Elkhorn coral

Acropora palmata

ORDER Scleractinia

FAMILY

Acroporidae

TAXONOMY

Madrepora palmata Lamarck, 1816, "American Ocean."

OTHER COMMON NAMES Spanish: Cuerno de alce.

PHYSICAL CHARACTERISTICS

Colonial; tree-like colonies up to 13 ft (4 m) across and 6.5 ft (2 m) tall, with thick branches broadly flattened near tips to resemble moose or elk antlers; tubular coral cups protrude from branch surface. Tissue tan or pale-brown, with tips of branches white.

DISTRIBUTION

Caribbean; Florida Keys, Bahamas, West Indies to Brazil. HABITAT

Subtidal zones to 65 ft (20 m); densely aggregated thickets common on windward reef slopes exposed to heavy wave action.

BEHAVIOR Nothing is known.

FEEDING ECOLOGY AND DIET

Feed on minute zooplankton and derive nutrition from zooxanthellae harbored within cells lining the digestive cavity.

REPRODUCTIVE BIOLOGY

Hermaphroditic polyps broadcast spawn once a year in August or September. Sperm and eggs are packaged together in bundles that float to the sea surface, where they break open and fertilization occurs. Planula larva are ready to settle 4-5 days after fertilization. Asexual reproduction occurs by fragmentation of colony branches. Damage to colonies caused by hurricanes is in part responsible for the large stands of A. palmata as broken branches reattach and produce new colonies.

CONSERVATION STATUS

All scleractinian corals are listed in CITES Appendix II. Population declines across the Caribbean led to a designation as Candidate Species for listing as Threatened or Endangered under the U.S. Endangered Species Act in 1999. Population declines have been attributed to disease outbreaks (white band disease), compounded locally by hurricanes, increased predation, bleaching, and other factors. Poor water quality because of land-derived pollutants, sewage, and sediment may stress elkhorn coral and increase its susceptibility to disease.

SIGNIFICANCE TO HUMANS

Major structural component of Caribbean coral reefs. Provides essential habitat for fishes and other reef invertebrates. Cuts and scratches resulting from contact with elkhorn coral are reportedly slow to heal. ♦

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