Reef: Difference between revisions

A '''reef''' is a ridge or [[shoal]] of rock, [[coral]], or similar relatively stable material lying beneath the surface of a natural body of water.<ref name="NatGeo" /> Many reefs result from natural, [[abiotic component|abiotic]] (non-living) processes such as [[deposition (geology)|deposition]] of sand or [[wave erosion]] planning down rock outcrops. However, reefs such as the [[coral reef]]s of tropical waters are formed by [[biotic component|biotic]] (living) processes, dominated by corals and [[coralline algae]]. [[Artificial reef]]s, such as shipwrecks and other man-made underwater structures, may occur intentionally or as the result of an accident. These are sometimes designed to increase the physical complexity of featureless sand bottoms to attract a more diverse range of [[organism]]s. They provide shelter to various aquatic animals which help prevent extinction.<ref>{{Cite journal |last1=Gilby |first1=Ben L. |last2=Olds |first2=Andrew D. |last3=Peterson |first3=Charles H. |last4=Connolly |first4=Rod M. |last5=Voss |first5=Christine M. |last6=Bishop |first6=Melanie J. |last7=Elliott |first7=Michael |last8=Grabowski |first8=Jonathan H. |last9=Ortodossi |first9=Nicholas L. |last10=Schlacher |first10=Thomas A. |date=September 2018 |title=Maximizing the benefits of oyster reef restoration for finfish and their fisheries |url=https://onlinelibrary.wiley.com/doi/10.1111/faf.12301 |journal=Fish and Fisheries |language= |volume=19 |issue=5 |pages=931–947 |doi=10.1111/faf.12301 |issn=1467-2960}}</ref> Another reason reefs are put in place is for aquaculture, and fish farmers who are looking to improve their businesses sometimes invest in them.<ref>{{Cite web |last=Geographic |first=National |date= |title=Reef |url=https://education.nationalgeographic.org/resource/reef/ |access-date=2024-12-09 |website=education.nationalgeographic.org |language=en}}</ref> Reefs are often quite near to the surface, but not all definitions require this.<ref name="NatGeo" />

Conversely, mounds lack a macroscopic skeletal framework. Instead, they are built by microorganisms or by organisms that also lack a skeletal framework. A microbial mound might be built exclusively or primarily by [[cyanobacteria]]. Examples of [[biostrome]]s formed by cyanobacteria occur in the [[Great Salt Lake]] in [[Utah]], United States, and in [[Shark Bay]] on the coast of [[Western Australia]].<ref name=":0" /><ref>{{Cite journal |last=Wood |first=Rachel |date=2001-12-15 |title=Are reefs and mud mounds really so different? |url=https://www.sciencedirect.com/science/article/pii/S0037073801001464 |journal=Sedimentary Geology |series=Carbonate Mounds: sedimentation, organismal response, and diagenesis |volume=145 |issue=3 |pages=161–171 |doi=10.1016/S0037-0738(01)00146-4 |bibcode=2001SedG..145..161W |issn=0037-0738}}</ref>

Cyanobacteria do not have skeletons, and individual organisms are microscopic. However, they can encourage the precipitation or accumulation of calcium carbonate to produce distinct sediment bodies in composition that have relief on the seafloor. Cyanobacterial mounds were most abundant before the evolution of shelly macroscopic organisms, but they still exist today. [[Stromatolite]]s, for instance, are microbial mounds with a laminated internal structure. Whereas, [[bryozoan]]s and [[crinoid]]s, common contributors to marine sediments during the [[Mississippian (geology)|Mississippian period]], produce a different kind of mound. Although bryozoans are small and crinoid skeletons disintegrate, bryozoan and crinoid meadows can persist over time and produce compositionally distinct bodies of sediment with depositional relief.<ref name=":0" /><ref>{{Cite webjournal |last=crossref |title=Chooser |url=https://chooser.crossref.org/ |access-date=2024-04-20 |website=chooser.crossref.org |language=en |doi=10.2307/3514838|jstor=3514838 }}</ref>

The [[Proterozoic]] [[Belt Supergroup]] contains evidence of possible [[microbial mat]] and dome structures similar to stromatolite and chicken reef complexes.{{clarify|what are chicken reef complexes?|date=November 2024}}<ref name=":0" /><ref>{{Cite journal |last=Schieber |first=Jürgen |date=1998 |title=Possible indicators of microbial mat deposits in shales and sandstones: examples from the Mid-Proterozoic Belt Supergroup, Montana, U.S.A. |url=https://sepm04.sitehost.iu.edu/PDF/JS-J24-microbial_mat_challenge |journal=Sedimentary Geology |volume=120 |issue=1 |pages=105–124|doi=10.1016/S0037-0738(98)00029-3 |bibcode=1998SedG..120..105S }}</ref>

Ancient reefs buried within [[stratigraphy|stratigraphic]] sections are of considerable interest to [[geologist]]s because they provide paleo-environmental information about the location in [[history of Earth|Earth's history]]. In addition, reef structures within a sequence of [[sedimentary rock]]s provide a discontinuity which may serve as a trap or conduit for [[fossil fuel]]s or mineralizing fluids to form [[petroleum]] or [[ore deposit]]s.<ref>{{Cite journal |lastlast1=Gorokhovich |firstfirst1=Yuri |last2=Learning |first2=Lumen |title=Coastal Geology: Shorelines |url=https://pressbooks.cuny.edu/gorokhovich/chapter/coastal-geology-shorelines/ |language=en}}</ref>

During the [[Cambrian]] Period, the conical or tubular skeletons of [[Archaeocyatha]], an extinct group of uncertain affinities (possibly sponges), built reefs.<ref>{{Cite web |title=Archaeocyathans |url=https://ucmp.berkeley.edu/porifera/archaeo.html#:~:text=The%20first%20archaeocyaths%20appear%20roughly,creation%20of%20the%20first%20reefs. |access-date=2024-04-20 |website=ucmp.berkeley.edu}}</ref> Other groups, such as the Bryozoa, have been important interstitial organisms, living between the framework builders. The corals which build reefs today, the [[Scleractinia]], arose after the [[Permian–Triassic extinction event]] that wiped out the earlier rugose corals (as well as many other groups). They became increasingly important reef builders throughout the [[Mesozoic]] Era.<ref>{{Cite journal |lastlast1=Pruss |firstfirst1=Sara B. |last2=Bottjer |first2=David J. |date=2005-09-01 |title=The reorganization of reef communities following the end-Permian mass extinction |url=https://www.sciencedirect.com/science/article/pii/S163106830500045X |journal=Comptes Rendus Palevol |volume=4 |issue=6 |pages=553–568 |doi=10.1016/j.crpv.2005.04.003 |bibcode=2005CRPal...4..553P |issn=1631-0683}}</ref> They may have arisen from a rugose coral ancestor.