Effects of mixed-species foraging groups on the feeding and aggression of juvenile parrotfishes

Many parrotfishes (Scaridae) co-occur in mixed-species aggregations as juve niles, but diverge in resource use and social structure as adults. Focal ob servations of three juvenile parrotfishes (Scarus coeruleus, Sparisoma auro frenatum, and Sparisoma viride) were conducted on inshore patch reefs in th e Florida Keys to determine how feeding and aggressive interactions vary wi th group participation. All three species spent more time in groups than al one, most often in groups of less than ten individuals. Feeding rates were significantly higher for S. viride when foraging in groups than when alone. All species fed most often from Halimeda, and overall diet composition was similar for fish whether feeding in groups or alone. The frequency of aggr essive interactions varied with group participation. Focal S. aurofrenatum were more aggressive when in groups than when alone, and both S. aurofrenat um and S. viride were attacked more often by damselfishes when they were al one than when in groups. In contrast, feeding rates, diet breadth, and aggr essive interactions of S. coeruleus were less affected by group participati on. Small mixed-species aggregations of coral reef fishes may be large enou gh for individuals to assume some of the benefits of group participation wh ile at the same time avoiding the costs of competition realized in larger g roups.