Disentangling diverse responses to climate change among global marine ecosystem models

Ryan F Heneghan,Jason D Everett,Jeroen Steenbeek,Marta Coll,Julia L Blanchard,Jan Volkholz,Nicolas Barrier,Tyler D Eddy,Anthony J Richardson,Derek P Tittensor,Travis C Tai,Colleen M Petrik,Olivier Maury,Didier Gascuel,Hubert Du Pontavice,Cheryl S Harrison ,Cm Bulman ,Maite Erauskin‐Extramiana ,Juliano Palacios‐Abrantes ,William W L Cheung ,Jérôme Guiet ,José A Fernandes-Salvador ,Phoebe A Woodworth‐Jefcoats ,Eric D Galbraith

doi:10.1016/j.pocean.2021.102659

Abstract

Climate change is warming the ocean and impacting lower trophic level (LTL) organisms. Marine ecosystem models can provide estimates of how these changes will propagate to larger animals and impact societal services such as fisheries, but at present these estimates vary widely. A better understanding of what drives this inter-model variation will improve our ability to project fisheries and other ecosystem services into the future, while also helping to identify uncertainties in process understanding. Here, we explore the mechanisms that underlie the diversity of responses to changes in temperature and LTLs in eight global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP). Temperature and LTL impacts on total consumer biomass and ecosystem structure (defined as the relative change of small and large organism biomass) were isolated using a comparative experimental protocol. Total model biomass varied between −35% to +3% in response to warming, and -17% to +15% in response to LTL changes. There was little consensus about the spatial redistribution of biomass or changes in the balance between small and large organisms (ecosystem structure) in response to warming, an LTL impacts on total consumer biomass varied depending on the choice of LTL forcing terms. Overall, climate change impacts on consumer biomass and ecosystem structure are well approximated by the sum of temperature and LTL impacts, indicating an absence of nonlinear interaction between the models’ drivers. Our results highlight a lack of theoretical clarity about how to represent fundamental ecological mechanisms, most importantly how temperature impacts scale from individual to ecosystem level, and the need to better understand the two-way coupling between LTL organisms and consumers. We finish by identifying future research needs to strengthen global marine ecosystem modelling and improve projections of climate change impacts.

Highlights

Water temperature and primary production play critical roles in marine processes
All models projected a decline of globally averaged consumer biomass in the Temperature Change simulation, with the exception of APECOSM (Fig. 2a)
The trajectory of global biomass change was switched in the lower trophic level (LTL) Change simulation from negative change to positive in comparison with the warming only simulation

Summary

Introduction

Water temperature and primary production play critical roles in marine processes. Higher temperatures accelerate reaction rates, with consequences ranging from the molecular to ecosystem scale, while primary production provides the fundamental source of energy for almost all marine life (Brown et al, 2004; Chavez et al, 2011). There has been a recent proliferation of spatially-explicit marine ecosystem models that simulate higher trophic level biomass and ecosystem structure at regional and global scales, driven by output from climate-ocean-biogeochemical models (Tittensor et al, 2018). These ecosystem models differ significantly in their design, level of complexity and implementation, reflecting different choices for how to represent fundamental marine ecosystem processes, as well as a diversity of model purpose and scope. Identifying sources of structural uncertainty in ensemble projections can point to critical weaknesses and thereby accelerate model improvement

Methods

Results

Discussion

Conclusion