Field Guide to Coral Diseases and Other Causes of Coral Mortality
The Significance of Coral Diseases
Although structures resembling the bacterial aggregates found in acroporid corals with white-band disease were first observed within coral tissue in the early 1900s (Duerdon, 1902) the first reports of disease affecting scleractinian corals did not appear until the early 1970s. Increasingly frequent observations of coral diseases in the wild have been given added importance by the lack of previous observations even on well-studied reefs. Therefore the possibility exists that the present widespread occurrence of coral diseases is a manifestation of a decline in the integrity of the marine environment. This possibility continues to fuel the production of an extensive and varied literature.
Both direct (Gladfelter 1982; Aronson and Precht 1997) and indirect (Garzon-Ferreira and Zea, 1992) mortality arising from disease has modified the composition and structure of coral reefs across the Caribbean by removing common and locally abundant species. Furthermore, the results of some field monitoring programmes suggest that the occurrence of disease, at least in the Florida Keys, has increased dramatically in the last few years (Porter et al. 1999). For most of the world's reefs a consensus of opinion exists that conditions during the past 20 years have been very different to those prevailing during the two decades prior to 1980. Although the exact nature of this global environmental change remains unknown, it is tempting to speculate, as many have done, that direct and indirect human impacts on reefs are responsible. However, beyond tantalising glimpses provided by studies which have examined the relationship between disease and water pollution (e.g. Mitchell and Chet 1975; Antonius 1981) the role of anthropogenic influence is extremely unclear. Indeed, this is beginning to be recognised as one of the most important yet most poorly understood aspects of coral diseases.
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