Tony Liang Essays (1680 words) - Anthozoa, Coral Reefs, Acroporidae

Tony Liang M. Poffenroth Biology 10 14 April 2016 Elkhorn Coral Acropora Palmata The Acropora palmata(Lamarck, 1816), or elkhorn coral, is a vital reef-building coral located in the Caribbean, Bahamas (Patterson, 2002), Florida Keys, Virgin Island, and Venezuela. A. palmata are typically found in shallow waters between one to five meters deep with water temperatures between 26 and 30 celsius. Scientific classification are Kingdom Animalia, Phylum Cnidaria, Class Anthozoa, Order Scleractinia, Family Acroporidae, Genus Acropora ,and Species Acropora palmata. The NOAA Fisheries has declared this species of coral to be threatened. The structure of the elkhorn coral is large and complex with many branches, that resemble elk antlers. These branches provide habitats for many other species such as lobsters, parrotfish, snapper shrimps and other reef fish in the caribbean. A. palmata colonies expand at an extremely fast pace; the average grow rate is 2- 3.9 inches or 5-10 centimeters per year and can eventually reach up to 3.7 meters or 12 feet in diameters (Gladfelter , 1982). The color shades range between brown to yellow-brown because of the symbiotic zooxanthellae, type of algae which provide corals with nutrients and remove waste products, living inside the tissue of the coral. Majority of elkhorn corals reproduce asexually when branches break off of the colony and attach to the substrate, and as a result forms a new colony called a fragmentation. Sexual reproduction can occur, when individual colonies are both male and female release millions of gametes once a year in August. Coral larvae begin life living in the plankton for a couple of days until larvae can find a suitable colony to settle in. Infectious disease is one of the major contributing factors in the massive decline in A. palmata (Muller, 2012). Such disease are caused by microorganisms such as bacteria, fungi, viruses, or protozoans that enter the coral, survive, and reproduce inside the coral exponentially which deteriorates the physiological health of the coral. Between 1996 and 1998, white-pox disease is responsible for approximately 85% decline of A. palmata throughout the Florida Keys (Holden, 1996). White-pox disease was first reported in 1996 on Eastern Dry Rocks Reef off Key West, Florida, and is linked with the bacteria Serratia marcescens. S. marcescens is a gram-negative motile bacterium that is mostly found within the gut of many vertebrates including humans, but it can also survive as a free-living microbe in soil and in seawater. Although the putative pathogen S. marcescens was not consistently found in corals displaying signs of white-pox disease, colonies that displayed signs of white-pox disease in the Bahamas appeared to be healthy. Such conflicting findings suggest that S. marcescens might not be the only causative agent of white-pox disease or that the bacteria might be the only pathogenic under certain environmental conditions. Field studies conducted in the reefs in the Florida Keys suggest that white-pox disease is contagious since elkhorn coral colonies with white-pox disease are clustered together (Sutherland, 2004). However it has not been scientifically confirmed since field studies did not take into account naturally clustered distribution of elkhorn coral colonies in the studied area. In addition, colony fragmentation within the population is a common form of asexual fragmentation for A. palmata. Because fragmentation is the dominant form of reproduction, elkhorn offsprings are located in close proximation with other colonies of the same genotype. For instance, in the Florida Keys, USA, patch reefs that contain several colonies of elkhorn coral but they all had the same genotype. Hence, without wholly knowing the distribution of coral genotypes, the clustering of white-pox infected coral may be a result of the genotypic susceptibility of clones, and not a result of white-pox being contagious. Environmental factors such as water temperature and irradiance can also exacerbate the likelihood of fostering disease outbreaks (Harvell, 2009). Temperature changes are found to be associated with white syndrome (Kline, 2008) documented in the Great Barrier Reef, Haulover Bay, reefs in St. John, and in the Florida Keys. White-pox is a seasonal disease that tends to increase during months of high ocean surface temperatures. Several studies suggest a positive correlation between the prevalence of infectious disease on A. palmata susceptibility to be more likely from the results of high water temperature(Roth, 2013), rather than from the result