Stony coral  (Barabattoia amicorum)

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

One of only two coral species belonging to the Barabattoia genus, Barabattoia amicorum is an uncommon component of coral reefs, which forms small, colourful mound-shaped colonies. Like other colony-forming corals, Barabattoia amicorum colonies are composed of numerous small polyps, which are soft-bodied animals, related to anemones. Each polyp secretes a hard skeleton called a corallite, which forms the bulk of the colony, with the living coral tissue comprising a thin veneer over the surface. In this species, the individual polyps form short, tubular mounds, that project from the surface of the main body of the colony. Each distinct, cylindrical unit has a ridged outer wall bearing numerous tiny tentacles, which surrounds a central depression—the oral disc—with the polyp mouth positioned in the middle. The polyp tissue varies in colour, exhibiting shades of brown, green or cream, with a paler oral disc (3).

Mainly occurring in tropical waters, Barabattoia amicorum is widely distributed throughout the Indo-West Pacific (1). Populations also occur in the Red Sea (1) and may also be found in the Arabian Gulf (4).

Barabattoia amicorum is found in shallow reef environments, especially on the rear side of reefs where the colonies are protected from strong wave action (3). It also occurs in lagoons, on areas of soft-substrate between reefs, and on sub-tidal rock to depths of at least 20 metres (1).

Like many coral species, Barabattoia amicorum is zooxanthellate, which means that its tissues contain large numbers of single-celled algae called zooxanthellae. The coral and the algae have a symbiotic relationship, in which the algae gain a stable environment within the coral's tissues, while the coral receives nutrients produced by the algae through photosynthesis. By harnessing the sun's energy in this way, corals are able to grow rapidly and form vast reef structures, but are constrained to live near the water surface (3).

While, on average, zooxanthellate coral can obtain around 70 percent of its nutrient requirements from zooxanthellae photosynthesis, the coral may also feed on zooplankton (5). The polyps' tentacles, which in this species are mostly extended at night, contain stinging cells called “nematocysts” that trap the drifting zooplankton, directing it into the central mouth, which also acts as an anus to excrete waste products after digestion (3) (5).

Barabattoia amicorum is capable of asexual reproduction, in which the colony proliferates through the production of clones that bud from the outer walls of the individual polyps, and by sexual reproduction, in which the polyps spawn large numbers of sperm and eggs. The fertilised eggs develop into planktonic larvae, which travel through the water column, before settling and metamorphosing into sessile polyps (3) (6).

Around one third of the world's reef-building corals are threatened with extinction (7). The principal threat to corals is the rise in sea temperature associated with global climate change. This leads to coral bleaching, where the symbiotic algae are expelled, leaving the corals weak and vulnerable to an increasing variety of harmful diseases (1). Other harmful effects of climate change include more frequent destructive, extreme weather incidents, as well as increased ocean acidification, which impairs a coral's ability to form a skeleton. These global threats are compounded by localised threats from pollution, destructive fishing practices, invasive species and human development (1) (7). While Barabattoia amicorum is currently widespread, the multitude of threats faced by this species, means that its conservation status could rapidly change (1).

Like all coral species, Barabattoia amicorum is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which means that any international trade is strictly controlled by the use of permits and annual quotas (2). In addition, Barabattoia amicorum falls within several Marine Protected Areas across its range (1).

Specific conservation measures recommended for this species include carrying out extensive studies of its population, biology, and ecology, along with more research into existing and potential threats. In response to the threat of climate change, artificial propagation and preservation of sperm and eggs may become necessary to safeguard Barabattoia amicorum against complete extinction (1).

View information on this species at the UNEP World Conservation Monitoring Centre.

Environment Agency - Abu Dhabi is a principal sponsor of ARKive. EAD is working to protect and conserve the environment as well as promoting sustainable development in the Emirate of Abu Dhabi.

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

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