Evidence for asymmetric assimilation of an anthropogenic resource subsidy in a freshwater food web

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Johnson, Laura
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University of Guelph

Anthropogenic subsidies occur readily, especially with growing human development neighboring natural systems. Considering the immense quantity of anthropogenic resources contributed to natural systems, determining how these subsidies permeate into native food webs is not well understood. Using a combination of stable isotope and fatty acid bio-tracers, my research attempts to estimate the pathway(s) of assimilation of an anthropogenic resource provided by freshwater cage aquaculture. My results point to an asymmetric assimilation of feed by native organisms into and through the structured food web. Specifically, two pelagic fish species (one an intermediate consumer and the other a top predator) show elevated trophic position and higher levels of essential fatty acids due to consumption of the feed, with no signs of consumption of feed through the littoral pathway. Further, I find that the assimilation of feed has an increasing effect on the proportions of n-3 LC PUFAs in the tissue of fish indicating that the feed subsidy has implications for fish health. My findings provide new insight into an emerging research area that asks how anthropogenic resource subsidies effect properties of food webs. Since many habitats experience both natural and anthropogenic subsidy inputs, the multiple tracer approach employed here shows promise for studying how subsidies may affect species health and behavior and food web structure and stability.

anthropogenic, resource subsidy, food web, aquaculture, stable isotopes, fatty acids