Can amino acid carbon isotope ratios distinguish primary producers in a mangrove ecosystem?

RATIONALE The relative contribution of carbon from terrestrial vs. marine primary producers to mangrove-based food webs can be challenging to resolve with bulk carbon isotope ratios (d13C). In this study we explore whether patterns of d13C values among amino acids (AAs) can provide an additional tool for resolving terrestrial and marine origins of carbon. METHODS Amino acid carbon isotope ratios (d13CAA) were measured for several terrestrial and marine primary producers in a mangrove ecosystem at Spanish Lookout Caye (SLC), Belize, using gas chromatography-combustion-isotope ratio mass spectrometry. The d13C values of essential amino acids (d13CEAA) were measured to determine whether they could be used to differentiate terrestrial and marine producers using linear discriminant analysis. RESULTS Marine and terrestrial producers had distinct patterns of d13CEAA values in addition to their differences in bulk d13C values. Microbial mat samples and consumers (Crassostrea rhizophorae, Aratus pisonii, Littoraria sp., Lutjanus griseus) were most similar to marine producers. Patterns of d13CEAA values for terrestrial producers were very similar to those described for other terrestrial plants. CONCLUSIONS The findings suggest that d13CEAA values may provide another tool for estimating the contribution of terrestrial and marine sources to detrital foodwebs. Preliminary analyses of consumers indicate significant use of aquatic resources, consistent with other studies of mangrove foodwebs. Copyright (c) 2012 John Wiley & Sons, Ltd.