Determination of aquatic food‐web structure based on compound‐specific nitrogen isotopic composition of amino acids

The nitrogen isotopic composition (δ 15 N) of amino acids is potentially useful as an alternative method for estimating the trophic levels of organisms in food webs. However, because this “amino acid method” has been constructed from the observations of only a few case studies of food‐consumer combinations in previous studies, the universality of the approach remains unclear. In this study, we investigated the δ 15 N signatures of amino acids in 17 photoautotrophs and the trophic relationships during four controlled feeding experiments using green algae, zooplankton, and fish. The results are consistent with those reported in previous studies, implying that the amino acid method can be applied to a variety of…