Acropora palmataElkhorn coral

Geographic Range

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. (NOAA Fisheries, 2002; National Marine Fisheries Service, 2008)


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)

  • Range depth
    1 to 20 m
    3.28 to 65.62 ft
  • Average depth
    3.5 m
    11.48 ft

Physical Description

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)

  • Sexual Dimorphism
  • sexes alike
  • Average length
    .75 m
    2.46 ft


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)


A majority of elkhorn coral reproduction involves asexual reproduction. Branches of the coral can break off and attach to substrate. The coral animals within the branch can then colonize the new area and begin a new colony.

Elkhorn coral also reproduce sexually. Each colony contains both male and female structures, and is simultaneously hermaphroditic. Millions of male and female gametes are released into the water at the same time (usually synchronized with other adjacent colonies). This sexual reproduction occurs once a year, usually in August or September on a full moon. The coral larva, or planula, will float in the water column as plankton for several days until they land on suitable substrate. The planula then metamorphose into colonial polyps. Thus, a new colony is started. (Bak, 1983; National Marine Fisheries Service, 2008)

  • Breeding interval
    Elkhorn coral spawn once a year.
  • Breeding season
    August to September

Elkhorn coral exhibit no parental care. (Adey, 1975; Bak, 1983)

  • Parental Investment
  • no parental involvement


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)

Communication and Perception

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, et al., 1993)

Food Habits

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)

Ecosystem Roles

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)

  • Ecosystem Impact
  • creates habitat
Mutualist Species
  • Zooxanthellae

Economic Importance for Humans: Positive

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, et al., 1993; National Marine Fisheries Service, 2008)

Economic Importance for Humans: Negative

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, et al., 1993; National Marine Fisheries Service, 2008)

Conservation Status

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)


Steve Grodsky (author), Rutgers University, Jin Jeon (author), Rutgers University, David Howe (editor, instructor), Rutgers University .


Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents


the nearshore aquatic habitats near a coast, or shoreline.


used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

colonial growth

animals that grow in groups of the same species, often refers to animals which are not mobile, such as corals.


active at dawn and dusk


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


An animal that eats mainly plants or parts of plants.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.


photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)


an animal that mainly eats plankton

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).


structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season


remains in the same area


non-motile; permanently attached at the base.

Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa


reproduction that includes combining the genetic contribution of two individuals, a male and a female


uses touch to communicate


The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


Adey, W. 1975. The algal ridges and coral reefs of St. Croix. Atoll Resource Bulletin, 187: 1-67.

Bak, R. 1983. Neoplasia, regeneration and growth in the reef building coral Acropora plamata. Marine Biology, 77: 221-227.

Bythell, J., E. Gladfelter, M. Bythell. 1993. Chronic and catastrophic natural mortality of three common Caribbean corals. Coral Reefs, 12: 143-152.

NOAA Fisheries, 2002. "General Fact Sheet: Atlantic Acropora Corals" (On-line pdf). NOAA Fisheries. Accessed December 05, 2007 at

National Marine Fisheries Service, 2008. "Elkhorn Coral (Acropora palmata)" (On-line). Office of Protected Resources, Species Information. Accessed December 20, 2008 at