White band disease
White band disease is characterized by complete coral tissue degradation of Caribbean acroporid corals. Two species are affected, Acropora palmata and A. cervicornis (Gladfelter, 1982). The disease exhibits a sharp demarcation between apparently healthy coral tissue and exposed coral skeleton. These signs are identical to White plague, except that white band is acroporid specific, whereas white plague has not been found on acroporids. Tissue loss usually proceeds from the base of the colony branch to the tip, although it can begin in the middle of a branch in A. cervicornis.
There are two distinct disease types that differ in the pattern of tissue loss. White band Type I exhibits tissue degradation associated with a line that migrates across the coral colony. There is no obvious microbial band, although the freshly exposed coral skeleton appears band like. Tissue lysis is always associated with the moving front (which differentiates Type I from Type II). The rate of tissue loss varies from mm to cm/day (Peters et al., 1983). White band Type II also exhibits tissue degradation as a band moves across a coral colony, however in this case the moving front may, at times, have a bleached zone that catches up to active tissue lysis (Ritchie and Smith, 1998) . The only way to distinguish the two types is to observe the band progression over time.
No known pathogen has been isolated (it has only been attempted for type II), although there is a documented shift in the composition of the population of bacteria present in the surface mucopolysaccharide layer. The shift is from domination by pseudomonads to domination by Vibrio carchariae (Ritchie and Smith, 1995). Histopathological examination of white band Type I diseased tissue may reveal aggregates of gram negative bacteria in affected tissue (Peters et al., 1983) .
White band disease affects acroporids throughout the Caribbean and has decimated populations at a regional scale (Gladfelter, 1982; Peters et al. 1983; Aronson and Precht, 1997, 2001).
Other coral diseases are:
- Aspergillosis, caused by the fungus Aspergillus sydowii, affects Gorgonian soft corals commonly known as sea fans.
- Black band disease, caused by a microbial consortium dominated by the cyanobacteria Phormidium corallyticum.
- Black necrosing syndrome Affects gorgonian from the Great Barrier Reef, possibly a fungal pathogen similar to aspergillosis.
- Brown band disease Reported only from the Great Barrier Reef, etiology at current unknown although the dense brown band preceding the disease lesion contains the presence of ciliates (although not to be mistaken with Helicostoma nonatum - see Willis et al. 2004).
- Dark spots disease Etiology currently unknown, possibly an environmental stressor rather than a true pathogenic disease.
- Rapid Wasting Syndrome, possibly caused by a fungus growing on areas damaged by feeding action of the parrotfish Sparisoma viride.
- Skeletal Eroding Band, associated with the ciliate Halofolliculina corallasia.
- White plague, caused by the bacterium Aurantimonas coralicida.
- White pox disease, caused by the bacterium Serratia marcescens.
- Yellow-band disease AKA Yellow blotch disease, thought to be caused by Vibrio spp.
- NOAA website on coral (public domain)
- from the same website, an article on bacterial bleaching (similar to White band disease)
- World Conservation Monitoring Centre Global Coral Disease Database