抄録
Carbon and nitrogen stable isotope ratios (δ13C and δ15N) are widely used to trace material flow in aquatic ecosystems. In this review, I first summarize the isotope values of potential food sources for benthic invertebrates reported from the Japanese coast. Then I give an example of food source analysis of benthic invertebrates in estuarine lagoons. The food sources exhibit distinctive δ13C values [riverine particulate organic matter (POM)/C3 plants, <-25‰; macroalgae, -25‰ to -13‰; marine POM, -20‰; microphytobenthos/seagrass, -20‰ to -10‰), although spatial and/or temporal variation are observed. In eutrophic estuaries, autochthonous phytoplankton comprise an important component of the estuarine POM pool. Most invertebrate species in the two studied lagoons utilize microalgae as their major diet item: suspension feeders depend mainly on microalgae in the water column (e.g., phytoplankton and re-suspended microphytobenthos), and deposit feeders and grazers depend mainly on benthic and epiphytic diatoms, respectively. Few species utilize river-derived detritus as their major food source. In the lagoons, the diet of the macrozoobenthos varies along two environmental gradients related to the biomass of autochthonous phytoplankton and distance from the river input (i.e., supply of river-derived materials). Stable isotope analyses are useful tools with which to trace material flow among terrestrial, estuarine, and marine ecosystems. In particular, they can help us to assess the food sources and feeding habits of benthic invertebrates in estuarine soft-bottoms．
