The effects of Acanthaster planci predation on populations of two species of massive coral

Abstract

Diploastrea heliopora and Leptoria phrygia were rare on 7 reefs of the central Great Barrier Reef unaffected at time of survey by major population outbreaks of the crown of thorns starfish Acanthaster planci, their population densities being 67.3 ha⁻¹ and 42.1 ha⁻¹ respectively. D. heliopora attained larger sizes (350–400 cm max. diam.) than did L. phrygia (150–200 cm). Recruits (up to 20 cm max. diam.) numbered 1.3 ha⁻¹ and 6.3 ha⁻¹ respectively. For D. heliopora 87% of colonies were >50cm and 48% were > 100 cm max. diam. For L. phrygia 30% of colonies were > 50 cm and 9% were > 100 cm. Ca 90% of colonies of both species were undamaged or only slightly damaged. On 7 reefs that had experienced major starfish outbreaks, their densities were 53.3 ha⁻¹ and 12.2 ha⁻¹ respectively. Recruits were again rare (2.2 ha⁻¹ and 1.1 ha⁻¹ respectively). The population size structure of D. heliopora was similar to that on the unaffected reefs but only 18% of L. phrygia colonies were > 50 cm max. diam. and none was > 100 cm. Whereas 60% of D. heliopora colonies exhibited little or no damage, more than half the surviving L. phrygia colonies had > 1/3 colony damage. D. heliopora is resistant to A. planci predation but L. phrygia is not. We suggest that L. phrygia is typical of the vast majority of massive corals the devastated populations of which will take decades to centuries to recover.