2000. Effects of a predatory site-attached fish on abundance and body size of early post-settled reef fishes from Gorgona Island

The effects of predation on early post-settlement stages of reef fishes were examined by comparing abundance and body size of fishes settled on standard coral units (SCU) with and without individuals of the small grouper Serranus psittacinus. Because of the strong site-attached behavior of this predator, adults of S. psittacinus remained associated with SCUs allowing an accurate control of its presence. Three of six analyzed species settled in lower abundance on SCUs with the predator, while the abundance of the remaining three species did not differ between experimental and control SCUs. In some cases the lower settlement in the predator treatment was due to predation by S. psittacinus, but in others such pattern can be explained by the avoidance of microhabitats with predators by settling larvae and by the simultaneous effect of S. psittacinus and transient predators. The absence of predatory effects on settler abundance of the remaining three species can be explained by anti-predatory traits (e.g. venomous fin spines, body toxins, and cryptic appearance). Because adaptations in morphology and behavior to avoid predation are common among reef fishes, predation as a factor controlling population replenishment, local abundance, and community structure of reef fishes cannot be suggested as a general rule. Conspecific juveniles of S. psittacinus had a larger body size in the predator treatment supporting the “bigger is better ” hypothesis. However, because most species exhibited low levels of variability in body size, size-dependent predation generally would have little effect on survivorship