Brain coral (Platygyra daedalea)

Also known as:	green brain coral, maze brain coral

Kingdom	Animalia
Phylum	Cnidaria
Class	Anthozoa
Order	Scleractinia
Family	Faviidae
Genus	Platygyra (1)

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

This coral gains its common name from the colony’s meandering, brain-like pattern of brown walls, separated by grey or green depressions known as ‘valleys’ (3) (4). Platygyra daedalea colonies are large, up to a metre or more in diameter (1) (4), and are typically mound-shaped or plate-like (encrusting) (3). However, there is wide variation in colony shape and form, which, intriguingly, appears unrelated to the species’ environment or genetic makeup (5) (6). Coral colonies are composed of polyps, tiny, anemone-like animals which secrete the coral skeleton. However, unlike in many other corals, the polyps of Platygyra daedalea colonies are not individually identifiable. Instead, all polyps within the colony share common walls, with the polyp ‘mouths’ aligned in valleys, which in this species typically measure up to 30 millimetres long and 6 millimetres wide (3) (4). The tentacles of the polyps are usually only extended at night (3).

Platygyra daedalea can be difficult to distinguish from the less common Platygyra lamellina, the two species sometimes being classed together in the past (6). However, it can be distinguished by its thinner, more flat-topped and straight-sided walls, and by having valleys that are wider than the separating walls. Platygyra daedalea also has characteristically ragged septa, the radial elements that project inwards from the skeletal wall of each polyp (3) (7) (8).

Platygyra daedalea is widely distributed throughout the Indian and Pacific Oceans, including in the Red Sea and Gulf of Aden, the Arabian Gulf, and around Australia and Southeast Asia (1) (4) (9).

Common over a variety of reef habitats, particularly back reef margins, Platygyra daedalea can be found at depths of up to 30 metres (1) (3) (9).

Platygyra daedalea is a hermatypic coral which has microscopic algae known as zooxanthellae living within its tissues. These produce energy-rich molecules through photosynthesis, transferring most of what is produced to the coral, and in return receiving protection from currents, access to sunlight, and some nutrients from the coral’s waste products. Since the zooxanthellae need sunlight for photosynthesis, corals such as Platygyra daedalea are restricted to clear, shallow, warm waters (3) (10).

Coral colonies grow through a form of asexual reproduction known as budding, in which polyps divide themselves to form new polyps (3). Corals can also reproduce sexually by spawning, which in Platygyra daedalea involves the release of gametes into the water, for external fertilisation. Platygyra daedalea is hermaphroditic, meaning that each polyp produces both eggs and sperm. Spawning in this species usually occurs once a year, sometimes twice, and in some areas may be timed to coincide with the monsoon, when sea surface temperatures are highest and wind conditions are slow and steady (11) (12).

Platygyra daedalea is thought to be a relatively ‘aggressive’ coral, producing elongated tentacles, known as ‘sweeper tentacles’, which can damage the tissues of neighbouring corals, helping Platygyra daedalea to compete for space on the reef (7).

Although widespread and common (1) (3), and believed to be relatively resilient to habitat loss and reef degradation (1), Platygyra daedalea faces a number of threats that are impacting coral reefs around the world, and so is assumed to be undergoing a population decline (1). An estimated 20 percent of the world’s coral reefs have already been destroyed (13), and a large percentage of those remaining are at risk of collapse as a result of human activities. These include overfishing, destructive fishing practices, coral mining, pollution, irresponsible tourism, and poor land management practices, which increase the amount of sediment, nutrients and pollutants entering the ocean (1) (10) (13).

In general, however, climate change may pose the greatest risk to corals, raising the risk of temperature extremes which can stress coral and cause it to lose its zooxanthellae. This process, known as ‘bleaching’, usually results in the death of the coral. Climate change may also lead to more severe, frequent storms, which can damage reefs, and rising carbon dioxide levels may lead to ocean acidification, which can reduce coral’s ability to create its hard skeleton (1) (10) (13). Such stresses may also make corals more susceptible to disease (1). In addition to these general threats, Platygyra daedalea is also the target of collection for the aquarium trade (1).

Platygyra daedalea is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in this species should be carefully regulated (2). Parts of its range occurs within Marine Protected Areas (1), which are set aside from unrestricted human activities and may include, for example, ‘no-take’ zones, where removal of marine life is prohibited. However, less than one percent of all marine habitats currently receive protection (14), and enforcement in these protected areas is often poor (10).

Conservation measures recommended for Platygyra daedalea include the establishment and management of new protected areas, the expansion of existing protected areas, and the management of diseases and parasites. In particular, further research is needed into the species’ abundance and population trends, its ecology, its resilience to various threats, and the potential impacts of collection for the aquarium trade. Suitable management measures, such as quotas and size limits for harvesting, are also required. In the future, techniques for artificially growing corals and for preserving their gametes may become important in the conservation of coral biodiversity (1), and ongoing reef monitoring and increased awareness will also be important tools in efforts to protect these fragile marine ecosystems (10).

For further information on brain coral and other coral species, see:

• Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townsville, Australia.

To find out more about the conservation of coral reefs see:

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

• Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
• Budding: type of asexual reproduction (reproduction that does not involve the formation of sex cells), in which new individuals develop from the parent organism, forming a swelling similar in appearance to a bud. The ‘bud’ slowly separates from the parent as it grows.
• Colony: relating to corals: organisms, such as corals, which are composed of numerous genetically identical modules (also referred to as zooids, polyps or ‘individuals’), which are produced by budding and remain physiologically connected.
• Fertilisation: the fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
• Gamete: a reproductive cell which carries the genetic information from their parent, and is capable of fusing with a gamete of the opposite sex to produce a fertilized egg. In animals, male gametes are called sperm and female gametes are called ova.
• Hermaphroditic: possessing both male and female sex organs.
• Hermatypic: reef-building corals. Most hermatypic corals have a close association with algae known as zooxanthellae, which live in their tissues. These corals are restricted to shallow, tropical, marine environments. Over time the accumulated deposition of calcium carbonate (limestone) by many hermatypic corals can form large limestone structures known as coral reefs.
• Photosynthesis: metabolic process characteristic of plants and algae, in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.
• Polyp: typically sedentary soft-bodied component of cnidaria, a group of simple aquatic animals including the sea anemones, corals and jellyfish. A polyp comprises a trunk that is fixed at the base, and a mouth that is placed at the opposite end of the trunk and is surrounded by tentacles.
• Spawning: the production or depositing of large quantities of eggs in water.

1. IUCN Red List (February, 2009)
   http://www.iucnredlist.org/
2. CITES (February, 2009)
   http://www.cites.org
3. Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townsville, Australia.
4. Carpenter, K.E. (1998) An introduction to the oceanography, geology, biogeography, and fisheries of the tropical and subtropical western and central Pacific. In: Carpenter, K.E. and Niem, V.H. (Eds) FAO Species Identification Guide for Fisheries Purposes. The Living Marine Resources of the Western Central Pacific, FAO, Rome. Available at:
   ftp://ftp.fao.org/docrep/fao/009/w7191e/w7191e10.pdf
5. Miller, K.J. (1992) Morphological variation in the scleractinian coral Platygyra daedalea (Ellis & Solander, 1786) - genetically or environmentally determined?. Proceedings of the Seventh International Coral Reef Symposium, 1: 550 - 556.
6. Miller, K.J. (1994) Morphological variation in the coral genus Platygyra: environmental influences and taxonomic implications. Marine Ecology Progress Series, 110: 19 - 28.
7. Lapid, E.D., Wielgus, J. and Chadwick-Furman, N.E. (2004) Sweeper tentacles of the brain coral Platygyra daedalea: induced development and effects on competitors. Marine Ecology Progress Series, 282: 161 - 171.
8. Hellyer, P. and Aspinall, S. (2005) The Emirates: A Natural History. Trident Press Limited, London.
9. Veron, J.E.N. (1993) Corals of Australia and the Indo-Pacific. University of Hawaii Press, Honolulu, Hawaii.
10. Miththapala, S. (2008) Coral Reefs. Coastal Ecosystems Series (Volume 1). Ecosystems and Livelihoods Group Asia, IUCN, Colombo, Sri Lanka. Available at:
    http://data.iucn.org/dbtw-wpd/edocs/2008-012.pdf
11. Mangubhai, S. and Harrison, P.L. (2006) Seasonal patterns of coral reproduction on equatorial reefs in Mombasa, Kenya. Proceedings of the Tenth International Coral Reef Symposium, 1: 106 - 114.
12. Mangubhai, S. and Harrison, P.L. (2008) Gametogenesis, spawning and fecundity of Platygyra daedalea (Scleractinia) on equatorial reefs in Kenya. Coral Reefs, 27: 117 - 122.
13. Wilkinson, C. (2004) Status of Coral Reefs of the World: 2004. Volume 1. Australian Institute of Marine Science, Townsville, Australia. Available at:
    http://www.crisponline.info/Portals/1/Skins/inside_fr/documents/0_statusofcoralreefs.pdf
14. UNEP: Fifty Key Facts about Seas and Oceans (July, 2009)
    http://www.unep.org/wed/2004/Downloads/PDFs/Key_Facts_E.pdf