Mushroom coral  (Ctenactis albitentaculata)

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

A member of the Fungiidae family of corals, also known as ‘mushroom corals’ due to their superficial resemblance to mushrooms, Ctenactis albitentaculata is a solitary, free-living coral. This means it is not attached to the substrate and does not form colonies. It is flat or dome-shaped and elongate in outline (3). 

Like other mushroom corals, Ctenactis albitentaculata also has a wide, slit-like mouth in the centre that extends across most of the polyp’s length (3) (4). Ctenactis albitentaculata is usually pale brown, except for bright white (1), short, tapered, widely-spaced tentacles, which protrude from the coral mainly at night but also partly during the day. The septa are neatly spaced and have long, tapered, triangular teeth (3).

Ctenactis albitentaculata occurs in the eastern Indian and western Pacific Oceans, where it ranges from Southeast Asia, to New Caledonia, the Philippines and Papua New Guinea, and as far east as Palau and the South Marianas (1).

Ctenactis albitentaculata is found on shallow reef slopes at depths of 6 to 20 metres (1) (3).

Mushroom corals can reproduce sexually or asexually (5). During sexual reproduction, eggs and sperm are released into the water, where the egg is fertilised and develops into a larva (3). Within a fortnight, the larva will settle on to a hard substrate (5). Asexually reproduced young coral can develop from partly buried, damaged or dying parent tissue. Either way, the result is a vase-shaped polyp that gradually grows into a flattened disc, attached to the substrate via a stalk (4). The stalk of the ‘mushroom’ eventually dissolves, and the coral becomes mobile. The newly mobile coral rests on the bottom where it will mature and reproduce (4) (5). 

The mobility of adult mushroom corals allows them to expand the reef by moving down-slope onto the soft substrate. This is an important process in reef ecosystems as it provides a hard substrate for other corals to establish, as well as shelter for other invertebrates (4) (5). 

When mushroom corals are in immediate contact with other hard corals, they secrete a mucus that can damage coral tissues and prevents the over-growth of these neighbouring corals. This mucus also plays a role in removing sediment from the coral, and facilitates food capture (4). However, mushroom corals receive the majority of their nutrition from symbiotic algae, known as ‘zooxanthellae', which live within their tissues. The algae provide the corals with nutrients through photosynthesis, and in return receive a stable environment in which to live (3).

With an estimated 20 percent of the world’s coral reefs already destroyed, Ctenactis albitentaculata faces many of the threats that are affecting coral reefs globally (6) (7). Worldwide, there is increasing pressure on coastal resources resulting from human population growth and development. There has been a significant increase in domestic and agricultural waste in the oceans, poor land-use practices that result in an increase in sediment running on to the reefs, and over-fishing, which can have knock-on effects on the reef (6). 

However, the major threat to corals is global climate change, with the expected rise in ocean temperatures increasing the risk of coral ‘bleaching’, in which the stressed coral expels its zooxanthellae, often resulting in the death of the coral (7). Climate change may also lead to more frequent, severe storms, which can damage reefs, and rising carbon dioxide levels may make the ocean increasingly acidic. Such stresses can also make corals more susceptible to disease, parasites and predators, such as the crown of thorns starfish (Acanthaster planci) (6) (7) (8).

Parts of the range of Ctenactis albitentaculata fall within Marine Protected Areas (1), although enforcement within these can often be poor (8). It also occurs in the Great Barrier Reef, off the coast of Australia, where a range of conservation and research programmes are underway (9). International trade in the mushroom coral should be carefully regulated under its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) (2). 

Recommended conservation measures for Ctenactis albitentaculata include research into its populations, abundance, ecology and resilience to threats, as well as monitoring and regulation of its harvest for the aquarium trade (1). It would also benefit from the expansion of Marine Protected Areas, together with further research into coral diseases and efforts to combat climate change (1) (7) (8).

Find out more about the conservation of coral reefs:

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