Brain coral (Platygyra sinensis)
|Size||Colony diameter: c. 1 m (1)|
- Like other corals, Platygyra sinensis forms colonies that consist of many small, anemone-like animals known as polyps.
- Each polyp of Platygyra sinensis secretes a hard skeleton, and in this species adjacent polyps share their skeleton walls.
- Platygyra sinensis is often known as a ‘brain coral’, as the surfaces of its colonies are covered in a meandering, brain-like pattern of ridges.
- Platygyra sinensis colonies display a wide range of colours, with some being quite dull in appearance while others are more brightly coloured.
Platygyra sinensis is classified as Least Concern (LC) on the IUCN Red List (1) and is listed on Appendix II of CITES (2).
Platygyra sinensis is a widespread coral that typically forms large, domed colonies (3) (4) (5) up to a metre or more in diameter (1). The diameter of its colonies often decreases with increasing water depth (4), and the colonies may sometimes also be flat (3) (4) (5).
Platygyra sinensis is often known as a ‘brain coral’ due to the meandering, brain-like pattern of ridges, or walls, across its surface. In this species, the walls are relatively thin (3) (5) and are usually separated by short ‘valleys’, although longer, meandering valleys do also sometimes occur (4). The colonies of Platygyra sinensis display a wide range of colours, with some being dull and others quite bright (3) (4) (5).
As in all corals, the colonies of Platygyra sinensis consist of numerous, anemone-like animals known as polyps, which have a sac-like body and a central ‘mouth’, surrounded by tentacles. The polyps secrete a hard skeleton, with the skeleton of an individual polyp being known as a ‘corallite’ (3) (6). In Platygyra sinensis, each corallite has internal projections, known as septa, which in this species are thin, evenly spaced, and have tooth-like indentations along their edges (3) (4) (5).
The corallites of Platygyra sinensis share common walls (3) (4) (5), and the mouths of the polyps are aligned along the colony’s valleys, with most valleys only having one mouth, but more elongated valleys sometimes having several (4) (5).
Platygyra sinensis is widespread in the Indian Ocean, including the Red Sea and Arabian Gulf, as well as in the western and central Pacific Ocean (1) (3) (4) (5).
Usually found at depths of up to 30 metres (1), Platygyra sinensis occurs in most types of reef habitat (1) (3) (4). However, it particularly favours the margins of back reefs, which are the more sheltered, shallower parts of the reef closest to the shore (1) (3).
Like all species in the Faviidae family, Platygyra sinensis is a zooxanthellate coral, meaning that it obtains most of its nutrients from symbiotic algae, known as zooxanthellae, which live within its tissues. The zooxanthellae provide the coral with nutrients through photosynthesis, but this restricts corals such as Platygyra sinensis to living in relatively clear, warm, shallow waters where photosynthesis can take place. In return for nutrients, the coral provides the zooxanthellae with a safe, stable environment in which to live (3) (6).
In addition to receiving nutrients in this way, Platygyra sinensis is able to supplement its diet with tiny zooplankton, which it catches using stinging cells on its tentacles. The tentacles of this species are usually only extended for feeding at night, and are retracted during the day (3).
Like other corals, Platygyra sinensis is able to reproduce asexually by a process known as ‘budding’, in which a polyp divides into two or more new polyps. Corals also reproduce sexually, usually by releasing large numbers of eggs and sperm into the water column, where the eggs are fertilised and develop into larvae. The larvae eventually settle onto the substrate and develop into polyps, starting new colonies (3).
Relatively little information is available on reproduction in Platygyra sinensis, but it is reported to have pink eggs and is hermaphroditic, with each polyp producing both eggs and sperm. In the Great Barrier Reef, off the coast of Australia, Platygyra sinensis has been recorded taking part in mass spawning events with other coral species, with most colonies releasing their eggs and sperm over a number of consecutive nights. Spawning in this region has been recorded in spring, between October and November, and usually occurs after a full moon. Platygyra sinensis has been found to spawn around three to four hours after sunset (7).
Although it is widespread and relatively common, and not currently considered at risk of extinction, Platygyra sinensis is assumed to be declining based on the loss and degradation of its reef habitats (1). Overall, around 20 percent of the world’s coral reefs have already been destroyed (8).
Like other corals, Platygyra sinensis faces a range of threats, the most serious of which is likely to be global climate change. Rising sea temperatures can cause corals to expel their zooxanthellae, weakening the coral and often resulting in death. This process, known as ‘bleaching’, can also make corals more vulnerable to disease. In addition, climate change may cause more frequent, violent storms, which can damage corals, while rising carbon dioxide levels are increasing ocean acidity and affecting the ability of corals to form their hard skeletons (1) (6) (8) (9).
Platygyra sinensis is also likely to be affected by more localised threats to reefs, including pollution, sedimentation, destructive fishing practices, invasive species, and human recreation and tourism (1) (6) (8) (9). Platygyra sinensis is also collected for the aquarium trade. Fortunately, its widespread distribution and large population help make this species more resilient to these threats (1).
Platygyra sinensis 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 controlled (2). Although parts of its range fall within Marine Protected Areas (1), enforcement in these areas is often poor (6).
Recommended measures for the conservation of Platygyra sinensis and other corals include further research into its populations, ecology and resistance to various threats, as well as disease control and the expansion of protected areas. It will also be important to take action to tackle global climate change, and to build greater awareness of the threats to corals (1) (6) (8). Techniques for artificially growing corals or for storing their eggs and sperm may also play a role in coral conservation in the future (1).
Due to the severity of the effects of climate change and ocean acidification on corals, it will be important to assess the conservation status of Platygyra sinensis again in the near future, to ensure that it has not become endangered (1).
Find out more about corals and their conservation:
Corals of the World Online:
The Coral Reef Alliance:
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- Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- Asexual reproduction: reproduction that does not involve the formation of sex cells (‘gametes’). In many species, asexual reproduction can occur by existing cells splitting into two, or part of the organism breaking away and developing into a separate individual. Some animals, including vertebrates, can also develop from unfertilised eggs; this process, known as parthenogenesis, gives rise to offspring that are genetically identical to the parent.
- Colony: a group of organisms living together. Individuals in the group are not physiologically connected and may not be related, such as a colony of birds. Another meaning refers to organisms, such as bryozoans, which are composed of numerous genetically identical modules (also referred to as zooids 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.
- Hermaphroditic: possessing both male and female sex organs.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Photosynthesis: metabolic process characteristic of plants 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.
- Septa: in a coral, radial elements that project inwards from the corallite wall (the skeletal wall of an individual coral polyp).
- Spawning: the production or depositing of eggs in water.
- Symbiotic: describes a relationship in which two organisms form a close association. The term is now usually used only for associations that benefit both organisms (a mutualism).
- Zooplankton: tiny aquatic animals that drift with currents or swim weakly in water.
IUCN Red List (December, 2012)
CITES (December, 2012)
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