Animal Diversity Web

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)

• Biogeographic Regions
• atlantic ocean
  • native

Habi­tat

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)

• Habitat Regions
• tropical
• saltwater or marine

• Aquatic Biomes
• reef
• coastal

• Other Habitat Features
• intertidal or littoral

• 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)

• Other Physical Features
• ectothermic
• radial symmetry

• Sexual Dimorphism
• sexes alike

• Average length

  .75 m

  2.46 ft

De­vel­op­ment

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)

• Development - Life Cycle
• metamorphosis
• colonial growth

Re­pro­duc­tion

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)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• simultaneous hermaphrodite
• sexual
• asexual
• fertilization
  • external
• broadcast (group) spawning
• oviparous

• 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

Lifes­pan/Longevity

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)

Be­hav­ior

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)

• Key Behaviors
• nocturnal
• crepuscular
• sessile
• sedentary
• colonial

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)

• Perception Channels
• visual
• tactile

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)

• Primary Diet
• herbivore
  • eats sap or other plant foods
• planktivore

• Animal Foods
• zooplankton

• Plant Foods
• sap or other plant fluids
• phytoplankton

• Other Foods
• detritus
• microbes

Pre­da­tion

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)

• Known Predators

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

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

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)

• Positive Impacts
• pet trade
• ecotourism
• research and education

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)

• IUCN Red List

  Critically Endangered
  More information

• IUCN Red List

  Critically Endangered
  More information

• US Federal List

  Threatened

• CITES

  Appendix III

• State of Michigan List

  No special status

Con­trib­u­tors

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

Ref­er­ences

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 http://​www.​nmfs.​noaa.​gov/​pr/​pdfs/​species/​acropora_​factsheet.​pdf.

Na­tional Ma­rine Fish­eries Ser­vice, 2008. "Elkhorn Coral (Acro­p­ora palmata)" (On-line). Of­fice of Pro­tected Re­sources, Species In­for­ma­tion. Ac­cessed De­cem­ber 20, 2008 at http://​www.​nmfs.​noaa.​gov/​pr/​species/​invertebrates/​elkhorncoral.​htm.