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Reproduction :: Diseases

Background » Coral Diseases

The diseases that affect coral are a major cause of large-scale coral mortality. The frequency of coral diseases has increased over the past 10 years. The various threats to the coral colonies make it difficult for the corals to resist the attack of new diseases. These diseases are wiping put coral colonies rapidly. If we do not care for the coral life, some day they may disappear from the world.

Black-band Disease

The Black-band disease is called so because it forms a black band over the coral colony. The disease is caused by a bacterium. When the disease attacks the coral, it destroys the coral, leaving behind a bare skeleton. Although the disease causes black bands most of the time, sometimes it can form bands that are dark maroon or brownish in color. This disease usually does not wipe out the entire coral colony; however, the spread and prevalence of the disease can be aggravated by sedimentation and other pollutants present in the ocean water.

Photo © NOAA

Coral Bleaching

Corals, when healthy, usually are yellow to brown in color. This color is given by the algae zooxanthellae that is found in the coral. When the coral is severely stressed, the zooxanthellae leave the coral. Without the algae, the coral loses its color and slowly turns white. If this continues for a long time, then it causes partial or total coral colony death. Coral bleaching is a major problem affecting many coral reefs in the world.

Photo © NOAA

Dark-Spots Disease

As its name suggests, this disease is characterized by dark spots. The spots can be dark purple, brown or dark gray in color. They start off as small spots on the coral and slowly expand outward, gradually affecting the entire coral. When the entire coral is affected by this disease, it can wipe out entire coral colonies rapidly. Dark-spots disease was first noticed in Colombia , but this condition appears to be more widespread in the Florida Keys and throughout the wider Caribbean recently.

Photo © NOAA

Red-band Disease

Red-band disease resembles black-band diseases except the color of the band is reddish to maroon in color. This disease is also caused by bacteria. There are two types of red-band disease, red-band disease 1 and red-band disease 2. The difference is in the way the disease spreads. In red-band disease 1, the bacterial filaments are loosely organized. In red-band disease 2, the bacteria spread like a net over the colony's surface. Red-band bacteria affect massive and stony corals.

Photo © NOAA

White-band Disease

White-band disease is believed to only affect staghorn and elkhorn corals. When a coral is affected by this disease, the tissues surrounding the coral skeleton peel off in a uniform band. The peeling starts at the base of the colony and gradually works it way to the branches. This disease is the main reason for the rapid decline in staghorn and elkhorn corals. This is considered the worst disease that affects corals. The affected coral has a white band which is sometimes mistaken for coral bleaching.

Photo © NOAA

White Plague	Photo © NOAA
White plague is similar to white-band disease except it affects different species of coral. The affected coral has a white band and the skeleton is exposed. The disease starts at the base and spreads upward and outward.

White Pox Disease	Photo © NOAA
White pox disease also affects elkhorn coral. This type of disease is a major problem in the Florida Keys and the Caribbean . The disease is characterized by white circular lesions on the surface of infected coral colonies. Once affected, the rate of tissue damage is rapid. No one knows what causes the disease, but some scientists think that is caused by a bacterium.

Yellow Blotch Disease	Photo © NOAA
This disease affects the brain and star corals. This disease begins as small blotches of pale yellow. In advanced stages of the disease, the tissue first affected dies and the skeleton gets exposed. The disease slowly kills the coral.