Blue coral  (Heliopora coerulea)

This unique species is the sole member of the order Helioporacea. Blue corals are thus named for their distinctive, permanently blue skeleton, which is generally hidden by greenish-grey or blue polyps (2). The coral polyp is basically an anemone-like animal that secretes a skeleton, at the base of which it is joined to other polyps to form a colony. The polyps of the blue coral each have eight tentacles (2), and the colonies form branching, plate-like or columnar colonies (3).

Occurs in the Indo-Western Pacific, generally between 25°N and 25°S, where it is relatively uncommon (4).

Blue corals occur in tropical waters, on intertidal reef flats and upper reef slopes (3).

Blue 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 (3). In return, the coral provides the zooxanthellae with protection, and access to sunlight.

Blue corals reproduce sexually by brooding. Instead of releasing eggs and sperm into the water where the fertilised egg develops into larvae, like many corals do, the larvae of blue corals develop inside the polyps. Each polyp produces one or two larvae, which subsequently attach themselves onto the colony before release. This may allow the larvae to develop further, and thus when the mature larvae are released into the water column it is able to settle in quickly. This means that the larvae will settle in a habitat that is already proven to be suitable for adult growth and reproduction. The larvae of blue coral have not been observed to swim, and thus dispersal of this coral is determined by water movement (5).

Blue 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 (6). Blue corals may also be threatened by over-harvesting for the coral trade, where it was one of the top ten genera of corals traded between 1985 and 1997 (7). It occurs primarily in the dead coral trade, as its beautiful skeleton makes it an attractive material for ornaments and jewellery, but they are also sometimes traded live for use in aquariums, where they do not usually survive more than a year (7).

Blue 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). Blue 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 (6).

For further information on this species see Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townville, Australia.

For further information on the conservation of coral reefs see:

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

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk