Comparing trophic structure and diversity in northern ecosystems using stable isotope data

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Change in trophic level of catches has become a key indicator of fisheries impact, ecosystem structure and health. Whether because of fishing pressure, climate change or other sources to physical or biological changes in an ecosystem, we propose to use isotope metrics in comparing key species and functional groups in ecosystems across the northern hemisphere. Layman et al. (2007) suggested an interesting approach for using stable isotopes in community-wide measures to represent a species trophic role based on a bi-plot of δ13C – δ15N where they proposed 6 different metrics of food-web properties. As a case study, we attempt to use the approach of Layman to compare two northern ecosystems in Norway (Sørfjord (Nilsen et al. 2008) and Ullsfjord) with American Georges Bank (Fry 1988) and Newfoundland Labrador (Sherwood and Rose 2005) using stable isotope data. The systems exhibit similar physical and biological properties and share many of the same species.