抄録
Grazing behavior of sea urchin, Strongylocentrotus nudus, was observed experimentally on algae, Undaria pinnatifida. The sea urchin made rather active movement in the case without algae compared to the case with algae although the moving was done at random. The sea urchin showed active movement around sunset and sunrise. Daily moving distance was 5-15m and daily moving time was 10-15 hours for the sea urchin. Grazing effect on young Undaria was examind at various densities of sea urchin. In the case of initial density for young Undaria at about 24/m2, about 85% Undaria survived after a 20 days period at sea urchin density 0.19/m2 but only 2% Undaria survived after a 6 days period at sea urchin density 3.0/m2. These results may simply explain occurrence of desert rocks in the northeast Pacific coast of Japan.
