What does a diseased coral look like, and how can you identify one on a scuba dive? Most coral diseases can be diagnosed visually.
1. BLACK BAND DISEASE (BBD)
Appearance: Black band disease is characterized by a black/dark-red ring or band noticeably separating healthy coral tissue from newly exposed coral skeleton. The bands are approximately 1-30 mm thick and may reach up to 2 m long. White specks or patches may be present on the surface of the black band.
Cause: Black band disease is caused by a variety of bacteria. The culprits include certain types photosynthetic cyanobacteria (blue-green algae) as well as non-photosynthetic bacteria. Sulfur bacteria are responsible for the white along the band.
Speed of Infection: Black band disease migrates across a coral colony at a rate of 3 mm to 2 cm per day. Bacteria consume and kill coral tissue while migrating.
Regions/Species Affected: 42 species of coral are known to be affected by black band disease. In the Western Atlantic, massive reef-building corals such as brain coral and star coral are the most commonly affected, although the disease has also been observed in other stony corals and sea fans. In the Caribbean, black band disease can be seen consuming brain coral and other stony corals, while in the Red Sea and the Indo-pacific, the disease affects Acroporid (branching) corals.
2. RED BAND DISEASE (RBD)
Appearance: The two types of Red band disease may be distinguished by their appearance.
Red band disease type 1: The band characteristics resemble those of black band disease; however the band is a red/dark-red in color.
Red band disease type 2: Reddish filaments extend over the surface of the coral in a net-like pattern.Cause: Bacteria are responsible for red band disease. The disease is caused by a photosynthetic cyanobacteria.
Speed of infection: The rate of infection of red band disease is slower than that of black band disease. However, the results are the same. The narrow band of cyanobacteria consumes and kills tissue as it moves slowly across the surface of the coral, leaving only the coral skeleton in its wake.
Regions/Species Affected: Red band disease affects massive corals (such as brain corals and star corals) and plating stony corals. In the Caribbean, the most common types of coral infected by red band disease are sea fans (gorgonians).
3. WHITE BAND DISEASE (WBD)
Appearance: The two known types of white band disease are nearly indistinguishable to the untrained eye. While there is no obvious band of bacteria (as there is on both black band disease and red band disease), either strain of white band disease can be identified by a clearly differentiated boundary between healthy coral and the exposed coral skeleton. This boundary marks the edge of the white band infection, which ranges in width from a few millimeters to a few centimeters. When observed in branching corals (such as staghorn coral) a white band infection will typically begin at the base of a coral branch and advance towards the branch's tip.
Cause: The organism causing white band disease has not yet been identified.
Speed of Infection: White band disease consumes coral at a rate of millimeters to centimeters of tissue per a day.
Regions/Species Affected: Caribbean acroporid (branching coral) populations have been reduced to less than 10% of their previous numbers by white band disease since the 1980s. In the Red Sea and the Indo-pacific, white band disease has been observed in massive corals (such as boulder corals and star corals), plating corals, and branching corals.
4. White Plague Disease
Appearance: The three known types of white plague disease are nearly indistinguishable from white band disease. A stripe of bare coral skeleton separates living coral tissue from dead coral colonized by algae. White plague disease usually starts at the base of a coral colony, and moves upwards and outwards until no living tissue is left.
Cause: White plague disease is caused by bacteria, Aurantimonas coralicida.
Speed of infection: The different strains of white plague disease infect coral colonies at varying rates. Type I is slowest of the strains, killing tissue at a rate of approximately 3 mm/day. Types II and III move across a piece of coral at a much faster rate, and may consume centimeters of live tissue on a single day.
Regions/Species Affected: White plague disease is epidemic in the Caribbean and affects a great variety of coral species. Types II and III infect up to 30 different species of coral, and Type I affects about 10 species. Large, reef building species of coral such as boulder brain coral and star coral complexes are especially hard hit by Type III.
KEEP READING: CORAL DISEASES 5-8
Now you know how to visually identify four common coral diseases. The next page includes information about white pox, dark spot, yellow blotch, and aspergillosis diseases. Keep reading . . .