Caribbean Coral the Endangered Elkhorn Coral found off the coast of Tulum

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Elkhorn coral (Acropora palmata) is considered to be one of the most important reef-building corals in the Caribbean. This species of coral is structurally complex with many large branches, closely resembles that of elk antlers. These branches create habitats for many other reef species such as lobsters, parrot-fish and snappers.

Thankfully, Elkhorn coral colonies are incredibly fast growing with an average growth rate of 5 to 10 centimetres (2.0 to 3.9 in) per year and can eventually grow up to 3.7 metres (12 ft) in diameter. The color of this coral species ranges from brown to a yellowish-brown which is a result of the symbiotic zooxanthellae that live inside the tissue of this coral species. Zooxanthellae is a type of algae which photosynthesizes to provide the coral with nutrients. The zooxanthellae are also capable of removing waste products from the coral.

Historically, the majority of elkhorn coral reproduction has occurred asexually; this occurs when a branch of the coral breaks off and attaches to the substrate forming a new colony (fragmentation). The degree to which local stands reproduce by fragmentation varies across the Caribbean but on average 50% of colonies are the result of fragmentation rather than sexual reproduction. Sexual reproduction occurs once a year in August or September when coral colonies release millions of gametes by broadcast spawning.  I am feeling some Tulum diving coming on in September to see the spawning.

Elkhorn coral exists in the Caribbean, the Bahamas, and Florida Keys.  It is  found primarily in shallow waters with temperatures between 26 to 30 °C (79 to 86 °F), and with significant water movement. This explains why there is more of this coral type in Tulum than Playa.  There is more water movement to the south as there is no protection from the Island of Cozumel south of Playa del Carmen.  Elkhorn Coral is one of the most abundant species in waters ranging from 1 to 5 metres (3.3 to 16 ft) deep, and a few colonies have been reported from waters as deep as 20 metres.

Elkhorn coral was once one of the most abundant species of coral in the Caribbean and the Florida Keys. Since 1980 it has been estimated that 90-95% of elkhorn coral has been lost. Threats to elkhorn coral include disease, coral bleaching, predation, climate change, storm damage, and human activity. All of these factors have created a synergistic effect that greatly diminishes the survival and reproductive success of elkhorn coral. Natural recovery of coral is a slow process and may never occur with this species because there are so many inhibitors to its survival.
Diseases that affect elkhorn coral include white pox disease, white band disease, and black band disease. White pox disease is a disease that only affects elkhorn coral. It is caused by a fecal enterobacterium, Serratia marcescens. The disease is very contagious and commonly moves from one colony to its nearest neighbor. White pox creates white lesions on the coral skeleton and results in an average tissue loss of 2.5 square centimetres (0.39 sq in) per day but can cause as much tissue loss as 10.5 square centimetres (1.63 sq in) per day. White band disease and black band disease have also greatly reduced the abundance of elkhorn coral. Diseases are one of the major causes of coral mortality, however, they are not well studied or understood.

Predators of Elkhorn coral include coral eating snails (Coralliophila abbreviata), polychaetes such as the bearded fireworm and damselfish. Predation by these organisms reduces the corals growth and ability to reproduce. Predation can eventually lead to the death of the coral colony.

There have been several efforts to conserve the Elkhorn coral which have had mixed results. The Florida Keys National Marine Sanctuary has served as a protected region for the area’s coral species. The Florida Keys National Marine Sanctuary has also developed plans for the protection and restoration of elkhorn coral. Restoration efforts have included attempts to re-attach coral fragments that were broken off during hurricanes or by ships. Attempts to re-attach coral fragments have also occurred in Puerto Rico and the Virgin Islands but all have had limited success.
In 2004, the Center for Biological Diversity requested the National Marine Fisheries Service (NMFS) placed elkhorn coral on the endangered species list. In 2005, NMFS decided that elkhorn coral qualified as an endangered species under the Endangered Species Act of 1973. On May 4, 2006 Elkhorn coral and Staghorn coral (A. cervicornis) were officially placed on the Endangered Species List.


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