Influence of Northward Redistribution of Marine Prey and Predator Species on the Trophic Dynamics of Environmental Contaminants and Nutrients in Arctic Marine Food Webs

The northward-range expansion of sub-Arctic species is altering species interactions, affecting the dynamics of nutrients and contaminants, in Arctic food webs. Arctic marine piscivores are switching from a diet historically dominated by Arctic cod to one comprised of sub-Arctic capelin and sand lance. Another change is the occurrence of killer whales in the Arctic and the presumed switch from a fish-based diet in temperate waters to one richer in marine mammals in the Arctic. My goal was to evaluate some of the consequences of these climate-driven ecological changes, by comparing contaminant and nutrient concentrations in shifting Arctic marine communities. Potentially due to migratory patterns, capelin had higher tissue concentrations and higher proportions of less volatile persistent organic pollutants (POPs), compared to Arctic cod. Yet, the magnitude of these differences was small. Furthermore, mercury concentrations were higher in Arctic cod relative to capelin. Concentrations of essential fatty acids were similar among these species, while selenium was higher in sand lance compared to Arctic cod. Thus, the replacement of Arctic cod with capelin and sand lance may not substantially decrease the food quality of prey available for predators. However, fatty acid markers suggested that capelin and sand lance were less dependent on sea ice-primary production, and their fatty acid and stable isotope feeding niches were wider compared to that of Arctic cod, suggesting an ecological advantage for these sub-Arctic fish over Arctic cod under climate change. Killer whales had blubber POP concentrations exceeding previously calculated effects thresholds for cetaceans, likely related to feeding on high trophic level prey in Arctic waters. A negative association of POPs with blubber concentrations of the biomarker vitamin E, but not vitamin A, in killer whales with fatty acid markers consistent with marine mammal consumption, suggested that feeding on this prey may put killer whales at higher risk of POP adverse effects on vitamin E homoeostasis. My research showed that changes in prey related to northward range-shifts can have consequences for predators, especially those at high trophic levels, highlighting the importance of considering top consumers and their interactions when studying climate change impacts on Arctic ecosystems