Utilization of terrestrial organic matter by the bivalve Corbicula japonica estimated from stable isotope analysis

Carbon and nitrogen isotopic ratios in tissue of the bivalve corbicula (Corbicula japonica) and particulate organic matter (POM) were measured along a salinity gradient in the Kushicla Estuary, Japan. The bivalve exhibited a gradual isotopic enrichment from the uppermost estuarine site (delta(13)C = -24.8parts per thousand and delta(15)N = 8.6parts per thousand) to the marine site (delta(13)C = -16.1parts per thousand and delta(15)N = 11.8parts per thousand). Using the concentration-weighted mixing model, the bivalves' food source is estimated from the isotope values for the bivalves and POM from terrestrial plants, marine phytoplankton and benthic microalgae. The results indicated that the contributions of benthic micro algae and phytoplankton were small, while terrestrial particulate matter is significantly important for the corbicula diet, although the contribution varies among sampling sites.