Star column coral  (Pavona clavus)

Pavona clavus is classified as Least Concern (LC) on the IUCN Red List (1) and is listed on Appendix II of CITES (3).

Pavona clavus is a widespread, common coral that forms large colonies, typically of several metres diameter. It is one of several coral species that play an important role in supporting the base of many reefs, especially at greater depths (1) (4) (5). Pavona clavus colonies usually have a ‘massive’ form, meaning that they are solid, and roughly spherical. Some thinner colonies may be encrusting (2). Larger colonies of Pavona clavus often form one or more columns, which may reach up to 10 centimetres wide and 1.5 metres high (2).

Like other colony-forming corals, colonies of Acropora granulosa are composed of numerous small polyps. The polyps secrete a hard calcareous skeleton, called a ‘corallite’, which over successive generations contributes to the formation of a coral reef. The corallites have thick, well-defined walls (4), while the septo-costae (skeletal elements that cross the corallite wall) are thick, straight and closely packed, and are arranged into two distinct alternating size orders (2). The septa all have steeply sloping inner margins, which are smooth on the edges and granulated on the sides (2).

Colonies of Pavona clavus are uniform pale grey, cream or brown (2) (4). This species shows very little geographic variation in its morphology, colour or abundance (4).

Pavona clavus is found from the Red Sea and the Gulf of Aden, throughout the Indian Ocean, to the far eastern Pacific (1) (2) (4). 

Colonies of Pavona clavus are common in shallow reef environments which are exposed to fairly strong currents (1) (2) (4). It is typically found on reef slopes at depths of 2 to 15 metres, where it will often form large, isolated stands of colonies (1).

In the eastern tropical Pacific region, colonies of Pavona clavus occur in rocky areas, except where the wave action is particular fierce. In other areas, Pavona clavus may also occur on soft bottoms (1).

Like other reef-building corals, Pavona clavus has many microscopic, photosynthetic algae, called zooxanthellae, living within the polyp tissues. The coral and the algae have a mutually beneficial relationship, where the coral provides protection for the algae, which in return provides energy and nutrients for the coral through photosynthesis (4) (6). Both Pavona clavus and its zooxanthellae are very sensitive to changes in water temperature and acidity, and any increase in the water temperature greater than one or two degrees Celsius above the normal average can stress the coral and cause ‘bleaching’, a phenomenon in which the coral expels it zooxanthellae and turns white (4) (6). Elevated sea temperatures are often associated with short-term events, such as the El Niño phenomenon, and long-term global warming trends (7).

Very little else is known about the biology of Pavona clavus. Preliminary results from a study on spawning and recruitment in this species suggest that it may reproduce seasonally, with peak spawning events restricted to around two months each year during the full moon (August and September in the eastern Pacific) (8).

Previous studies on other Pavona species suggest that corals in this genus are typically ‘broadcast’ spawners , meaning they release, buoyant, mucus-laden egg masses into the water, which may contain as many as 9,000 to 28,000 eggs per square centimetre. It is likely that Pavona clavus is able to reproduce both sexually and asexually, with most colonies of other Pavona species containing both gonochoric (colonies composed of a single sex) and hermaphroditic populations (9).

The age of first maturity in most reef building corals is typically three to eight years, with individuals often living for more than ten years in healthy reef environments (1).

Corals are particularly affected by the changing global climate, with rising sea temperatures and ocean acidification, which both cause mass coral bleaching events, contributing to significant declines in coral populations. Pavona clavus was badly affected by the 1998 El Niño bleaching event, despite the fact that this species appears to be more resilient to changes in its environment than many other corals (1).

The increased severity of storms and climatic events is having huge negative impacts on reef health worldwide. Coral disease in particular is emerging as a serious threat, while other threats to corals include fisheries, human development and recreation, habitat degradation, invasive species and pollution (1).

In addition to its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES), which means that trade in this species should be carefully monitored (1) (3), Pavona clavus is found in several Marine Protected Areas (MPAs) in Mexico, Costa Rica, Panama, Columbia and Ecuador (1).

Recommended conservation measures for Pavona clavus include research on its taxonomy, ecology, habitat, pathogens and disease. Identifying the threats to this species, its resilience to these threats, and how the species recovers, are also crucial for planning effective conservation measures. Colonies of Pavona clavus would benefit from establishing new Protected Areas, as well as from the expansion of existing MPAs (1).

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

For further information on the conservation of coral reefs:

• Reef Check:
  http://www.reefcheck.org
• The Coral Reef Alliance:
  http://www.coralreefalliance.org