Which coral species is commonly called elkhorn coral?

Elkhorn coral is commonly called Acropora palmata.

Acropora palmata earned its common name from its thick, branching colonies, which resemble the antlers of an elk. It is a major reef-building coral of the Caribbean and nearby western Atlantic, where its interlocking branches create shelter and nursery habitat for fish and other reef organisms.

The species usually grows in clear, shallow, high-energy water, often around 1 to 5 metres deep. Its branching form can grow rapidly—roughly 5 to 10 centimetres per year under favorable conditions—and broken branches can attach elsewhere and form new colonies. This asexual reproduction by fragmentation is especially important for recovery, although the coral also reproduces sexually.

Elkhorn coral is not the same as staghorn coral, Acropora cervicornis, whose branches are generally narrower and more cylindrical. Acropora palmata has suffered a severe Caribbean decline because of disease, warming seas, algae, storms, pollution, and other stresses. In the United States, it was listed as threatened under the Endangered Species Act in 2006, and restoration programs now use nurseries and outplanting to rebuild genetically diverse colonies.