Cauliflower corals (Pocillopora spp.)
|Also known as:||brown stem corals, brush corals|
Listed on Appendix II of CITES (1).
This hardy, widespread and common coral can easily be identified by the presence of wart-like growths, called verrucae, which cover the colonies (2). The colonies can be fairly solid and dome-shaped, or branching with branches that are either flattened and blade-like, or fine and irregular (3). Species of Pocillopora corals vary greatly in appearance, depending on environmental conditions. For example, species situated on shallow reefs with heavy wave action are often stunted, whilst those in deep water are thin and open. The tentacles born on each polyp are usually only extended at night (2).
Pocillopora corals are distributed widely in the Indian and Pacific Oceans (3).
Cauliflower corals occur in habitats ranging from exposed reef fronts to protected lagoons and lower reef slopes. One species, P. molokensis, occurs only in deep water (3).
The polyps of Pocillopora corals are hermaphrodite; they each possess four sets of male and four sets of female gonads (2). Pocillopora can reproduce asexually as well as sexually. Unlike many corals, the coral larvae develop inside the polyps rather than in the water column. When the mature larvae are released into the water, the larvae can remain free-swimming for several weeks before settling on the substrate. They can even become partly polyp-like during this period, enabling feeding to occur before settling and commencing skeleton formation (2). Pocillopora can also successfully reproduce asexually via fragmentation (5).
Pocillopora corals are hermatypic corals, and therefore 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 (2). In return, the coral provides the zooxanthellae with protection, and access to sunlight. The wide geographic distribution of Pocillopora corals is probably due to rafting, whereby small colonies attach to floating objects, such as pumice, where they can travel great distance to remote places (3). The polyps can also obtain nutrition by capturing tiny prey using their tentacles.
Cauliflower 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). Another potential threat is over-harvesting. Pocillopora is one of four genera that constitute the majority of the dead coral trade. Indonesia and Fiji have export quotas for this coral, but in 1997, the amount of Pocillopora traded greatly exceeded the quota, showing a failure to regulate the trade (5). However, Pocillopora is thought to be fairly resilient to collection due to their success at asexual reproduction through fragmentation (5).
Pocillopora 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). Pocillopora is one of the genera that can be fairly successively cultivated, due to its fast growth rate and the ease at which it can be propagated by fragmentation. Growing tips are collected from large colonies in the wild, and the fragments are cultivated in the sea suspended from fishing lines until large enough to be sold in the aquarium trade. Whilst the initial collection does have impact on wild populations, cultivation poses less threat than complete wild harvesting (5). Pocillopora 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).
For further information on this species see Veron, J.E.N. (1986) Corals of Australia and the Indo-Pacific. Angus & Robertson Publishers, London, UK.
For further information on the conservation of coral reefs see:
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- Asexually: 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.
- Colonies: 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.
- Fragmentation: fragmentation is a form of asexual reproduction where a new organism grows from a fragment of the parent. Each fragment develops into a mature, fully grown individual.
- Hermaphrodite: possessing both male and female sex organs.
- Hermatypic: reef-building corals. Most hermatypic corals have a close association with algae known as zooxanthellae, which live in their tissues. These corals are restricted to shallow, tropical, marine environments. Over time the accumulated deposition of calcium carbonate (limestone) by many hermatypic corals can form large limestone structures known as coral reefs.
- Larvae: 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.
- Photosynthesis: 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.
- Polyp: typically sedentary soft-bodied component of Cnidaria (corals, sea pens etc), which comprise of a trunk that is fixed at the base; the mouth is placed at the opposite end of the trunk, and is surrounded by tentacles.
- Sexually: 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).
- Symbiotic: describing a close relationship between two organisms. This term usually refers to a relationship that benefits both organisms.
CITES (June, 2007)
- Veron, J.E.N. (1986) Corals of Australia and the Indo-Pacific. Angus & Robertson Publishers, London, UK.
- Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townsville, Australia.
- Green, E. and Shirley, F. (1999) The Global Trade in Corals. World Conservation Press, Cambridge, UK.
- Wilkinson, C. (2004) Status of Coral Reefs of the World. Australian Institute of Marine Science, Townsville, Australia.