Deciphering the structure of the West Greenland marine food web using stable isotopes (δ13C, δ15N)

The Arctic is facing major environmental changes impacting marine biodiversity andecosystem functioning. One way of assessing the responses of an ecosystem to these changes is to quantitatively study food web dynamics. Here, we used stable isotope (delta N-15 and delta C-13) analyses of 39 Arctic marine species to investigate trophic relationships and isotopic niches of the West Greenland foodweb in 2000-2004. The lowest delta N-15 values were found for suspension feeding blue mussel (Mytilus edulis; 6.1 %) and the highest for polar bear (Ursus maritimus; 20.2 %). For delta C-13, copepods (Calanus spp.) had the lowest values (-20.4 %) and snow crab (Chionoecetes opilio) the highest values (-15.8 %). Our results show that the three trophic enrichment factor (TEF) approaches used to quantify species trophic positions (fixed TEF of 3.8 and 3.4 % or scaled TEF) did not generally affect trophic modelling and provided similar conclusions. Overall, the findings in this study are in good agreement with previous investigations of other Arctic marine ecosystems. Interestingly, we found little overlap of core isotopic niches used by the four investigated functional groups (mammals, seabirds, fish and invertebrates), except for seabirds and fish where an overlap of 24 % was found. These results provide new insights into species and functional group interactions, as well as into the food web structure and ecosystem functioning of an important Arctic region that can be used as a template to guide future modelling of carbon, energy and contaminant flow in the region.