Omnivory and food chain length of aquatic food webs: Influence on trophic structure and contaminant dynamics

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Food webs provide the pathways and movement of energy, nutrients and contaminants within a biological community or ecosystem. In simple terms, they are representations of who eats whom. Where animals are positioned in food webs, from primary producers (i.e., plants) to top predators (e.g., polar bears), has a major impact on the animal’s biological and ecological characteristics and their vulnerability to man’s actions. Food webs are a central tenant of ecology and a unifying metric for developing management and conservation plans but are complex and spatially and temporally dynamic. With increasing stress on aquatic ecosystems, including invasive species, climate change, pollution and resource overexploitation, there is a pressing need to understand the mechanisms and processes that underpin the structure and function of food webs. Unfortunately, this is a difficult task, particularly in aquatic ecosystems that are not easily observed. Recently, the development of chemical tracers has improved our ability to study aquatic ecosystems and has provided new insights into food webs. This research proposal is focused on quantifying two critically important characteristics of food webs: omnivory and food chain length. Omnivory is most commonly associated with eating animals and plants but it is a more complex characteristic of organisms that reflects feeding on different trophic levels and/or from different habitats. Food chain length reflects the number of trophic levels in an ecosystem and has implications for the number of animals an ecosystem can support. Animals that are omnivores are believed to provide stability to ecosystems by utilizing different types of foods, but the prevalence of omnivory and how it varies with food chain length remains un-quantified. Both of these characteristics structure food webs and have a profound influence on the accumulation of contaminants, such as PCBs and mercury, into fish and wildlife and ultimately humans. Using a range of chemical tracers, including stable isotopes and DNA of stomach contents, I will quantify omnivory, food chain length and contaminants in aquatic ecosystems of the Great Lakes and Arctic marine environment using state-of-the-art techniques such as stable isotopes and DNA analysis of stomach contents. The Great Lakes hold >80% of North America’s fresh water and are critical to Canada’s economic and social well being, supporting large commercial and recreational fisheries. The Arctic is a priority for Canada but this understudied biome faces increasing pressure from resource development, increased shipping and fishing and climate change. Both of these ecosystems are experiencing ecosystem change making management challenging and predicting contaminant exposure and effects difficult. If we are to effectively manage and preserve these vital ecosystems and the services they provide, there is a need to better understand the importance of omnivory and food chain length, and their influence on contaminants, through dedicated field and laboratory studies.