Growth line analysis of Tapes (Ruditapes) phillipinarum showed that growth was stunted during the summer for individuals living in the higher tidal zone of the Kuzuma area at the Obitsu River mouth,wWhere Zostera beds are well developed. Shells from the Kaneda area exhibited rapid growth in the spring and early summer, and their growth during mid summer was greater than those in the Kuzuma area. Diatom assemblages in the gut of Tapes Phillipinarum were similar to the benthonic diatom assemblages at the same location, suggesting that the diet for Tapes phillipinarum was based mainly on the benthonic diatom fraction. δ13c values for the Tapes Phillipinarum ranged between -13 to -15‰ or -14 to -16‰ as estimated diet values, indicating that they have a mixed diet including benthonic diatoms (-19 to -16‰) , zooplankton (-15 to -17‰) and/or fragments from zostera beds (-11 to -15‰). Amual variations in the biomass, sampled in l m grid units, showed that the benthonic diatom fraction increased during the spring and summer, and that the quantity of benthonic diatoms in the Kaneda area was greater than in the Kuzuma area.
