Hemicentrotus pulcherrimus, Pseudocentrotus depressus, and Heliocidaris crassispina co-occur in the field in the temperate waters of southern Japan. Hemicentrotus pulcherrimus produces the bitter pulcherrimine in ripe ovaries in autumn and moves to shallow algal communities for reproductive success in winter. Ecological studies on the changes in community structure in northern Japan, which this sea urchin has invaded, are needed. In the past five years, some ecological knowledge of H. crassispina has been obtained. Insufficient information is available to characterize P. depressus, which is the most important species in the sea urchin fishery in southern Japan. Evaluation of the population size is needed.