Transverse coral (Leptastrea transversa)
|Size||Length: colonies rarely exceed 25 cm in diameter (1)|
Classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES (2).
A relatively common coral species (1), Leptastrea transversa forms small, low-growing colonies that usually take the appearance of colourful, flattened mounds (3). Like other colony-forming corals, Leptastrea transversa 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 have shared, ridged walls forming a honeycomb-like structure. The walls bear numerous tiny tentacles, which surround a central depression—the oral disc—with the polyp mouth positioned in the middle. The polyp tissue varies in colour, usually appearing grey, green or yellow becoming darker towards the sides of the colony (3).
Leptastrea transversa is mainly distributed throughout tropical regions of the Indo-West Pacific (1). Populations do, however, occur from as far west as the east coast of Africa, the Red Sea and the Arabian Gulf, east as far as the islands of the east-central Pacific (1).
Leptastrea transversa is found in a variety of coral reef environments, commonly between depths of 9 to 20 metres, but may occasionally be found closer to the surface from 1 to 5 metres, and as deep as 30 metres. Colonies may occur on subtidal rock, rocky reefs, lagoons, and on areas of rubble found between reefs (1).
Like many coral species, Leptastrea transversa 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 (4). The polyps' tentacles, which in this species are extended during the night and sometimes during the day, contain stinging cells called “nematocysts”. These trap the drifting zooplankton, directing it into the central mouth, which also acts as an anus to excrete waste products after digestion (3) (4).
Leptastrea transversa is capable of asexual reproduction, in which the colony proliferates through the production of clones that bud from 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) (5).
Around one third of the world's reef-building corals are threatened with extinction (6). 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) (6). While Leptastrea transversa is currently widespread, the multitude of threats faced by this species, means that its conservation status could rapidly change (1).
Like all coral species, Leptastrea transversa 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, Leptastrea transversa 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 Leptastrea transversa against complete extinction (1).
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- 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.
- Planktonic: aquatic organisms that drift with water movements; may be either phytoplankton (plants), or zooplankton (animals).
- Sessile: permanently attached; not freely moving.
- Symbiotic: describing 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 (June, 2009)
CITES (June, 2009)
- Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townsville, Australia.
- Barnes, R.S.K., Calow, P., Olive, P.J.W., Golding, D.W. and Spicer, J.I. (2001) The Invertebrates: A Synthesis, 3rd Edition. Blackwell Science, Oxford.
- Richmond, R.H. and Hunter, C.L. (1990) Reproduction and recruitment of corals: comparisons among the Caribbean, the Tropical Pacific, and the Red Sea. Marine Ecology Progress Series, 60: 185 - 203.
- Carpenter, KE et al. (2008) One-Third of Reef-Building Corals Face Elevated Extinction Risk from Climate Change and Local Impacts. Science, 321: 560 - 563.