Black band disease as a possible factor of the coral decline at the northern reef-flat of Yongxing Island, South China Sea

Abstract

Black band disease (BBD), characterized by the Cyanobacterial dominated pathogenic consortium, is thought to play a key role in the global decline of the coral reef ecosystems. The present paper originally documents a case of BBD from Yongxing Island (Xisha Islands, South China Sea), and further probes the reasons of this abnormal phenomenon. Prior to 2007, corals at northern reef-flat of Yongxing Isand were in healthy growth. Catastrophic coral mortality occurred between 2007 and 2008. The 16S rRNA gene sequencing and PCR amplification, with universally conserved primers, were applied to detect the contagious bacterial community of the microbial mat. The results demonstrated that six bacterial divisions constituted the clone libraries derived from the BBD mat, and that Cyanobacteria are the most diversely represented group that inhabit BBD bacterial mats, despite the fact that species in five others divisions (α-Proteobacteria, γ-Proteobacteria, Bacteroidetes, Verrucomicrobia and Actinobacteria) are also consistently diverse within the BBD mats of diseased coral. Other factors such as coral bleaching, typhoons, ocean acidification and crown-of-thorns starfish outbreaks, are not primarily responsible for the coral mortality within such a short time interval. The disaster expansion of BBD associated with Cyanobacterial blooms is a more likely mechanism impacting these coral reefs. Excessive human activity enhances the eutrophication of the marine water of the reefal region and may result in occurrence of the BBD.