Abstract
The distribution pattern of Pillucina pisidium in intertidal Zostera japonica beds at Uchinoura, Tanabe Bay, Wakayama, Japan was studied and compared with other environments. P. pisidium was distributed widely throughout the study area. The mean density (± SD) of P. pisidium was 1,892.9 ± 3,795.3 and 394.7 ± 265.1 individuals/m2 in the Z. japonica beds and the bare sandy bottom, respectively. The mean wet weight at each location was 32.4 ± 46.7 and 14.4 ± 13.8 g/m2, respectively. Despite the large differences between the two means, neither differed significantly between the two locations. The density and the wet weight of P. pisidium were each compared among the four areas: area facing the open ocean, area within an enclosed inlet, river mouth area and tidal flat area. Both were highest in the Z. japonica beds in the area facing the open ocean and lowest in the bare sandy bottom in the area within enclosed inlet. The mean shell length of P. pisidium was highest in the area facing the open ocean and lowest in the river mouth area. The density and the wet weight of P. pisidium were each both negatively correlated with the total organic carbon (TOC) and the silt-clay content in the sediment. These results show that P. pisidium is densely distributed in the intertidal zone, especially in Z. japonica beds, with low TOC and silt-clay contents. In conclusion, Z. japonica beds presumably play an important role in providing suitable habitats for P. pisidium.
