Ensemble Projections of Future Climate Change Impacts on the Eastern Bering Sea Food Web Using a Multispecies Size Spectrum Model

Jonathan C P Reum,Albert J Hermann,Kirstin K Holsman,Anne B Hollowed,André E Punt,Julia L Blanchard,Amanda Faig,Kerim Aydin,Alan C Haynie,Wei Cheng

doi:10.3389/fmars.2020.00124

Abstract

Characterization of uncertainty (variance) in ecosystem projections under climate change is still rare despite its importance for informing decision-making and prioritizing research. We developed an ensemble modeling framework to evaluate the relative importance of different uncertainty sources for food web projections of the eastern Bering Sea (EBS). Specifically, dynamically downscaled projections from Earth System Models (ESM) under different greenhouse gas emission scenarios (GHG) were used to force a multispecies size spectrum model (MSSM) of the EBS food web. In addition to ESM and GHG uncertainty, we incorporated uncertainty from different plausible fisheries management scenarios reflecting shifts in the total allowable catch of flatfish and gadids and different assumptions regarding temperature-dependencies on biological rates in the MSSM. Relative to historical averages (1994–2014), end-of-century (2080–2100 average) ensemble projections of community spawner stock biomass, catches, and mean body size (±standard deviation) decreased by 36% (±21%), 61% (±27%), and 38% (±25%), respectively. Long-term trends were, on average, also negative for the majority of species, but the level of trend consistency between ensemble projections was low for most species. Projection uncertainty for model outputs from ∼2020 to 2040 was driven by inter-annual climate variability for 85% of species and the community as a whole. Thereafter, structural uncertainty (different ESMs, temperature-dependency assumptions) dominated projection uncertainty. Fishery management and GHG emissions scenarios contributed little (

Highlights

Anthropogenic climate change is expected to have significant impacts on ocean biogeochemistry, primary and secondary production, and the distribution and productivity of higher trophic level species (Doney et al, 2012; Mora et al, 2013; Pecl et al, 2017)
We show that aggregate community SSB, catches, and mean body weight, are likely to decrease by 2090 but ensemble projections for the majority of individual species were a mixture of increasing and decreasing trends
Structural uncertainty dominated long-term (2060–2100) projections for many aggregate and species-level variables, which contrasts with global climate model ensemble projections of physical variables

Summary

Introduction

Anthropogenic climate change is expected to have significant impacts on ocean biogeochemistry, primary and secondary production, and the distribution and productivity of higher trophic level species (Doney et al, 2012; Mora et al, 2013; Pecl et al, 2017). Models of varying complexity have been used to project potential impacts on community structure, size composition, and fishery catches, and to evaluate management strategies under climate change Efforts to quantify uncertainty in climate-forced ecological projections have lagged, which limits their utility for informing ecosystem approaches to management and decisionmaking (Payne et al, 2015; Cheung et al, 2016). Regional studies have evaluated structural uncertainty using model ensembles that consist of different formulations of species interactions (Gårdmark et al, 2013) or biogeochemical processes (MacKenzie et al, 2012; Meier et al, 2012; Niiranen et al, 2013). Scenario uncertainty could encompass implementations of different policies, for instance, that impact fisheries regulations or coastal land use patterns. Ensemble modeling is widely used in weather and climate forecasting (e.g. Murphy et al, 2004; Berliner and Kim, 2008), but remains underutilized with respect to climate-driven ecosystem projections (Cheung et al, 2016)

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Conclusion