The covefage of H. ovalis Hooker f. in a mixed Zostera meadow, Z. marina L. and Z. caespitosa Miki was investigated to examine the effect of interspecific competition on its distribution. The coverage of H. ovalis in the vicinity of Z. caespitosa was lower than that of Z. marina. This result suggested that the growth of H. ovalis was inhibited in Z. caespitosa meadow. The canopy height of Z. caespitosa was higher than that of Z. marina, which caused to light reduction in the vicinity of Z. caespitosa. Z. marina canopies decreased due to the feeding behavior of fish. Intercepting light by Z. caespitosa canopies migght be a factor responsible for the poor coverage of H. ovalis in the Z. caespitosa meadow.
