The physical and chemical changes of sediment after rearing of the subcrenated ark shell Scapharca kagoshimensis for one week in a laboratory were examined. Surface sediments (layer 0-2 cm in depth) were used for the analysis of moisture content, loss on ignition, acid-volatile sulphide and redox potential. It was found that moisture content and loss on ignition did not show significant differences between the controls (initial and control groups) and the experimental groups (ark shell groups). The levels of acid-volatile sulphide in the experimental samples were not lower than those in the controls, and the redox potentials of the groups were not higher than those of the controls. These results suggest that the bioturbation activity of subcrenated ark shells has limited effect on bottom sediments.