Low sulfur isotopic signatures (δ^<34>S) of macrozoobenthos from a brackish lagoon: contribution of microbially reduced sulfides

Stable sulfur isotope ratios (δ^S) of infaunal bivalves (Macoma contabulata, Nuttallia olivacea, and Ruditapes philippinarum) and polychaetes (Hediste spp.; consisted of H. atoka and H. diadroma) collected from two stations in the Gamo Lagoon (Japan) were determined to assess trophic pathways in highly reductive, estuarine soft-bottom habitats. The stations were characterized by distinctive sediment characteristics (Station A, sandy sediment with low sulfide content; Station B, muddy and sulfide-rich sediment). Soft tissues of the consumers exhibited much more depleted δ^S values (+3.2 to +12.1‰) than those of dissolved sulfate in the water column (+20.6 to +20.8‰). The value for each species was 1.6 to 5.3‰ lower at Station B than at Station A. These results suggest the assimilation of sulfides in the sediment (δ^S; -23.2 to -22.7‰) via microbial trophic pathways. In this lagoon, benthic microalgae and/or other microbes in the sediment are the most probable ^S-depleted food source for the consumers. Interspecies variations in δ^S values are explained by the different dietary contribution of the ^S-depleted diets versus ^S-enriched phytoplankton and are closely related to different feeding habits (i.e., surface-deposit feeding, facultative suspension feeding, and obligatory suspension feeding).論文Articl