A common coral species in the tropical western Atlantic, the rough star coral is easily recognised by its small, flat or dome-shaped colonies, with short, meandering grooves and thick, fleshy ridges (3)(4). Like other colony-forming corals, each rough star coral colony is composed of numerous small polyps - soft-bodied animals related to anemones. Each groove contains a single, long polyp with many mouths arranged into a row, and surrounded by tentacles that direct food into the mouths, where it is digested in a sac-like body cavity. One of the most remarkable and ecologically important features of Scleractinia corals is that the polyps secrete a hard skeleton, called a ‘corallite’, which over successive generations contributes to the formation of a coral reef. The coral skeleton forms the bulk of the colony, with the living polyp tissue comprising only a thin veneer (3). Living colonies of the rough star coral range in colour from varying degrees of light green to yellow, usually with the ridges being lighter in colour than the darker groove floors (3)(4)(5).
Like many coral species, the rough star coral 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 safe, 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 relatively rapidly and form vast reef structures, but are constrained to live near the water surface. While, on average, zooxanthellate coral can obtain around 70 percent of its nutrient requirements from zooxanthellaephotosynthesis, the coral may also feed on zooplankton(3).
With an estimated 20 percent of the world’s coral reefs already destroyed, the rough star coral 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. Consequently, 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. 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 sea star (Acanthaster planci) (6)(7)(8).
In addition to being listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which makes it an offence to trade this species without a permit, the rough star coral also forms part of the reef community in numerous marine protected areas, including the Florida Keys National Marine Sanctuary (1)(2). To specifically conserve this species, recommendations have been made for a raft of studies into various aspects of its biology, population status, habitat and threats to its survival (1).
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Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
Relating to corals: corals composed of numerous genetically identical individuals (also referred to as zooids or polyps), which are produced by budding and remain physiologically connected.
Metabolic process characteristic in which carbon dioxide is broken down, using energy from sunlight. Organic compounds are made and oxygen is given off as a by-product.
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.
Relationship in which two organisms form a close association. The term is now usually used only for associations that benefit both organisms (a mutualism).
Tiny aquatic animals that drift with currents or swim weakly in water.
Single-celled dinoflagellates that form symbiotic relationships with hermatypic ‘reef-building’ corals.
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