Small knob coral (Plesiastrea versipora)

A small knob coral colony
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Small knob coral fact file

Small knob coral description

GenusPlesiastrea (1)

One of just two species in its genus, Plesiastrea versipora forms large colonies, which can measure several metres in diameter at high latitudes, but are usually smaller in the tropics (1) (3). The colonies usually have a rounded shape in exposed, shallow areas, and are more flat and plate-like on reef slopes, where light intensity is low (1). Frequently lobed, they may be yellow, cream, green or brown in colour, usually being pale in the tropics and brightly coloured at higher latitudes.

As in all corals, each colony is formed from many tiny, anemone-like animals, known as polyps, which secrete the hard coral skeleton. In this species, each individual polyp possesses its own, conical wall, bearing numerous short tentacles, of two alternating sizes, which surround a central ‘mouth’. Plesiastrea versipora can be distinguished from the related Plesiastrea devantieri by its more numerous septa, the radial elements that project inwards from the skeletal walls of the polyps (3).


Small knob coral biology

Plesiastrea versipora is a zooxanthellate coral, meaning it has microscopic algae, known as zooxanthellae, living within its tissues. The algae produce energy-rich nutrients for the coral through photosynthesis, and in return the coral provides the algae with a protected, stable environment, and access to sunlight (3) (6) (7). Although this restricts most corals to living in clear, shallow, warm waters where photosynthesis can take place, Plesiastrea versipora is unusual in that it is one of the few zooxanthellate corals with a distribution that extends into more temperate latitudes (4). Corals may also supplement the diet with zooplankton, which are caught by stinging cells on the tentacles (3) (6) (7). Unlike many other corals, in Plesiastrea versipora the tentacles are sometimes extended during the day (3).

Plesiastrea versipora colonies can grow through asexual reproduction, in a process known as extratentacular budding, in which new polyps form on the side of the parent polyp. Corals can also reproduce sexually, producing large numbers of sperm and eggs, which in Plesiastrea versipora are released into the water. The fertilised eggs develop into larvae, which travel in the water column before settling and developing into polyps (3).


Small knob coral range

Plesiastrea versipora is the most widely distributed coral within the Indo-Pacific (4), occurring in the western and northern Indian Ocean, the Red Sea, Gulf of Aden and Arabian Gulf, around Australia and South East Asia, and in the western and central Pacific Ocean (1) (3). It is the only tropical coral species to occur along the full length of the southern coast of Australia, where it forms a distinct subspecies (5).


Small knob coral habitat

This coral occurs in most reef environments, but particularly in shaded places such as under overhangs, and may be found at depths of up to 40 metres. In temperate locations, it is also found on rocky foreshores that are protected from strong wave action (1) (3).


Small knob coral status

Classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES (2).

IUCN Red List species status – Least Concern


Small knob coral threats

Around a third of all reef-building coral species are now threatened with extinction (8), with an estimated 20 percent of the world’s coral reefs already having been destroyed (9). The main threat to corals is global climate change, with an expected rise in ocean temperatures increasing the risk of coral bleaching, in which the stressed coral expels its zooxanthellae, often resulting in death. Climate change is also expected to lead to more severe, frequent storms, which can damage reefs, and rising carbon dioxide levels may lead to ocean acidification, which can reduce the ability of coral to create its hard skeleton. Such stresses can also make corals more vulnerable to disease (1) (6) (8) (9).

These global threats are compounded by more localised human impacts, such as coral harvesting, disturbance by fisheries, development, irresponsible tourism, invasive species, and pollution (1) (6) (8) (9). Plesiastrea versipora has been found to be relatively susceptible to bleaching, potentially putting it at greater risk (10), although it is currently still widespread and fairly common throughout its range (1).


Small knob coral conservation

All coral species are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) (2), meaning that international trade in corals should be carefully monitored and controlled. Plesiastrea versipora also occurs in some Marine Protected Areas (1), although enforcement in these areas is often poor (6), and overall less than one percent of all the world’s oceans are currently protected (11).

Specific conservation measures recommended for this coral include further research into its biology and populations, and into the impacts of various threats, and the creation and management of more protected areas, as well as the control of diseases and parasites. Ongoing monitoring and increased awareness of the threats to coral reefs will also be important in their protection, and techniques such as artificial propagation and the storage of coral gametes (eggs and sperm) may also become important strategies in maintaining coral biodiversity (1) (6).

View information on this species at the UNEP World Conservation Monitoring Centre.
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To learn about efforts to conserve Plesiastrea versipora see:

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Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
A group of organisms living together. Individuals in the group are not physiologically connected and may not be related, such as a colony of birds. Another meaning refers to organisms, such as bryozoans, which are composed of numerous genetically identical modules (also referred to as zooids or ‘individuals’), which are produced by budding and remain physiologically connected.
A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.
Typically sedentary soft-bodied component of cnidaria, a group of simple aquatic animals including the sea anemones, corals and jellyfish. A polyp comprises a trunk that is fixed at the base, and a mouth that is placed at the opposite end of the trunk and is surrounded by tentacles.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
Tiny aquatic animals that drift with currents or swim weakly in water.


  1. IUCN Red List (July, 2009)
  2. CITES (July, 2009)
  3. Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townsville, Australia.
  4. Rodriguez-Lanetty, M. and Hoegh-Guldberg, O. (2002) The phylogeography and connectivity of the latitudinally widespread scleractinian coral Plesiastrea versipora in the Western Pacific. Molecular Ecology, 11: 1177 - 1189.
  5. Veron, J.E.N. (1995) Corals in Space and Time: The Biogeography and Evolution of the Scleractinia. Cornell University Press, Ithaca, New York.
  6. Miththapala, S. (2008) Coral Reefs. Coastal Ecosystems Series (Volume 1). Ecosystems and Livelihoods Group Asia, IUCN, Colombo, Sri Lanka. Available at:
  7. Veron, J.E.N. (1993) Corals of Australia and the Indo-Pacific. University of Hawaii Press, Honolulu, Hawaii.
  8. Carpenter, KE et al. (2008) One-third of reef-building corals face elevated extinction risk from climate change and local impacts. Science, 321: 560 - 563.
  9. Wilkinson, C. (2004) Status of Coral Reefs of the World: 2004. Volume 1. Australian Institute of Marine Science, Townsville, Australia. Available at:
  10. McClanahan, T.R., Ateweberhan, M., Graham, N.A.J., Wilson, S.K., Sebastián, C.R., Guillaume, M.M.M. and Bruggemann, J.H. (2007) Western Indian Ocean coral communities: bleaching responses and susceptibility to extinction. Marine Ecology Progress Series, 337: 1 - 13.
  11. UNEP: Fifty Key Facts about Seas and Oceans (July, 2009)

Image credit

A small knob coral colony  
A small knob coral colony

© Adrian Baddeley

Adrian Baddeley


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