Bacteria associated with skeletal tissue growth anomalies in the coral Platygyra carnosus

Scleractinian corals with growth anomalies, often referred to as 'tumors', have been reported globally. A recent survey of Hong Kong waters showed that > 60% of Platygyra carnosus colonies developed tumors. Here we report for the first time, the bacterial community associated with tumors in P. carnosus over different seasons and locations in Hoi Ha Wan Marine Park and Port Shelter. Culture-based methods for strain isolation and molecular techniques of 16S rRNA analysis for strain identification were used, as well as the culture-independent technique terminal-restriction fragment length polymorphism. We tested the hypothesis that the community composition would be considerably different between healthy and tumor corals and aimed to investigate whether potential differences because of tumors would override the seasonal and spatial influences. Our analysis detected only minor differences between the communities associated with the healthy and tumor corals, indicating that tumors are not associated with major changes in the bacterial community structure. In contrast, community structure was strongly influenced by the location and season, with greater Alphaproteobacteria diversity in the winter than in the summer. This study demonstrated that the coral-associated bacterial community composition was more related to environmental variables (i.e. season and location) than to disease (i.e. tumor).