抄録
The barren grounds, so-called “Isoyake” in Japanese, exist along the southwest coasts of Hokkaido, Japan. In the lsoyake area, the sea urchin, Strongylocentrotus nudus, dominates the rock bed, and results in disappearance of the kelp, Laminana religiosa, in all except shallow water refuge. In order to develop the technology of kelp afforestation in the Isoyake area, seasonal changes of selected environmental factors, e.g. water movement, temperature, vegetation and grazers were observed continuously during 1998-1999 in Oshoro Bay. The environments for establishment of kelp forest were summarized; sea urchins were removed to deeper zones by strong water movement and kelp buds were protected from overgrazing during winter. Destructive pressure of the sea urchins occurred on kelp beds with little strong water movement and rock bed for kelp (annual algae) was protected from being occupied by perennial algae during summer. The authors propose two methods to increase kelp forest in lsoyake areas: 1) seasonal control of excess grazing pressure using fences and, 2) adjustment of the sea bed depth with concrete blocks and stone which increased wave velocity and therefore reduced urchin grazing pressure.
