DIET SHIFT IN THE SAND SHRIMP CRANGON URITAI ALONG THE ESTUARY-MARINE GRADIENT

Spatial and temporal variations in the diet of Crangon uritai were examined using stable isotope and stomach content analyses. The sand shrimp and its potential prey were collected from Yura Estuary (3-5 m), shallow coast (5-10 m), and deep coast (30-60 m) stations of Tango Sea from April 2006 to February 2007. The measurements of the length (carapace and total lengths) and feeding habit (stomach content and stable isotope ratios) of C. uritai showed that this shrimp changed its diet during migrations between the estuary and marine environments. This species consumes a variety of food at the lower estuary: mysid Orientomysis japonica, small crustaceans particularly amphipod Melita hoshinoi, and bivalve Veremolpa micra. The abundant mysid O. japonica at the shallow coast and juveniles of unidentified bivalve species at the deep coast were the favored food throughout the year. The delta C-13 and delta N-15 variations in C. uritai confirmed the spatial and temporal diet shift in gut content composition as the sand shrimp grow and migrate along the estuary-marine gradient.