A world-wide disease of corals that is characterised by a dark ring, or band, that separates apparently healthy coral tissue from freshly exposed coral skeleton. It migrates across coral colonies and completely degrades coral tissue. The infecting agent is a synergestic assortment of photosynthetic and non-photosynthetic bacteria. For more details and illustrations, see: http://www.coral.noaa.gov/coral_disease/black_band.shtm.