Analysls of Denslty and Distribution Patterns In Chrysophrys auratus (Pisces: Sparidae) Within a Reef Environment: An Experimental Approach

Density estimates for the fish Chrysophrys auratus (Forster) were obtained w i t h ~n a shallow subtidal reef system in North-eastern New Zealand by transect counts.The mean density in 6 reef areas during December 1978 varied from 2.8 to 139 individuals 500 rx2.The time of day at which counts were made did not influence our estimates of density.A further series of replicated counts in 7 reef areas from December 1978 to April 1980 revealed large seasonal differences in density.These differences resulted from a summer influx of first year (0') C. auratus into the reef system.Peak densities of O + individuals exceeded 250 ind.500 in some reef areas.In autumn and winter the density of 0' individuals dropped to less than 5 ind.500 m-' This influx of O+ individuals was recorded in both 1979 and 1980.Older individuals showed no seasonal trends in density.During summer a positive exponential relationship was detected between the percentage cover of the turfing alga Corallina offjclnalis and the density of 0' Chrysophrys auratus (n = 11, r = 0.79).These fish fed In the Corallina turf.Experimental removal of replicated 25 m-2 areas of C. officionalis resulted in a 50 to 70 % decline in fish feeding rates.At adjacent uncleared control sites there was no significant change in feeding rate, but aggressive interactions between 0' fish showed an increase ranging from 58 to 217 %.These results suggest that 0' C. auratus defend local feeding sites over areas of Corallina turf.