Effects of a predatory fish on the recruitment and abundance of Caribbean coral reef fishes

The importance of postrecruitment factors in determining assemblage structure of coral reef fishes is one of the most controversial topics in community ecology. To document the effects of predation on postlarval recruitment and the abundance of resident reef fishes, I manipulated small piscivorous fish on 12 model patch reefs located in uniform seagrass habitat in the U.S. Virgin Islands. Six reefs served as controls and 6 were used for predator removals. Weekly censuses were conducted for 2 mo before and after predator manipulations to document effects of removals. Removals of the squirrelfish Holocentrus adscensionis had a significant effect the recruitment and abundance of other species. During the first removal experiment, which was conducted during a peak recruitment period, high densities of squirrelfish depressed postlarval recruitment and juvenile abundance of grunts Haemulon spp., the most abundant species on the reefs. Following peak recruitment of grunts, a second squirrelfish removal resulted in increases in juvenile grunt abundance on predator-removal reefs. These results indicate the importance of postrecruitment factors, particularly predation, in structuring assemblages of coral reef fishes al a small spatial scale.