SpinyheadPlay freeElkhorn coral Acropora palmata
Elkhorn coral is a large, branching stony coral whose flattened, antler-like branches give it its name. It was once the dominant reef-building coral in shallow, wave-exposed parts of Caribbean reefs, forming dense thickets that broke up wave energy and protected shorelines. Colonies are usually golden brown because of the symbiotic algae living in their tissue. It grows relatively fast for a coral, but its populations have collapsed since the late 1970s and it is now a high-priority species for protection and restoration.
How to recognize it
- broad, flattened antler-like branches
- branches taper to thick, pale growing tips
- golden-brown to tan colour
- rough, finely toothed surface from small corallites
- grows in shallow, surf-battered zones
- branches point upward and outward from the crest
| Size | Colonies commonly reach a few metres across; branches can be over a metre long and thick as an arm. Large thickets can reach several metres in height and extent. |
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| Range | Caribbean Sea, Florida Keys, the Bahamas, and the Gulf of Mexico (including Flower Garden Banks, rarely). It is generally absent from Bermuda and Brazil. |
| Habitat | Shallow, high-energy reef crests and upper fore reef, typically from near the surface to about 5 m, and occasionally down to roughly 10-20 m. It needs clear, well-lit, wave-swept water. |
| Diet | Like other reef-building corals, it gets much of its energy from photosynthetic symbiotic algae (zooxanthellae) within its tissue. It also captures plankton with stinging tentacles, mainly at night. |
| Conservation | Listed as Critically Endangered on the IUCN Red List and as Threatened under the US Endangered Species Act. Caribbean populations declined by an estimated 90 percent or more since the late 1970s, mainly due to white band disease, along with bleaching from warming seas, hurricane damage, pollution, sedimentation, and predation by snails and fireworms. Active restoration efforts include coral nurseries and outplanting of fragments. |
Life and behavior
Elkhorn coral is a colonial animal made of many tiny polyps. It grows quickly for a coral, often several to ten or more centimetres per year in good conditions. Colonies spread mainly by fragmentation: storm-broken branches can reattach and grow into new colonies, producing large stands of genetically identical clones. It also reproduces sexually by broadcast spawning, releasing eggs and sperm in synchronized events a few nights after the full moon in late summer. Successful sexual recruitment is now very rare in many places, partly because few genetically distinct colonies remain.
Its family: Staghorn and table corals (Acroporidae)
Acroporid corals are fast-growing, mostly branching or plating reef builders with a skeleton made of tiny, porous corallites. They are major framework builders on shallow reefs worldwide, though they are often fragile and sensitive to heat, disease, and storms. The family is especially diverse in the Indo-Pacific, while the Caribbean has only a few species.
Similar species
- Staghorn coral Acropora cervicornis Has thin, cylindrical, antler-like branches rather than broad flattened ones, and typically grows a little deeper in calmer water.
- Fused staghorn coral Acropora prolifera A hybrid of elkhorn and staghorn that is intermediate in form, with branches somewhat flattened and bushier, often with a mix of thin and broad branches.
- Moose antler or other branching fire coral Millepora complanata Fire coral forms smooth, yellowish-brown blades, lacks visible polyps, and stings on contact; elkhorn has a rougher surface with distinct tiny corallites.