ABSTRACT
Four types of Okinawan Echinometra mathaei live sympatrically around the intertidal zone. Their micro-habitats, however, are different among the four types. (Nishihira et al., 1991). In order to understand the difference in the micro-habits, comparative experimental investigations were done in respect to tolerance to low/high temperature, salinity changes and desiccation. The results are as follows. Tolerance to low temperature (3–5°C): Type C = Type D > Type B = Type A. Tolerance to high temperature (34–37°C): Type C > Type D > Type B > Type A. Tolerance to salinity changes: Type C > Type D > Type B > Type A. Tolerance to desiccation: Type C = Type D ?= Type B > Type A. These results show that the physiological differences among the four types are reflection of their habitat differences. The reproductive season of the four types was in summer. Although the patterns of the gonadal index fluctuation and percentage of the animals with mature gonads were different among the four types, there was a synchronous drop of gonadal index and percentage of mature gonads. This indicates that there was spawning in late-September in Type A, B, C and in mid-September in Type D. Since reciprocal cross-fertilization was successful between Type C and Type D in laboratory (Uehara and Shingaki, 1986), the difference in the spawning seasons of Type C and D may contribute to the reproductive isolation between these two types.
