Introduction
Most coral diseases and syndromes happen as a result of stress. The stresses that affect coral reefs can include changes in water temperature, differences in the amount of ultraviolet radiation they are exposed to and the amount of sedimentation and pollutants that settle in and around the reefs. These issues have increased dramatically in the past decade, causing many scientists to be concerned as they attempt to determine the set of causes that are killing off the world’s coral reefs (Peters, 1997). Two of the more common types of coral disease are black band disease and coral bleaching.
Main body
Black band disease is noticeable on corals as it forms a black circular or crescent shaped band on the coral itself, killing the tissue underneath it. According to Richardson (et al, 1997), the disease is caused by a cyanobacteria working on concert with nematodes, ciliate protozoans, flatwords and fungal filaments. However, it is the cyanobacteria that gives the illness its black band characteristic. The disease is relatively common. After having been discovered in 1972 in Florida and Belize, it has since been found in Fiji, Australia, the Philippines and 23 other countries throughout the world (Green & Bruckner, 2000). As the disease progresses, coral tissue not touched by the black band appears healthy and normal, but tissue passed over by the black band, which moves as much as two centimeters in a given day, is left dead and skeletal, leaving room for other organisms to move in and begin infecting the rest of the coral tissue (McCarty & Peters, 2000). This form of coral disease typically attacks massive reef-building corals, but has also been observed attacking stony corals, sea fans and acroporid corals. Two corals that seem to be relatively immune to the disease include Caribbean staghorn and elkhorn corals (NMFS, 2001). Black band disease is usually more active when temperatures rise toward the end of the summer and when corals are stressed by pollution and sedimentation (Richardson, 1998).
Coral bleaching is another coral illness that is typically caused by rising temperatures and coral stresses and typically occurs in stony corals. In this process, a stressed coral begins to loose its coloration, usually a yellow or brownish color, allowing the white skeleton of the coral to show through. This is, again, a disease that has seen dramatic increase in recent years as it has become prevalent in a number of different coral species (Glynn, 1996). Like Black Band Disease, coral bleaching does not usually affect the entire coral, but manifests itself in patches and rings throughout the community. It is believed to be caused by increased exposure to higher light levels, greater amounts of exposure to ultraviolet radiation, changes in temperature and salinity or high turbidity (Glynn, 1996). Bleaching affects the coral adversely by reducing the rate of skeletal growth, decreasing reproductive rates, reducing the coral’s ability to shed sediment and weakening its ability to resist invasion of competing species or other diseases (Glynn, 1996). If bleaching continues for a prolonged period of time, it, too, can cause total colony death.
Conclusion
These are only two of the many diseases that can affect the world’s coral systems, which in turn has the potential to significantly affect the world’s food supply and the health of our oceans. While exact causes and progression is not always known, it is clear in both of these illnesses that global climate change is significantly affecting our coral reefs and attention is required if they are to survive. Further research is necessary to more fully understand these issues in order to develop an appropriate means of responding.
Works Cited
Glynn, P.W. “Coral reef bleaching: Facts, hypotheses and implications.” Global Change Biology. Vol. 2, (1996):495-509.
Green, E. and A. W. Bruckner. “The significance of coral disease epizootiology for coral reef conservation.” Biological Conservation. Vol. 96, (2000):347-361.
McCarty, H. and E. Peters. “The Coral Disease Page.” (2000). Web.
National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration. “Diseases of Reef-building Corals.” (2001). 2008. Web.
Peters, E.C. “Diseases of coral reef organisms.” Life and Death of Coral Reefs. Birkeland, C. (ed.). New York: Chapman & Hall, 1997.
Richardson, L.L., K.G. Kuta, S. Schnell, and R.G. Carlton. “Ecology of the black band disease microbial consortium.” Proc. 8th Intl. Coral Reef Symp. 1, (1997): 597-600.
Richardson, L.L. “Coral diseases: What is really known?” Trends in Ecology and Evolution. Vol. 13, (1998): 438-443.