Recent studies suggest that coral diseases are affecting a greater number of species, are increasing in frequency and distribution, and are spreading to new regions faster than ever recorded in the past. Although coral diseases are receiving greater attention from the scientific community, most diseases have not been fully characterized, and their etiologies, including the causative agents, remain largely unknown. Identification of the causative agents, quantification of the distribution, abundance and impact of coral diseases, and the possible associations of coral disease with anthropogenic stressors are high priority research areas needed for effective coral reef management.
Coral diseases occur in response to biotic and abiotic stressors.
Biotic diseases are caused by microrganisms such as bacteria, cyanobacteria, fungi, protozoans, and possibly viruses, although they may be exacerbated by abiotic factors. Some biotic diseases are highly contagious, and they probably spread through direct contact, through passive dispersal of pathogenic agents via water currents, or via biological vectors. Abiotic diseases, such as bleaching occur in response to physical or chemical stress, and are non-infectious. The recent emergence of coral diseases may be a consequence of deteriorating water quality that favors the proliferation of microorganisms, or of a reduced ability of a coral to defend itself against pathogenic organisms or abiotic stresses. In the 1990s there has been an emergence of newly described coral diseases with new types of tissue conditions not observed in the past.