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Abstract
The diminutive (<5.0 cm length) aspidochirotid sea cucumber Holothuria difficilis exhibits asexual propagation through transverse fission. The temporal pattern of fission was monitored in a population of H. difficilis at One Tree Island, Southern Great Barrier Reef (GBR), the first such study for this species. Asexual reproduction occurs year round with enhanced incidence of splitting in winter (May to September) when >50% of individuals were fission products. Inversely related to the temporal pattern of fission, the mean individual weight of H. difficilis increased from ca. 0.8 g in May to ca. 2.0 g in November. This doubling in individual weight over 6 months was largely due to regeneration. Gonads were only seen in large (4.0–5.0 cm length) H. difficilis. This species has a small egg (164 μm diameter). Although the population dynamics of H. difficilis at One Tree Island and elsewhere on the GBR is dominated by asexual clonal reproduction, the presence of gonads indicates that sexual reproduction does occur. Asexual reproduction of H. difficilis is compared with that documented for other tropical fissiparous aspidochirotids.
