Nitrogen isotope analysis of amino acids for estimating trophic position of coastal marine species in a cold region

抄録

Difference in the stable nitrogen isotope ratio (δ¹⁵N value) between two types of amino acids within a single organism has been employed as a powerful tool for estimating the trophic position (TP) of the organism in food webs. However, accuracy of the TP values estimated relies on the consistency of trophic elevation in the δ¹⁵N value across diverse organisms and among diverse environments. Indeed, little is known the applicability of this tool for organisms found in cold environments. In the present study, we determined the δ¹⁵N values of amino acids for 10 species collected in a coastal marine environment of Hokkaido, a humid continental climate zone in Japan, to evaluate whether this tool is applicable to marine species found in cold regions. The δ¹⁵N values of glutamic acid and phenylalanine determined in the present study illustrate diverse TP values for the species, as 0.7-1.0 for primary producers (i.e., macroalgae), 1.9-2.3 for herbivores (e.g., zooplankton and sea urchin), and 2.3-3.7 for omnivores and carnivores (e.g., crab and fish). These results indicate that the TP values estimated in the present study are basically consistent with actual TP for producers and herbivores and with the literature TP values for the same or similar species of omnivores and carnivores from temperate regions, and thus provide evidence that this tool is basically applicable to estimate the TP of marine species found in cold regions. On the other hand, low TP value was estimated for one species, goby, suggesting that further studies will be required, particularly for identifying mechanisms responsible for the low TP values estimated for such species.