Surface scars on massive corals as evidence of previous crown-of-thorns starfish (Acanthaster planci) outbreaks on the Great Barrier Reef

In April 1985, massive corals on 5 mid-shelf reefs (Green Island, Feather Reef, John Brewer Reef, Rib Reef and Wheeler Reef) and 1 outer-shelf reef (Potter Reef) were surveyed for feeding scars caused by the crown-of thorns starfish (Acanthaster planci). Each reef, with the exception of Wheeler Reef, had experienced crown-of-thorns starfish outbreaks between 1962 and 1985.The survey involved 2 divers using SCUBA equipment swimming along randomly placed 200 m (approximately) sections of the reef perimeter. These swims were carried out in a slow meandering pattern covering as much of the reef slope as possible to a depth of approximately 12m. Various size classes of Diploastrea heliopora and a number of species of Porites were surveyed. Each individual colony encountered was recorded in 1 of 4 diameter categories and 1 of 4 proportional damage categories. The height difference between the scarred surface and the living surface was measured using a specially built PVC height gauge.Shallow cores (to 20 cm) were taken in the dead surfaces of some Porites colonies for the purpose of dating the dead surface. For each colony, measurements were made of total height, maximum diameter, the diameter perpendicular to the maximum diameter, and 5 independent measurements of the heights between adjacent 'steps', where a 'step' is the distance between adjacent dead or living and dead surfaces normal to the lower surface. The cores were bleached, sun dried and logged. The dead surfaces were then dated using a fluorescent banding technique. This study set out to examine the feasibility of eliciting reliable data on previous crown-of-thorns (Acanthaster planci) aggregations by dating surface scars on massive corals. The objectives of the surveys were to assess the level of damage caused by the most recent Acanthaster planci outbreaks on various size classes of Porites and Diploastrea, and to locate suitable specimens for detailed measurement and dating of scars. This research was a component of 'The Crown-of thorns Study', which was supported by the Commonwealth Community Employment Program'