So the first species I decided to tackle was a coral; gee, what a surprise. For those of you who don’t know, coral and their reefs are what held my interest in the ocean after my dolphin phase ended.
Acropora palmata, or the Elkhorn coral, is a species of branching coral that can be found in the Caribbean. This was one of the corals I had to learn to identify for an independent study and class my last semester of college, and one that I became very familiar with during an experiment I planned and executed. Elkhorn coral are also one of my favorite corals to find while swimming in their waters. Typically it appears brown to brownish-yellow in color and it has wide flattened branches that resemble…drum roll…elk or moose antlers. It looks very similar to one of its’ cousins in the same genius, Acropora cervicornis (Staghorn Coral), but its’ cousin has thin cylindrical branches that look like the rack of a buck.
In shallow, unprotected waters Elkhorn branches will grow to be rounder and stouter, like fat fingers, to help protect the coral against violent waves and storm surge by decreasing their surface area. Colonies found in more moderate depths, where wave action has less of an impact on the structure, have long, wide, and flattened branches like the leaves of palm trees.
Have you ever stuck your hand out the window in a moving vehicle? If not, you should try it next time, but please be careful—impacts from high-speed bugs hurt! When you stick your hand out the window with your fingers splayed out like a turkey, you feel less resistance from the wind because it has space to move around your fingers. When your fingers are close enough that they’re touching, you feel more resistance from the wind because now it has to move around your hand because there’s not enough space between your fingers.
The same happens with Elkhorn coral in high energy water, meaning lots of intense waves, they produce thick round branches to allow enough space for the water to flow through and reducing any potential damage to their structure. Outlining the Elkhorn branches are white terminal corallites, which are hard cups made of calcium carbonate secreted by the coral. A corallite is like the home of an individual polyp, it is a hard structure that houses the polyp and allows the individual a place to hide and retract itself when it’s not gathering food.
The Elkhorn coral was once abundant in the Florida Keys, but are now more scarce and scattered in the area. In the Bahamas and the Caribbean they are considered to be common, since they can be frequently found, but not at every dive site or reef. Divers saw a lot more of these coral before the 1990s, but since then they have suffered high mortality rates due to storms, bleaching, and most commonly by White-band Disease, a disease that I will discuss more later−just know that it is a disease that affects species of coral.
One of the cooler things that I learned about this coral is that you can determine the direction of the surge, or the typical movement of water, by the direction the branches grow. Elkhorn branches grow parallel to the direction the surge takes, much like some trees grow in the direction of the prevailing wind on land.
Elkhorn coral can be found between 1−35 feet of depth, and they prefer areas of constant water movement caused by incoming waves. They can grow rapidly under optimum conditions, growing up to five to six inches a year. Because of their rapid growth for reef builders, the family Acroporidae is commonly used in reef restoration and growth programs. They make for a good starting block for man-made or rehabilitated reefs.
If you see this coral while diving or snorkeling, please do not touch it, and try to keep your equipment from getting caught in it. While not extremely fragile, it can still break under pressure. So please be careful while you swim and enjoy the view from a far; reefs are very important not only to the ocean but to us as well!
Source: Humann P, DeLoach N. 2013. Reef coral identification: Florida, Caribbean, Bahamas. 3rd ed. Jacksonville, Florida: New World Publications.