Characterizing niche differentiation among marine consumers with amino acid δ13C fingerprinting

Marine food webs are highly compartmentalized and characterizing the trophic niches among consumers is important for predicting how impact from human activities affect the structuring and functioning of marine food webs. Biomarkers such as bulk stable isotopes have proven to be powerful tools to elucidate trophic niches, but they may lack in resolution, particularly when spatio-temporal variability in a system is high. To close this gap, we investigated whether carbon isotope (δ13C ) patterns of essential amino acids (EAAs), also termed d13CAA fingerprints, can characterize niche differentiation in a highly dynamic marine system. Specifically, we tested the ability of d13CAA fingerprints to differentiate trophic niches among six functional groups and ten individual species in the Baltic Sea. We also tested whether fingerprints of the common zooplanktivorous fishes, herring and sprat, differ among four Baltic Sea regions with different biochemical conditions and phytoplankton assemblages...