The Faroe-Shetland Channel (FSC) is an important gateway for dynamic water exchange between the North Atlantic Ocean and the Nordic Seas. In recent years it has also become a frontier for deep-water oil exploration and petroleum production, which has raised the risk of oil pollution to local ecosystems and adjacent waterways. In order to better understand the factors that influence the biodegradation of spilled petroleum, a prerequisite has been recognized to elucidate the complex dynamics of microbial communities and their relationships to their ecosystem. This research project was a pioneering attempt to investigate the FSC’s microbial community composition, its response and potential to degrade crude oil hydrocarbons under the prevailing regional temperature conditions. Three strategies were used to investigate this. Firstly, high throughput sequencing and 16S rRNA gene-based community profiling techniques were utilized to explore the spatiotemporal patterns of the FSC bacterioplankton. Monitoring proceeded over a period of 2 years and interrogated the multiple water masses flowing through the region producing 2 contrasting water cores: Atlantic (surface) and Nordic (subsurface). Results revealed microbial profiles more distinguishable based on water cores (rather than individual water masses) and seasonal variability patterns within each core. Secondly, the response of the microbial communities to crude oil was investigated in laboratory-based microcosms. Microbial communities from all water masses exhibited hydrocarbon biodegradation activity at average FSC temperatures (4°C), albeit with markedly delayed and potentially slower response in comparison to those exposed to moderate control temperatures (20°C). A collection of bacterial isolates, comprising of 230 FSC strains with putative hydrocarbonoclastic activity was created, which included psychrotolerant members belonging to the genera Marinobacter, Pseudoalteromonas, Cycloclasticus, Halomonas, Thalassolituus and Glaciecola. Lastly, a sophisticated molecular technique called DNA-based stable isotope probing (DNA-SIP) was used to directly target and identify hydrocarbon-degrading taxa that may not be easily amenable to cultivation. Using DNA-SIP, hydrocarbonoclastic FSC strains affiliated with the genera Phaeobacter and Lentibacter were identified, along with strains affiliated with known hydrocarbon-degraders from the genera Thalassolituus, Alcanivorax, Oleispira, Glaciecola, Marinobacter and Cycloclasticus. Correlating the findings from all three experiments, revealed that ~41% of the baseline FSC microbial community constituted bacteria affiliated to genera with hydrocarbon-degrading capacities. Their response to the presence of hydrocarbons, however, appeared to be largely influenced by temperature. This work is the first to establish a microbial baseline for the FSC and to investigate the microbial repose to crude oil in the water column of the region. Results are expected to contribute to the development of biotechnologies and oil-spill mitigation strategies tailored for the FSC region in the event of an oil spill
