The crown-of-thorns starfish, Acanthaster planci, on the great barrier reef

• Authors: R. E. Reichelt;R. H. Bradbury;P. J. Moran
• Venue: Mathematical and Computer Modelling: An International Journal
• Year: 1990

Acanthaster planci, the crown-of-thorns starfish, is a large mobile starfish with a propensity for rapidly fluctuating populations, sometimes reaching very large numbers, on coral reefs of the Indo-Pacific region. The starfish eats hard corals, and large populations can cause rapid change in a coral reef by removing much of the live coral cover. The starfish life cycle includes a pelagic larval stage that lasts for about 2 weeks during the summer. The factors controlling the initiation and propagation of the outbreaks are not well-known. There are a range of hypotheses including physical effects, such as concentration of larvae by advective processes, and biological effects, such as change in nutrient levels influencing larval survivorship and changes in predator populations affecting the rate of population growth. Human impact on the system leading to changes in these parameters has also been suggested to have affected the size and frequency of starfish outbreaks. A range of modelling work on the Acanthaster phenomenon has been done, including non-spatial population models of the starfish and its predators and prey, spatial models of starfish aggregations and physical models of water circulation, i.e. larval transport models, at a range of spatial scales. Gaps in field data and modelling effort are identified. Some of the greatest problems lie in the following areas: •understanding the dynamics of adult starfish when they are at very low densities (non-outbreaking); •understanding the reproductive physiology of adult starfish with particular reference to range of conditions under which viable gametes are produced; •determining whether human activity has influenced the size and/or frequency of outbreaks over time scales of decades; •the processes regulating larval survivorship in the plankton and at the immediately post-settlement phase; •prediction of potential sites for recruitment, early detection of outbreak-size recruitment events and predicting the future course of starfish outbreaks after the initial recruitment has been detected.