ABSTRACT: A large-scale comparative study of 3 crown-of-thorns starfish (COTS) impacted reefs and 3 non-impacted (control) reefs in the central region of the Great Barrier Reef was undertaken. The principal objective was to investigate a long-term functional response of herbivorous fish to a potentially greater food resource in the form of increased abundances of turf algae on COTS affected reefs. Measurement of substratum cover and feeding ecology of Acanthurus nigrofuscus and Scarus frenatus was made on the windward reef slope of all reefs at a depth of 3 to 7 m. Significantly higher abundances of turf algae in comparison with live coral cover occurred on COTS affected reefs, while the opposite pattern occurred on non-affected reefs. However, no obvious difference was detected in the overall dietary composition of A. nigrofuscus, variability being more apparent at a temporal scale. There was no difference in feeding rates of roving herbivores (2 species) between impacted and control reefs. Furthermore, one component of the turf algal assemblage (thick turfs) showed increases in abundance in winter on affected reefs, while on non-affected reefs, thick turfs did not exhibit this seasonal pattern. A similar trend was observed for Cyanophyta (blue-green algae) in the dietary assemblage of A. nigrofuscus, although different sampling times and lack of detailed knowledge of epilithic algal community (EAC) composition made direct correlations difficult to infer. Whether this increased turf algal resource is prompting a numerical or growth response from herbivorous fishes is currently being investigated.

KEY WORDS: Herbivorous fish . Crown-of-thorns starfish . Functional response . Feeding ecology . Acanthurus nigrofuscus

Published in MEPS Vol. 132 (1996) on February 29
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996