Gathering knowledge on mesopelagic ecosystems: insights from a parsimonious modelling approach

SEAPODYM-LMTL is the Lower (zooplankton) and Mid (micronekton) Trophic levels model of the Spatial Ecosystem And POpulation DYnamic Modeling framework. Currently, there is one zooplankton and 6 micronekton functional groups defined according to their vertical behavior and development times. The model is global and spatially explicit with transport described through a system of advection-diffusion equations. The vertical dimension is simplified into three layers -- epipelagic, upper and lower mesopelagic -- defined relatively to the euphotic depth. There are three vertically migrant and three non-migrant functional groups. The model is parsimonious with only a few parameters (6 for the zooplankton and 11 for the micronekton) that control the energy transfer efficiency from the primary production and the mortality and time of development that are linked to the water temperature. A data assimilation framework has been implemented to estimate those parameters.  We present briefly the latest results and future challenges of this model. They include the validation of vertical layer boundaries, the first zooplankton and micronekton parameters estimation using existing biomass observations, and the developments needed to use large global datasets of acoustic data.