Staghorn coral  (Astreopora expansa)

Classified as Near Threatened (NT) on the IUCN Red List (1) and listed on Appendix II of CITES (2).

One of the most distinctive species in its genus, the variably brown, pink or dark green colonies of Astreopora expansa take the form of flat, bifacial plates arranged in tiers or whorls. In common with other colony-forming corals, the colonies are comprised of a vast assemblage of tiny, soft polyps, each of which is equipped with numerous tentacles that extend at night to direct food into a central mouth. The polyps secrete a hard skeleton known as a ‘corrallite’, which over time contribute to the formation of coral reefs (3).

Astreopora expansa has an Indo-West Pacific distribution ranging from Mozambique up to the Red Sea and the Arabian Gulf, and east to Japan, Southeast Asia, Australia, and the islands of the western Pacific (1).

Occurs in shallow reef environments from depths of 5 to 15 metres (1) (3).

In common with other corals in the Acroporidae family, Astreopora expansa is zooxanthellate, living in symbiosis with unicellular algae known as zooxanthellae, which are essential to the coral’s growth and survival. Protected within the coral tissue, the algae provide the host with nutrients and energy, whilst also helping to remove metabolic wastes. The cost of this symbiosis is that zooxanthellate corals are constrained to live in relatively shallow waters, where the algae are able to photosynthesise (3).

Although a zooxanthellate coral can obtain on average around 70 percent of its nutrient requirements through the photosynthesis of zooxanthellae, the coral may also feed on zooplankton, dissolved organic matter, and planktonic bacteria (4).

Around one third of the world’s reef building corals are threatened with extinction (5). The principal threat to corals is the rise in sea temperature associated with global climate change. This leads to coral bleaching, where the symbiotic algae are expelled, leaving the corals weak and vulnerable to an increasing variety of harmful diseases. Climate change is also expected to increase ocean acidification and result in a greater frequency of extreme weather events such as destructive storms. The global impact of climate change on coral reefs is compounded by localised threats from pollution, destructive fishing practices, invasive species, human development, harvesting for the aquarium trade and other activities (1) (5).

Although Astreopora expansa is still relatively widespread and common in parts of its range, evidence of an overall global decline in coral habitat is an indication that this species is almost certainly declining (1).

In addition to being listed on Appendix II of CITES (2), which makes it an offence to trade Astreopora expansa without a permit, this coral falls within several Marine Protected Areas across its range. To conserve Astreopora expansa, recommendations have been made for a raft of studies into various aspects of its taxonomy, biology and ecology, including an assessment of threats and potential recovery techniques (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:
  www.reefcheck.org
• The Coral Reef Alliance:
  www.coralreefalliance.org