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43-577: Kriegers Flak is a reef located in the Baltic Sea , north of Rügen , south of Skåne with its west most point about 15 km east of Møn . It is named after the Danish naval officer Christian Krieger, who in 1840 mapped the Baltic Sea. The Danish part of the reef has at its most shallow place a depth of 16 m. The reef spans the exclusive economic zones of Denmark, Germany and Sweden and

86-717: A stub . You can help Misplaced Pages by expanding it . Reef Earth's largest coral reef system is the Great Barrier Reef in Australia, at a length of over 2,300 kilometres (1,400 miles). The word "reef" traces its origins back to the Old Norse word rif, meaning "rib" or "reef". Rif comes from the Proto-Germanic term ribją meaning "rib". Reefs may be classified in terms of their origin, geographical location, depth, and topography . For example

129-445: A barrier reef forms a calcareous barrier around an island, resulting in a lagoon between the shore and the reef. Conversely, an atoll is a ring reef with no land present. The reef front, facing the ocean, is a high energy locale. Whereas, the internal lagoon will be at a lower energy with fine grained sediments. Both mounds and reefs are considered to be varieties of organosedimentary buildups, which are sedimentary features, built by

172-429: A fairly massive hard stony calcium carbonate structure on which other reef organisms like sponges and seaweeds can grow, and provide a habitat for mobile benthic organisms. These biotic reef types take on additional names depending upon how the reef lies in relation to the land, if any. Reef types include fringing reefs , barrier reefs , and atolls . A fringing reef is a reef that is attached to an island. Whereas,

215-649: 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 biostromes formed by cyanobacteria occur in the Great Salt Lake in Utah , United States, and in Shark Bay on the coast of Western Australia . Cyanobacteria do not have skeletons, and individual organisms are microscopic. However, they can encourage

258-611: A major constituent of the fossil record of the first forms of life on Earth. They peaked about 1.25 billion years ago (Ga) and subsequently declined in abundance and diversity, so that by the start of the Cambrian they had fallen to 20% of their peak. The most widely supported explanation is that stromatolite builders fell victim to grazing creatures (the Cambrian substrate revolution ); this theory implies that sufficiently complex organisms were common around 1 Ga. Another hypothesis

301-530: A means of providing shelter and protection from a harsh environment. Lichen stromatolites are a proposed mechanism of formation of some kinds of layered rock structure that are formed above water, where rock meets air, by repeated colonization of the rock by endolithic lichens . Some Archean rock formations show macroscopic similarity to modern microbial structures, leading to the inference that these structures represent evidence of ancient life, namely stromatolites. However, others regard these patterns as being

344-615: A tropical coral fringing reef, or a temperate rocky intertidal reef. A variety of biotic reef types exists, including oyster reefs and sponge reefs , but the most massive and widely distributed are tropical coral reefs . Although corals are major contributors to the framework and bulk material comprising a coral reef, the organisms most responsible for reef growth against the constant assault from ocean waves are calcareous algae, especially, although not entirely, coralline algae . Oyster larvae prefer to settle on adult oysters and thereby develop layers building upwards. These eventually form

387-643: A unique ecosystem in the Mexican desert. Alchichica Lake in Puebla , Mexico has two distinct morphologic generations of stromatolites: columnar-dome like structures, rich in aragonite , forming near the shore line, dated back to 1,100 years before present (ybp) and spongy-cauliflower like thrombolytic structures that dominate the lake from top to the bottom, mainly composed of hydromagnesite , huntite , calcite and dated back to 2,800 ybp. The only open marine environment where modern stromatolites are known to prosper

430-516: A well-exposed example of the thrombolite-stromatolite-metazoan reefs that developed during the Proterozoic period, the stromatolites here being better developed in updip locations under conditions of higher current velocities and greater sediment influx. Modern stromatolites are mostly found in hypersaline lakes and marine lagoons where high saline levels prevent animal grazing. One such location where excellent modern specimens can be observed

473-717: Is Hamelin Pool Marine Nature Reserve , Shark Bay in Western Australia . In 2010, a fifth type of chlorophyll , namely chlorophyll f , was discovered by Min Chen from stromatolites in Shark Bay. Halococcus hamelinensis , a halophilic archaeon , occurs in living stromatolites in Shark Bay where it is exposed to extreme conditions of UV radiation, salinity and desiccation . H. hamelinesis possesses genes that encode enzymes employed in

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516-430: Is an active area of research in geology. Multiple morphologies of stromatolites may exist in a single local or geological strata, relating to the specific conditions occurring in different region and water depths. Most stromatolites are spongiostromate in texture, having no recognisable microstructure or cellular remains. A minority are porostromate , having recognisable microstructure; these are mostly unknown from

559-503: Is estimated to be able to accommodate 1600  MW worth of offshore wind farms of these three countries. As such, it is the site of the German 288 MW offshore wind farm Baltic 2 , and of the Danish 600 MW offshore wind farm Kriegers Flak . A 640 MW Swedish wind farm proposed by Vattenfall received preliminary approval by Sweden in May 2022. This Danish location article is

602-404: Is that protozoa such as foraminifera were responsible for the decline, favoring formation of thrombolites over stromatolites through microscopic bioturbation . Proterozoic stromatolite microfossils (preserved by permineralization in silica) include cyanobacteria and possibly some forms of the eukaryote chlorophytes (that is, green algae ). One genus of stromatolite very common in

645-640: Is the Exuma Cays in the Bahamas. Laguna de Bacalar in Mexico's southern Yucatán Peninsula has an extensive formation of living giant microbialites (that is, stromatolites or thrombolites). The microbialite bed is over 10 km (6.2 mi) long with a vertical rise of several meters in some areas. These may be the largest sized living freshwater microbialites, or any organism, on Earth. A 1.5 km stretch of reef-forming stromatolites (primarily of

688-539: The Holocene , living forms are rare. Stromatolites are layered, biochemical, accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains in biofilms (specifically microbial mats), through the action of certain microbial lifeforms, especially cyanobacteria . They exhibit a variety of forms and structures, or morphologies, including conical, stratiform, domal, columnar, and branching types. Stromatolites occur widely in

731-546: The 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. The Proterozoic Belt Supergroup contains evidence of possible microbial mat and dome structures similar to stromatolite and chicken reef complexes. Rocky reefs are underwater outcrops of rock projecting above

774-476: The Rigs-to-Reefs program), scuttling ships , or by deploying rubble or construction debris . Other artificial reefs are purpose built (e.g. the reef balls ) from PVC or concrete. Shipwrecks become artificial reefs on the seafloor. Regardless of construction method, artificial reefs generally provide stable hard surfaces where algae and invertebrates such as barnacles , corals, and oysters attach;

817-513: The geologic record is Collenia . The connection between grazer and stromatolite abundance is well documented in the younger Ordovician evolutionary radiation ; stromatolite abundance also increased after the Late Ordovician mass extinction and Permian–Triassic extinction event decimated marine animals, falling back to earlier levels as marine animals recovered. Fluctuations in metazoan population and diversity may not have been

860-525: The Nettle Cave at Jenolan Caves , NSW , Australia. The cyanobacteria live on the surface of the limestone and are sustained by the calcium-rich dripping water, which allows them to grow toward the two open ends of the cave which provide light. Stromatolites composed of calcite have been found in both the Blue Lake in the dormant volcano, Mount Gambier and at least eight cenote lakes including

903-591: The Precambrian but persist throughout the Palaeozoic and Mesozoic . Since the Eocene , porostromate stromatolites are known only from freshwater settings. Time lapse photography of modern microbial mat formation in a laboratory setting gives some revealing clues to the behavior of cyanobacteria in stromatolites. Biddanda et al. (2015) found that cyanobacteria exposed to localized beams of light moved towards

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946-905: The accumulation of attached marine life in turn provides intricate structure and food for assemblages of fish. Stromatolite Stromatolites ( / s t r oʊ ˈ m æ t ə ˌ l aɪ t s , s t r ə -/ stroh- MAT -ə-lytes, strə- ) or stromatoliths (from Ancient Greek στρῶμα ( strôma ) , GEN στρώματος ( strṓmatos )  'layer, stratum' and λίθος ( líthos )  'rock') are layered sedimentary formations ( microbialite ) that are created mainly by photosynthetic microorganisms such as cyanobacteria , sulfate-reducing bacteria , and Pseudomonadota (formerly proteobacteria). These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral " microbial mats ". In turn, these mats build up layer by layer, growing gradually over time. This process generates

989-481: The adjacent unconsolidated surface with varying relief. They can be found in depth ranges from intertidal to deep water and provide a substrate for a large range of sessile benthic organisms, and shelter for a large range of mobile organisms. They are often located in sub-tropical, temperate, and sub-polar latitudes. Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about

1032-420: The amount of oxygen in the primeval Earth's atmosphere through their continuing photosynthesis (see Great Oxygenation Event ). They use water, carbon dioxide, and sunlight to create their food. A layer of polysaccharides often forms over mats of cyanobacterial cells. In modern microbial mats, debris from the surrounding habitat can become trapped within the polysaccharide layer, which can be cemented together by

1075-444: The calcium carbonate to grow thin laminations of limestone . These laminations can accrete over time, resulting in the banded pattern common to stromatolites. The domal morphology of biological stromatolites is the result of the vertical growth necessary for the continued infiltration of sunlight to the organisms for photosynthesis. Layered spherical growth structures termed oncolites are similar to stromatolites and are also known from

1118-417: The characteristic lamination of stromatolites, a feature that is hard to interpret, in terms of its temporal and environmental significance. Different styles of stromatolite lamination have been described, which can be studied through microscopic and mathematical methods. A stromatolite may grow to a meter or more. Fossilized stromatolites provide important records of some of the most ancient life. As of

1161-405: The cyanobacteria form clumps that then expand outwards, with individual members remaining connected to the colony via long tendrils. This may be a protective mechanism that affords evolutionary benefit to the colony in harsh environments where mechanical forces act to tear apart the microbial mats. Thus these sometimes elaborate structures, constructed by microorganisms working somewhat in unison, are

1204-585: The fossil record of the Precambrian but are rare today. Very few Archean stromatolites contain fossilized microbes, but fossilized microbes are sometimes abundant in Proterozoic stromatolites. While features of some stromatolites are suggestive of biological activity, others possess features that are more consistent with abiotic (non-biological) precipitation. Finding reliable ways to distinguish between biologically formed and abiotic stromatolites

1247-477: The fossil record. Thrombolites are poorly laminated or non-laminated clotted structures formed by cyanobacteria, common in the fossil record and in modern sediments. There is evidence that thrombolites form in preference to stromatolites when foraminifera are part of the biological community. The Zebra River Canyon area of the Kubis platform in the deeply dissected Zaris Mountains of southwestern Namibia provides

1290-608: 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. They may have arisen from a rugose coral ancestor. Rugose corals built their skeletons of calcite and have a different symmetry from that of

1333-696: The genus Scytonema ) occurs in Chetumal Bay in Belize , just south of the mouth of the Rio Hondo and the Mexican border. Large microbialite towers up to 40 m high were discovered in the largest soda lake on Earth Lake Van in eastern Turkey. They are composed of aragonite and grow by precipitation of calcite from sub-lacustrine karst-water. Freshwater stromatolites are found in Lake Salda in southern Turkey. The waters are rich in magnesium and

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1376-486: The interaction of organisms and their environment. These interactions have a synoptic relief and whose biotic composition differs from that found on and beneath the surrounding sea floor . However, reefs are held up by a macroscopic skeletal framework, as what is seen on coral reefs. Corals and calcareous algae grow on top of one another, forming a three-dimensional framework that is modified in various ways by other organisms and inorganic processes. Conversely, mounds lack

1419-445: The light, or expressed phototaxis , and increased their photosynthetic yield, which is necessary for survival. In a novel experiment, the scientists projected a school logo onto a petri dish containing the organisms, which accreted beneath the lighted region, forming the logo in bacteria. The authors speculate that such motility allows the cyanobacteria to seek light sources to support the colony. In both light and dark conditions,

1462-674: The location in Earth's history . In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits . Corals, including some major extinct groups Rugosa and Tabulata , have been important reef builders through much of the Phanerozoic since the Ordovician Period. However, other organism groups, such as calcifying algae, especially members of

1505-507: The mine closed in 1978. The combination of a low sedimentation rate, high calcification rate, and low microbial growth rate appears to result in the formation of these microbialites. Microbialites at an historic mine site demonstrates that an anthropogenically constructed environment can foster microbial carbonate formation. This has implications for creating artificial environments for building modern microbialites including stromatolites. A very rare type of non-lake dwelling stromatolite lives in

1548-410: The only factor in the reduction in stromatolite abundance. Factors such as the chemistry of the environment may have been responsible for changes. While prokaryotic cyanobacteria reproduce asexually through cell division, they were instrumental in priming the environment for the evolutionary development of more complex eukaryotic organisms. They are thought to be largely responsible for increasing

1591-436: 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. Stromatolites , for instance, are microbial mounds with a laminated internal structure. Whereas, bryozoans and crinoids , common contributors to marine sediments during

1634-598: The red algae ( Rhodophyta ), and molluscs (especially the rudist bivalves during the Cretaceous Period) have created massive structures at various times. During the Cambrian Period, the conical or tubular skeletons of Archaeocyatha , an extinct group of uncertain affinities (possibly sponges), built reefs. Other groups, such as the Bryozoa, have been important interstitial organisms, living between

1677-721: The repair of UV induced damages in DNA by the processes of nucleotide excision repair and photoreactivation . Other locations include Pampa del Tamarugal National Reserve in Chile; Lagoa Salgada , Rio Grande do Norte , Brazil, where modern stromatolites can be observed as both bioherms (domal type) and beds; and in the Puna de Atacama of the Andes. Inland stromatolites can be found in saline waters in Cuatro Ciénegas Basin ,

1720-476: The result of natural material deposition or some other abiogenic mechanism. Scientists have argued for a biological origin of stromatolites due to the presence of organic globule clusters within the thin layers of the stromatolites, of aragonite nanocrystals (both features of current stromatolites), and of other microstructures in older stromatolites that parallel those in younger stromatolites that show strong indications of biological origin. Stromatolites are

1763-421: The rugosan corals (which disappeared in the late Permian). An artificial reef is a human-created underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, block the use of trawling nets, or improve surfing . Many reefs are built using objects that were built for other purposes, for example by sinking oil rigs (through

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1806-471: The scleractinian corals, whose skeletons are aragonite . However, there are some unusual examples of well-preserved aragonitic rugose corals in the Late Permian . In addition, calcite has been reported in the initial post-larval calcification in a few scleractinian corals. Nevertheless, scleractinian corals (which arose in the middle Triassic) may have arisen from a non-calcifying ancestor independent of

1849-782: The stromatolite structures are made of hydromagnesite . Two instances of freshwater stromatolites are found in Canada, at Pavilion Lake and Kelly Lake in British Columbia . Pavilion Lake has the largest known freshwater stromatolites, and NASA has conducted xenobiology research there, called the " Pavilion Lake Research Project ." The goal of the project is to better understand what conditions would likely harbor life on other planets. Microbialites have been discovered in an open pit pond at an abandoned asbestos mine near Clinton Creek , Yukon , Canada. These microbialites are extremely young and presumably began forming soon after

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