Starry cup coral  (Acanthastrea bowerbanki)

Acanthastrea bowerbanki is classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (2).

Acanthastrea bowerbanki is a relatively rare coral that forms small, encrusting colonies (3). Its colonies are usually pale grey or brown, and are often mottled in appearance (3). As in all corals, each colony of Acanthastrea bowerbanki is composed of numerous coral polyps, which are anemone-like animals that secrete a hard coral skeleton, known as ‘corallite’. Over successive generations, the build-up of corallites contributes to the formation of coral reefs (3).

Each Acanthastrea bowerbanki polyp possesses numerous tentacles which are extended at night in order to capture tiny zooplankton. These give an overall furry appearance to the coral (3) (4).

Acanthastrea bowerbanki is rare but widely distributed, being found in the Indo-West Pacific, including the waters of Australia and South East Asia, Japan and the East China Sea (1).

Acanthastrea bowerbanki is found primarily in shallow waters on lower reef slopes, which are protected from potentially damaging wave motion. The species may be found to depths of approximately 20 metres (1) (4). 

The polyps of Acanthastrea bowerbanki, like those of other reef-building corals, have a symbiotic relationship with single-celled algae, called ‘zooxanthellae’, which lives within their tissues (3). Both parties gain from this relationship, with the photosynthetic zooxanthellae producing nutrients which nourish the coral polyp, and the coral providing the zooxanthellae with a protected environment and access to sunlight near the waters surface. It is thought that the coral can obtain around 70 percent of its nutrient requirements from this relationship (3). However, this reliance on sunlight for photosynthesis means that corals such as Acanthastrea bowerbanki are limited to living in relatively shallow, clear waters (3) (5).

Coral colonies can generally reproduce both sexually and asexually. The process by which they reproduce asexually is known as budding and involves the coral polyp dividing to form new polyps (3). For reproducing sexually, Acanthastrea bowerbanki is hermaphroditic, meaning each polyp produces both eggs and sperm, which are released into the water for external fertilisation. The age of first maturity for most reef-building corals is approximately three to eight years (6). 

Coral species face numerous global threats and it is estimated that 20 percent of the world’s coral reefs have already been destroyed (7) (8). Many of the remaining reefs are facing collapse or even extinction due to factors such as climate change and human interference. Localised human impacts, such as coral harvesting, pollution and impacts from fisheries and tourism all serve to damage coral reefs. Increasing temperatures resulting from climate change also increase the risk of coral ‘bleaching’, whereby the symbiotic zooxanthellae are lost, which often results in the death of the coral (7).

Acanthastrea bowerbanki is particularly susceptible to predation by the crown of thorns starfish (Acanthaster planci) (1). This species feeds on a wide range of coral species and is a voracious predator, having been known to wipe out large areas of coral reef (1). Outbreaks of the starfish may occur regularly and, due to the slow growth rate of coral, reefs may take decades to recover from such attacks (5) (7).

As with all coral species, Acanthastrea bowerbanki is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES). Therefore, trade in this species should be carefully regulated. Parts of the range of Acanthastrea bowerbanki fall within Marine Protected Areas, which offer reefs and the marine environment some degree of protection. However, regulation of these protected areas has proved to be somewhat difficult (1).

Recommended conservation measures for Acanthastrea bowerbanki include further research into its taxonomy, biology, population and habitat status. Techniques for artificial propagation, such as cryo-preservation (freezing) of gametes, may prove to be important tools in the maintenance of coral diversity (1).

Find out more about corals and coral conservation:

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