Seasonal changes in feeding activity of the sea urchin Strongylocentrotus nudus in Oshoro Bay, southwestern Hokkaido

Bimonthly observations of feeding activity of the sea urchin Strongylocentrotus nudus transplanted from coralline flats were carried out between September 1989 through July 1990 by providing the kelp Laminaria religiosa in Oshoro Bay, the Sea of Japan coast of Kokkaido, Japan. Feeding activity of the sea urchins varied chiefly with their annual reproductive cycle. Feeding activity was high in May when their gonads were in the growing stage, while feeding activity was low in September when gonads were in the pre-mature. The sea urchins could not feed in winter due to low temperature (ca. 5°C) and high wave action. It was suggested that the sea urchins on coralline flats should be transplanted to calm inlets before June and provided with the kelps as a diet in order to promote the growth of their gonads in short-period.