Pavona cactus is a scleractinian coral, meaning that it is a ‘hard’ coral with a limestone skeleton (3). It is pale brown or greenish-brown in colour and typically has thin, upright fronds and twisted branches (4)(5), but may develop thicker fronds when growing in shallow areas with strong waves (4). Pavona cactus may grow as an isolated colony or may form large colonies that can cover over ten metres (4)(5). Until very recently it was thought to be the same species as the cactus coral (Pavona decussata), but studies have now shown that Pavona decussata and Pavona cactus are in fact two distinct species (4).
On the Great Barrier Reef Pavona cactus has been shown to reproduce sexually, although this species also reproduces asexually. It does so by fragmentation (8), a form of asexual reproduction where a new organism grows from a fragment of the parent into a mature, fully grown individual. However, more work is needed on this species’ biology as little information is available at present.
In common with many other corals, Pavona cactus has microscopic algae (zooxanthellae) living within its tissues. Through photosynthesis, these symbiotic algae produce energy-rich molecules that the coral can use as nutrition. In return, the coral provides the zooxanthellae with protection and access to sunlight (9)(10).
This coral occurs in lagoons and on the upper slopes of reefs (5)(7), where there is a slight current (7), as well as turbid waters protected from waves (5). It is often found growing amid colonies of the cactus coral Pavona decussata(4).
Pavona cactus is facing a number of threats, including rising water temperatures due to climate change, resulting in coral bleaching. During coral bleaching, the symbiotic algae are expelled, leaving the corals weak and vulnerable to an increasing variety of harmful diseases. This is a threat faced by all corals, although it has been observed that Pavona cactus is less susceptible to bleaching effects than some other coral species (11).
Another problem facing Pavona cactus is the increasing amount of carbon dioxide in the atmosphere. Because Pavona cactus and other scleractiniancorals grow through building their calcified skeleton, the increase of carbon dioxide in the atmosphere reduces the carbonate ions available for the corals to use, thus limiting their growth(12).
Now that Pavona cactus has been confirmed as a species in its own right, further research into its biology will help inform future conservation actions for this species. Sadly, on a larger scale, it has been deemed that the environmental threats caused by climate change may already be too severe for most corals. A meeting in October 2009 saw scientists discuss the ambitious idea of freezing coral in liquid nitrogen so as to preserve them for reintroduction when the global climate has stabilized (13).
Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
Relating to asexual reproduction: reproduction that does not involve the formation of sex cells, such as sperm and eggs. Asexual reproduction only involves one parent, and all the offspring produced by asexual reproduction are identical to one another.
Relating to corals: corals composed of numerous genetically identical individuals (also referred to as zooids or polyps), which are produced by budding and remain physiologically connected.
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.
Relating to sexual reproduction: a form of reproduction that involves fertilization of a female cell or egg, by a male sperm. It usually involves two parents, one of either sex, but in some species individuals are hermaphrodite (possess both male and female sex organs).
Describes a relationship in which two organisms form a close association. The term is now usually used only for associations that benefit both organisms (a mutualism).
Willis, B.L. and Ayre, D.J. (1985) Asexual reproduction and genetic determination of growth form in the coral Pavona cactus: biochemical, genetic and immunogenic evidence. Oecologia, 65: 516-525.
Pillay, K. Asahida, T. Chen, C. Terashima, H. and Ida, H. (2006) ITS ribosomal DNA distinctions and the genetic structures of populations of two sympatric species of Pavona (Cnidaria: Sceleractina) from Mauritius. Zoological Studies, 45(1): 132-144.
Veron, J.E.N. (1986) Corals of Australia and the Indo-Pacific. Australian Institute of Marine Science, Townsville, Australia.
Erhardt, H. and Moosleitner, H. (1998) Marine Atlas, Volume 2: The Joint Aquarium Care of Invertebrates. Mergus, Melle, Germany.
Ayre, D.J. and Wills, B.L. (1988) Population structure in the coral Pavona cactus: clonal genotypes show little phenotypic plasticity. Marine Biology, 99: 495-505.
Barnes, R.D. (1987) Invertebrate Zoology. Fifth Edition. Saunders College Publishing, U.S.
Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Sciences, Townsville, Australia.
Craig, P., Birkeland, C. and Belliveau, S. (2001) High temperatures tolerated by a diverse assemblage of shallow-water corals in American Samoa. Coral Reefs, 20: 185-189.
Marubini, F., Ferrier-Pages, C. and Cuif, J.P. (2003) Suppression of skeletal growth in scleractinian corals by decreasing ambient carbonate-ion concentration: a cross-family comparison. Proceedings of the Royal Society, 270: 179-184.
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