The effect of coupling higher trophic level modules on the dynamics of three models of lower trophic level

This study demonstrates a proof of concept for two-way coupling between generic higher-trophic-level (HTL) biomass models —fish and macrobenthos— and three lower-trophic-level (LTL) models used by Copernicus Marine Services. The ECOSMO E2E model is a functional group type ecosystem model with fish and macrobenthos within a standard NPZD (nutrient–phytoplankton–zooplankton–detritus) framework. By reprogramming fish and macrobenthos into independent modules (ECOSMO-E2E v2.0), we can now couple them flexibly with multiple LTL models of similar class as ECOSMO. We utilise the Framework for Aquatic Biogeochemical Models (FABM) to couple ECOSMO-E2E v2.0 with three LTL models: ECOSMO, ERSEM, and ERGOM. Our test setup focuses on a 1D water column in the central North Sea, simulated with the General Ocean Turbulence Model (GOTM). For simplicity, we ignore horizontal fish movement in our experiments. The model simulated fish biomass compares well with the observed annual fish biomass from International Bottom Trawl Survey estimates. Additionally, we explore how two-way coupling affects the LTL biomass dynamics in different model configurations. Our results emphasize the necessity of including HTL components in marine ecosystem models. Two-way coupling not only simulates realistic fish and macrobenthos fields but also provides spatially and temporally explicit closure terms to LTL model fields.