[A-CG39] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG39-P05] Seasonal variation in feeding pressure of bivalves estimated from stable isotope ratios and its productivities in Midori River Tidal Flats, Japan

Nana Yamashita¹, *Tomohiro Komorita¹, Tatsuya Ozaki¹, Rikuto Honda¹, Noriyuki Ando² (1.Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, 2.Kumamoto Prefectural Fisheries Center)

Keywords:Feeding pressure, Density dependent effect, secondary production, tidal flats

Suspension-feeding bivalve communities often occur in high densities, reducing the abundance of primary producers. However, there is no comparison between primary production and food consumption throughout the year. In addition, growth of high-density bivalve communities decreases by density-dependent effect, but there are no comparisons of growth of natural bivalve populations over a wide area and over the same period. In this study, we conducted the distribution surveys and periodic surveys on Ruditapes philippinarum on Midori River tidal flats in Kumamoto, Japan. In distribution surveys, we measured clam abundance and biomass at 100 sites on the tidal flat in June and August, and the relationship between biomass and secondary production per individual. In the periodic surveys, we examined seasonal variation in the feeding impact by clams on each primary producer by primary production in the water column and bottom sediment, contribution rates of food source estimated from carbon-nitrogen stable isotope ratios, and feeding rates of R. philippinarum from secondary production. In the results, there was an upward convex relationship between individual secondary production and the biomass of the clam in the distribution survey. At the fixed station, the biomass was the highest however relatively low individual secondary production. In the periodic survey, clams depended on benthic microalgae more than 70% for their diet, and feeding pressure for microphytobenthos and phytoplankton was about 6 to 30 at the fixed station. The result suggests that high-density bivalve population has a significant impact on primary producers, and that high-density R. philippinarum population are supported by primary production of transported benthic microalgae.