How best to include the effects of climate-driven forcing on prey fields in larval fish individual-based models

If we intend to examine the indirect effects of climate variability on the vital rates of key marine species, climate-induced changes in the spatial-temporal dynamics of prey must be resolved. Recently, structured population simulations have been coupled to ecosystem (nutrient-phytoplankton-zooplankton-detritus, NPZD) models to derive prey fields. Model-derived prey fields offer advantages (e.g. increased spatial-temporal coverage, direct links to climate forcing). In contrast, employing structured population simulations (e.g. stage-based copepod models) has several disadvantages, including the lack of realistic utilization of phytoplankton production, the absence of boundary condition data and a vastly increased coupled model complexity. To avoid the pitfalls limiting the utility of structured population models, we argue for a more simple approach for obtaining a size-structured prey field using NPZD model estimates of bulk zooplankton carbon and in situ zooplankton abundance-at-size data. The approach was developed to obtain prey fields for a larval fish individual-based model (IBM), but the method may offer wide applicability. Moreover, our approach greatly simplifies the coupling of NPZD models and larval fish IBMs and is an example of the reduction in model complexity that will be critical to the development of end-to-end ecosystem models that use, for example, a rhomboid approach to examine trophodynamic climate impacts at basin scales.