Planula brooding and sex allocation in the coral Goniastrea aspera

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The plasticity of allocation between life history traits and of sex allocation in the sessile colonial coral Goniastrea aspera was examined by field survey and transplant experiment at two zones (lower intertidal and reef edge) of a fringing reef at Sesoko Island, Okinawa. A field survey showed that colony density, colony size, and polyp size were greater at the lower intertidal zone than at the reef edge zone. Mortality of transplanted fragments was higher at the reef edge zone than at the lower intertidal zone. These results suggest that the environment at the lower intertidal zone was more favorable for G. aspera. There was, however, no significant difference in the growth rate and reproductive effort of the transplanted fragments between the two zones. In contrast, sex allocation to testis was higher at the lower intertidal zone than at the reef edge zone in the transplanted fragments. Both spawning of gametes and brooding of planulae are known in G. aspera, and natural colonies at the lower intertidal zone brooded more planulae than those at the reef edge zone. Therefore, it is suggested that G. aspera produced more sperm at the habitat where number of brooded planulae was larger. It is considered that, in order to increase the possibility of cross-fertilization, G. aspera colonies exhibited the plasticity to allocate more resources to sperm where number of brooded planulae was larger.