Abstract

To determine the effect of asexual reproduction by transverse fission on the population structure of holothurians, ensities and individual weights of Holothuria atra (JÄÄger,1833)and Stichopus chloronotus (Brandt, 1835)were measured over a 26-month period on near-shore reefs of the Great Barrier Reef. Densities of H.atra (0.01—0.69 individuals m ^–2 )and S. chloronotus (0.11—1.67) did not increase during periods of intense asexual reproduction, and the density on each reef remained relatively stable.The effect of fission was clearly visible in the weight —frequency distributions of both species. The average individual wet weight in each population declined (H. atra from 105/134 g to 64/94 g in two respective populations;S. chloronotus from 128/302 g to 82/190 g in two respective populations) with the onset of fission in early winter, and more individuals in the weight range of fission products were found. The biomass followed the seasonal trend of the average weights for both species, with minimum values in winter. A conceptual model based on these and previous findings identified five possible factors (mortality, habitat stability, optimum individual size, food availability, larval supply) involved in promoting or repressing transverse fission, and the model indicated the consequences for the population.