Patchy Necrosis
This disease has been described from the elkhorn (A. palmata) coral. Irregular necrosis occurs across the corallum surface. The starting point for the fairly rapid necrosis appears to be randomly scattered, with tissue loss progressing outward from the initiation points.
Aspergillosis
A fungal (Aspergillis sydowii.) mediated disease causing erosion was found in the Netherland Antilles to affect the sea fans of the genus Gorgonia. It is likely that this widespread disease affects other octocorals, as well (Cervino 1997). Interestingly, the fungus seems to have originated from the land, not the ocean, somewhere off the Western coast of Africa and Saharan dust is the possible carrier of the fungal spores. The spores do not reproduce underwater, and isolation from exposure prevents this disease.
Dark Spots Disease
Originally called "medallones,", this disease was first reported off the coast of Colombian Montastraea sp. and Siderastrea sp. It has now been found on Stephonocoenia sp. It was later named "lunares oscuros", or dark spots. It appears as small dark roundish depressions in the corallum surface which grow outward, forming a ring of dead corals. A dark band may be present in later stages, but it is not like the black band of BBD (Diaz 1998)
White pox
This disease, common to Acropora palmata in the Florida Keys, appears as mottled splatters of bleached tissue across the corallum surface. Tissue necrosis occurs in the last stages. It has been described as "a white rash, as though bleach has been splattered on an otherwise healthy stand." (Bruckner, Bruckner 1998).
Rapid Wasting Disease (RWD)
Investigated largely by Ray Hayes of Howard University, Rapid Wasting Disease (RWD) is a recent finding (1996) that is characterized by areas of eroded skeleton and marginal tissue necrosis. A filamentous fungus was orignially.implicated as a possible contributor to the erosion at the parrotfish bite area. The apparent loss of the solidity of the calcium matrix of the skeleton is a hallmark of this disease. It is now known that this is not a disease, but that repeat biting behavior of the stoplight parrotfish, Sparisoma viride, is the cause (Bruckner and Bruckner 2000). If bite marks can lead to invasions by other microorganisms is another question.
Shut Down Reaction (SDR)
Rapid tissue sloughing of corals was first described and named by Antonius in 1977 as Shut Down Reaction (SDR). It is considered to be one of the "White Syndromes." The disease is characterized by a rapid sloughing of tissue that starts at a weakened area and progresses outward at up to 10 cm per hour. It does not stop until the entire coral is consumed. Even a slight scratch in the coral surface can trigger an SDR reaction. Stressed corals are highly susceptible, and the disease is contagious. If the sloughed tissue contacts another coral, SDR is initiated in the contacted coral within 5 to 10 minutes. Healthy corals that are contacted by a coral in Shut Down Reaction are usually subject to a slow progression resembling WBD. It is not known whether SDR and WBD have the same underlying mechanism of disease or whether they are entirely different. It may likely that they are the same, since progressive WBD can suddenly become an SDR. Strangely, the occurrence of SDR has only been described by Antonius, and he has (to my knowledge) never followed up with either microscopic analysis or further work on this disease (Peters pers. comm.). SDR seems to follow very closely the pattern of tissue loss of rapid tissue necrosis (RTN) in the popular aquarium literature. While Antonius implicated severe or continuing stress as initiating an SDR, Peters (personal communication) notes that this reaction of rapid cell necrosis might be brought on by extreme environmental stress of water quality or temperature change.
Conclusion
Many of the above-described diseases have no pathogen that has been conclusively shown to be a causative agent, although studies are continuing. Most, if not all, are suspected to be at least partly a result of human encroachment and anthropogenic degradation of the climatic and oceanic environment. The fact that these diseases are being found most commonly in near-shore areas of high stress to corals is what appears to be significant; an attribute common to reefs worldwide even if diseases are still found in the absence of pathogens. Fortunately, few of the diseases are yet found in aquarium corals, although this may change as the disease incidence in the wild begins to occur more frequently in areas in which aquarium specimens are collected. By that time, it is hoped that more will be understood in terms of the cause and treatment for disease-based coral mortality.
This disease has been described from the elkhorn (A. palmata) coral. Irregular necrosis occurs across the corallum surface. The starting point for the fairly rapid necrosis appears to be randomly scattered, with tissue loss progressing outward from the initiation points.
Aspergillosis
A fungal (Aspergillis sydowii.) mediated disease causing erosion was found in the Netherland Antilles to affect the sea fans of the genus Gorgonia. It is likely that this widespread disease affects other octocorals, as well (Cervino 1997). Interestingly, the fungus seems to have originated from the land, not the ocean, somewhere off the Western coast of Africa and Saharan dust is the possible carrier of the fungal spores. The spores do not reproduce underwater, and isolation from exposure prevents this disease.
Dark Spots Disease
Originally called "medallones,", this disease was first reported off the coast of Colombian Montastraea sp. and Siderastrea sp. It has now been found on Stephonocoenia sp. It was later named "lunares oscuros", or dark spots. It appears as small dark roundish depressions in the corallum surface which grow outward, forming a ring of dead corals. A dark band may be present in later stages, but it is not like the black band of BBD (Diaz 1998)
White pox
This disease, common to Acropora palmata in the Florida Keys, appears as mottled splatters of bleached tissue across the corallum surface. Tissue necrosis occurs in the last stages. It has been described as "a white rash, as though bleach has been splattered on an otherwise healthy stand." (Bruckner, Bruckner 1998).
Rapid Wasting Disease (RWD)
Investigated largely by Ray Hayes of Howard University, Rapid Wasting Disease (RWD) is a recent finding (1996) that is characterized by areas of eroded skeleton and marginal tissue necrosis. A filamentous fungus was orignially.implicated as a possible contributor to the erosion at the parrotfish bite area. The apparent loss of the solidity of the calcium matrix of the skeleton is a hallmark of this disease. It is now known that this is not a disease, but that repeat biting behavior of the stoplight parrotfish, Sparisoma viride, is the cause (Bruckner and Bruckner 2000). If bite marks can lead to invasions by other microorganisms is another question.
Shut Down Reaction (SDR)
Rapid tissue sloughing of corals was first described and named by Antonius in 1977 as Shut Down Reaction (SDR). It is considered to be one of the "White Syndromes." The disease is characterized by a rapid sloughing of tissue that starts at a weakened area and progresses outward at up to 10 cm per hour. It does not stop until the entire coral is consumed. Even a slight scratch in the coral surface can trigger an SDR reaction. Stressed corals are highly susceptible, and the disease is contagious. If the sloughed tissue contacts another coral, SDR is initiated in the contacted coral within 5 to 10 minutes. Healthy corals that are contacted by a coral in Shut Down Reaction are usually subject to a slow progression resembling WBD. It is not known whether SDR and WBD have the same underlying mechanism of disease or whether they are entirely different. It may likely that they are the same, since progressive WBD can suddenly become an SDR. Strangely, the occurrence of SDR has only been described by Antonius, and he has (to my knowledge) never followed up with either microscopic analysis or further work on this disease (Peters pers. comm.). SDR seems to follow very closely the pattern of tissue loss of rapid tissue necrosis (RTN) in the popular aquarium literature. While Antonius implicated severe or continuing stress as initiating an SDR, Peters (personal communication) notes that this reaction of rapid cell necrosis might be brought on by extreme environmental stress of water quality or temperature change.
Conclusion
Many of the above-described diseases have no pathogen that has been conclusively shown to be a causative agent, although studies are continuing. Most, if not all, are suspected to be at least partly a result of human encroachment and anthropogenic degradation of the climatic and oceanic environment. The fact that these diseases are being found most commonly in near-shore areas of high stress to corals is what appears to be significant; an attribute common to reefs worldwide even if diseases are still found in the absence of pathogens. Fortunately, few of the diseases are yet found in aquarium corals, although this may change as the disease incidence in the wild begins to occur more frequently in areas in which aquarium specimens are collected. By that time, it is hoped that more will be understood in terms of the cause and treatment for disease-based coral mortality.
