Isotope enrichment in mangrove forests separates microphytobenthos and detritus as carbon sources for animals

Microphytobenthos (MPB) and mangrove detritus were labeled with a carbon isotope ((13)C) in separate experiments to quantify their contributions to the nutrition of major faunal components within a mangrove forest. Within 7 d of MPB labeling, crabs (Parasesarma erythrodactyla and Australoplax tridentata) and foraminifera (Ammonia beccarii and Trochammina inflata) were enriched. A. tridentata became more enriched (e. g., hepatopancreas, 522 parts per thousand) than P. erythrodactyla (110 parts per thousand), and A. beccarii (245 parts per thousand) became more enriched than T. inflata (12 parts per thousand). Addition of labeled mangrove detritus (-11.5 parts per thousand final enrichment vs. -28.8 parts per thousand for controls) to sediment resulted in enrichment of P. erythrodactyla (hepatopancreas, -21.2 parts per thousand vs. -26.6 parts per thousand for controls), A. tridentata (hepatopancreas, -24.2% vs. -27.1 parts per thousand) and A. beccarii (-21.0 parts per thousand vs. -25.1 parts per thousand) within 7 d. Compartment modeling showed that MPB contributed 93% of the nutrition for A. tridentata and 33% of the nutrition for P. erythrodactyla and that MPB provided more nutrition to A. beccarii (14%) than to T. inflata (minimal). There was a complementary estimated contribution of mangrove detritus to the diets of P. erythrodactyla (80%, A. beccarii (97%), and A. tridentata (minimal), although these estimates should be viewed with caution, due to low initial enrichment and the apparent short temporal persistence of (13)C-labeled detritus added to sediments. T. inflata was barely enriched in either experiment and may rely on a carbon source not considered. The combination of isotope labeling and compartment modeling is relatively new to ecology and shows potential for revealing differences in the patterns of use of algae and macrophyte detritus by consumers.