In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water yet shallow enough to be a hazard to ships. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere A shoal or sandbar (also called sandbank) is a somewhat Linear Landform within or extending into a body of Water, A ship /ʃɪp/ is a large vessel that floats on water Ships are generally distinguished from Boats based on size Many reefs result from abiotic processes—deposition of sand, wave erosion planning down rock outcrops, and other natural processes—but the best-known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and calcareous algae. In Biology, abiotic components are non-living Chemical and Physical factors in the environment. Coral reefs are Aragonite structures produced by living organisms found in marine waters with little to no nutrients in the water The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many Calcareous refers to a Sediment, Sedimentary rock, or Soil type which is formed from or contains a high proportion of Calcium carbonate in the Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms

Reefs can be created artificially either by special construction or through deliberately sinking ships, but one can argue that these "reefs" are not real ones, as it is seldom the case that an artificial obstruction would be created that is a hazard to shipping. These structures are usually created to enhance physical complexity on generally featureless sand bottoms in order to attract a diverse assemblage of organisms, especially fish. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Thus, "artificial reef" is a misnomer, though firmly established as the term used for man-made underwater habitat structures. An artificial reef is a man-made underwater structure typically built for the purpose of promoting marine life in areas of generally featureless bottom

Contents 1 Biotic reef types 2 Geologic reef definition 3 Geologic reef structures 4 See also 5 External links

Biotic reef types

There are a number of biotic reef types, including oyster reefs, but the most massive and widely distributed are tropical coral reefs. The common name oyster is used for a number of different groups of Bivalve Mollusks most of which live in marine habitats or Brackish water. Coral reefs are Aragonite structures produced by living organisms found in marine waters with little to no nutrients in the water 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 calcarous algae, especially, although not entirely, species of coralline algae. Coralline algae are Red algae in the Family Corallinaceae of the order Corallinales.

Geologic reef definition

Geologists define reefs and related terms (for example, bioherm, biostrome, carbonate mound) using the factors of depositional relief, internal structure, and biotic composition. There is no consensus on one universally applicable definition. A useful definition distinguishes reefs from mounds as follows. Both are considered to be varieties of organosedimentary buildups: sedimentary features, built by the interaction of organisms and their environment, that have synoptic relief and whose biotic composition differs from that found on and beneath the surrounding sea floor. Reefs are held up by a macroscopic skeletal framework. Coral reefs are an excellent example of this kind. Corals and calcareous algae grow on top of one another and form a three-dimensional framework that is modified in various ways by other organisms and inorganic processes. By contrast, mounds lack a macroscopic skeletal framework. Mounds are built by microorganisms or by organisms that don't grow a skeletal framework. A microbial mound might be built exclusively or primarily by cyanobacteria. Excellent examples of biostromes formed by cyanobacteria occur in the Great Salt Lake of Utah (USA), and in Shark Bay, Western Australia.

Cyanobacteria do not have skeletons and individuals are microscopic. Cyanobacteria encourage the precipitation or accumulation of calcium carbonate and can produce compositionally distinct sediment bodies that have relief on the seafloor. Cyanobacterial mounds were most abundant before the evolution of shelly macroscopic organisms, but they still exist today (stromatolites are microbial mounds with a laminated internal structure). Bryozoans and crinoids, common contributors to marine sediments during the Mississippian (for example), produced a very different kind of mound. Bryozoans are small and the skeletons of crinoids disintegrate. However, bryozoan and crinoid meadows can persist over time and produce compositionally distinct bodies of sediment with depositional relief.

Geologic reef structures

Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about the location in Earth's history. Stratigraphy, a branch of Geology, studies rock layers and layering ( stratification) A geologist is a contributor to the Science of Geology, studying the physical structure and processes of the Earth and planets of the solar system The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present 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. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust. Petroleum ( L petroleum, from Greek πετρέλαιον, lit An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining Corals, including some major extinct groups Rugosa and Tabulata, have been important reef builders through much of the Phanerozoic since the Ordovician period. The Rugosa Rose is also sometimes just called "Rugosa" The Rugosa, also called the Tetracoralla, are an extinct order The tabulate corals, forming the order Tabulata, are an Extinct form of Coral. The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 However, other organism groups, such as calcifying algae, especially members of the red algae Rhodophyta, and mollusks (especially the rudist bivalves during the Cretaceous period) have created massive structures at various times. The red algae (Rhodophyta ˌroʊdəˈfaɪtə roʊˈdɒfɨtə from Greek: ῥόδον (rhodon = rose + φυτόν (phyton = plant thus red plant are Rudists are a group of bizarrely shaped marine Heterodont Bivalves that arose during the Jurassic, and became so diverse during the The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of During the Cambrian period, the conical or tubular skeletons of Archaeocyatha,an extinct group of uncertain affinities (possibly sponges), built reefs. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The Archaeocyatha or archaeocyathids ("ancient cups" were Sessile Other groups, such as the Bryozoa have been important interstitial organisms, living between the framework builders. Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some The corals which build reefs today, the Scleractinia, arose after the Permian-Triassic extinction that wiped out the earlier rugose corals (as well as many other groups), and became increasingly important reef builders throughout the Mesozoic Era. Scleractinia, also called Stony Corals, are exclusively marine animals they are very similar to Sea anemones but generate a hard skeleton The Permian is a geologic period and system that extends from 299 The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago The Mesozoic Era is one of three geologic eras of the Phanerozoic eon. They may have arisen from a rugose coral ancestor. Rugose corals built their skeletons of calcite and have a different symmetry from that of the scleractinian corals, whose skeletons are aragonite. Calcite is a carbonate mineral and the most stable polymorph of Calcium carbonate ( Ca[[carbon C]] O 3 Aragonite is a Carbonate mineral, one of the two common naturally occurring polymorphs of Calcium carbonate, Ca[[carbon C]] O 3 However, there are some unusual examples of well preserved aragonitic rugose corals in the late Permian. The Permian is a geologic period and system that extends from 299 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 the rugosan corals (which disappeared in the late Permian).

See also

• Benjamin Kahn

• Shears N. Benjamin Kahn is an Israeli marine biologist. He has been fighting for the survival of the Red Sea Reef, which began dying when giant fish T. (2007) Biogeography, community structure and biological habitat types of subtidal reefs on the South Island West Coast, New Zealand. Science for Conservation 281. p 53. Department of Conservation, New Zealand. [1]

External links

• Coral Reefs of the Tropics: facts, photos and movies from The Nature Conservancy
• NOAA Photo Library
• Reef Environmental Education Foundation
• NOS Data Explorer - A portal to obtain NOAA National Ocean Service data

The Nature Conservancy is a US charitable Environmental organization working to preserve the Plants, Animals, and natural communities

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