=http://www.nature.com/articles/ngeo1926|journal=Nature Geoscience|language=en|volume=6|issue=9|pages=725–734|doi=10.1038/ngeo1926|bibcode=2013NatGe...6..725B|issn=1752-0894|url-access=subscription}}</ref> The first part of this filter is the anaerobic bacteria and archaea underneath the seafloor that consume methane through the [[anaerobic oxidation of methane]] (AOM).<ref name=":2" /> If the flux of methane flowing through the sediment is too large, and the anaerobic bacteria and archaea are consuming the maximum amount of methane, then the excess methane is consumed by free-floating or symbiotic aerobic bacteria above the sediment at the seafloor. The symbiotic bacteria have been found in organisms such as tube worms and clams living at cold seeps; these organisms provide oxygen to the aerobic bacteria as the bacteria provide energy they obtain from the consumption of methane. Understanding how efficient the benthic filter is can help predict how much methane escapes the seafloor at cold seeps and enters the water column and eventually the atmosphere. Studies have shown that 50–90% of methane is consumed at cold seeps with bacterial mats. Areas with clam beds have less than 15% of methane escaping.<ref name=":1" /> Efficiency is determined by a number of factors. The benthic layer is more efficient with low flow of methane, and efficiency decreases as methane flow or the speed of flow increases.<ref name=":2" /> Oxygen demand for cold seep ecosystems is much higher than other benthic ecosystems, so if the bottom water does not have enough oxygen, then the efficiency of aerobic microbes in removing methane is reduced.<ref name=":1" /> The benthic filter cannot affect methane that is not traveling through the sediment. Methane can bypass the benthic filter if it bubbles to the surface or travels through cracks and fissures in the sediment.<ref name=":1" /> These organisms are the only biological sink of methane in the ocean.<ref name=":2" />

=== Comparison with other communities ===
{{Main|Deep sea communities|Hydrothermal vent}}

[[File:Expl1771 - Flickr - NOAA Photo Library.jpg|thumb|right|{{center|''[[Lamellibrachia]]'' tube worms and mussel at a cold seep}}]]

Cold seeps and [[hydrothermal vent]]s of deep oceans are communities that do not rely on [[photosynthesis]] for food and energy production.<ref name="Vanreusel 2010" /> These systems are largely driven by [[chemosynthetic]] derived energy.<ref name="Vanreusel 2010" /> Both systems share common characteristics such as the presence of reduced chemical compounds ([[Hydrogen sulfide|H<sub>2</sub>S]] and [[hydrocarbonate]]s), local [[hypoxia (environmental)|hypoxia]] or even [[Anoxic waters|anoxia]], a high abundance and metabolic activity of bacterial populations, and the production of [[wikt:autochthonous|autochthonous]], organic material by [[chemoautotrophic]] bacteria.<ref name="Vanreusel 2010" /> Both hydrothermal vents and cold seeps show highly increased levels of metazoan biomass in association with a low local diversity.<ref name="Vanreusel 2010" /> This is explained through the presence of dense aggregations of foundation species and [[epizoic]] animals living within these aggregations.<ref name="Vanreusel 2010" /> Community-level comparisons reveal that vent, seep, and organic-fall macrofauna are very distinct in terms of composition at the family level, although they share many dominant [[taxa]] among highly sulphidic habitats.<ref name="Bernardino 2012" />

However, hydrothermal vents and cold seeps also differ in many ways. Compared to the more stable cold seeps, vents are characterized by locally-high temperatures, strongly fluctuating temperatures, pH, sulfide and oxygen concentrations, often the absence of sediments, a relatively young age, and often-unpredictable conditions, such as waxing and waning of vent fluids or volcanic eruptions.<ref name="Vanreusel 2010" /> Unlike hydrothermal vents, which are volatile and [[ephemeral]] environments, cold seeps emit at a slow and dependable rate. Likely owing to the cooler temperatures and stability, many cold seep organisms are much longer-lived than those inhabiting hydrothermal vents.

=== End of cold seep community ===
{{Main|Deep water coral}}

Finally, as cold seeps become inactive, tubeworms also start to disappear, clearing the way for [[coral]]s to settle on the now-exposed carbonate substrate.<ref name="Hsing 2010" /> The corals do not rely on hydrocarbons seeping out of the seafloor.<ref name="Hsing 2010" /> Studies on ''[[Lophelia pertusa]]'' suggest they derive their nutrition primarily from the ocean surface.<ref name="Hsing 2010" /> Chemosynthesis plays only a very small role, if any, in their settlement and growth.<ref name="Hsing 2010" /> While deepwater corals do not seem to be chemosynthesis-based organisms, the chemosynthetic organisms that come before them enable the corals' existence.<ref name="Hsing 2010" /> This hypothesis about establishment of [[deep water coral]] reefs is called hydraulic theory.<ref>{{cite journal | last1 = Hovland | first1 = M. | last2 = Thomsen | first2 = E. | year = 1997 | title = Cold-water corals—are they hydrocarbon seep related? | journal = Marine Geology | volume = 137 | issue = 1–2| pages = 159–164 | doi = 10.1016/S0025-3227(96)00086-2 | bibcode = 1997MGeol.137..159H }}</ref><ref>Hovland M. (2008). ''Deep-water coral reefs: unique biodiversity hot-spots''. 8.10 Summary and re-iteration of the hydraulic theory. [[Springer Science+Business Media|Springer]], 278 pp. {{ISBN|978-1-4020-8461-4}}. Pages [https://books.google.com/books?id=CIc7w6SuhY8C&dq=hydraulic+theory+coral&pg=PA204 204]-205.</ref>