Black-band Disease - The Offline Version

In the early 1970s, Arnfried Antonius reported instances of a discrete band of soft black material moving over the surface of some species of massive star corals and brain corals on reefs in the western Caribbean. The band apparently "consumed" live coral tissue as it passed over the colony surface, leaving behind bare coral skeleton. The band moved at the rate of a few millimeters per day. Thus, a soccer-ball-sized coral head might lose all of its tissue in a few months. The disease became known as black-band disease (BBD).

Black-band disease on a brain coral, Puerto Rico. Photo by E.C. Peters.
Appearance	This disease is characterized by a black mat, a few millimeters to centimeters (about 1/4 inch to 2 inches) wide, on the surface of coral tissue, moving across the surface of the skeleton, leaving behind bare white skeleton. The remaining coral tissue appears normal in color, morphology, and behavior.
Close-up of microbial mat of BBD on M. cavernosa. Photo by H. McCarty.
Cause	Rutzler and Santavy identified the major component of the black mat as Phormidium corallyticum, a photosynthesizing, gliding, filamentous cyanobacterium. A consortium of microorganisms, including the cyanobacterium Spirulina, sulfur-oxidizing and sulfate-reducing bacteria, heterotrophic bacteria, and other microorganisms, are present in the band and contribute to the loss of coral tissue. Recent experiments indicate that coral tissue is killed by the lack of oxygen deep in the band next to the tissue and by exposure to hydrogen sulfide produced by these microorganisms. The organic compounds released by the dying coral cells apparently provide food for the microorganisms in the consortium (Carlton and Richardson, 1995). Healthy corals can become infected with BBD when in contact with an infected colony, but injured colonies are most susceptible. The incidence and prevalence of BBD increase when corals are stressed by sedimentation, nutrients, toxic chemicals, and warmer than normal temperatures. For example, the advance of BBD-microbial mats on corals slows down or the mats completely disappear during the winter in the Florida Keys, increasing in prevalence and rate of advance again during the summer (Kuta and Richardson,1996).
Distribution	BBD has been reported on reefs around the world, throughout the Caribbean, in the Indo-Pacific, and the Red Sea. Members of the coral family Faviidae are usually affected. In the tropical western Atlantic these species include the brain corals Diploria strigosa, D. labyrinthiformis, Colpophyllia natans, and the star corals Montastraea cavernosa, M. annularis, M. franksi, and M. faveolata. Other corals that can be infected by this microbial mat are Siderastrea siderea, fire corals and gorgonians (sea plumes), and staghorn (acroporid) corals on the Great Barrier Reef.
Impact	BBD is usually encountered only infrequently on reefs (Edmunds, 1991), although there have been recent outbreaks at several sites, notably Looe Key in the Florida Keys National Marine Sanctuary, Jamaica, and off Fiji, resulting in loss of tissue from many coral colonies (Peters, 1993; Littler and Littler, 1996; Bruckner et al., in press). An outbreak such as these is also known as an epizootic. Loss of tissue from a colony can be partial, with the remaining coral tissue continuing to grow after the mat disappears. The bare coral skeleton can be colonized by filamentous algae and other organisms. These organisms erode the skeleton and prevent the settlement of new corals.