disease

disease

´╗┐White Band Disease
By Mitchell Jones
White band disease was discovered when biologists observed the peeling of tissue from colonies of Elkhorn and staghorn corals in waters of the U.S. Virgin Islands. This tissue loss resulted in a distinct line of bare white skeleton, after which this disease is named. Although scientists are unsure about the cause of this disease, it is suspected that algal overgrowth of the coral maybe the primary cause. White band disease progresses from the base of the colony up towards the tips of the branches. Bare, white coral skeleton is left behind, colonized by filamentous algae.
White band disease has had a devastating impact on the corals in the Caribbean, with the infection of approximately half of the shallow water Elkhorn corals within the first five years after this disease was first observed. White band disease also devastated reefs in the Florida Keys, killing 95% of all Acropora corals. Even today, the presence of this disease is still evident on many reefs throughout the Caribbean.
There are two variants of white band disease, type I and type II. In Type I of white band disease, the tissue remaining on the coral branch shows no sign of coral bleaching, although the affected colony may appear lighter in colour overall. However, a variant of white band disease, known simply as white band disease Type II, which was found on Staghorn colonies near the Bahamas, does produce a margin of bleached tissue before it is lost. Type II of white band disease can be mistaken for coral bleaching. By examining the remaining living coral tissue for bleaching, one can delineate which type of the disease affects a given coral.
No known pathogen has been isolated for white band disease, although there is a shift of bacterial composition in the surface layer where the band eats away as the coral tissue. The bacteria shifts from a dominant pseudomonad population to an increasingly dominant Vibrio carchariae population. Histopathological...

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