Characterization of the Microbial Community Structure and Function During the Natural Attenuation of Oil in Marine Environments Using In Situ Microcosms

Climate change, the opening of the northwest passage, the production and transportation of oil reserves in addition to the large size and number of ocean-going vessels, are putting all Canada's oceans at an elevated risk for an oil spill. Responses to marine oil spills include physical (skimming and recovery), chemical (dispersants, herders) and biological processes (biodegradation). Natural attenuation, a weathering process that includes physical, chemical and biological action on spilled oil, is a potential remediation strategy that needs to be explored and exploited. In the Canadian context, we are using genomics approaches to better understand the natural populations of oil degrading microorganisms in our oceans, their diversity, spatial and temporal dynamics, and locations that may be more vulnerable to oil spills. The purpose of this study was to perform an evaluation of the effectiveness of an in situ microcosm experimental system to study indigenous microbial communities that have oil degrading potential and to determine whether this experimental system could have an impact on acute toxicity to various marine organisms. In situ microcosms are slitted columns that contain support matrices such as clay beads or river rocks, with or without an oil coating. Columns can be incubated in different locations, at different depths and different time periods, during which microbial biofilm develops on the support materials. By using oil coated and uncoated matrices, comparative microbial community data that demonstrates the response of the microbial community to the presence of oil can be obtained. Long-term incubations (1 year) conducted at CFS-Alert showed that known oil-degrading bacteria (Colwellia, Oleibacter, Thalassolituus, Cycloclasticus, Oceanobacter and Alcanivorax) became dominant only on the oil coated matrices, confirming their presence in the local seawater. Acute toxicity tests were performed in aquaria on a variety of test organisms to evaluate the possible effects of oil components leaching into the water from the in situ microcosms. Limited and transient toxicity to only two tested organisms (green sea urchin fertilization and green algal growth). Considering the analyses were conducted in a closed circulation system, it is highly likely that in an open ocean environment, toxicity would be negligible. Data from these studies will be valuable to support guidelines for the exploitation of natural attenuation as an alternative response measure (ARM) to address oil spills in Canadian waters.