Elkhorn coral
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| Acropora palmata |
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. Despite its name, the coral structure more closely resembles that of moose antlers, as opposed to elk horns. These branches create habitats for many other reef species such as lobsters, parrot-fish, snappers, and other reef fish. Elkhorn coral colonies are incredibly fast growing with an average growth rate of 5-10 cm per year and can eventually grow up to 12 feet in diameter. The color of this coral species ranges from brown to a yellowish-brown. This color 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 colony of the coral breaks off and attaches to the substrate forming a new colony. It was believed that this resulted in low genetic variance amongst the remaining populations of elkhorn coral, however, recent research shows that the amount of sexual reproduction has been increasing and has resulted in more genetic diversity. Sexual reproduction occurs once a year in August or September when coral colonies release millions of gametes by broadcast spawning.
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[edit] Distribution
Elkhorn coral exist in the Caribbean, the Bahamas, and Florida Keys. Its range reaches as far north as Biscayne National Park, Florida and as far south as Venezuela. However, as a result of climate changes, the range of elkhorn coral has expanded northward along the Florida Peninsula and into the northern parts of the Gulf of Mexico.
Elkhorn coral are found primarily in shallow waters with moderate temperatures (between 26-28 C) with significant water movement. They are one of the most abundant species in waters ranging from 1-5 m deep, but small amounts can be found in waters as deep as 20 m.
[edit] Threats
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 affect 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 marcenscens. 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 centimeters per day but can cause as much tissue loss as 10.5 square centimeters 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 for coral mortatlility, however, they are not well studied or understood.
Elkhorn coral are also victim to predation from polychaetes and fish, 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.
[edit] Conservation
There have been several efforts to conserve 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.
Attempts are also being made to conserve the coral by culturing coral fragments. The Florida Keys National Marine Sanctuary, the National Oceanographic and Atmospheric Administration, and Mote Marine Laboratory all are having limited success with coral nurseries in the Florida Keys and Puerto Rico.
The National Oceangraphic and Atmospheric Administration(NOAA) has developed and tested several ecological methods to restore this coral. These methods include removing coral predators and reintroducing herbivores to the ecosystems to feed on harmful algae that grows on the coral.
In 2004, the Center for Biological Diversity requested National Marine Fisheries Service (NMFS) to place 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.
[edit] External links
[edit] References
Grober-Dunsmore, Rikki; Victor Bonito, Thomas K. Frazer (Sept. 8, 2006). "Potential inhibitors to recovery of Acropora palmata in populations in St. John, US Virgin Islands". Marine Ecology Progress Series 321: 123–132. Inter-Research.
Mayor, Philippe A.; Caroline S. Rogers, Zandy M. Hillis-Starr (Mar. 7, 2006). "Distribution and abundance of elkhorn coral, Acropora palmata, and prevalence of white-band disease at Buck Island Reef National Monument, St. Croix, US Virgin Islands". Coral Reefs 25 (2): 239–242.
Patterson, Kathryn; James W. Porter, Kim B. Ritche, Shawn W. Polson, Erich Mueller, Esther C. Peters, Deborah L. Santavy, Garriet W. Smith (June, 19 2002). "The etiology of white pox, a lethal disease of the Caribbean elkhorn coral, Acropora palmata". PNAS 99 (13): 8725–8730.
Precht, William F.; Richard B. Aronson (Aug. 2004). "Climate flickers and range shifts of reef corals". Frontiers in Ecology and the Environment 6 (2): 307–314. The Ecological Society of America.
Willams, Jr., Ernest H.; Paul J. Baterls, Lucy Bunkley-Williams (Dec, 1999). "Predicted disappearance of coral-reef ramparts: a direct result of major ecological disturbances". Global Change Biology 5 (8): 839–845. Blackwell Science Ltd..
