Black band disease

Example of Black band disease progression on a colony of Diploria strigosa.

Black band disease is characterized by complete coral tissue degradation due to a pathogenic microbial consortium that appears as a dark red or black migrating microbial mat.^[1] The mat is present between apparently healthy coral tissue and freshly exposed coral skeleton.

Appearance

Black band disease on a brain coral in Caribbean Sea near Bahia de la Chiva on the island of Vieques, Puerto Rico

Black Band disease was first observed on reefs in Belize by A. Antonius, who described the pathogen he found infecting massive corals as Oscillatoria membrancea, a bluegreen alga.^[2] The band color may be blackish brown to red depending on the vertical position of a cyanobacterial population associated with the band. The vertical position is based on a light intensity-dependent photic response of the cyanobacterial filaments, and the color (due to the cyanobacterial pigment phycoerythrin) is dependent on the thickness of the band. The band is approximately 1 mm thick and ranges in width from 1 mm to 7 cm. White specks may be present on surface, at times forming dense white patches. The pathogenic microbial mat consortium moves across coral colonies at rates from 3 mm to 1 cm/day. Tissue death is caused by exposure to an anoxic, sulfide-rich microenvironment associated with the base of the band.

Composition

Buck Island Reef National Monument, 2010

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 four 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^[3][4]

Taxonomy

Several species of cyanobacteria have been found associated with black band disease (Frias-Lopez et al.,2002; Cooney et al., 2002), the most well-known of which is Phormidium corallyticum.^[5] Sulfide-oxidizing bacteria, dominated by Beggiatoa spp. (Ducklow and Mitchell, 1979), are present in well-developed bands and exhibit visible vertical migrations within the band matrix (Richardson, 1996; Viehman and Richardson, 2006). When present on the band surface Beggiatoa appears white due to intracellular inclusions of stored elemental sulfur. Sulfate-reducing bacteria dominated by Desulfovibrio spp. (Ducklow and Mitchell, 1979; Frias-Lopez et al.,2002; Cooney et al., 2002) are present at the base of the band and are responsible for producing high concentrations of sulfide within the band matrix (Carlton and Richardson, 1995). Light microscopic observation of black band reveals motile (gliding) filaments of P. corallyticum that are 4 mm wide, with one round end and one narrow (sharply tapering) end. Also present are gliding Beggiatoa filaments (1–4 mm wide) that are non-pigmented but contain highly refractive intracellular granules of elemental sulfur. Numerous gram-negative bacteria (small rods) are also present but not identifiable using light microscopy. The bacterial population has been characterized using molecular techniques and was found to contain over 500 species of bacteria that are different from bacterial communities found in the water column, healthy coral tissue, or dead coral skeleton (Frias-Lopez et al., 2002; Cooney et al., 2002). The functional role of this diverse population of bacteria is not known.

Black band disease affects 42 species of coral in a worldwide distribution. The only known reservoir is within cyanobacterial biofilms that are present on sediments in depressions of healthy black band disease susceptible corals.^[4]

See also

• Aspergillosis, caused by the fungus Aspergillus sydowii, affects Gorgonian soft corals commonly known as sea fans.
• Black necrosing syndrome AKA Dark spots disease, probably caused by a fungus.
• Brown band disease AKA Red band disease, probably caused by ciliates (possibly Helicostoma nonatum) and cyanobacteria.
• Rapid Wasting, possibly caused by a fungus growing on areas damaged by feeding action of the parrotfish Sparisoma viride.
• Skeletal Eroding Band, caused by the ciliate Halofolliculina corallasia.
• White band disease The cause of this disease remains unknown.
• White plague, caused by the bacterium Aurantimonas coralicida.
• White pox disease, caused by the bacterium Serratia marcescens.
• Yellow-band disease AKA Yellow blotch disease.

References

External links

• NOAA website on coral (public domain)
• World Conservation Monitoring Centre Global Coral Disease Database

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