ABSTRACT: Density, biomass and fish-habitat correlations were estimated for selected species of herbivorous fish on crown-of-thorns starfish (COTS) impacted and control reefs in the central Great Barrier Reef. The objective was to investigate a long-term numerical and/or biomass response to increased food availability (algal turfs) on COTS affected reefs. Out of 14 variates investigated, 2 showed evidence of a numerical response on COTS affected reefs. Importantly, total number of individuals and total biomass showed no response. Instead, a negative effect (i.e. higher abundances on control reefs) was detected for Zebrasoma scopas, although this was attributable to very high abundances on one of the non-impacted reefs (Coil). Density of Siganus corallinus was higher on COTS impacted reefs; however, this was not greater than variability over time. On COTS affected reefs, there was a negative correlation of herbivorous fish with thick turf algal abundance and a positive correlation with live coral cover, whereas on non-affected reefs, there were a similar number of positive and negative correlations with thick turf algae and live coral. Additionally, a distinct cross-shelf trend in length frequency of Acanthurus nigrofuscus was observed. Differences in food availability, wave energy and intraspecific competition were hypothesized to be important factors in this observed distribution.

KEY WORDS: Herbivorous fish . Coral reefs . Crown-of-thorns starfish . Numerical response . Fish-habitat correlations . Acanthurus nigrofuscus . Natural disturbance

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