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# Coral Diseases

## Corals Tutorial

Coral diseases generally occur in response to biological stresses, such  as bacteria, fungi and viruses, and nonbiological stresses, such as  increased sea surface temperatures, ultraviolet radiation and  pollutants. One type of stress may exacerbate the other.

The frequency of coral diseases has increased significantly over  the last 10 years, causing widespread mortality among reef-building  corals. Many scientists believe the increase is related to  deteriorating water quality associated with human-made pollutants and  increased sea surface temperatures. These factors may allow for the  proliferation and colonization of microbes. However, exact causes for  coral diseases remain elusive. The onset of most diseases likely is a  response to multiple factors. 

While the pathologies, or mechanisms by which many diseases act upon  the coral polyp are not well known, the effects that these diseases  have on corals has been well documented. Black-band disease, discolored  spots, red-band disease, and yellow-blotch/band disease appear as  discolored bands, spots or lesions on the surface of the coral. Over  time, these progress across or expand over the coral’s surface  consuming the living tissue and leaving the stark white coral skeleton  in their wake. Other diseases, such as rapid wasting, white-band,  white-plague, white-pox, and stony coral tissue loss disease, often cause large patches of living coral  tissue to slough off, exposing the skeleton beneath. Once exposed, the  coral’s limestone skeleton can be a fertile breeding ground for algae  and encrusting invertebrates. The colonization and overgrowth of the  exposed coral skeleton by foreign organisms often results in the health  of the entire colony taking a downward spiral from which it seldom  recovers.

This large brain coral  is being attacked by black-band disease. This is the only coral disease  that can be successfully treated. Learn more and view a larger image.

Yellow-band disease can  rapidly spread over a coral, destroying the delicate underlying  tissues. On the left is a massive coral in the early stages of attack  by yellow band disease. On the right is the same coral several weeks  later. Note how rapidly the area of destroyed tissue has expanded. Learn more and view a larger image.

### Corals Lessons

              - Welcome
              - What are Corals?
              - Zooxanthellae What's That?
              - How Do Stony Corals Grow?
              - How Do Coral Reefs Form?
              - Where Are Coral Reefs Found?
              - How Do Corals Reproduce?
              - Importance of Coral Reefs
              - Natural Threats to Coral Reefs
              - Anthropogenic Threats to Corals
              - Coral Diseases
              - Protecting Coral Reefs
              - References
              - Roadmap to Resources 
              - Subject Review (PDF)

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