Parameterization and tuning of the Bay of Biscay Atlantis model v1

Abstract. This paper describes the parameterization and calibration of an end-to-end Atlantis model for the Bay of Biscay, characterising spatially the structure and functioning of the ecosystem. The Bay of Biscay is considered rich in terms of ecological diversity and different oceanographic events such as coastal upwelling, coastal run-off and river plumes, and seasonal currents, take place in the area. These features, in addition to the different pressures caused by human activities and management criteria, demand for concurrent modelling of all the characteristics of the Bay of Biscay ecosystem in order to improve our understanding of the system and its functioning. The modelled area is 145 970 km² and was divided into 36 spatial polygons, each with multiple vertical layers. The model was composed by 54 functional groups, ranging from primary producers to top predators. Our results highlighted the importance of lower trophic levels to the pelagic system and how the trophic interactions among phytoplankton and zooplankton groups impact the structure of the ecosystem. The results also demonstrate the importance of having accurate and precise data for biological processes and showed the need of further study in the age-specific data such as biomass and weight distribution per age and diet interactions between juvenile and adult fish stages. Overall, the Bay of Biscay Atlantis model has been shown to be a tool that has the potential to improve our understanding of the spatial functioning of the Bay of Biscay ecosystem that will help establishing management measures of human activities.