Quantitative contribution of primary food sources for a mangrove food web in Setiu lagoon from East coast of Peninsular Malaysia, stable isotopic (δ¹³C and δ¹⁵N) approach

Applying stable isotopes to explore insight into the food web structure in marine ecology have been increasing recently. Tropical mangrove forest, one of the vital marine habitats, has been received intensive attentions in the field. However, there is still controversy about the important roles of primary carbon sources provide to consumers in the ecosystem. In this study, stable isotopic (¹³C and ¹⁵N) ratios were used to determine food web and to estimate quantitative contributions of primary carbon sources for invertebrates and four fish species in the tropical mangrove from Setiu lagoon, Malaysia using the Bayesian mixing model (SIAR). The primary nutrient sources showed δ¹³C values ranging from −18.7 to −31.1‰ and δ¹⁵N from 2.5 to 3.8‰. The wide range of the isotopic composition of consumers (−26.1 to −18.4‰ and 4.3 to 10.2‰ for δ¹³C and δ¹⁵N, respectively) indicated that a variety of carbon sources provided to the intertidal mangrove food webs. Mixing model outputs indicated that mangrove-derived carbon was important food sources for gastropod, Littoraria carinifera, Neritina violacea, N. coromandeliana, N. cornucopia, Cerithdea quadrata, and sesarmid crab, while the benthic microalgae (BMA) mainly fueled to Cerithidea djadjariensis, Cerithium coralium, fiddler crab and the crenate crab Thalamita crenata. Two Scylla species relied largely on BMA and SOMs. Bivalve species mainly assimilated phytoplankton-derived carbon, however, the difference of stable carbon isotope ratios among these bivalve species might relate to feeding selectivity or a small portion of BMA contributed to their diets. The model also resulted that BMA and seston sources might be important to the studied fish species rather than mangrove-derived carbon sources. However, further studies are needed to elucidate insight into the fish food web, and to determine whether there is ecological connectivity between habitats inside and outside of the lagoon.