Exploring bacterial diversity in Acropora pharaonis: Implications for coral health and growth anomalies

Coral growth anomalies (GA) affect many coral genera across the world, yet the etiology of GAs remains unknown, with limited knowledge of associated bacteria. In this study, we investigated bacterial associations between the growth anomalies (GAs) and healthy (H) portions of coral colonies in Acropora faraonis for two seasons to understand microbial dynamics. Additionally, we examined bacteria in water (W), which could be affecting coral bacterial communities. We found that alpha diversity remained consistent between healthy and GA coral tissues, but their relative abundances differed significantly. Notably, differential analysis revealed the abundance of Endozoicomonas spp., differed significantly between GA and H tissue, although it remains the dominant genus in both GA and H tissue. The high relative abundance of Endozoicomonas spp. in both GA and healthy tissue underscores its potential role in maintaining coral health. Structural modifications in GAs, such as changes in polyp sizes or densities, could be responsible for these differences in bacterial abundance. Similarly, microbial community composition remained consistent between seasons but differed in abundance again. We found differences between microbial communities of GAs and water, but no significant differences were observed between GAs and H, and no previously established bacterial pathogens were detected in GA tissue. These findings describe bacterial community patterns in GAs, but their potential role in its pathogenesis remains unknown. Further metagenomic and meta-transcriptomic analyses are needed to understand potential bacterial involvement in GAs. Additionally, investigating viruses and fungi in GA tissue is recommended to gain deeper insights into GA pathogenesis.