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Biology

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Like other reef-building corals, the polyps of Porites corals have microscopic algae (zooxanthellae) living within their tissues. Through photosynthesis, these symbiotic algae produce energy-rich molecules that the coral polyps can use as nutrition. In return, the coral provides the zooxanthellae with protection and access to sunlight (3). Porites colonies also commonly house a wide variety of other fauna (3). The majority of corals are hermaphrodite, and thus colonies possess both male and female reproductive organs. However, Porites corals have separate male and female colonies. With a few exceptions, fertilization is internal and therefore depends on free-swimming sperm from male colonies reaching the polyps of female colonies. The fertilised eggs then develop into larvae within the female polyp's body cavity (2). When released, the larvae settle quickly close to the parent colony. Whilst this means that, unlike spawning corals, the coral is not easily dispersed, brooding corals have the advantage of their young settling in an environment that has already proved suitable for successful reproduction (3). Most of the spherical and hemispherical Porites species are tolerant of sedimentary environments, partly because they protect themselves with a thick film of mucous (3).
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Conservation

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Porites corals are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which means that trade in this species should be carefully regulated (1). Indonesia and Fiji have export quotas for Porites corals (1). Porites corals will form part of the marine community in many marine protected areas (MPAs), which offer coral reefs a degree of protection, and there are many calls from non-governmental organisations for larger MPAs to ensure the persistence of these unique and fascinating ecosystems (4).
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Description

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Porites corals form some of the largest of all coral colonies, with some reaching an incredible eight metres in height (2). The growth rate of Porites coral is very slow, perhaps only nine millimetres a year, therefore these giant colonies may be up to 1,000 years old, putting them among the oldest life forms on earth (2). Coral colonies are composed of many individual coral polyps, which are basically anemone-like animals that secrete a skeleton. The many polyps of a colony are joined together at the base of their skeletons (3). The colonies of Porites corals may form flat, branching, spherical or hemispherical structures; some hemispherical colonies may be over five meters across (3). The coral polyps possess tentacles which, in most species, are extended only at night, when they give the coral a furry appearance (2).
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Habitat

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Porites corals can be found in a wide range of coral reef environments. Many Porites species are very common in shallow water, and most species are tolerant of areas where sediment accumulates (3).
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Range

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Occurs in tropical waters around the world (3).
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Status

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Listed on Appendix II of CITES (1).
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Threats

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Porites corals face the many threats that are impacting coral reefs globally. It is estimated that 20 percent of the world's coral reefs have already been effectively destroyed and show no immediate prospects of recovery, and 24 percent of the world's reefs are under imminent risk of collapse due to human pressures. These human impacts include poor land management practices that are releasing more sediment, nutrients and pollutants into the oceans and stressing the fragile reef ecosystem. Over fishing has 'knock-on' effects that results in the increase of macro-algae that can out-compete and smother corals, and fishing using destructive methods physically devastates the reef. A further potential threat is the increase of coral bleaching events, as a result of global climate change (4). The predatory starfish, Acanthaster planci, or 'crown-of-thorns starfish', feeds on a wide range of coral species. For little understood reasons, outbreaks of this starfish occur at regular intervals, and large numbers of starfish can have devastating effects on the reef. They can eat so much that they can kill most of the living coral in a region, which may take the reef up to fifteen years to fully recover (5). Due to the exceptionally slow growth rate of Porites corals, these species may not be able to fully recover in the time before the next starfish outbreak, and thus may be sent into a period of prolonged decline (6). An additional potential threat arises from collection for the coral trade. Porites is one of four genera that constitute the majority of the dead coral trade, for ornaments and jewellery. Live Porites are also collected at a lower level for the aquarium industry, and has previously been traded for biomedical purposes. This trade, which probably supplied a specialised market for the use of coral in bone grafts, peaked in 1992 but has since declined to extremely low levels (7).
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Porites

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In intertidal reef-flat environments, massive Porites form characteristic microatoll formations, with living tissues around the perimeter, and dead skeleton on the exposed upper surface. Microatoll growth is predominantly lateral, as vertical growth is limited by a lack of accommodation space.[2]
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Small colony of Porites porites

Porites is a genus of stony coral; they are small polyp stony (SPS) corals. They are characterised by a finger-like morphology. Members of this genus have widely spaced calices, a well-developed wall reticulum and are bilaterally symmetrical. Porites, particularly Porites lutea, often form microatolls.[3] Corals of the genus Porites also often serve as hosts for Christmas tree worms (Spirobranchus giganteus).

Aquarium trade

Specimens of Porites are sometimes available for purchase in the aquarium trade. Due to the strict water quality, lighting and dietary requirements, keeping Porites in captivity is very difficult.

Most Porites that are collected have Christmas tree worms (Spirobranchus giganteus) that bore into the coral, serving as additional aesthetic livestock. These particular Porites specimens are called "christmas tree worm rocks" or "christmas tree worm coral".

Paleoclimatology

Porites corals have been shown to be accurate and precise recorders of past marine surface conditions.[4] Measurements of the oxygen isotopic composition of the aragonitic skeleton of coral specimens indicate the sea-surface temperature conditions and the oxygen isotopic composition of the seawater at the time of growth.[5] The oxygen isotopic composition of seawater can indicate the precipitation/evaporation balance because oxygen atoms of the more abundant mass 16 will preferentially evaporate before the more rare mass 18 oxygen. The relationship between temperature, precipitation, and the oxygen isotopic composition of Porites corals is important for reconstructing past climates, and associated large-scale patterns such as the El-Nino Southern Oscillation, the Intertropical Convergence Zone, and the mean state of the climate system.

Ecology and biogeography

Corals in the genus Porites are found in reefs throughout the world. It is a dominant taxon on the Pandora platform of the Great Barrier Reef. Potts et al. (1985) identified 7 dominant species: P. lobata, P. solida, P. lutea, P. australiensis, P. mayeri, P. murrayensis, and P. anae. The oldest of six colonies in this reef was approximately 700 years old, and was estimated to be growing at 10.3 mm per year.[6]

Meyer and Schultz (1985) demonstrated that P. furcata has a mutualistic relationship with the schools of French and white grunts (Haemulon flavolineatum and H. plumierii) that rest in their heads during the day. The fish provide it with ammonium, nitrates, and phosphorus compounds. Coral heads with resting grunts experience significantly higher growth rates and nitrogen composition than those without.[7]

Representatives of this genus are found in both the Indo-Pacific and Caribbean basins.

Physiology

Some species in this genus demonstrate high levels of halotolerance. In the Gulf of Thailand P. lutea tolerates daily tidal shifts of 10-30‰ salinity. Moberg et al. (1997) determined that when the salinity declines, the symbiotic zooxanthellae decrease their photosynthesis rate as the coral contracts its polyps to protect them. The corals maintain their metabolic rate by temporarily switching to heterotrophy, consuming prey such as brine shrimp and other zooplankton.[8]

Porites growth rates can be determined by examining annual rings in their skeleton. This method was used to determine that P. astreoides grows its skeleton about the central axis by approximately 3.67mm/year, calcifies at approximately 0.55g/cm²/year, and increases density in this region of the body at approximately 1.69g/cm³/year.[9] Additionally, Meyer and Schultz (1985) reported that coral growth varies seasonally. They observed that P. furcata's growth rate peaked between May and August, which is summertime in their Caribbean habitat.[10]

Threats

Threats to corals in the genus Porites include predation, climate change, and anthropogenic pollution. When exposed to increased temperatures and copper, P. cylindrica slowed its rate of production. Additionally, the symbiotic zooxanthellae reduced their photosynthesis rate when exposed to both stressors.[11]

Done and Potts (1992) observed that when settled, larvae in Porites are vulnerable to competition from other corals and predation from sea urchins. Additionally, mortality likelihood increases following strong storms.[12]

Species

References

  1. ^ WoRMS (2018). "Porites Link, 1807". WoRMS. World Register of Marine Species. Retrieved 2018-08-22.
  2. ^ van Woesik, R.; Golbuu, Y.; Roff, G. (2015). "Keep up or drown: adjustment of western Pacific coral reefs to sea-level rise in the 21st century". Royal Society Open Science. 2 (7): 150181. Bibcode:2015RSOS....250181V. doi:10.1098/rsos.150181. PMC 4632590. PMID 26587277.
  3. ^ Flora, C.J.; Ely P.S. (2003). "Surface Growth Rings of Porites lutea Microatolls Accurately Track Their Annual Growth" (PDF). Northwest Science. 77 (3): 237–245. Retrieved 2009-10-30.
  4. ^ Lough, Janice M. (2010). "Climate records from corals". Wiley Interdisciplinary Reviews: Climate Change. 1 (3): 318–331. doi:10.1002/wcc.39.
  5. ^ Thompson, D. M. (2011). "Comparison of observed and simulated tropical climate trends using a forward model of coralδ18O". Geophysical Research Letters. 38 (14): n/a. Bibcode:2011GeoRL..3814706T. doi:10.1029/2011GL048224.
  6. ^ Potts, D.C.; Done, T.J.; Isdale, P.J.; Fisk, D.A. (1985). "Dominance of a Coral Community in the Genus Porites Scleractinia". Marine Ecology Progress Series. 23 (1): 79–84. Bibcode:1985MEPS...23...79P. doi:10.3354/meps023079.
  7. ^ Meyer, J.L.; Schultz, E.T. (1985). "Tissue Condition and Growth Rate of Corals Associated with Schooling Fish". Limnol. Oceanogr. 30 (1): 157–166. Bibcode:1985LimOc..30..157M. doi:10.4319/lo.1985.30.1.0157.
  8. ^ Moberg, F.; Nystrom, M.; Kautsky, N.; Tedengren, M.; Jarayabhand, P. (1997). "Effects of reduced salinity on the rates of photosynthesis and respiration in the hermatypic corals Porites lutea and Pocillopora damicornis". Marine Ecology Progress Series. 157: 53–59. Bibcode:1997MEPS..157...53M. doi:10.3354/meps157053.
  9. ^ Elizalde-Rendon, E.M.; Horta-Puga, G.; Gonzalez-Diaz, P.; Carricart-Ganivet, J.P. (2010). "Growth characteristics of the reef-building coral Porites astreoides under different environmental conditions in the Western Atlantic". Coral Reefs. 29 (3): 607–614. Bibcode:2010CorRe..29..607E. doi:10.1007/s00338-010-0604-7. S2CID 20491507.
  10. ^ Meyer, J.L.; Schultz, E.T. (1985). "Tissue Condition and Growth Rate of Corals Associated with Schooling Fish". Limnol. Oceanogr. 30 (1): 157–166. Bibcode:1985LimOc..30..157M. doi:10.4319/lo.1985.30.1.0157.
  11. ^ Nystrom, M.; Nordemar, I.; Tedengren, M. (2001). "Simultaneous and sequential stress from increased temperature and copper on the metabolism of the hermatypic coral Porites cylindrica". Marine Biology (Berlin). 138 (6): 1225–1231. doi:10.1007/s002270100549. S2CID 85015152.
  12. ^ Done, T.J.; Potts, D.C. (1992). "Influences of habitat and natural disturbances on contributions of massive Porites corals to reef communities". Marine Biology (Berlin). 114 (3): 479–493. doi:10.1007/BF00350040. S2CID 83505538.
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Porites: Brief Summary

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 src= In intertidal reef-flat environments, massive Porites form characteristic microatoll formations, with living tissues around the perimeter, and dead skeleton on the exposed upper surface. Microatoll growth is predominantly lateral, as vertical growth is limited by a lack of accommodation space.  src= Small colony of Porites porites

Porites is a genus of stony coral; they are small polyp stony (SPS) corals. They are characterised by a finger-like morphology. Members of this genus have widely spaced calices, a well-developed wall reticulum and are bilaterally symmetrical. Porites, particularly Porites lutea, often form microatolls. Corals of the genus Porites also often serve as hosts for Christmas tree worms (Spirobranchus giganteus).

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Porites

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Porites est le nom d'un genre de coraux massifs, souvent caractérisé par des digitations (forme évoquant des doigts).

Certains Porites forment des blocs extrêmement solides et compacts : ce sont des organismes dits « bioconstructeurs » qui participent à la construction des récifs biogènes.

Répartition

On trouve les porites dans les eaux tropicales chaudes de la Mer Rouge, du bassin Indo-Pacifique tropical, des Caraïbes et de l’Atlantique tropical.

Description

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Un bénitier (Tridacna maxima) dans un Porites nodifera.
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Gros plan sur les polypes d'un Porites asteroides.
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Un Porites en Floride.

Ce sont généralement des coraux extrêmement compacts et solides, à croissance lente et à durée de vie longue. Ils sont considérés comme plus résistants aux prédateurs (poissons perroquets, étoiles de mer corallivores...) que les coraux à croissance rapide, et abritent souvent de nombreux symbiotes (vers tubicoles, bénitiers, huîtres corallicoles...). Ils constituent donc un élément à la fois central et fragile des écosystèmes coralliens.

En outre, la solidité de leur squelette fait qu'à leur mort, leur corps ne se désagrège pas mais forme un nouveau substrat dur sur lequel de nombreux autres organismes pourront élire domicile : ils constituent ainsi des briques essentielles à la formation d'un récif de corail, où ils font partie des principales espèces fondatrices.

Les colonies de porites peuvent être encroûtantes, aplaties (foliacées), ramifiées ou massives en forme de dôme. Les colonies en forme de dôme peuvent atteindre 8 m de hauteur et être âgées de près de 1000 ans.

Alimentation

La principale source de son alimentation vient de sa symbiose avec les zooxanthelles. La source secondaire de son alimentation, c'est, comme tous les cnidaires, le plancton qu'il attrape avec ses tentacules urticantes[1].

Liste sous-taxons

Selon World Register of Marine Species (31 janvier 2014)[2] : ...

Selon ITIS (31 janvier 2014)[3] :

Voir aussi

Notes et références
  1. Muséum Aquarium de Nancy, « Porites », sur especeaquatique.museumaquariumdenancy.eu (consulté le 24 février 2021)
  2. World Register of Marine Species, consulté le 31 janvier 2014
  3. Integrated Taxonomic Information System (ITIS), www.itis.gov, CC0 https://doi.org/10.5066/F7KH0KBK, consulté le 31 janvier 2014

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Porites: Brief Summary

provided by wikipedia FR

Porites est le nom d'un genre de coraux massifs, souvent caractérisé par des digitations (forme évoquant des doigts).

Certains Porites forment des blocs extrêmement solides et compacts : ce sont des organismes dits « bioconstructeurs » qui participent à la construction des récifs biogènes.

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