African pillow coral  (Siderastrea savignyana)

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

The African pillow coral is a beautiful coral species with elaborately-shaped skeletal walls and neatly arranged septa that form a fan-like shape (3) (4). Growing in an encrusting form or low mounds up to one metre in diameter, like other colony-forming corals, colonies of the African pillow coral are composed of numerous small polyps, soft-bodied animals related to anemones. Each polyp bears numerous tentacles that direct food into a central mouth, where it is digested in a sac-like body cavity. One of the most remarkable and ecologically important features of corals is that the polyps secrete a hard skeleton, which over successive generations contributes to the formation of a coral reef. The coral skeleton forms the bulk of the colony, with the living polyp tissue comprising only a thin veneer. Living colonies of the African pillow coral are pale tan, with dark centres and thick white walls (3). 

The African pillow coral has a wide distribution, ranging from the Red Sea and the south-west Indian Ocean, through the eastern Indian Ocean and Southeast Asia to the west-central Pacific (1).

The African pillow coral  is found in shallow reefs or sand lagoons, often with colonies embedded in sand, down to depths of around ten meres (1) (3) (4). This species is one of the hardiest Scleractinia corals and, as a result, is often found in very high salinity and high temperature environments (1).

Like many coral species, the tissue of the African pillow coral contains large numbers of single-celled algae called zooxanthellae. The coral and the algae have a symbiotic relationship in which the algae gain a safe, stable environment within the coral's tissues, while the coral receives nutrients produced by the algae through photosynthesis. By harnessing the sun's energy in this way, corals are able to grow rapidly and form vast reef structures, but are constrained to live near the water surface. While, on average, zooxanthellate coral can obtain around 70 percent of its nutrient requirements from zooxanthellae photosynthesis, the coral may also feed on zooplankton (3). 

With an estimated 20 percent of the world’s coral reefs already destroyed, the African pillow coral faces many of the threats that are affecting coral reefs globally (5) (6). Worldwide there is increasing pressure on coastal resources resulting from human population growth and development. There has been a significant increase in domestic and agricultural waste in the oceans, poor land-use practices that result in an increase in sediment running on to the reefs, and over-fishing, which can have ‘knock-on’ effects on the reef (6). However, the major threat to corals is global climate change, with the expected rise in ocean temperatures increasing the risk of coral ‘bleaching’, in which the stressed coral expels its zooxanthellae, often resulting in the death of the coral. Climate change may also lead to more frequent, severe storms, which can damage reefs, and rising carbon dioxide levels may make the ocean increasingly acidic. Such stresses can also make corals more susceptible to disease, parasites and predators, such as the crown-of-thorns sea star (Acanthaster planci) (5) (6) (7).

In addition to being listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which makes it an offence to trade this species without a permit, the African pillow coral also forms part of the reef community in numerous marine protected areas, including the Kiunga Marine National Reserve in Kenya (1) (2) (8). To specifically conserve the African pillow coral, recommendations have been made for a raft of studies into various aspects of its biology, population status, habitat and threats to its survival (1).

View information on this species at the UNEP World Conservation Monitoring Centre.

Environment Agency - Abu Dhabi is a principal sponsor of ARKive. EAD is working to protect and conserve the environment as well as promoting sustainable development in the Emirate of Abu Dhabi.

For further information on the conservation of coral reefs, see:

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