Elkhorn coral, or Acropora palmate, is a species of coral thought to be native to the Caribbean Sea. The coral is so named because it looks like the antlers found on many species of elk. Elkhorn coral are considered key to the structural integrity and ecology of the coral reefs surrounding many landmasses within the Caribbean. Their numbers decreased rapidly beginning in the 1970s due to both environmental and man-made factors.
Many reef fish found in the Caribbean Sea and the Gulf of Mexico use the elkhorn coral as a habitat. The coral grows at a rapid rate, and many reach a diameter of over 12 feet (3.5 meters). They appear yellow to brown because of the zooxanthellae algae that live on them. These algae have a symbiotic relationship with the elkhorn coral. The coral is incapable of photosynthesis and depends on the algae to gather the nutrients it needs to survive, and the algae have a place to live.
Largely an asexual species, elkhorn coral reproduces primarily by fragmentation. Fragmentation occurs when pieces of the larger colonies fall off. These former branches attach themselves to a new base and begin anew.
Sexual reproduction can take place once a year, usually between August and September. The planula larvae, the coral's sexual offspring, are released into the passing current and picked up by plankton. After a few days, the few planula that survive metamorphose and form a new colony once they find a suitable base.
This species remains on the critically endangered list due to a rapid decline in numbers since the 1970s. In 2011, the amount of elkhorn coral found in the Caribbean Sea has dropped by approximately 90% since then. Environmental factors such as hurricanes and storms have been known to cause large scale population losses, but these can be easily overcome, as the elkhorn's primary mode of asexual reproduction allows new colonies to take the place of those eradicated by physical damage.
Other factors pose a more serious threat to the coral's survival. A continuous increase in temperature has led the elkhorn coral to retreat from its normal domain, while coral bleaching and diseases have led to the annihilation of entire ranges of coral for miles along the coastlines. These make its capacity for asexual reproduction ineffective and pose additional hardships for its sexual mode of reproduction.