Abstract
Abstract: Stable carbon and nitrogen isotopes were analyzed for 3 mangrove crabs, Uca vocans, Sesarma mederi, and Scylla serrata, and their food resources in a mangrove-fringed estuary in Thailand. Isotope compositions of mangrove biota ranged from -14.9 to -31.1‰ for δ13C, and from 2.9 to 12.5‰ for δ15N. The isotopic composition showed that U. vocans was a herbivore, feeding mainly on epiphytic algae and macroalgae, while S. mederi was a herbivore and/or detritivore, feeding heavily on mangrove leaves and detritus. The diet compositions of U. vocans and of S. mederi did not change as each species grew. On the other hand, the diet composition of S. serrata changed as it grew; small sizes were omnivorous, feeding probably on small crabs and plant materials, while medium and large sizes were predominantly carnivores, feeding on a variety of slow moving invertebrates such as worms, crabs and mollusks. Our results show that stable isotope analysis can be used as an alternative to conventional food web analysis approaches. The δ13C and δ15N values were useful source and trophic indicators, respectively.
