AIMS Crown-of-Thorns Starfish

Crown-of-thorns starfish Questions & Answers

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REPRODUCTION

26. How does the crown-of-thorns starfish reproduce?

The crown-of-thorns starfish reproduces sexually. Females shed eggs into the water which are fertilised by sperm released from nearby males (see Fig. 12). Starfish need to be examined internally to determine their sex. As yet there are no data to indicate the relationship between rates of fertilisation and the density of spawning starfish. The rate of fertilisation of eggs would be expected to increase with greater numbers of spawning starfish and/ora decrease in the distance between them.

Figure 12
A male crown-of-thorns starfish spawning in the field. The bell-shaped posture normally is adopted by both male and female starfish during spawning.

Fertilisation may be synchronised amongst small aggregated groups of starfish since a chemical compound (pheromone) has been isolated from spawning females which is thought to induce males close by to release sperm. Synchronisation and aggregation of spawning starfish are likely to be extremely important in promoting the increased fertilisation of eggs and the settlement of large numbers of larvae. Recent studies have shown that a large female starfish (about 40 cm in diameter) may produce about 60 million eggs during one spawning season.

The spawning season for the crown-of-thorns starfish on the Great Barrier Reef is from about November to January when water temperatures are highest. It is not known whether the starfish spawn continuously, in discrete bursts, or only once during this period. Furthermore, there is no information on the variability in spawning of different aggregations around the same reef. That is; Do all starfish on the same reef generally spawn in the same period? Or are they like spot fires going off at different times and locations on the one reef? Knowledge of these processes (especially the size of the larval clouds which are produced during spawning) would provide useful information to assist scientists attempting to understand the dynamics of dispersal and settlement of larvae of the crown-of-thorns starfish.

Unlike some species the crown-of-thorns starfish is not known to reproduce asexually. That is, an entire new starfish cannot form from just a small part (eg. arm) of its body.

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