Common Identified Coral Diseases
Aspergillosis is a lesion producing fungal infection of Caribbean soft corals. It affects 6 sp. of sea fans and sea whips and is widespread throughout the Caribbean. The pathogen is Aspergillosis sydowii, a terrestrial fungus (Geiser et al., 1996), which infects gorgonia after germination of spores on the coral surface. This is followed by penetration and spread of hyphae in coral tissue, resulting in highly visible lesions. Lesions may be associated with complete loss of tissue and skeleton, and often occur at multiple sites across an infected colony. Purple galls may be produced by the coral host to encapsulate fungal hyphae. If such galls are present, fungal hyphae are visible if the gall is cut open. One known reservoir is African dust. See (Alker et al., 2001; Geiser et al., 1998; Kim and Harvell, 2002; Kim et al., 2000; Nagelkerken et al., 1997a,b; Smith et al., 1996, 1998.)
Infected colony of Gorgonia ventalina
Aspergillosis is caused by the terrestrial fungus Aspergillus sydowi. The disease results in lesions associated with degraded gorgonian tissue. Gorgonia counteract the disease by encapsulating fungal hyphae in purple pigmented galls.
Bacterial Bleaching-Disease Overview
Bleaching caused by a specific bacterial infection (as opposed to a response to environmental stress) occurs when loss of zooxanthellae is due to a toxin produced by the intracellular bacterial pathogen. Bacterial bleaching occurs in the Mediterranean scleractinian coral Oculina patagonica. Two known bleaching pathogens are Vibrio shiloi and V. patogonica (Kushmaro et al., 2001, in press) . Initial pathogen attachment to coral is specific to a b-galactose containing receptor in the coral host surface mucopolysaccharide layer. Subsequent invasion of coral host tissue is followed by temperature dependent intracellular growth of bacteria. Production of a heat sensitive toxin results in lysis of the zooxanthellae. Disease signs consist of loss of zooxanthellae, with coral tissue intact, and differs from environmental bleaching in that Vibrio shiloi or patogonica are present in the affected tissue. The reservoir is not known. (See Kushmaro et al., 1996, 1998; Ben-Haim et al., 1999; Banin et al., 2000, 2001, in press.)
Oculina patagonica partially bleached colony (in the field)
Bacterial bleaching is caused by a specific bacterial/coral interaction. Specificity includes recognition by the pathogen of host (coral) surface receptors; invasion of coral tissue; multiplication of bacteria in coral tissue; and release of bacterial toxins that cause bleaching.
Black Band -Disease Overview
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. The mat is present between apparently healthy coral tissue and freshly exposed coral skeleton. 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.
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, sulfate-reducing, and sulfide-oxidizing bacteria. The black band disease microbial consortium is structurally and functionally identical to cyanobacterial-dominated microbial mats found in other illuminated, sulfide-rich environments (Carlton and Richardson, 1995; Richardson et al., 1997) .
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 (Rützler and Santavy, 1983) .
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, in press). 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 (Richardson, 1997) .
Black Band Disease
Black band disease is characterized by a dark ring, or band, that separates apparently healthy coral tissue from freshly exposed coral skeleton. It migrates across coral colonies completely degrading coral tissue. A closeup view reveals that the band is composed of numerous microorganisms, here revealed as a dark community of phosynthetic cyanobacteria (“bluegreen algae”) and white specks of sulfur bacteria.
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Dark Spots -Disease Overview
Dark spots disease is present as dark (brown or purple) pigmented areas of tissue on scleractinian corals. There is no known pathogen. The pigmented areas may or may not overly recessed areas of coral skeleton. The coral tissue remains intact, although at times lesions and coral tissue death are observed in the centers of the spots. ( Gil-Agudelo and Garzon-Ferreira, 2001) . This disease is widespread throughout the Caribbean.
There is no known pathogen for dark spots disease, which is recognized by darkly pigmented patches on coral tissue. Tissue loss is minimal, if present.
White Band -Disease Overview
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 plague, except that white band is acroporid specific (and 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 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 (and 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 psuedomonads 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).
White Band type II in Acropora cervicornis
There are two etiologies of white band disease, type I and type II. In type I, tissue destruction is associated with the moving front of the band. In type II, there is at times a bleached zone between the area of tissue degradation and the moving front. If the bleached zone is not present, type I is visually indistinguishable from type II. No pathogen has been isolated.
White Plague -Disease Overview
Plague is characterized by a sharp line between apparently healthy coral tissue and freshly exposed coral skeleton. There is no obvious microbial band present. Plague is caused by the bacterial pathogen Aurantimonas coralicida, gen nov. sp. nov. (Denner et al., IJSEM, in press). Disease signs (rate and pattern of disease progression and virulence) vary between three distinct types. Plague Type I, documented in the 1970s and 1980s, starts at the sides of colonies, with tissue destruction at a rate of 3 mm/day. Six species were reported to be affected (Dustan, 1977, Dustan and Halas, 1987). Plague Type II, first documented in 1995, starts at the base of a coral colony and progresses upward, with tissue destruction up to 2 cm/day. A bleached zone between healthy tissue and exposed skeleton (<3 mm) may be present (Richardson et al. 1998a,b). Plague type III, first seenin 1999, starts on the sides or top of colonies and destroys tissue at high rates of dm/day. It is found on massive Montastraea annularis and Colpophyllia natans. Plague is currently epidemic throughout the Caribbean, and affects 33 sp. of Caribbean scleractinian corals (Weil et al, in press). The reservoir is not known.
Plague (synonym: white plague)
White Pox -Disease
White pox is characterized by coral tissue degradation that occurs in association with circular lesions on the Caribbean scleractinian coral Acropora palmata. Rapid loss of tissue progresses along a distinct line, or with small remnants of tissue sometimes present near the margin of, irregularly shaped patches anywhere on the upper or lower surfaces of Acropora palmata branches. The average rate of tissue loss is 2.5 cm2/day, although rates up to 10.5 cm2/day can occur. It is caused by the bacterium Serratia marcescens, a well-known species that is widespread in both terrestrial and aquatic environments as well as in mammalian and arthropod hosts (Patterson et al., 2002).
White Pox (synonym: acroporid serratiosis)
White pox is characterized by circular lesions. The pathogen is Serratia marcescens, a gram negative member of the enterobacteria.
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Yellow Band -Disease
Yellow band is characterized by large rings or patches of bleached, yellow tissue on Caribbean scleractinian corals. It affects Montastraea annularis and M. faveolata and is widespread throughout the Caribbean. Tissue loss is extremely slow (cm/year). When yellow band infected corals are also bleached the yellow band can blend in with bleaching signs; after recovery from bleaching the band becomes visible again. No pathogen has been discovered, although loss of zooxanthellae pigments and zooxanthellae cells in affected tissue have been documented (Cervino et al., 2001). Yellow band associated zooxanthellae have lower mitotic indices (number of dividing cells), and it has been suggested that this disease affects the zooxanthellae and not the coral (Cervino et al., 2001).
Yellow band is characterized by a bleached zone that expands in a halo. Tissue loss is minimal (cm/yr). No pathogen has been isolated.
Yellow band on Montastraea faveolata
Information on this page is courtesy NOAA, go to http://www.coral.noaa.gov/coral_disease/ for more up-to-date and detailed information