Can amino acid carbon isotope ratios distinguish primary producers in a mangrove ecosystem?
BACKGROUND
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 (δ(13)C). In this study we explore whether patterns of δ(13)C values among amino acids (AAs) can provide an additional tool for resolving terrestrial and marine origins of carbon.


METHODS
Amino acid carbon isotope ratios (δ(13)C(AA)) 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 δ(13)C values of essential amino acids (δ(13)C(EAA)) 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 δ(13)C(EAA) values in addition to their differences in bulk δ(13)C values. Microbial mat samples and consumers (Crassostrea rhizophorae, Aratus pisonii, Littoraria sp., Lutjanus griseus) were most similar to marine producers. Patterns of δ(13)C(EAA) values for terrestrial producers were very similar to those described for other terrestrial plants.


CONCLUSIONS
The findings suggest that δ(13)C(EAA) 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.
Leibniz-Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany.
Thomas
T
Larsen
Matthew J
MJ
Wooller
Marilyn L
ML
Fogel
Diane M
DM
O'Brien
D000596:Amino Acids / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D059001:Aquatic Organisms / Q000737:chemistry / Q000378:metabolism; D001531:Belize; D002247:Carbon Isotopes / Q000032:analysis* / Q000737:chemistry; D016002:Discriminant Analysis; D017753:Ecosystem; D020387:Food Chain; D010944:Plants / Q000737:chemistry / Q000378:metabolism; D043982:Rhizophoraceae / Q000737:chemistry* / Q000378:metabolism; D012624:Seaweed / Q000737:chemistry / Q000378:metabolism
D000596:Amino Acids; D002247:Carbon Isotopes