Observations on naturally and artificially diseased tropical corals: A scanning electron microscope study.

Scanning electron microscopic (SEM) observations of naturally and artificially diseased corals reveal that the disease is characterized by a filamentous matrix of cyanobacterial andBeggiatoa filaments. Spiral bacteria are commonly embedded in the matrix. The artificial disease is not manifested as the characteristic "black line disease" and does not contain filaments of cyanobacteria. This suggests that cyanobacteria are necessary for the black line phenomenon. The colorless, sulfide-oxidizing bacteriumBeggiatoa, however, is always associated with the disease.