Lamarck's sheet coral  (Agaricia lamarcki)

Lamarck’s sheet coral is classified as Vulnerable (VU) on the IUCN Red List (1) and is listed on Appendix II of CITES (2).

As its name suggests, Lamarck’s sheet coral (Agaricia lamarcki) forms broad, flat, plate or sheet-like colonies, which are relatively thick and sometimes overlap. Large colonies may even form flattened, whorl-like structures. Lamarck’s sheet coral is normally yellowish-brown or brown, sometimes with greyish tints (3).

As with all corals, the colonies of Lamarck’s sheet coral comprise numerous polyps, anemone-like animals which secrete the coral skeleton. The individual coral skeletons of Lamarck’s sheet coral, known as ‘corallites’, are normally 3.1 to 4.5 millimetres in diameter (3). In this species, the underside of the colony is smooth, while the upper surface bears concentric rows of ridges, with straight or network-like valleys possessing white, star-shaped polyps.

Lamarck’s sheet coral is similar in appearance to the related Graham’s sheet coral (Agaricia grahamae), but has larger corallites and possesses white polyp ‘mouths’, which are absent in Graham’s sheet coral (4) (5).

Lamarck’s sheet coral is found in the Caribbean Sea, the Gulf of Mexico and around Florida and the Bahamas (1).

Lamarck’s sheet coral is normally found on sloping reefs or in channels and deep lagoons. Although it has been recorded at a depth of 76 metres, it is most commonly found at depths of 15 to 25 metres. It may be found at shallower depths in turbid waters (1).

Like many other corals, Lamarck’s sheet coral is a ‘zooxanthellate’ coral, receiving much of its nutrition as a result of the symbiotic relationship it has with single-celled algae, known as zooxanthellae. These organisms live and photosynthesise within the coral tissues, providing organic nutrients to nourish the polyp, and in return receiving protection and access to sunlight. Corals of this type generally grow faster in clear, shallow waters, with easier access to light (4).

Each polyp of Lamarck’s sheet coral also possesses a ring of stinging tentacles, which are capable of capturing minute zooplankton (4). These tentacles are, however, rarely extended during the day and the majority of the coral’s nutrition is obtained from the zooxanthellae (6).

Corals are capable of reproducing sexually or asexually. Like some other Agaricia species, Lamarck’s sheet coral is thought to be a ‘brooding’ species, whereby fertilisation occurs internally. The larvae develop within the polyp prior to release into the water (7). The age of maturity for most reef-building corals is approximately three to eight years (8).

Despite its wide distribution, Lamarck’s sheet coral is relatively rare, and like all corals, it faces numerous threats. Of major concern to corals worldwide is global climate change, which may lead to more severe, frequent storms, ocean acidification and an increase in ocean temperatures, in turn leading to coral ‘bleaching’. Due to their thin tissues, corals are highly sensitive to bleaching events, in which the zooxanthellae are lost, leading to increased disease susceptibility and often death. Coral diseases also affect coral reefs worldwide, and are considered a major contributory factor in reef destruction (1).

Localised human impacts, including fisheries, development, pollution, sedimentation, tourism and coral harvesting, also place additional stress on sensitive coral reef habitats (9). It is estimated that, globally, 20 percent of coral reefs have been destroyed (1).

Along with all coral species, Lamarck’s sheet coral is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that trade in this coral should be highly regulated. In the United States, Lamarck’s sheet coral is found in many Marine Protected Areas, offering some degree of protection, and harvesting of corals for commercial purposes is illegal in U.S. waters (1).

Further research is required into the biology, population and habitat requirements of Lamarck’s sheet coral and other coral species to determine the most appropriate conservation measures. Techniques for artificial propagation, such as the cryo-preservation (freezing) of gametes, may prove to be an important advance in the protection of coral diversity (1).

To find out more about corals and coral conservation, see:

• Reef Check:
  http://www.reefcheck.org/
• The Coral Reef Alliance:
  http://www.coral.org/
• Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townsville, Australia.