Acropora palmata
elkhorn coral

Elkhorn coral is present in coral reefs from southern Florida southward to the northern coasts of Venezuela. The coral has native populations throughout this range, most notably in the Bahamas and the Caribbean. (National Marine Fisheries Service, 2008; NOAA Fisheries, 2002)

Elkhorn coral is found in shallow water, generally ranging from 1 to 5 meters deep. Elkhorn coral is a tropical species and inhabits waters with a temperature range of 66 tol 86 degrees F. This coral tolerates salinities within the normal range of 33 to 37 parts per thousand. Elkhorn coral often establishes in heavy surf close to shore, where the preferential exposed reef crests create an optimal habitat. (National Marine Fisheries Service, 2008; NOAA Fisheries, 2002)

Elkhorn coral maintains a relatively large coral body. Elkhorn coral was named after its branching pattern, which is remnant of an elk’s antlers. These antler-like branches are sturdy and thick. The color of the coral, due to the symbiotic zooanthellae, ranges from yellow to a yellowish-brown. (NOAA Fisheries, 2002)

In elkhorn coral, eggs and sperm are released into the water column and fertilization occurs near the surface. After about 78 hours, larvae of planula develop cilia, giving them the appearance of “fuzzy balls.” Motility is observed at this stage. Larvae remain in surface waters during their early development aided by high lipid content. The coral larvae live in the plankton for 3 to 5 days until finding a suitable area to settle. Few larvae actually survive. Those that do, metamorphose into the polyp stage. These polyps then contribute to the development of a new colony. (Adey, 1975; National Marine Fisheries Service, 2008)

Elkhorn coral reaches its maximum size at 10 to 12 years old. Elkhorn coral’s branches can increase in length as fast as 2-4 inches per year. While a colony can persist for centuries, individual coral polyps usually live for 2 to 3 years. (NOAA Fisheries, 2002)

Elkhorn coral is a sessile, colonial species. The polyps feed at night and retract into the secreted coral body during the day. Each polyp secrets part of the mineral colony structure, made of calcium carbonate. Also, each elkhorn coral polyp is symbiotic with algae called zooxanthellae, from which they receive oxygen and energy. The algae are sheltered by the coral, and use the carbon dioxide and other coral waste as nutrients. (National Marine Fisheries Service, 2008; NOAA Fisheries, 2002)

Although elkhorn coral polyps do not communicate with other polyps directly, they do exhibit some behaviors indicating some sort of perceptive response. For example, the release of gametes for breeding occurs with all polyps at the same time per breeding season. On a full moon in August or September, the polyps will release gametes; this is an indication of perception of light (length of day), temperature, and nightime light from the moon. The polyps also exhibit a form of tactile response in that they react to touch and release venomous nematocytes. (Adey, 1975; Bythell, Gladfelter, and Bythell, 1993)

Elkhorn coral get much of their food energy from the algae symbionts that live in their tissues. The polyps provide the algae protection, suitable habitat, and waste products that the algae use as nutrients In return, the zooxanthellae produce surplus sugars that the polyps use as food. Elkhorn coral polyps also use their tentacles to capture small particles of detritus and also small organisms, including phytoplankton, microbes, and small zooplankton. (Adey, 1975; NOAA Fisheries, 2002)

Elkhorn coral rely on their excreted coral bodies to retract into and hide from predators. These predators include many species of damselfish (Pomacentridae), which suck and pluck the coral polyps out of the coral body. Fireworms (such as Hermodice carunculata) and corallivorous snail species in the family Coralliophilidae range over the coral colony grazing on polyps. (National Marine Fisheries Service, 2008; NOAA Fisheries, 2002)

Elkhorn coral is a major component of many reef ecosystems. Its physical structure provides essential refuges for reef animals, both young and adult, as well as food for many species. (National Marine Fisheries Service, 2008; NOAA Fisheries, 2002)

Elkhorn coral offers no direct economic negativities, although is does offer a reflection of negative humans impacts. The destruction of coral reefs due to rising ocean temperatures and an runoff is causing severe economic damage in ecotourism and coastal fisheries. The anthropogenic effects on Elkhorn coral will lead to negative economic implications. (Bythell, Gladfelter, and Bythell, 1993; National Marine Fisheries Service, 2008)

The presence of elkhorn coral has several major economic implications for humans. Ecotourism in the Caribbean relies on healthy reefs, with not only healthy coral, but a healthy ecosystem full of interesting things to see such as fish and other marine animals. The pet trade, in the form of troical reef fish, is supported by healthy coral popualtions which house juvenille reef fish. Elkhorn coral also builds many reefs that are researched extensively, such as those in the Florida keys and the Caribbean. (Bythell, Gladfelter, and Bythell, 1993; National Marine Fisheries Service, 2008)

Populations of elkhorn coral have declined drastically since the 1980's. Estimates are in the range of 90-95% reduction in abundance since 1980 in areas where loss has been quantified. Reductions of 75-90% were observed in some areas such as the Florida keys in 1998 due to bleaching and hurricane damage. The species is listed as Threatened under the U.S. Endangered Species Act, and Critically Endangered by the IUCN. Like all stony corals (Scleractinia) it is listed in Appendix II of CITES, so international trade is somewhat limited. (National Marine Fisheries Service, 2008; NOAA Fisheries, 2002)