Location influences size-selective predation on newly settled reef fish

Abstract

Demersal fish usually settle to established fish assemblages that include suites of gape-limited predators, whose compositions vary among locations. We investigated the extent to which predation was size-selective on a species of newly settled coral reef fish, the damselfish Pomacentrus amboinensis (Bleeker 1868), among 3 lagoonal sites on 1 reef. The 3 sites at Lizard Island, Great Barrier Reef, Australia, differed in species composition and relative abundance of predators. Fish at the end of their larval phase were caught in light traps and tattooed for individual recognition. They were then paired so that there was a 1 mm difference between partners, and placed on small patch reefs at the base of the 3 shallow lagoonal sites. Large individuals survived significantly better than small individuals in 1 out of 3 sites. One site displayed the reverse trend, even though non-significant, and the third site showed no evidence of selection. Selection was strongest at the site where predators of small reef fishes were in highest densities and water currents were strongest. Strong water currents appeared to emphasise size-related differences in swimming ability and increase the vulnerability of small fish at this site. Our results suggested that the occurrence of size-selection for this species at settlement will depend on the composition of the predator assemblage and prevailing environmental conditions; these both interact with the performance attributes of prey, and all 3 variables may be location-specific.