Size-selectivity of predatory reef fish on juvenile prey

For organisms with complex life cycles, the selective nature of predation during high mortality transitional periods is thought to play a large role in determining the community structure of later life stages. Here we investigate the dynamic nature of size selection by predators on coral reef fishes during the transitional early post-settlement period. A series of aquarium-based predator choice trials were used to examine the selective nature of 4 predatory fish species (Pseudochromis fuscus, Thalassoma lunare, Synodus dermatogenys and Cephalopholis microprion) known to be responsible for a majority of predation on early juvenile reef fish. A single species of common dam-selfish (Pomacentrus amboinensis) was used as a model prey species. Experiments were conducted on both naive settlement-stage individuals and more 'experienced' early juveniles in order to examine the changing dynamic of the interactions through time. The intensity and direction of size selection was found to differ significantly between predator species during both the settlement and early juvenile stage trials, with some species preferentially removing smaller individuals, while others removed larger individuals or were non-selective. Predator gape size played a limited role across all interactions, while selectivity was not found to differ with changing predator ontogeny. Our results highlight the complexity of predator-prey relationships within multi-species communities and suggest that no specific expression of a phenotypic trait holds a definitive survival advantage during all encounters. Instead, prey survival will in part be determined by the suite of predators present at the location of settlement, and how they interact with the available prey community.