Sensitivity of the fish community to different prey fields and importance of spatial-seasonal patterns

Summary

Different fish species and life stages depend not only on food abundance, but also on the size of planktonic prey, and (mis-)matches in time and space with suitable prey may influence the growth and survival of fish during their lifetime. We explored the sensitivity of a fish community to spatial-temporal differences in plankton prey fields. Data from 5 different lower trophic level models in the North Sea (Delft3D-WAQ, ECOHAM, ECOSMO, HBM-ERGOM and NORWECOM) were used to force the food web model OSMOSE which simulates spatially and temporally explicit higher trophic level fish dynamics. The estimated fish biomass levels were clearly and positively linked to zooplankton biomass, and sensitivity studies varying zooplankton biomass revealed that spatial and temporal variation in zooplankton drives the differences in absolute fish biomass. More zooplankton size bins resulted in less fish biomass due to size-based foraging constraints (i.e. a smaller proportion of bins falls within the prey size range of a fish, resulting in a decrease in available food). Nevertheless, we found a consistent response across models in the relative biomass contribution and spatial patterns of selected fish groups, indicating low sensitivity of the composition of the simulated fish community to the zooplankton input. The robustness of the outcome will aid model acceptance and implementation into management action. Relative, not absolute, changes in primary and secondary production may therefore be used to study the effects of management scenarios on fish communities.