Reef Coral Disease

Concern has been expressed about the diminishing coral reefs and steps are being taken to try and alleviate the problem. While it has been suggested that much damage is caused by shipping, which is no doubt true to a certain extent, and scuba divers - again another contributing factor - there are diseases and environmental causes that as yet are still not fully understood.

Below is a list of just some of the diseases that have been noted and researched, with answers in some areas still pending.

• Black-band Disease - In identifying Black Band Disease - or BBD - biologists revealed the major constituent of the black mat - that appears as a slim band of dark material which gradually moves over the coral, as a group of micro-organisms which photosynthesise. As the band of organisms slowly glides over the coral it kills the coral tissue by cutting off the oxygen and producing hydrogen sulphide. Compounds are released by the coral cells as they die and this feeds the micro-organisms. Gradually all the coral tissue is killed leaving behind just the white skeleton. While healthy coral can contract the disease from the affected coral, it happens much more readily if the coral is under stress. Stress occurs when there is high sedimentation, if the temperatures are warmer than normal, lack of nutrients or toxic chemicals. Further stress can be caused by being "handled" by a large number of divers, making them susceptible to infection through the damage that is caused to the membrane. Rates of infection appear to drop in the colder months only to speed up again when it becomes warmer and the numbers of visitors increase.

• Bleaching - Bleaching in coral has been associated with exposure to increased ultraviolet radiation from the sun, high levels of light, abnormal swings in temperature or salinity, high murk and sedimentation causing reduced light levels, and other possible catalysts. It would seem to be a stress response of the coral and some species are more susceptible to bleaching than others under the same conditions. More recently however, it has been discovered that bacteria can also cause bleaching and that a change in the type of bacteria inhabiting the surface mucous membrane may occur when bleaching happens. It has not been shown that a bacterium is the cause of bleaching at this juncture. Some indications are that a micro-parasite may be one cause by infecting algae that lives symbiotically in the coral cells.

• White-band Disease – Specifically Staghorn coral (Acropora cervicornis) and Elkhorn coral (Acropora palmata) are affected by this disease. Telltale signs of White-band disease are identical to the White Plague, except that White Plague has not been found on acroporids and White-band Disease is acroporids specific. The disease is characterized by complete coral tissue degradation.

• Red-band Disease

• Yellow-band Disease

• Dark Spots Disease

• Rapid Wasting

• White Plague - Aurantimonas coralicida causes White Plague. It progressively destroys coral tissue and leaves the area appearing bleached. Aurantimonadaceae is a small marine bacterial family, which created havoc in especially the Caribbean.

• White Pox

• Tumours and Skeletal Anomalies

Much more research is needed before we are fully cognizant of all the causes for the death of the coral reefs but one area in which we can help is by making sure we follow the recommended diving etiquette and maintaining a "look but don't touch" policy. More underwater national parks need to be created with monitoring of the level of visitation that occurs in any one area. If we can spread the load so that all the reefs have a limited load placed upon them it will go a long way towards helping - by preventing damage to the coral tissue and leaving the coral susceptible to infection.