"Elkhorn coral is found on coral reefs in southern Florida, the Bahamas, and throughout the Caribbean. Its northern limit is Biscayne National Park, Florida, and it extends south to Venezuela; it is not found in Bermuda. Once found in continuous stands that extended along the front side of most coral reefs, the characteristic "Acropora palmata zone" supported a diverse assemblage of other invertebrates and fish. These zones have been largely transformed into rubble fields with few, isolated living colonies." (NOAA Fisheries OPR)

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.

Biogeographic Regions: atlantic ocean (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Widepsread distribution in the tropical western Atlantic, including the Gulf of Mexico, southern Florida, Bahamas, Haiti, Puerto Rico, Jamaica, Cuba, Lesser Antilles, Panama, Belize and Nicaragua. Smith (1971): Florida Keys, Bahamas. Colin (1978): Caribbean. Cairns (1982): Belize. Nelson (1988), Farrell et al. (1983), Tunnell (1988), Jordan (1992): Mexican Gulf. Jaap (1984), Jaap et al. (1988, 1989), Burns (1985), White and Porter (1985): Florida Keys. Lang et al. (1988): Bahamas. Goreau (1959), Goreau and Wells (1967): Jamaica. Roberts (1971): Cayman Islands. Kuhlmann (1974), Zlatarski and Estalella (1982): Cuba. A63ALM01FCUS, A70PRE01FCUS, A89GOE01FCUS: Puerto Rico. A82BRA01FCUS: Haiti. A74LEW01FCUS, A87TOM01FCUS: Barbados. A82ROG01FCUS, A83ROG01FCUS, A82GLA01FCUS, A90EDM00FCUS: Virgin Islands. A79DUN01FCUS, A76GOO01FCUS, A72ROB01FCUS, A68ADA01FCUS: lesser Antilles. A74SCA01FCUS, A78FOC01FCUS, A79BAK02FCUS: Curacao and Bonaire. A82GLA01FCUS: Nicaragua. A84LAS02FCUS, A82HIG01FCUS: Panama.

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.

Average length: .75 m.

Sexual Dimorphism: sexes alike

"Elkhorn coral was formerly the dominant species in shallow water (3 ft-16 ft (1-5 m) deep) throughout the Caribbean and on the Florida Reef Tract, forming extensive, densely aggregated thickets (stands) in areas of heavy surf. Coral colonies prefer exposed reef crest and fore reef environments in depths of less than 20 feet (6 m), although isolated corals may occur to 65 feet (20 m)." (NOAA Fisheries OPR)

• Marine

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.

Range depth: 1 to 20 m.

Average depth: 3.5 m.

Habitat Regions: tropical ; saltwater or marine

Aquatic Biomes: reef ; coastal

Other Habitat Features: intertidal or littoral

Habitat Type: Marine

Comments: Occupies depth range from 0-17 m, but typically occurs between 1-5 m (Goreau and Wells, 1967).

A67GOR01FCUS: 0 to 17 m, but typically 1 to 5 m depth. A82CAI01FCUS: turbulent shallow waters, reef crest, high spur and groove zone (1 to 8 m). B84JAA00FCUS: spur and groove, transitional reefs. J88WHE00FCUS: spur and groove. A77MAR01FCUS: linear patch reefs. A87TOM01FCUS: back reef, reef flat, spur and groove. A79DUN01FCUS: leeward patch reefs. A89DAH00FCUS: rear zone (1-2 m), breaker zone (1.3-3.5 m) and fore reef (5 m).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

SEDENTARY

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.

Animal Foods: zooplankton

Plant Foods: sap or other plant fluids; phytoplankton

Other Foods: detritus ; microbes

Primary Diet: herbivore (Eats sap or other plant foods); planktivore

"Elkhorn coral, like many corals, receive most of their energy and oxygen from symbiotic organisms called zooxanthellae." (NOAA Fisheries OPR)

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.

Ecosystem Impact: creates habitat

Mutualist Species:

• Zooxanthellae

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.

Known Predators:

• a fireworm Hermodice carunculata 
• coralliophilid snails Coralliophilidae 
• damselfishes Pomacentridae 

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: Information is needed on the number of occurrences in the tropical western Atlantic.

1000 - 2500 individuals

Comments: Limited to shallow-water hard-bottom communities including reef rubble communities, reef crests, reef flats, spur and groove reefs and transitional reefs (Goreau and Wells, 1967; Cairns, 1982; Tomascik and Sander, 1987).

"Over the last 10,000 years, elkhorn coral has been one of the three most important Caribbean corals contributing to reef growth and development and providing essential fish habitat." (NOAA Fisheries OPR)

A84PET01FCUS, A82GLA01FCUS, A81ANT02FCUS, A81BAK01FCUS: white band disease, algal tumors due to damselfish, gastropod predators. A84LAS02FCUS, A89GOE01FCUS, A90GHI01FCUS, A90WIL01FCUS: susceptible to bleaching (loss of zooxanthellae) due to adverse environmental conditions. A82ROB00FCUS, A79JAA00FCUS: upper temperature limit cited at 35.8 degrees Celsius. A92COL01FCUS: salinity tolerance range between 18 and 40 ppt. J89JAA00FCUS: environmentally sensitive; requires clear, well-circulated water.

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.

Perception Channels: visual ; tactile

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.

Development - Life Cycle: metamorphosis ; colonial growth

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.

"Like counting rings in the trunk of a tree, the age of corals can be determined by examining coral growth rings." (NOAA Fisheries OPR)

"The coral larvae (planula) live in the plankton for several days until finding a suitable area to settle, but very few larvae survive to settle and metamorphose into new colonies. The preponderance of asexual reproduction in this species raises the possibility that genetic diversity may be very low in the remnant populations." (NOAA Fisheries OPR)

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.

Breeding interval: Elkhorn coral spawn once a year.

Breeding season: August to September

Key Reproductive Features: iteroparous ; seasonal breeding ; simultaneous hermaphrodite; sexual ; asexual ; fertilization (External ); broadcast (group) spawning; oviparous

Elkhorn coral exhibit no parental care.

Parental Investment: no parental involvement

Szmant (1986): sexual mode is hermaphroditic protogynous. Gametogenesis for females takes place between September to May, while for males is from May to July. Spawning season is in August with external development. Highsmith (1982): juveniles uncommon, principal mode of localized recruitment is via fragmentation.

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.

US Federal List: threatened

CITES: appendix iii

State of Michigan List: no special status

IUCN Red List of Threatened Species: critically endangered

United States

Rounded National Status Rank: NNR - Unranked

Rounded Global Status Rank: G3 - Vulnerable

Reasons: Widepsread distribution in the tropical western Atlantic but is restricted to shallower hard-bottom communities. Considered highly threatened and ecologically fragile due to high sensitivity to temperature, salinity, disease, mechanical damage, sedimentation, and eutrophication.

Global Short Term Trend: Decline of 50-70%

Comments: Populations in southern Florida and the Lesser Antilles have declined dramatically since the turn of the century due to land use practices, disease, and catastrophic storm events.

"The dominant mode of reproduction for elkhorn coral is asexual fragmentation; this life history trait allows rapid population recovery from physical disturbances such as storms. However, this mode of reproduction makes recovery from disease or bleaching episodes (in which entire colonies or even entire stands are killed) very difficult. The large role of asexual reproduction for this species increases the likelihood that genetic diversity in the remnant populations may be very low. Scientists are becoming increasingly concerned for this species based on its demographic paramaters; specifically, how species recruitment and genetic diversity affect recovery potential." (NOAA Fisheries OPR)

Degree of Threat: A : Very threatened throughout its range communities directly exploited or their composition and structure irreversibly threatened by man-made forces, including exotic species

Comments: Conidered extremely susceptible to sedimentation, bleaching, disease, eutrophication, anchor damage and boat groundings (Jaap, 1979; Bak, 1981; Gladfelter, 1982; Peters, 1984). Tilmant (1987): extensive damage in Biscyane National Park, Florida from boat groundings. Rogers (1988): diver-related damage in USVI. Dustan and Halas (1987): extensive anchor damage in Florida.

"NMFS finalized the ESA listing of elkhorn and staghorn coral on May 4, 2006 (71 FR 26852). NMFS designated critical habitat for elkhorn and staghorn corals in November 2008." (NOAA Fisheries OPR)

"Florida Keys National Marine Sanctuary (FKNMS), the largest coral reef management entity in the region, has developed a management plan for the Sanctuary's corals that includes protective activities, such as zoning, channel markings, and restoration efforts.

Restoration activities have included efforts to re-attach Acropora fragments generated by ship groundings and hurricane events; these efforts have had mixed success. Similar efforts to re-attach coral fragments have also been made in Puerto Rico and the U.S. Virgin Islands.

Other restoration efforts have included attempts to culture and settle coral larvae with very limited success. New techniques for restoring Acropora are currently being pursued. Such new techniques involve enhancing sexual recruitment, reestablishing ecological roles within reef systems (e.g. herbivorous urchins), and other methods for controlling predators and disease.

In 1998, the United States Coral Reef Task Force was established by Presidential Executive Order 13089 to coordinate and strengthen efforts for protecting coral reef ecosystems. The Task Force is co-chaired by the Departments of Commerce and Interior, and includes leaders of 12 federal agencies, seven U.S. states and territories, and three freely associated states. In 2002, the Task Force adopted a resolution calling for the development of Local Action Strategies, which are locally-driven plans for collaborative and cooperative action among federal, state, territory, and non-governmental partners to reduce key threats on valuable coral reef resources. Three Local Action Strategies have been developed within the range of elkhorn coral for Florida, Puerto Rico, and the U.S. Virgin Islands. These strategies are underway and will be implemented over a three-year period (FY2005-2007)."

(NOAA Fisheries OPR)

Biological Research Needs: Data needed on trend of extant populations throughout tropical western Atlantic.

Global Protection: Few to several (1-12) occurrences appropriately protected and managed

Comments: Numerous protected occurrences in the Florida Keys National Marine Sanctuary, Biscayne National Park and Dry Tortugas, Florida.

Needs: Mooring buoys should be installed near extant populations. All extant populations should be included in marine protected areas.

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.

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.

Positive Impacts: pet trade ; ecotourism ; research and education

Stewardship Overview: Populations on nearshore reef communities need to be monitored for viability as related to water quality.