Acropora corals, commonly called staghorn or elkhorn corals, are one of the world’s most abundant and recognizable corals. There are over 150 species of Acropora in the world’s oceans. If you’re just starting to learn about coral identification, check out our post about coral biology to understand important terms for identification.
First, look at some of the characteristics that define the genus Acropora. Once you can identify the genus, you can start looking for different species. This should be easy in the Caribbean, as there are just three species of Acropora: Acropora cervicornis (staghorn coral); Acropora palmata (elkhorn coral); and Acropora prolifera (fused staghorn coral).
One key feature that distinguishes Acropora from other corals is the prominent axial corallite, located right on the tip of each branch. Only Acropora corals have an axial corallite, which part of the coral skeleton and home to the polyp. In the images below, you can see the Acropora branch tips have prominent axial corallites. Acropora can be plating, branching, encrusting, or form thick blades. Each of these aforementioned growth forms and species have the prominent axial corallite in common.
Acropora cervicornis grows into cylindrical branches with a large corallite at the tip of each branch. It’s commonly called staghorn coral because the pointed branches rise from the reef like antlers.
Staghorn coral is, hands-down, the most ecologically valuable species in the Caribbean. As the colony grows, the branches create a three-dimensional lattice where juvenile fish can hide from larger predators.
This is the only species of Caribbean coral that creates such a complex habitat, but it is not invincible. Heavy anchors, storms, and a stray fin kick can all damage stands of staghorn coral. And since Acropora grows in the shallowest parts of the reef, it is also susceptible to coral bleaching and other diseases.
This coral can be rare or locally abundant depending on where you dive. In areas where staghorn corals have died off, coral restoration can help rejuvenate degraded habitats.
Acropora palmata is the king of all Caribbean corals. Elkhorn coral grows into thick, robust branches and is the most important reef-building species in the Caribbean. You will notice that each large blade ends with several axial corallites, which helps identify it as an Acropora coral.
Like its thinner cousin staghorn coral, elkhorn colonies provide complex habitat for juvenile fish. Palmata also creates habitat for larger fish, since the spaces between each branch can be much wider than staghorn coral. Colonies growing close to shore can also help buffer the coastline from storms and waves.
Acropora palmata was once a dominant species in the Caribbean but unfortunately, it has fallen between 90 and 95 percent in abundance since 1980. This coral is now listed as critically endangered.
Fused staghorn coral
Acropora prolifera is the most difficult Acropora species to identify in the Caribbean. It’s a hybrid of cervicornis and palmate, so it’s difficult to predict just how this coral will present itself.
Since this coral is a hybrid, it can display characteristics of both species. Each colony is unique, however, regarding whether A. cervicornis or A. palmata is dominant. We’ll admit to having a hard time distinguishing this species, however, a few colonies were present in Tela, Honduras.
The common name for this coral is fused staghorn coral. It is possible to find colonies with long, staghorn-like branches that fan out in an elkhorn shape, but it’s also possible to see colonies with elkhorn-like blades that feature staghorn branches fused together.