抄録
We studied the factors affecting decline of seaweed beds by unmanned aerial vehicle ( UAV) survey,
diving-survey and past findings along south-west coast of Hokkaido, Japan. It was considered that the
feeding damage by sea urchin, the lack of seaweed seed such as zoospore, germ and the shortage of
stable substrate were main factors of decline of seaweed beds, in addition to the increase in water
temperature and the lack of nutrient. In order to restore the seaweed beds, it is necessary to act not only
artificial formation of seaweed beds with stones and concrete blocks but also density management of sea
urchin, and transplantation of mother seaweed and seaweed seed. In addition, it is very important to
reduce the management cost of seaweed beds, define the enforcement standard and update the
techniques against environmental changes.