As coral polyps are living creatures, so too are they susceptible to diseases in the ocean's waters. There are several diseases that threaten their health and their survival. Man's misuse of the earth and her lands, oceans and air has resulted in diseases that have appeared in coral reefs across the world.
At this time, coral bleaching appears to be the greatest threat to coral reefs across the world. Coral bleaching is the result of the tiny creatures in the coral, the polyps becoming stressed. The stress could be the result of water temperature changes, over fishing, increased UV radiation and simply the effects of man farming, over fishing, over constructing.
The coral contains microscopic algae called zooxanthellae, which reside in a symbiotic balance within the membranes of the polyps. Stress causes the polyps to reject these tiny algae, which disrupt the oxygen process as well as nutrient levels. For a short period of time, the coral will recover, but when the rejection is for long periods of time, the polyps die and the coral turns white. It is the algae that reside in the membranes of the polyps that give coral its many colors because the polyp itself is colorless.
Black band disease is one that consists of a multitude of bacteria that creates what appears to be a black mat. This black mat slowly travels over the face of the coral and smothers the polyps, while the hydrogen sulfide produced by the bacteria kill or injure the polyps. Black band does not always kill off all the polyps, and some do recover, but the damage to the structure will not allow for new coral to grow. This particular disease appeared back in the 1970s and is sporadic and not found in all reefs across the world.
Three other diseases similar to black band disease with the same devastating effects to coral reefs have been identified and studied. The first disease is the red band disease, which attacks the hard coral, resulting in the same devastation to the coral reefs. The second is a yellow band disease that has appeared on the Great Barrier Reef in Australia. The third is the white band disease found in the Caribbean.
No matter which band disease coral has been infected with, the results are the same, permanent damage to the coral reefs. Coral structures are weakened, the symbiotic relationships threatened, and reproduction hampered. And these bands can easily move from one coral reef to another by the moment of the ocean water. Many countries across the world have found instances of these band diseases in their coral beds.
Other diseases with devastating effects exist as well, often called plagues or poxes because of their appearances and the damage or destruction rendered to the coral reefs. Perhaps these are simply symptoms, critical symptoms of a larger gradual collapse of the world's eco system. If man has created the conditions for such diseases to appear and flourish, what else has he done?