ECOSMO E2E v2.0: Generic modules of higher-trophic-level fish and macrobenthos functional groups compatible for two-way coupling to lower-trophic-level model hosts through FABM coupler

Abstract. The ECOSMO E2E v2.0 model includes functional-group-type fish and macrobenthos modules that can be two-way coupled to N(nutrient) P(phytoplankton) Z(zooplankton) D(detritus) type lower-trophic level (LTL) models. The model has been reprogrammed from the previous version, ECOSMO E2E v1.0, into independent fish and macrobenthos modules. This new version utilises the conceptual advantage of the Framework for Aquatic Biogeochemical Models (FABM), which provides an interface for coupling ecosystem models of diverse types. The coupling is exemplified by employing three different LTL models widely used in Copernicus Marine Services applications (ECOSMO, ERSEM, and ERGOM). The flexible design of the ECOSMO E2E v2.0 allows it to be coupled to LTL models and applied to regions beyond the example given in this paper. We present a proof of concept showing the two-way coupling of the E2E v2.0 with these LTL models, implemented in the central North Sea. We use a 1D water column model based on the General Ocean Turbulence Model for simulating the physics. The control simulation includes one macrobenthos functional group and two fish functional groups: a predominantly planktivorous group and a predominantly bentho-piscivorous group. The modelled annual cycle of fish production is consistent with the patterns observed in fish biomass estimates from the International Bottom Trawl Survey in the North Sea. We present a model intercomparison of simulations from coupling the E2E model with different LTL models to explore the ecosystem dynamics of the central North Sea. We assess the effects of two-way coupling between lower and higher trophic levels on plankton dynamics, nutrient cycling, and fish production. Two-way coupling induces stronger and more realistic top-down control on zooplankton and phytoplankton than simplified LTL closures, modifying both biomass and seasonal patterns. Macrobenthos enhance detritus remineralisation, leading to elevated bottom-layer nutrient concentrations. Fish production strongly depends on macrobenthos, and the impacts on LTL fields vary between models according to trophic structure. We show that differences in prey composition among different models further drive non-additive ecosystem responses that shape fish and macrobenthos production.