What is Elkhorn Coral?

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.

Elkhorn coral is a prominent reef-building species of coral, named for its resemblance to elk antlers. It thrives in shallow waters where sunlight can support its symbiotic algae, zooxanthellae, which provide the coral with energy through photosynthesis. This branching coral is crucial for marine biodiversity, offering habitat and protection for various marine organisms.

Elkhorn coral is predominantly found in the Caribbean Sea, the Bahamas, and the Florida Keys. It favors shallow, warm waters typically ranging from 1 to 5 meters in depth. These regions provide the optimal conditions of light and temperature that elkhorn coral requires for growth and survival.

Elkhorn coral plays a vital role in coastal ecosystems by creating complex structures that serve as habitats for a multitude of marine species. Its large branches help dissipate wave energy, protecting shorelines from erosion. Additionally, it contributes to the growth and stability of coral reefs, which are among the most diverse ecosystems on the planet.

Elkhorn coral is under threat from several fronts, including climate change, ocean acidification, pollution, overfishing, and disease. Rising sea temperatures can lead to coral bleaching, where the coral expels its symbiotic algae and becomes more susceptible to disease and death. Human activities have also significantly impacted its populations, leading to its listing as a critically endangered species.

Elkhorn coral reproduces both sexually and asexually. In sexual reproduction, corals release sperm and eggs into the water, resulting in larvae that settle and form new colonies. Asexually, elkhorn coral can propagate through fragmentation, where broken pieces of the coral, due to storms or human activity, reattach to the substrate and grow into new colonies.

Conservation efforts for elkhorn coral include protective legislation, such as its inclusion under the Endangered Species Act, and the establishment of marine protected areas. Scientists are also engaged in active restoration projects, such as coral gardening, where fragments of elkhorn coral are grown in nurseries and then transplanted back into the wild to help restore damaged reefs.