Ecosystem size structure response to 21st century climate projection: large fish abundance decreases in the central North Pacific and increases in the California Current

Abstract

Output from an earth system model is paired with a size-based food web model to investigate the effects of climate change on the abundance of large fish over the 21st century. The earth system model, forced by the Intergovernmental Panel on Climate Change (IPCC) Special report on emission scenario A2, combines a coupled climate model with a biogeochemical model including major nutrients, three phytoplankton functional groups, and zooplankton grazing. The size-based food web model includes linkages between two size-structured pelagic communities: primary producers and consumers. Our investigation focuses on seven sites in the North Pacific, each highlighting a specific aspect of projected climate change, and includes top-down ecosystem depletion through fishing. We project declines in large fish abundance ranging from 0 to 75.8% in the central North Pacific and increases of up to 43.0% in the California Current (CC) region over the 21st century in response to change in phytoplankton size structure and direct physiological effects. We find that fish abundance is especially sensitive to projected changes in large phytoplankton density and our model projects changes in the abundance of large fish being of the same order of magnitude as changes in the abundance of large phytoplankton. Thus, studies that address only climate-induced impacts to primary production without including changes to phytoplankton size structure may not adequately project ecosystem responses.

Modelling the community size-spectrum: recent developments and new directions

“…spectrum models for ecosystem-based management Jacobsen et al, 2016) spectrum models for climatic projections Merino et al, 2012;Woodworth-Jefcoats et al, 2013) global ecosystem models (Maury, 2010;Carozza et al, 2016) Fig. 1.…”

“…Therefore, with warming the increasing food assimilation on the resource fails to completely balance the increasing biomass loss and dissipation of the fish community. Many community size-spectrum models use the Arrhenius equation to account for the impact of temperature on the community size-spectrum (Maury et al, 2007a;Andersen and Pedersen, 2009;Blanchard et al, 2012;Merino et al, 2012;Woodworth-Jefcoats et al, 2013). In addition to the impact of temperature on communities' intercepts (heights), the impact of temperature on the speed of the energy flow within communities may affect other properties, such as their resilience to perturbations or the intensity of trophic cascades (Andersen and Pedersen, 2009).…”

“…However, with their BiOeconomic mArine Trophic Size-spectrum (BOATS) model, Carozza et al (2016) attempt to link temperature variations to a change in the size structure of the resource spectrum. This coupling between resource and temperature is also indirectly introduced in models of the community size-spectrum applied to address climate and fisheries issues and forced by outputs of coupled ocean and biogeochemistry models (Maury, 2010;Woodworth-Jefcoats et al, 2013). In these models, the size distribution of the resource on which the fish communities are feeding is represented by distinct compartments for small and large phytoplankton and eventually small zooplankton or detritus.…”

Parameter uncertainty of a dynamic multispecies size spectrum model

“…Size spectrum models are increasingly being used to help us understand the structure of marine ecosystems and establish abundance baselines of marine communities and their responses to the potential effects of fishing and climate change (Benoît and Rochet 2004;Blanchard et al 2009Blanchard et al , 2012Law et al 2009;Jacobsen et al 2013;Maury and Poggiale 2013;Woodworth-Jefcoats et al 2013;Law et al 2015). Several approaches exist spanning a wide range of model complexity: simple community models, trait-based models, and more detailed multispecies models ).…”

The effects of seasonal processes on size spectrum dynamics

“…Dynamic size spectrum models are increasingly being used to understand structure and dynamics of marine systems, including the effects of fishing and climate change (Blanchard et al 2012;Woodworth-Jefcoats et al 2013) and inclusion of multispecies dynamics to address questions related to fisheries (Blanchard et al 2014;Spence et al 2016). However, so far, these models have simplified reproductive processes and focused on interannual changes in plankton levels.…”