Spatial variability in size and sex and sexual expression in the tropical corallimorpharian Rhodactis (= Oiscosoma) indosinensis Carlgren, 1943, were studied at Wanlitung in southern Taiwan (120°41'E; 22°01'N). Rhodactis indosinensis formed three bowl-like aggregations in the study site. The mean body sizes of R. indosinensis individuals were significantly larger in the middle of an aggregation than at the margin. Females were located in the middle of each aggregation, and males were scattered around the margins. When mature females were transplanted from the middle of the aggregation to the margin, they had significantly decreased in size and changed into males by eight months later. When reproductively inactive polyps were transplanted from the margin of the aggregation to the middle, they had increased in size and developed into males by eight months later. This positional separation of the sexes may result from different environmental factors which exist between the middle and the margin of an aggregation.
Sex change, Size variability
