A modeling study of the effects of size- and depth-dependent predation on larval survival

The form of the predation pressure experienced by larval stages of marine invertebrates is largely unknown. However, it is believed that the type, timing and rate of larval predation are critical in determining recruitment to adult populations. In this study, a time and depth-dependent model of the growth and behavior of larvae of the Eastern oyster, Crassostrea virginica, was used to investigate the effects of different forms of size-and depth-dependent predation on larval survivorship. The simulated larval survival for a cohort experiencing size-dependent predation showed that the greatest percent of the cohort survived to competent settlement size when the predation pressure decreased with increasing larval size. Additional simulations that included different types of depth-dependent predation showed that the interaction between vertical larval migration behavior and predation determined the percent of the cohort that survived to settlement size. The simulated distributions show that a higher percent of larvae survive when the predation pressure is concentrated in the surface waters. A lower percent of larvae survive to competent settlement size when the predation pressure is concentrated near the bottom. The different forms of size-and depth-dependent predation result in variations in the number of larvae present in the water column during each larval development stage. Thus, different forms of predation impact the number of larvae available for dispersal throughout the marine environment. These results have important implications concerning the exchange of genetic material between populations.