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

Abstract

Microphytobenthos (MPB) and mangrove detritus were labeled with a carbon isotope (13C) 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%) than P. erythrodactyla (110%), and A. beccarii (245%) became more enriched than T. inflata (12%). Addition of labeled mangrove detritus (211.5% final enrichment vs. 228.8% for controls) to sediment resulted in enrichment of P. erythrodactyla (hepatopancreas, 221.2% vs. 226.6% for controls), A. tridentata (hepatopancreas, 224.2% vs. 227.1%) and A. beccarii (221.0% vs. 225.1%) 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 13C-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.