Exploring the role of movement in determining the global distribution of marine biomass using a coupled hydrodynamic – Size-based ecosystem model

• We have developed a global marine ecosystem model that resolves phytoplankton, zooplankton and fish.
• Plankton dynamics are simulated as part of an Earth System Model.
• Fish dynamics are simulated offline, using a simple size-based food web model.
• The abundance and distribution of contemporary fish biomass is estimated, and found to be highly sensitive to movement.
• Our work contributes to efforts to model upper trophic marine species at a global scale with mechanistic ecosystem models.

Modeling the dynamics of marine populations at a global scale – from phytoplankton to fish – is necessary if we are to quantify how climate change and other broad-scale anthropogenic actions affect the supply of marine-based food. Here, we estimate the abundance and distribution of fish biomass using a simple size-based food web model coupled to simulations of global ocean physics and biogeochemistry. We focus on the spatial distribution of biomass, identifying highly productive regions – shelf seas, western boundary currents and major upwelling zones. In the absence of fishing, we estimate the total ocean fish biomass to be ∼2.84×109∼2.84×109 tonnes, similar to previous estimates. However, this value is sensitive to the choice of parameters, and further, allowing fish to move had a profound impact on the spatial distribution of fish biomass and the structure of marine communities. In particular, when movement is implemented the viable range of large predators is greatly increased, and stunted biomass spectra characterizing large ocean regions in simulations without movement, are replaced with expanded spectra that include large predators. These results highlight the importance of considering movement in global-scale ecological models.