Abstract
The barren ground, so-called Isoyake in Japanese, maintained at south-west coasts of the Sea of Japan,
Hokkaido, Japan. In the Isoyake area, the sea urchin, Strongylocentrotus nudus, dominate on the bed rock, and
occurrence of the kelp, Laminaria religiosa, was limited in the refuge at shallower zones. Fisheries in the coasts
had large problem that the sea urchin could not grow up to the commercial size with inadequate foods. To develop
the kelp forest technology in the Isoyake area, seasonal change of some environmental factors, water movement,
water temperature, vegetation, and distribution of grazer, were observed continuously during 1998 to 1999 in
Oshoro Bay. Environments for occurrence of kelp forest were characterized ; the sea urchins took refuge in
deeper zone from strong water movement and buds of the kelp were protected from over grazing pressure during
Winter. Moreover destructive pressure of the sea urchin occurred on kelp bed with no strong water movement
and rock bed for kelp (amual algae) was protected from occupied of peremial algae during summer. We proposed
two methods to increase the kelp forest in Isoyake area. 1) Seasonal control of excess grazing pressure using
fence. 2) Adjust the depth with block and stone to remove the urchin by increasing velocity.
