Spatial variability of carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in an Arctic marine food web

Stable isotopes of carbon (delta C-13) and nitrogen (delta N-15) were used to examine trophic structures in an arctic marine food web at small and large spatial scales. Twelve species, from primary consumers to Greenland shark, were sampled at a large spatial scale near the west and east coasts of Greenland. There was a significant positive latitudinal effect on d15N values, which varied by 2 to 5% over the sample range. This latitudinal pattern was also illustrated by the negative correlation between the productive open-water period and baseline delta N-15 values. At a smaller spatial scale, 8 species from the Nuuk Fjord were compared with species sampled in waters immediately offshore. All values of delta N-15 and delta C-13 (except for Calanus finmarchicus) were more enriched inshore than offshore. The use of C. finmarchicus delta N-15 and delta C-13 values as a baseline explained a portion of the spatial variability in isotopes, attributing some of the variation to physical and biological sources. Hence, significant differences in isotopic signatures on both large and small spatial scales were less related to food web structure than to different physical and biological properties of the water masses. Accordingly, the results illustrate the importance of spatial variability when interpreting trophic structure from stable isotopes.