What Is Elkhorn Coral?

Elkhorn coral (Acropora palmata) is considered to be one of the most important reef-building corals in the Caribbean. This species of coral is structurally complex with many large branches. The coral structure closely resembles that of elk antlers. These branches create habitats for many other reef species such as lobsters, parrot-fish, snappers, and other reef fish. Elkhorn coral colonies are incredibly fast growing with an average growth rate of 5 to 10 centimeters (2.0 to 3.9 in) per year and can eventually grow up to 3.7 meters (12 ft) in diameter. The color of this coral species ranges from brown to a yellowish-brown. This color is a result of the symbiotic zooxanthellae that live inside the tissue of this coral species. Zooxanthellae is a type of algae which photosynthesizes to provide the coral with nutrients. The zooxanthellae are also capable of removing waste products from the coral.

Elkhorn coral was once one of the most abundant species of coral in the Caribbean and the Florida Keys. Since 1980 it has been estimated that 90-95% of elkhorn coral has been lost. Threats to elkhorn coral include disease, coral bleaching, predation, climate change, storm damage, and human activity. All of these factors have created a synergistic effect that greatly diminishes the survival and reproductive success of elkhorn coral. Natural recovery of coral is a slow process and may never occur with this species because there are so many inhibitors to its survival.

Diseases that affect elkhorn coral include white pox disease, white band disease, and black band disease. White pox disease is a disease that only affects elkhorn coral. It is caused by a fecal enterobacterium, Serratia marcescens. The disease is very contagious and commonly moves from one colony to its nearest neighbor. White pox creates white lesions on the coral skeleton and results in an average tissue loss of 2.5 square centimeters (0.39 sq in) per day but can cause as much tissue loss as 10.5 square centimeters (1.63 sq in) per day. White band disease and black band disease have also greatly reduced the abundance of elkhorn coral. Diseases are one of the major causes of coral mortality, however, they are not well studied or understood.

Predators of elkhorn coral include coral eating snails (Coralliophila abbreviata), polychaetes such as the bearded fireworm and damselfish. Predation by these organisms reduces the corals growth and ability to reproduce. Predation can eventually lead to the death of the coral colony.