Corals, like other living organisms, are affected by diseases that usually end their existence. Corals are found in environments that have to change its conditions depending on the seasons. These diseases are caused by biotic and abiotic stressors. Biotic stressors are the pathogens and parasites that cause the coral disease in them. Abiotic factors are the changes in the environment like the changes in salinity, temperature, or light.
Diseases Caused by Pathogens
Pathogens are largely responsible for coral diseases such as Black Aggressive Band, Black Band Disease, Bacterial Infection, Black Overgrowing Cyanophyta, Fungal Infection, and Lethal Orange Disease. Identification of these pathogens is impossible due to the uncertainty of trying to determine the type of pathogen attacking the coral. To prove that the fungi or bacteria present may have caused the disease or that the coral may have fed on an already decomposing tissue is the challenging part.
The pathogens move at a relative small pace on the surface of the coral colony while leaving behind in its trail bare skeletal coral which will be colonized by algae at a rapid pace. The exposed skeleton is separated from the living tissue by a narrow band of tissue which is attacked by the pathogens which qualify as a coral disease. Most of these pathogens are identified by scientists as protozoans, fungi, and bacteria.
Bacterial infections like the Black Band Disease are the most contagious and quick-spreading, affecting the entire colony of corals. Fungal infections only affect massive or platy corals. The Caribbean corals are affected by disease due to the limited circulation of water and the growing population surrounding the areas where the corals exist.
Coral Disease: Black Band Disease
Black Band Disease is characterized by the formation of a black band on the surface of the coral. The pathogenic consortium completely degrades the coral tissue. The black band consists of bacteria that have a synergy relationship to each other. These bacteria are both photosynthetic and non-photosynthetic. Phormidium corallyticum is one of the known bacterium to cause Black Band Disease. The population of bacteria is found to have over 500 species of bacteria different from other bacteria in dead coral tissue, healthy coral tissue, and in the water column. Black Band Disease is known to affect 42 species of coral around the globe.
Coral Disease: White Plague
White Plague is a coral disease that is caused by a bacterium Aurantimonas coralicida but it is difficult to prove this since other bacteria are present in causing the disease. The White Plague bacteria is contagious and it was first discovered in the Florida Keys. When the coralicidas bacterium infects a healthy coral tissue, it forms lesions on the part of the colony. Type I was discovered in 1984. Further research has discovered different types of White Plague. Type II was discovered in 1995, and had spread around the Florida Keys affecting 17 species of coral. Type III of the White Plague was discovered in 1999.