Reproduction and Life Cycle

         Stichopus chloronotus is known to reproduce asexually via transverse fission, as well as sexually via spawning and the resulting planktotrophic larvae (Harriott 1980). The life cycle is biphasic, meaning that it has a larval stage that is not similar to the adult stage. Asexual reproduction on the Great Barrier Reef occurs during winter (from May to July) and rates of fission seem to vary between reefs and zones within reefs (Uthicke 1997). They likely reach sexual maturity at one year of age, and spawning generally occurs during the summer season (Franklin 1980). It has been hypothesised that asexual reproduction is important for maintaining populations in a given area, whereas sexual reproduction is probably more important for inhabiting new areas and connecting populations (Conand et al. 2002). This is possible, because the larvae of S. chloronotus are plankotrophic and can spread quite far in comparison to adults (Conand et al. 2002).

Asexual Reproduction

         Rates of asexual reproduction vary greatly across habitats (Uthicke 1997). Generally asexual reproduction rates are much higher in near shore environments, and this could be due to a number of factors (Uthicke 2001a). One reason for this may be that nutrient inputs are often higher near shore than further from the shore, and asexual reproduction may be regulated by food availability (Uthicke 1997). Asexual reproduction may eventually result in some populations having highly skewed sex ratios, with at least one population found to be almost entirely male (Uthicke et al. 1999). Often populations with high asexual reproduction rates have very low genetic diversity and many genetically identical individuals (Uthicke et al. 1999). Studies of asexual reproduction in S. chloronotus have found that most individuals have gonads, which is a sign that even asexually reproducing individuals participate in sexual reproduction at some point too (Uthicke et al. 1999). Populations of S. chloronotus on the Great Barrier Reef also show signs of higher fission rates when they are closer to the mainland (Uthicke et al. 1999). Populations that are not undergoing high rates of asexual reproduction are often made up of larger individuals at a lower density (Conand et al. 1998). Body weight and densities seem to correlate with asexual reproduction, although it is not known whether small body weight is a cause or consequence of asexual reproduction (Uthicke et al. 1999). The combination of sexual and asexual reproduction seems to keep populations stable by balancing mortality rates (Uthicke 2001a). Sexual recruitment to areas of high asexual reproduction appears to be rare and this probably contributes to the low genetic diversity in some populations, compounding the issue of asexual reproduction (Uthicke et al.1999). It has been hypothesised that several central factors may lead to increased asexual reproduction. These factors are high food or energy availability alone, or in conjunction with habitat favouring small individuals (Uthicke 2001a), although no definitive conclusions have been made about what is most important.

Sexual Reproduction

          Sexual reproduction in Stichopus chloronotus is accomplished through broadcast spawning and the resulting plaktotrophic larvae (Harriott 1980). The larval life span is unknown, but it is estimated to be between 20 and 40 days, after which they settle and metamorphose into juveniles (Uthicke et al. 1999). Sexual maturity is generally reached by one year of age (Franklin 1980) or when the specimen weighs greater than 50 g (Hoareau and Conand 2001). Spawning typically takes place during the warm season, and excessively warm temperatures can affect the reproductive season by shifting or prolonging it (Hoareau and Conand 2001). Stichopus chloronotus specimens are either male or female, never hermaphroditic, and one can often find more males than females in a given population, although the cause of this is not yet known (Hoareau and Conand 2001).