An updated end-to-end ecosystem model of the Northern California Current reflecting ecosystem changes due to recent marine heat waves

Abstract

The Northern California Current is a highly productive marine upwelling ecosystem that is economically and ecologically important. It is home to both commercially harvested species and those that are federally listed under the U.S. Endangered Species Act. Recently, there has been a global shift from single-species fisheries management to ecosystem-based fisheries management, which acknowledges that more complex dynamics can reverberate through a food web. Here, we have integrated new research into an end-to-end ecosystem model (i.e., physics to fisheries) using data from long-term ocean surveys, phytoplankton satellite imagery paired with a vertically generalized production model, a recently assembled diet database, fishery catch information, species distribution models, and existing literature. This spatially-explicit model includes 90 living and detrital functional groups ranging from phytoplankton, krill, and forage fish to salmon, seabirds, and marine mammals, and nine fisheries that occur off the coast of Washington, Oregon, and Northern California. This model was updated from previous regional models to account for more recent changes in the Northern California Current (e.g., increases in market squid and some gelatinous zooplankton such as pyrosomes and salps), to expand the previous domain to increase the spatial resolution, to include data from previously unincorporated surveys, and to add improved characterization of endangered species, such as Chinook salmon (Oncorhynchus tshawytscha) and southern resident killer whales (Orcinus orca). Our model is mass-balanced, ecologically plausible, without extinctions, and stable over 100-year simulations. Ammonium and nitrate availability, total primary production rates, and model-derived phytoplankton time series are within realistic ranges. As we move towards holistic ecosystem-based fisheries management, we must continue to openly and collaboratively integrate our disparate datasets and collective knowledge to solve the intricate problems we face. As a tool for future research, we provide the data and code to use our ecosystem model.

Marine heatwaves disrupt ecosystem structure and function via altered food webs and energy flux

“…Leveraging time series abundance data of 361 taxa (grouped into 86 functional groups, see Supplementary Data 1) from six long term surveys, diet information from a new diet database, and previous modeling efforts, we built two food web networks (pre- and post-onset of MHWs, hereafter pre-MHW and MHW) using an extension of the popular Ecopath ecosystem modeling framework (Ecotran 36,37,39 ). Our comparative analysis of these two food web networks shows that lower trophic level biomass and energy pathways experienced greater changes after onset of MHWs than upper trophic levels (Figs.…”

“…It has long been assumed that gelatinous prey are trophic dead ends, due to their low energy content 42 , although advances in more recent methods suggest that gelatinous prey might be more important than previously believed 43 . In the Northern California Current, it appears that pyrosomes are not consumed as readily as jellies 36,41,44 . This may be because they are more difficult to digest, offer lower energy content, or remain novel to the food web such that predators have not yet responded.…”

“…2, 3). Yet, despite this increase in abundance, commercial fisheries in the U.S. have not shown any change in jack mackerel landings [PacFIN, http://pacfin.psmfc.org/] 36 , which might suggest jack mackerel is an under-utilized resource that can support substantial fishery landings. Adapting harvest strategies to account for changes in ecosystem structure could represent a significant step towards climate-resilient fisheries.…”

“…We accomplished this with small changes to the diet matrix of the pre-MHW model to move pressure off of phytoplankton (see supplemental preMHW_DietChanges.csv). See previous food web models for more information about data used, model-building, and mass-balancing procedures 36,37 .…”

“…Here, we compare two end-to-end ecosystem food web models of the Northern California Current representing time periods immediately preceding (1999-2012) and following (2014-2022) the onset of a prolonged period of thermal anomalies (Fig. 1a) marked by at least two well-described marine heatwaves [36][37][38] to make inferences about ecosystem-level changes that have occurred since the onset of these recent extreme warming events. We estimate the effects of MHWs on the energy flow between producers and consumers across scales from individual functional groups to the entire food web network.…”