Independent and interactive effects of reduced seawater pH and oil contamination on subsurface sediment bacterial communities.

Ocean acidification may exacerbate the environmental impact of oil hydrocarbon pollution by disrupting the core composition of the superficial (0-1 cm) benthic bacterial communities. However, at the subsurface sediments (approximately 5 cm below sea floor), the local biochemical characteristics and the superjacent sediment barrier may buffer these environmental changes. In this study, we used a microcosm experimental approach to access the independent and interactive effects of reduced seawater pH and oil contamination on the composition of subsurface benthic bacterial communities, at two time points, by 16S rRNA gene-based high-throughput sequencing. An in-depth taxa-specific variance analysis revealed that the independent effects of reduced seawater pH and oil contamination were significant predictors of changes in the relative abundance of some specific bacterial groups (e.g., Firmicutes, Rhizobiales, and Desulfobulbaceae). However, our results indicated that the overall microbial community structure was not affected by independent and interactive effects of reduced pH and oil contamination. This study provides evidence that bacterial communities inhabiting subsurface sediment may be less susceptible to the effects of oil contamination in a scenario of reduced seawater pH.