Annual black bands in skeletons of reef corals (Scleractinia)

Dark discolorations appear concentrated as black bands in the fresh skeletons of massive reef corals (Porites), often restricted to the upper 7.5 cm of the coral skeleton. The pattern of these bands
runs parallel to that of the skeletal density bands, the black bands occurring in the low density part of the pairs of high/low density bands. The black bands do not result from the inclusion of foreign material by the coral but are characterized by high concentrations of a dark fungus. We suggest that the dark banding pattern correlates to an annual variation in the organic content of the skeleton. Highest concentrations of the dark mycelia are reached where the fruiting bodies are formed. The fruiting bodies occur in groups and open through small dead areas on the living coral surface into the
surrounding seawater. We found Infected colonies in 6 massive Porites species but only at 2 locations, Salayer and Take Bone Rate (Southwest Sulawesi) In the eastern Indonesian Archipelago. At these
locations up to 33 % of the colonies showed the fungus discolorations. There appears to be no obvious effect on the strength of the coral skeletons, the main ecological effect of the fungus is that the formation of fruiting bodies interferes with the integrity, maintenance and growth of the living coral surface. This is the first example of a fungus being involved in spatial competition on coral reefs.