Tracing carbon transfer through food webs is a major challenge in ecological science. Recently, stable carbon isotopic composition (δ¹³C) of amino acids (AAs) has been increasingly used for tracing the source and flow of carbon in the ecosystem. It becomes a powerful tool for studies of food web structure, animal migration and habitat use. On the other hand, the application is still limited due to the experimental difficulties. We have developed an improved analytical method based on a multi-dimensional high-performance liquid chromatography (HPLC) and a nano-scale elemental analyzer/isotope-ratio mass spectrometry (EA/IRMS) for the high-precision δ¹³C measurement of proteinogenic AAs.
    Based on the new method, we analyzed a couple of representative species collected from northwest Pacific (spear squid, Heterololigo bleekeri and blue mackerel, Scomber australasicus). The δ¹³C of AAs in these two species showed a similar pattern. δ¹³C values varied over 30‰ with Phe and Leu being most ¹³C depleted and Gly being most enriched. The results support the hypothesis that some non-essential AAs like Gly in marine higher consumers are largely biosynthesized de novo.