The influence of light intensity on the vertical distribution and feeding of Japanese sand lance Ammodytes personatus larvae in Osaka Bay

Abstract

The vertical distribution and feeding of Japanese sand lance Ammodytes personatus larvae were examined based on the data obtained by 5 times of MTD depth-discrete net tows in Osaka Bay during daytime in January 1991, January and February 1992, and January 1993. Vertical distributions of light intensity, temperature, salinity, and copepods abundance were also measured. Sand lance larvae were abundant in 1-10 m depth (especially at 5 m depth), while the vertical profiles of temperature and salinity were not stratified. The value of fullness of gut of larvae (F.G.) declined with increasing depth, whereas the vertical distribution of copepods was not consistent with F.G. The data from laboratory experiments demonstrated that light intensity lower than 102 lx is insufficient for feeding of sand lance larvae (14 days after hatching, mean T.L.=6.8 mm) on rotifers. In the field, light intensity lower than 102 lx occurred at 15-20 m depth. These facts suggest that the distribution depth of sand lance larvae during daytime is strongly related to light intensity necessary for feeding.