Predator-prey relations at a spawning aggregation site of coral reef fishes

Predation is a selective force hypothesized to influence the spawning behavior of coral reef fishes. This study describes and quantifies the predatory activities of 2 piscivorous (Caranx melampygus and Aphareus furca) and 2 planktivorous (Melichthys niger and M. vidua) fishes at a coral reef fish-spawning aggregation site in Johnston Atoll (Central Pacific). To characterize preda- tor-prey relations, the spawning behavior of prey species was quantified simultaneously with mea- surements of predatory activity, current speed and substrate topography. The activity patterns of pis- civores was typical of neritic, daylight-active fish. Measured both as abundance and attack rates, predatory activity was highest during the daytime, decreased during the late afternoon, and reached a minimum at dusk. The highest diversity of spawning prey species occurred at dusk, when pisci- vores were least abundant and overall abundance of prey fishes was lowest. The abundance and predatory activity of the jack C. melampygus were positively correlated with the abundance of spawning prey, and therefore this predator was considered to have a flexible prey-dependent activ- ity pattern. By contrast, the abundance and activity of the snapper A. furca were generally not corre- lated with changes in abundance of spawning fishes. Spawning prey fishes were more common over substrates with complex topography, where refuges from piscivores were abundant. Piscivores dif- ferentially selected group-spawning species during spawning rushes over pair-spawning and non- spawning fishes. Overall attack rates by piscivores on adult spawning fishes were higher than by planktivores feeding on recently released eggs. The triggerfishes M. niger and M. vidua fed most actively at dusk and selected as prey those species of reef fishes that produced eggs of large size.