Carbon Sources of Sediment and Epifaunal Food Sources in a Tropical Mangrove Forest in North Sulawesi, Indonesia

The stable isotope ratios of nitrogen (delta N-15) and carbon (delta C-13) were applied in this study to analyze sediment carbon sources and primary food sources of epifauna in an oceanic mangrove forest in tropical North Sulawesi, Indonesia. Proportional contribution of mangrove-derived carbon to the food sources was compared among epifauna belonging to different feeding guilds. The sediment in the mangrove site with a depleted delta C-13 signature (-28.02 parts per thousand +/- 0.24 parts per thousand) mainly consists of mangrove-derived carbon. Analysis using Bayesian stable isotope mixing model in the R program shows that mangrove-derived carbon can dominate the food sources of a majority of the epifauna (11 out of the total 18 species), especially 2 sesarmid crabsParasesarma semperiandSesarmasp., crabEpixanthus dentatus, and snailsTerebralia sulcataandOptediceros breviculum, which belong to various feeding guilds. Mangrove-derived carbon has a proportional contribution to the food sources of fiddle crabTubuca coarctataand 3 littorinid snails (Littorariaspp.) close to that of suspended particulate organic matter. Three planktophagous bivalve species (Anadara antiquata, Anadarasp. andCallista erycina) were found to mainly feed on seagrass-derived materials. Mean proportional contributions of mangrove-derived carbon to the food sources were 50.15%, 59.60%, 46.20% and 27.58% for the carnivorous, omnivorous, phytophagous and planktophagous groups, respectively. The results suggest that mangrove-derived carbon can directly (viagrazing plant tissues) or indirectly (viadeposit feedings) make an important contribution to the food sources of epifauna in the oceanic mangrove forest where the allochthonous input of organic carbon is low.