RESPONSE OF HERBIVOROUS FISHES TO CROWN-OF-THORNS STARFISH ACANTHASTER PLANCI OUTBREAKS .2. DENSITY AND BIOMASS OF SELECTED SPECIES OF HERBIVOROUS FISH AND FISH-HABITAT CORRELATIONS

Density, biomass and fish-habitat correlations were estimated for sele cted species of herbivorous fish on crown-of-thorns starfish (COTS) im pacted and control reefs in the central Great Barrier Reef. The object ive was to investigate a long-term numerical and/or biomass response t o increased food availability (algal turfs) on COTS affected reefs. Ou t of 14 variates investigated, 2 showed evidence of a numerical respon se on COTS affected reefs. importantly, total number of individuals an d total biomass showed no response. Instead, a negative effect (i.e. h igher abundances on control reefs) was detected for Zebrasoma scopas, although this was attributable to very high abundances on one of the n on-impacted reefs (Coil). Density of Siganus corallinus was higher on COTS impacted reefs; however, this was not greater than variability ov er time. On COTS affected reefs, there was a negative correlation of h erbivorous fish with thick turf algal abundance and a positive correla tion 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 l ength frequency of Acanthurus nigrofuscus was observed. Differences in food availability, wave energy and intraspecific competition were hyp othesized to be important factors in this observed distribution.