Abstract
Predation on eggs and larvae is a major factor influencing recruitment in marine fishes. The predator-prey relationship between the bay anchovy (Anchoa mitchilli) and the sea bream (Archosargus rhomboidalis) was examined in laboratory experiments. In the first series of experiments, 40-45 day old bay anchovy were provided two-day-old sea bream at densities of 0.1 to 2.0 liter('-1) in experiment durations ranging from 15 minutes to one hour. Predation rates increased from 0 to 44.5 prey h('-1) as larval sea bream density and experiment duration increased. For each experiment duration sigmoid functional response equations were fit. A series of experiments also was run to record predator behavior. The components of this behavior were then used to predict the number of sea bream larvae that would be consumed over the range of prey densities and experiment durations that were tested. Comparisons of prey consumption rates predicted by the functional response models, the behavior-based model and the experimental results revealed that the behavior-based model was the best predictor. Effects of prey age and condition on predation rate also were investigated. Sea bream eggs and larvae, 1 to 12 days old and reared at either high or low food densities, were fed to juvenile bay anchovies. Predation rates on eggs and yolk-sac larvae were lower than on first-feeding larvae (two-days-old) but decreased rapidly as larval age (and size) increased. Predation on larvae reared at low food densities did not decrease as rapidly with age as those of larvae reared at high food densities. The effect of an alternate prey, the copepod Acartia tonsa, on predation rates on fish larvae was examined. Although the presence of copepods reduced the predation rate on fish larvae, larval fish remained the preferred prey until ratios of copepods to larvae were approximately 40:1; at higher ratios bay anchovy juveniles switched from larvae to copepods. The model simulated both stochastically and deterministically the effects of predator density and size on larval cohort survival from hatching to 12 days of age and compared the importance of these effects with those experimentally investigated (prey density, prey age and food density offered to the prey). Predator density and size had the greatest effect on sea bream larvae mortality, followed by sea bream larvae density. Density of sea bream larvae food had the least effect. (Abstract shortened with permission of author.)