Field measurement of feeding and movement rates of the crown-of-thorns starfish Acanthaster planci (L.)

Abstract

The feeding and movement rates of Acanthaster planci (L.) were measured by monitoring tagged individuals on Davies and Little Broadhurst Reefs in the central Great Barrier Reef. Measurements were made on four occasions between October 1987 and October 1988. New samples ( n = 20) of starfish were monitored each time. Feeding rates in summer (October samples) were about twice that in winter (June sample) but were significantly depressed following the summer spawning season (January sample). Large adult A. planci (⩾ 40 cm) killed a mean 161 cm 2 of coral·d −1 in winter and 357–478 cm 2·d −1 in summer. Smaller starfish (20–39 cm) killed 66 cm 2·d −1 and 155–234 cm 2·d −1 in winter and summer, respectively. Movement rates of A. planci averaged 2.8 m·d −1 at Davies Reef (low density starfish/high coral cover) and 10.3 m·d −1 at Little Broadhurst Reef (high density/low coral). Within the Davies Reef population movement rates were highest in areas of low coral cover and large starfish were more mobile than smaller ones. These accurate measurements of feeding rate of A. planci on the Great Barrier Reef for the first time have important implications for management of coral reefs. Thus, modelling starfish density, coral cover and feeding rate indicates that A. planci populations can fluctuate by several orders of magnitude without causing noticeable coral damage. A threshold level of 1000 A. planci · km −2 (10·ha −1)is proposed as the limit above which depletion of live coral cover on reefs will occur. Control of starfish to much below this level would be little benefit.