Impacts of oil pollution on sub-Arctic and Arctic marine invertebrates: a study on blue mussels and beyond

Oil pollution from human activities continues to be a significant threat to marine animals despite advancements in the safety of oil extraction and transportation. Oil spills and their effects are highly complex and unique, and much is yet to be understood about some of the major exposure pathways and the toxic impacts of compositional changes of oil after it has been spilled. This dissertation aimed to expand our knowledge regarding exposure pathways that had previously been severely understudied or overlooked entirely. First, I explored the potential differences in toxicity between non-biodegraded and biodegraded oil to the blue mussel, Mytilus spp. Biodegradation by microbes is a process that changes the composition of oil and can lead to a full mineralization of those compounds that are accessible to the microbes. The results obtained from this experiment paint a complex picture, and challenge the generally held belief that biodegradation could lead to a decrease in oil toxicity. Second, I explored the eIects of oil on blue mussels, and specifically how these eIects change depending on the exposure pathway. Oil can get trapped in, or adsorbed to, marine snow, which are aggregates consisting of (dead) phytoplankton cells, fecal pellets, fibers, and minerals, and which are responsible for the downward transport of organic matter to the ocean floor. The question posed in this study was whether the eIects of oil would change depending on the exposure route, i.e. when it is taken up as droplets or trapped within a natural food source, marine snow. I found that marine snow seems to moderate the effects of oil on blue mussels, compared to the uptake of free droplets. This was unexpected, but supported by all endpoints measured (clearance rate, condition index, and measured DNA damage). Possibly, the nutritional value of the aggregates, or simply the concentration of food particles outbalance any negative eIects from the oil. Finally, I conducted a meta-analysis of oil toxicology studies using invertebrates from the arctic and sub-arctic regions, to explore how the vast knowledge we have gathered regarding oil toxicity could be consolidated. Such a meta-analysis had not been attempted before due to serious challenges in comparing methods and results across oil toxicology studies. Even though these challenges persist and led to many studies not being usable in a quantitative meta-analysis, I could still elucidate trends that are worth exploring. For example, I found that ecologically relevant endpoints tend to be relatively insensitive to oil pollution, while endpoints that might not be as relevant for a wider population can be highly sensitive markers of oil exposure or effects. Together, the results from this dissertation add to our understanding of some of the impacts of oil pollution on marine organisms, but highlight the complexities of oil toxicology research and the need to increase comparability across studies.