Thin leaf lettuce coral  (Agaricia tenuifolia)

The thin leaf lettuce coral is classified as Near Threatened (NT) on the IUCN Red List (1) and listed on Appendix II of CITES (2).

A delicate coral with flat, thin, upright plates, the thin leaf lettuce coral (Agaricia tenuifolia) forms elongated colonies which are brown, greenish or rust coloured with pale margins and orange tentacles (3) (4). On reefs exposed to particularly high energy waves, the thin leaf lettuce coral forms box-like networks that are resistant to wave destruction. In lagoon environments with little wave actions, this species forms delicate frameworks (1). 

The colonies of the thin leaf lettuce coral are composed of numerous tiny, anemone-like animals called polyps. The polyps secrete a hard skeleton, and the skeleton of each individual polyp is known as a ‘corallite’ (3). The corallites of the thin leaf lettuce coral are arranged in rows separated by ridges. The coral skeleton forms the bulk of the colony, with the living polyp tissue comprising only a thin veneer. Over successive generations, the growth of the corallites contributes to the formation of a coral reef (3).

The thin leaf lettuce coral occurs in the Caribbean Sea and the southern Gulf of Mexico. It is common and abundant in the southern and western Caribbean but is less common elsewhere (1).

The thin leaf lettuce coral is found on shallow reefs, where it occurs in areas exposed to waves, between depths of 1 and 15 metres (1).

The thin leaf lettuce coral receives the majority of its nutrition from symbiotic algae, known as zooxanthellae, which live within its tissues. The algae provide the coral with nutrients through photosynthesis, and in return receive a stable environment in which to live. A dependence on photosynthesis restricts corals such as the thin leaf lettuce coral to living in relatively shallow, clear, warm waters, but enables them to grow quickly and form large reef structures (3). The thin leaf lettuce coral also feeds actively on tiny zooplankton, which it catches using stinging cells on the tentacles of the polyps (3). 

The thin leaf lettuce coral is hermaphroditic, meaning that each polyp contains both male and female sex organs (5). This species releases eggs and sperm into the water for external fertilisation, and the resulting larvae drift in the water column before eventually settling onto the substrate and developing into polyps (3) (6).

In addition to reproducing sexually, corals are able to reproduce asexually by budding, forming new polyps by the division of existing polyps (3).

With an estimated 20 percent of the world’s coral reefs already destroyed, the thin leaf lettuce coral faces many of the threats that are affecting coral reefs globally (7) (8). 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 (7). 

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 (8). 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) (7) (8) (9).

Parts of the range of the thin leaf lettuce coral fall within Marine Protected Areas (1), although enforcement within these can often be poor (9). International trade in the thin leaf lettuce 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 the thin leaf lettuce coral 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) (9).

For further information on the conservation of coral reefs, see:

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