Purpose Microbial communities play a significant role in maintaining the health of Great Barrier Reef (GBR) ecosystems, however, the influence of sediment composition and other environmental factors such as temperature and wave regime on microbial communities are largely unknown. Here we show how sediment composition and exposure influences bacterial communities across the inner section of the GBR (Cleveland Bay, Halifax Bay and Dunk Island) between 2016 and 2018.

Materials and methods Sediment traps were installed and routinely deployed (~ every 3 months) at eight sites in the inshore GBR and analysed for water chemistry, sediment geochemistry and organic characteristics and associated bacterial communities.

Results and discussion Results showed a significant variation in water turbidity, sediment collection rate and geochemistry across the trap sites. Bacterial communities also significantly varied along the inner GBR, with the shift in relative abundance of Actinobacteria, Acidobacteria, Planctomycete, Verrucomicrobia and Chloroflexi being the main cause of the bacterial community dynamics. The variation in spatial patterns of bacterial communities was highly correlated with water turbidity and the geochemical characteristics of associated sediments (e.g., K, Fe, Mn, Co, Al, Cr, Ca) collected across the marine trap sites.

Conclusion Our findings indicate that sediment composition and collection rate (and linked water turbidity) can change the spatial patterns of bacterial communities by creating environmental gradients along the inner section of the GBR.