Dynamic responses of bacterial communities in three species of corals during the 2017 bleaching event in subtropical Hong Kong waters

Bacteria play important roles in coral health, yet little is known about the dynamics of coral-associated bacterial communities during coral bleaching. Here, we reported the bacterial communities prevalent in three scleractinian corals (Montipora peltiformis, Pavona decussata and Platygyra carnosa) during and after the 2017 bleaching event in Hong Kong. Amplicon sequencing of 16S rRNA was used to determine bacterial communities. Our results revealed that the bacterial composition and dominant bacteria aviaries among three corals species: Synechococcus CC9902 (Cyanobacteria) in M. peltiformis, Anoxybacillus and Geobacillus (Firmicutes) in Pa. decussata, and Endozoicomonas (Proteobacteria) in Pl. carnosa. Increased bacterial diversity from healthy to bleached and recovered status was observed in M. peltiformis which was more susceptible to bleaching. Whereas, two resilient corals Pa. decussata and Pl. carnosa had higher microbial diversity and they have more similar bacterial composition in the health and bleached conditions. Our results showed that the dominant Synechococcus CC9902 have significant correlation with condition shift of M. peltiformis in the bleaching event. Whereas, Anoxybacillus and Geobacillus in Pa. decussata had a more constant bacterial composition, which may attribute to functional stability and resilience under thermal stress. Our study reveals the coral?associated microbial diversity and their dynamics in different conditions in the field, providing a reference to explain how coral-associated bacteria respond to environmental stress under climate change.