SPATIAL VARIABILITY OF SIZE AND SEX IN THE TROPICAL CORALLIMORPHARIANRHODACTIS (=DISCOSOMA) INDOSINENSIS (CNIDARIA, CORALLIMORPHARIA) IN TAIWAN

Spatial variability in size and sex and sexual expression in the tropi cal corallimorpharian Rhodactis (= Discosoma) indosinensis Carlgren, 1 943, were studied at Wanlitung in southern Taiwan (120 degrees 41'E; 2 2 degrees 01'N). Rhodactis indosinensis formed three bowl-like aggrega tions in the study site. The mean body sizes of R. indosinensis indivi duals were significantly larger in the middle of an aggregation than a t 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 ha d significantly decreased in size and changed into males by eight mont hs later. When reproductively inactive polyps were transplanted from t he margin of the aggregation to the middle, they had increased in size and developed into males by eight months later. This positional separ ation of the sexes may result from different environmental factors whi ch exist between the middle and the margin of an aggregation.