Fluorescence grass coral (Galaxea fascicularis)

Also known as: Starburst coral
Synonyms: Anthophyllum hystrix, Galaxea aspera, Galaxea cespitosa, Galaxea hexagonalis, Galaxea hystrix, Galaxea lawisiana, Madrepora cuspidata, Madrepora divergens, Madrepora fascicularis, Madrepora organum, Sarcinula ellisii, Sarcinula fascicularis, Sarcinula hexagonalis, Sarcinula irregularis
GenusGalaxea (1)

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

Although usually growing as small cushion-shaped or domed colonies, Galaxea fascicularis is also capable of producing massive or columnar colonies of over five metres across (1) (3) (4). Like other corals, the colonies are composed of numerous tiny, anemone-like polyps, which secrete the hard coral skeleton (3). The skeleton of an individual polyp is known as a ‘corallite’, and in Galaxea fascicularis these comprise solid walled, cylindrical tubes, usually under 10 millimetres in diameter, which are linked together by thin, blister-like horizontal plates, or ‘coenosteum’ (3) (4).

Galaxea fascicularis colonies have a distinctly spiky appearance, with the polyps elevated on the long, tubular corallites, and having septa that project sharply outwards. This coral is usually green, grey, red or brown in colour, commonly with tentacles and septa of contrasting colours, and with conspicuous white tips to the tentacles (3) (4) (5). Although often forming even-surfaced colonies, Galaxea fascicularis may also show a sub-branching growth form, sometimes in response to the action of boring organisms such as the date mussel (Lithophaga) (4).

Galaxea fascicularis is found across the Indian Ocean and western and central Pacific Ocean, from the Red Sea, Arabian Gulf and east coast of Africa, to Australia and South East Asia, and as far east as Fiji and Samoa (1) (3) (4).

This coral is common in a wide range of reef environments that are protected from strong wave action, and typically occurs at depths of up to 15 metres (1) (3) (4) (5). Galaxea fascicularis is often a dominant species on inshore fringing reefs, sometimes to the exclusion of all other corals (1) (3) (4).

Galaxea fascicularis is a hermatypic coral, receiving most of its nutrients from microscopic algae, known as zooxanthellae, which live within its tissues. These produce energy-rich molecules through photosynthesis, and in return receive a stable environment, protection from currents and access to sunlight. The coral is also able to supplement its diet with tiny zooplankton, caught using stinging cells on the tentacles, which in this species are extended during the day (3) (4) (6).

Galaxea fascicularis is able to reproduce asexually by a process known as budding, in which polyps divide into two or more daughter polyps. Corals also reproduce sexually, producing large numbers of sperm and eggs (3). Galaxea fascicularis is hermaphroditic, meaning each polyp produces both eggs and sperm, which are released into the water for external fertilisation. The fertilised eggs develop into larvae, which drift in the water column before settling and developing into polyps. In this species, sexual reproduction is thought to occur annually, in spring or summer, with the eggs turning from white to pink in colour when mature, and eggs and sperm being released at night (7) (8). This has been recorded to occur a few days after the full moon around the Great Barrier Reef in Australia (8). When Galaxea colonies die and break up, the tubular coral skeletons remain, and often become a major component of coral rubble on beaches (4).

Coral reefs are facing a range of serious threats worldwide, with an estimated 19 percent of reefs already lost (9), and around a third of all reef-building corals now threatened with extinction (10). The major threat to corals is global climate change, which is likely to lead to more frequent, severe storms, which can damage reefs, and to increase the risk of coral ‘bleaching’, in which high ocean temperatures cause the stressed coral to expel its zooxanthellae, often resulting in death. Rising carbon dioxide levels may also increase ocean acidity, reducing the ability of coral to create its hard skeleton (1) (6) (9) (10).

These global threats are compounded by direct human impacts, from coral harvesting, overfishing and destructive fishing methods, irresponsible tourism, invasive species, pollution and sedimentation. These combined stresses can also make corals more susceptible to disease, parasites, and predators, with the voracious crown of thorns starfish (Acanthaster planci) posing a particular threat (1) (6) (9) (10). Although Galaxea fascicularis is still common and widespread, so potentially making it more resilient to global threats, it is also targeted for the aquarium trade, with over 20,000 pieces exported in 2005 alone (1).

Like all corals, Galaxea fascicularis is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in this coral should be carefully monitored and controlled (2). Parts of the species’ range fall within Marine Protected Areas (1), and Galaxea fascicularis also occurs on the famous Great Barrier Reef, off the coast of Australia, where extensive coral research programmes and a variety of conservation actions are underway (12). However, enforcement in many Marine Protected Areas is poor (6), and overall less than one percent of all marine habitats currently receive protection (11).

Specific conservation measures recommended for Galaxea fascicularis include fisheries management, such as quotas and size limits for collection, as well as population surveys to monitor the effects of harvesting for the aquarium trade (1). As with other corals, further research into the species, together with disease and parasite management, artificial propagation techniques, and the establishment and effective protection of new Marine Protected Areas, will also be important for its conservation (1) (9). Action to conserve coral reefs is now considered urgent if these important and incredibly diverse ecosystems are to survive (9).

To find out more about corals and their conservation see:

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  1. IUCN Red List (December, 2009)