Sulfur isotopic variations in soft tissues of five benthic animals from the reductive, tidal-flat sediments in northern Kyushu, Japan

The sulfur nutrition of five benthic animals living in or on reductive, tidal-flat sediments has been studied by using the sulfur isotopic signatures of their soft tissues. The mean 8345 values (+6.1parts per thousand to + 13.8parts per thousand, relative to the Canyon Diablo troilite reference) of these animals' tissues are lower than those of many common marine animals, which have values close to those of seawater sulfate-sulfur (+21parts per thousand). This indicates that these animals use a S-34-depleted sulfur source, which may be derived from bacterial sulfide in the sediments (less than -20parts per thousand). The animals that inhabit such sediments are adapted to an anoxic environment, where toxic hydrogen sulfide prevails. Due to the sulfide-rich habitat, benthic animals are expected to assimilate hydrogen sulfide directly during detoxification, or to prefer a diet which has a low 15345 signature. Variations in 8345 values of the sampled molluscs were fairly small, whereas migratory shrimp and fish tended to have larger variations, implying that migratory animals feed on diverse prey, while the molluscs feed on a common food, or their assimilative capacity for sulfide-sulfur does not vary among individuals. A gastropod inhabiting the surface of the reductive