Abstract
The sea urchin, Anthocidaris crassispina, is a common herbivore on shallow rocky coasts in the warm temperate region of Japan. Although, this sea urchin is known as the cause of continuing “barren sea urchin grounds” in the situation of high densities, there are limited data about its population dynamics. To understand the population dynamics, especially the causes for it reaching high densities, monitoring of A. crassispina was carried out at a boulder coast on Tachibana Bay, Nagasaki Prefecture, Japan, over a fourteen-year period. The densities of A. crassispina varied from 0.03 to 3.8 ind./m2, Their densities dramatically decreased in the years 1991, 1995, and 2003, and the causes must be the disturbances due to typhoons. After those decreases, their densities rapidly increased by the large recruitment and remained high as long as a typhoon did not strike. From these results, temporally occurring large recruitments and high survival rates except for typhoon were the causes to make A. crassispina high densities. Because the high recruitments only occurred in the years when a typhoon struck, the disturbance by the typhoon must have some positive effects on the recruitment of A. crassispina.
