Multi-year seabed environmental baseline in deep-sea offshore oil prospective areas established using microbial biodiversity.

Microorganisms are the ocean's first responders to marine pollution events, yet baseline studies rarely focus on microbial communities. Temporal and spatial microbial biodiversity baselines were established using bacterial 16S rRNA gene amplicon sequencing of seafloor sediments in a deep-water oil prospective area along the Scotian Slope off Canada's east coast sampled during 2015-2018. Bacterial diversity was generally similar in space and time, with members of the family Woeseiaceae detected consistently in >1 % relative abundance, similar to seabed sediments in other parts of the world. Anomalous biodiversity results at one site featured lower Woeseiaceae as well as higher levels of bacterial groups specifically associated with cold seeps such as Aminicenantes. This was unexpected given that site selection was based on sediment geochemistry not revealing any petroleum hydrocarbons in these locations. This finding highlights the sensitivity and specificity of microbial DNA sequencing in environmental monitoring. Microbiome assessments like this one represent an important strategy for incorporating microbial biodiversity as a new and useful metric for establishing robust environmental baselines that are necessary for understanding ecosystem responses to marine pollution.