The relationship between the abundance of juvenile Japanese littleneck Ruditapes philippinarum and the bottom condition and water movement in Mikawa Bay [Japan]

"The relationship between distribution of juvenile Japanese littleneck Ruditapes philippinarum and physical environment, especially bottom condition and water current, was investigated in west Mikawa-bay. Sediment samples were collected by Smith-Mclntyre grab. These samples were sieved with 1mm mesh screen and bivalves were picked up and measured shell length. The oxydised layer and the reduced layer of substratum were observed throughout the transparent corer, and then upper 10cm of cored sediments were used for particle size analysis. The water current of the bay was analyzed by the three dimensional hydrodynamic model. The juveniles always distributed more abundantly in the mouth of Yahagi river than in other stations. The thickness of oxidized layer in bottom sediment was more than 20cm in the river mouth, whereas most of other station showed less than 10cm. The landward water current in bottom and lower strata of the river was observed according to the numerical analysis. Thus, it was considered that the bottom condition and the water movement contributed to the survival of juveniles and the entrainment of planktonic larvae to the habitat, respectively."