In most corals, the tentacles are retracted by day and spread out at night to catch plankton and other small organisms. Shallow-water species of both stony and soft corals can be zooxanthellate, the corals supplementing their plankton diet with the products of photosynthesis produced by these symbionts. [21] The polyps interconnect by a complex and well-developed system of gastrovascular canals, allowing significant sharing of nutrients and symbionts. [23] a b c Bowen, James (2015). The Coral Reef Era: From Discovery to Decline: A history of scientific investigation from 1600 to the Anthropocene Epoch. Springer. pp.5–7. ISBN 978-3-319-07479-5. a b W3C TR CSS3 Color Module, HTML4 color keywords. W3C. (May 2003). Retrieved on 21 September 2008. Tabulate corals occur in limestones and calcareous shales of the Ordovician period, with a gap in the fossil record due to extinction events at the end of the Ordovician. Corals reappeared some millions of years later during the Silurian period, and tabulate corals often form low cushions or branching masses of calcite alongside rugose corals. Tabulate coral numbers began to decline during the middle of the Silurian period. [88]

The classification of corals has been discussed for millennia, owing to having similarities to both plants and animals. Aristotle's pupil Theophrastus described the red coral, korallion, in his book on stones, implying it was a mineral, but he described it as a deep-sea plant in his Enquiries on Plants, where he also mentions large stony plants that reveal bright flowers when under water in the Gulf of Heroes. [3] Pliny the Elder stated boldly that several sea creatures including sea nettles and sponges "are neither animals nor plants, but are possessed of a third nature ( tertia natura)". [4] Petrus Gyllius copied Pliny, introducing the term zoophyta for this third group in his 1535 book On the French and Latin Names of the Fishes of the Marseilles Region; it is popularly but wrongly supposed that Aristotle created the term. [4] Gyllius further noted, following Aristotle, how hard it was to define what was a plant and what was an animal. [4] The Babylonian Talmud refers to coral among a list of types of trees, and the 11th-century French commentator Rashi describes it as "a type of tree (מין עץ) that grows underwater that goes by the (French) name "coral." [5] Ries JB, Stanley SM, Hardie LA (July 2006). "Scleractinian corals produce calcite, and grow more slowly, in artificial Cretaceous seawater". Geology. 34 (7): 525–28. Bibcode: 2006Geo....34..525R. doi: 10.1130/G22600.1.Mass coral spawning often occurs at night on days following a full moon. [43] [47] A full moon is equivalent to four to six hours of continuous dim light exposure, which can cause light-dependent reactions in protein. [43] [44] Corals contain light-sensitive cryptochromes, proteins whose light-absorbing flavin structures are sensitive to different types of light. This allows corals such as Dipsastraea speciosa to detect and respond to changes in sunlight and moonlight. [43] [44] [48]

Nybakken, J.W. (2004). Marine Biology, An Ecological Approach. Pearson/Benjamin Cummings. ISBN 978-0-8053-4582-7. Bourne, D.G., Morrow, K.M. and Webster, N.S. (2016) "Insights into the coral microbiome: underpinning the health and resilience of reef ecosystems". Annual Review of Microbiology, 70: 317–340. doi: 10.1146/annurev-micro-102215-095440. a b "Threats to Coral Reefs". Coral Reef Alliance. 2010. Archived from the original on 1 December 2011 . Retrieved 5 December 2011. The Persian polymath Al-Biruni (d.1048) classified sponges and corals as animals, arguing that they respond to touch. [6] Nevertheless, people believed corals to be plants until the eighteenth century when William Herschel used a microscope to establish that coral had the characteristic thin cell membranes of an animal. [7]Later, coral jewelry was hugely fashionable in the Victorian period, when the romance of tropical exploration was at its peak. Coral was also popular during the 1920s, when artisans incorporated the material into Art Deco jewelry. It was again popular during the hippie years of the 1960s and 1970s. Overall, coral enjoys enduring fashionability as a color of adornment. Administration, US Department of Commerce, National Oceanic and Atmospheric. "existing and potential value of coral ecosystems with respect to income and other economic values". coralreef.noaa.gov. Archived from the original on 2018-02-05 . Retrieved 2018-02-04. {{ cite web}}: CS1 maint: multiple names: authors list ( link)