Black Band Disease
By Mitchell Jones
Tolerating a very narrow range of environmental conditions including temperature, salinity, and solar radiation, reefs are very sensitive to damage from environmental changes. Corals, in particular, are susceptible to a number of diseases including black band disease, white band disease, and coral bleaching.
Black band disease was first described in the early 1970s as a black band moving on the surface of star corals and brain corals. It destroys live tissue as it moves over the surface of the colonies, leaving behind bare white skeleton. This disease may kill entire colonies within a matter of a few months, however tissue loss from a colony can be only partial with recovery after the black band disappears. This black band consists primarily of the filamentous cyanobacterium Phormidium corallyticum along with other microorganisms. Research has shown that the death of coral tissue is caused by lack of oxygen as well as exposure to hydrogen sulfide in the tissue adjacent to this black bacterial band
The black band microbial consortium consists of an assortment of photosynthetic and non-photosynthetic bacteria that co-exist synergistically. The consortium has three functionally and physically dominant members as well as numerous heterotrophic members whose role in the disease is as yet unknown. The three functionally dominant members are populations of cyanobacteria and sulfide-oxidizing and sulfate-reducing bacteria. The black band disease microbial consortium is structurally and functionally identical to cyanobacterial-dominated microbial mats found in other illuminated, sulfide-rich environments.
Black band disease occurs when corals are stressed by environmental factors including sedimentation, nutrient levels, pollution, and high water temperatures but a main cause is cyanobacteria.
Several species of cyanobacteria have been found associated with black band disease, the most well-known of which is Phormidium corallyticum. Sulfide-oxidizing bacteria, dominated by Beggiatoa, are present in well-developed bands and exhibit visible vertical migrations within the band matrix. When present on the band surface Beggiatoa appears white due to intracellular