An Evaluation of the Effects of Marine Oil-spills, Remediation Strategies, and Shipwrecks on Microbial Community Structure and Succession

The evaluation of how Bacteria respond to oil-contamination, and the application of dispersants and biosurfactants, in North Sea seawater microcosms is the focus of Chapter Two. Analysis revealed that dispersants and biosurfactants, which significantly reduced the interfacial tension between oil and water, significantly increased growth of obligate hydrocarbonoclastic bacteria (OHCB) in 24 hours, translating into significantly enhanced alkane-biodegradation. Early sampling of microcosms revealed how the OHCB Oleispira, hitherto considered a psychrophile, can dominate bacterial communities at the relatively high temperature of 16ºC. Bacterial response to oil-pollution is examined further in Chapter Three, where an in situ oil-slick is compared to a chemically dispersed oil-slick in the North Sea. Results suggest a lack of hydrocarbon-degrading bacteria (HCB) growth, even in samples with measurable hydrocarbons, could potentially be attributed to phosphorous limitation. Whilst the Ecological Index of Hydrocarbon Exposure, which quantifies the proportion of a bacterial community with hydrocarbon-biodegradation potential, revealed an extremely low score, highlighting a limited capacity for the environment, at the time of sampling, to naturally attenuate oil. Analysis of sediments contaminated by the Agia Zoni II oil-spill (Greece, 2017), in Chapter Four, demonstrated significant growth of HCB five-days post-oil-spill. Whilst the relative abundance of HCB declined as oil was removed, a legacy effect was observed, with the OHCB Alcanivorax and Cycloclasticus persisting for several months after the oil-spill. Finally, analysis of sediments around a North Sea shipwreck (HMS Royal Oak), in Chapter Five, revealed low levels of pyrogenic polycyclic aromatic hydrocarbons and little evidence of HCB, indicating sediments showed no long-term impact by previous oil-pollution from the shipwreck. This thesis not only advances our understanding of microbial response to oil-spills, remediation strategies, and shipwrecks, in a range of marine environments, but also highlights the importance of harnessing such knowledge and data to advance post-incident monitoring guidelines and models.