Relationships between size and reproductive output in the crown-of-thorns starfish

Studies of pre-spawning crown-of-thorns starfish Acanthaster (COTS) collected from the Great Barrier Reef showed average female gonad mass of 16 % (±8 s.d.) and for males 12 % (±6 s.d.). In females up to 34 % of the body mass could be devoted to gonad. Based on these data, we also derived relationships between diameter gonad weight and reproductive output for both male and female starfish. Due to the large average size of individuals in this study (39.2 ± 0.3 cm diameter), the potential oocyte production of females was between 29 and 38 million eggs per season for average size starfish. The highest oocyte production was estimated to be >100 million oocytes, which is the highest ever recorded for an individual female starfish. These relationships imply that the largest Acanthaster reported may have fecundities greater than 200 million eggs per season. The gonad mass of male starfish is similarly high, and in combination with measured concentrations of sperm exuded from the gonopore (5.2 × 1010 ml−1) the sperm output of an average sized male is estimated to be 1.1 × 1013 sperm. This high level of sperm production may be a key factor allowing this species to sustain itself and even initiate outbreaks at low population densities. We suggest that management targets for maintaining COTS at pre-outbreak thresholds should take account of starfish size as well as starfish density, especially given extreme reproductive potential of large starfish in pre-outbreak populations.