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Unidad de excelencia María de Maeztu CEX2019-000940-M

Significance Nuclear conflict poses the chilling prospect of triggering abrupt global cooling, and consequently, severely reduced crop production. However, the impacts on marine fisheries are unknown. If agricultural yields fall on land, could we turn to the sea instead? Here, we show that agricultural losses could not be offset by the world’s fisheries, especially given widespread overfishing. Cold temperatures and reduced sunlight would decrease the growth of fish biomass, at worst as much as under unmitigated climate change. Although intensified postwar fishing could yield a small catch increase, dramatic declines would ensue due to overharvesting. However, effective prewar fisheries management would create a substantial buffer of fish in the ocean, greatly increasing the oceans’ potential contribution during a global food emergency., Nuclear war, beyond its devastating direct impacts, is expected to cause global climatic perturbations through injections of soot into the upper atmosphere. Reduced temperature and sunlight could drive unprecedented reductions in agricultural production, endangering global food security. However, the effects of nuclear war on marine wild-capture fisheries, which significantly contribute to the global animal protein and micronutrient supply, remain unexplored. We simulate the climatic effects of six war scenarios on fish biomass and catch globally, using a state-of-the-art Earth system model and global process-based fisheries model. We also simulate how either rapidly increased fish demand (driven by food shortages) or decreased ability to fish (due to infrastructure disruptions), would affect global catches, and test the benefits of strong prewar fisheries management. We find a decade-long negative climatic impact that intensifies with soot emissions, with global biomass and catch falling by up to 18 ± 3% and 29 ± 7% after a US–Russia war under business-as-usual fishing—similar in magnitude to the end-of-century declines under unmitigated global warming. When war occurs in an overfished state, increasing demand increases short-term (1 to 2 y) catch by at most ∼30% followed by precipitous declines of up to ∼70%, thus offsetting only a minor fraction of agricultural losses. However, effective prewar management that rebuilds fish biomass could ensure a short-term catch buffer large enough to replace ∼43 ± 35% of today’s global animal protein production. This buffering function in the event of a global food emergency adds to the many previously known economic and ecological benefits of effective and precautionary fisheries management.

Although zooplankton are the primary energy pathway from phytoplankton to fish, we understand little about how climate change will modify zooplankton communities and their role in marine ecosystems. Using a trait-based marine ecosystem model resolving key zooplankton groups, we assess climate change impacts on zooplankton community composition and implications for marine food webs globally. We find that future oceans favour food webs increasingly dominated by carnivorous (chaetognaths, jellyfish and carnivorous copepods) and gelatinous filter-feeding zooplankton (larvaceans and salps). By providing a direct energetic pathway from small phytoplankton to fish, the rise of gelatinous filter-feeders largely offsets the increase in trophic steps between primary producers and fish from declining phytoplankton production and increasing carnivorous zooplankton. However, our results indicate that future fish communities face not only reduced carrying capacity from falling primary production, but also lower quality diets as environmental conditions increasingly favour gelatinous zooplankton.

16 pages, 6 figures, 3 tables, supplementary data https://doi.org/10.1016/j.pocean.2021.102659.-- Code and data availability: The experimental protocol in this paper has no code associated with it. Forcing data from CMIP5 used for the protocol, and the FishMIP model outputs presented in this paper are available on the ISIMIP servers (https://www.isimip.org/), 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, JDE was funded by Australian Research Council Discovery Projects DP150102656 and DP190102293. MC, JS, NB and OM received financial support by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 817578 (Triatlas project). CH received funding from the Open Philanthropy Project. NB and OM also acknowledge the support of the French ANR project CIGOEF (grant ANR-17-CE32-0008-01). DPT acknowledges funding from the ISI-MIP project to support a workshop on this topic, and the Jarislowsky Foundation. EDG received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 682602, BIGSEA). RFH was funded by the Spanish Ministry of Science, Innovation and Universities through the Acciones de Programación Conjunta Internacional (PCIN-2017-115). MC acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S) to the Institute of Marine Science (ICM-CSIC). TDE acknowledges funding from the ISIMIP project to support a workshop on this topic and the Fisheries and Oceans Canada Atlantic Fisheries Fund. All authors declare no conflict of interest with respect to this study. JAFS received funding from the European Union’s Horizon 2020 FutureMARES project (#869300).

In a nuclear war, bombs targeted on cities and industrial areas would start firestorms, injecting large amounts of soot into the upper atmosphere, which would spread globally and rapidly cool the planet. The soot loadings would cause decadal disruptions in Earth’s climate, which would impact food production systems on land and in the oceans. In 1980s, investigations of nuclear winter impacts on global agricultural production and food availability for 15 nations, but new information now allows us to update those estimates. Recently, several studies analyzed changes of major grain crops and marine wild-catch fisheries for different scenarios of regional nuclear war using sophisticated models. However, the impact on the total food supply available to humans is more complex. Here we show that considering all food sources and potential adaptation measures, such as using animal feed directly for humans, famine would result for most of Earth even from a war between India and Pakistan using less than 3% of the global nuclear arsenal. We look at the climate impacts from a range of scales from regional to global nuclear war, and estimate the total amount of food calories available in each nation, including crops, livestock, and fisheries, for each year following a nuclear holocaust. Our findings quantify the global indirect impacts of nuclear war away from target areas, and demonstrate the need to prevent any scale of nuclear war.

It has long been hypothesized that aquatic biomass is evenly distributed among logarithmic body mass size-classes. Although this community structure has been observed locally among plankton groups, its generality has never been formally tested across all marine life, nor have its impacts by humans been broadly assessed. Here, we bring together data at the global scale to test the hypothesis from bacteria to whales. We find that biomass within most order of magnitude size-classes is indeed remarkably constant, near 1 Gt wet weight (1015 grams), but that bacteria and whales are markedly above and below this value, respectively. Furthermore, human impacts have significantly truncated the upper one-third of the spectrum. Size-spectrum theory has yet to provide an explanation for what is possibly life’s largest scale regularity.One Sentence SummaryHuman activities have fundamentally altered one of life’s largest scale patterns; a global power law size distribution spanning bacteria to whales.

Description, Human activity has altered one of life’s largest-scale patterns: a global power law size distribution from bacteria to whales., It has long been hypothesized that aquatic biomass is evenly distributed among logarithmic body mass size classes. Although this community structure has been observed regionally, mostly among plankton groups, its generality has never been formally tested across all marine life over the global ocean, nor have the impacts of humans on it been globally assessed. Here, we bring together data at the global scale to test the hypothesis from bacteria to whales. We find that biomass within most order of magnitude size classes is indeed remarkably constant, near 1 gigatonne (Gt) wet weight (1015 g), but bacteria and large marine mammals are markedly above and below this value, respectively. Furthermore, human impacts appear to have significantly truncated the upper one-third of the spectrum. This dramatic alteration to what is possibly life’s largest-scale regularity underscores the global extent of human activities.

22 pages, 5 figures, 1 table, supplementary information https://doi.org/10.1038/s41558-021-01173-9.-- Data availabilityAll standardized forcing variables from the ESMs are available at https://doi.org/10.48364/ISIMIP.575744.1; all outputs from the MEMs are available via ISIMIP (https://www.isimip.org/gettingstarted/data-access/).-- Code availabilityAll code used to analyse simulations is available at https://github.com/Fish-MIP/CMIP5vsCMIP6, Projections of climate change impacts on marine ecosystems have revealed long-term declines in global marine animal biomass and unevenly distributed impacts on fisheries. Here we apply an enhanced suite of global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish-MIP), forced by new-generation Earth system model outputs from Phase 6 of the Coupled Model Intercomparison Project (CMIP6), to provide insights into how projected climate change will affect future ocean ecosystems. Compared with the previous generation CMIP5-forced Fish-MIP ensemble, the new ensemble ecosystem simulations show a greater decline in mean global ocean animal biomass under both strong-mitigation and high-emissions scenarios due to elevated warming, despite greater uncertainty in net primary production in the high-emissions scenario. Regional shifts in the direction of biomass changes highlight the continued and urgent need to reduce uncertainty in the projected responses of marine ecosystems to climate change to help support adaptation planning, This work was supported by the Jarislowsky Foundation (D.P.T.), the Natural Sciences and Engineering Research Council of Canada Discovery Grant programme (D.P.T., H.K.L., T.D.E., W.W.L.C., J.P.-A. and V.C.); Australian Research Council (ARC) Discovery Projects DP170104240 (J.L.B. and C.N.), DP190102293 (J.L.B., C.N., A.J.R., J.D.E. and D.P.T.) and DP150102656 (J.D.E.); the European Union’s Horizon 2020 research and innovation programme under grant agreements 817578 (TRIATLAS) (M.C., J.S., L.S., O.M., L.B., Y.-J.S., N.B. and J.R.), 869300 (FutureMARES) (J.A.F.-S.,Y.-J.S. and M.C.) and 862428 (MISSION ATLANTIC (J.A.F.-S, Y.-J.S. and M.C.); the Spanish National Project ProOceans (PID2020-118097RB-I00) (M.C. and J.S.); the Open Philanthropy Project (C.S.H.); the United Kingdom Research and Innovation (UKRI) Global Challenges Research Fund (GCRF) One Ocean Hub (NE/S008950/1) (K.O.-C. and L.S.); the Simons Foundation (nos. 54993, 645921) (G.L.B.); the Belmont Forum and BiodivERsA under the BiodivScen ERA-Net COFUND programme (SOMBEE project, ANR-18-EBI4-0003-01) (Y.-J.S. and N.B.); the MEOPAR Postdoctoral Fellowship Award 2020–2021 and the Ocean Frontier Institute (Module G) (A.B.-B.); the French ANR project CIGOEF (grant ANR-17-CE32-0008-01) (O.M., L.B. and J.R.); the California Ocean Protection Council Grant C0100400, the Alfred P. Sloan Foundation and the Extreme Science and Engineering Discovery Environment (XSEDE) allocation TG-OCE170017 (D.B. and J.G.); the National Oceanographic and Atmospheric Association (NA20OAR4310441, NA20OAR4310442) (C.M.P.). M.C. acknowledges the Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S) to the Institute of Marine Science (ICM-CSIC)

Size-based ecosystem modeling is emerging as a powerful way to assess ecosystem-level impacts of human- and environment-driven changes from individual-level processes. These models have evolved as mechanistic explanations for observed regular patterns of abundance across the marine size spectrum hypothesized to hold from bacteria to whales. Fifty years since the first size spectrum measurements, we ask how far have we come? Although recent modeling studies capture an impressive range of sizes, complexity, and real-world applications, ecosystem coverage is still only partial. We describe how this can be overcome by unifying functional traits with size spectra (which we call functional size spectra) and highlight the key knowledge gaps that need to be filled to model ecosystems from bacteria to whales.

Unidad de excelencia María de Maeztu CEX2019-000940-M Despite their critical role as the main energy pathway between phytoplankton and fish, the functional complexity of zooplankton is typically poorly resolved in marine ecosystem models. Trait-based approaches-where zooplankton are represented with functional traits such as body size-could help improve the resolution of zooplankton in marine ecosystem models and their role in trophic transfer and carbon sequestration. Here, we present the Zooplankton Model of Size Spectra version 2 (ZooMSSv2), a functional size-spectrum model that resolves nine major zooplankton functional groups (heterotrophic flagellates, heterotrophic ciliates, larvaceans, omnivorous copepods, carnivorous copepods, chaetognaths, euphausiids, salps and jellyfish). Each group is represented by the functional traits of body size, size-based feeding characteristics and carbon content. The model is run globally at 5° resolution to steady-state using long-term average temperature and chlorophyll a for each grid-cell. Zooplankton community composition emerges based on the relative fitness of the different groups. Emergent steady-state patterns of global zooplankton abundance, biomass and growth rates agree well with empirical data, and the model is robust to changes in the boundary conditions of the zooplankton. We use the model to consider the role of the zooplankton groups in supporting higher trophic levels, by exploring the sensitivity of steady-state fish biomass to the removal of individual zooplankton groups across the global ocean. Our model shows zooplankton play a key role in supporting fish biomass in the global ocean. For example, the removal of euphausiids or omnivorous copepods caused fish biomass to decrease by up to 80%. By contrast, the removal of carnivorous copepods caused fish biomass to increase by up to 75%. Our results suggest that including zooplankton complexity in ecosystem models could be key to better understanding the distribution of fish biomass and trophic efficiency across the global ocean.

Zooplankton are the linchpin of the marine ecosystem, serving as the main energy pathway from primary producers to higher trophic level organisms, such as fish. Despite their critical role, zooplankton are typically oversimplified or ignored altogether in current marine ecosystem models, and we have limited understanding of how variation in the zooplankton affects energy transfer from phytoplankton to fish. An alternative to resolving the enormous taxonomic diversity of the zooplankton is to focus on functional traits, such as body size, feeding strategy and body composition, since these are the factors that determine an organism’s fitness in any given environment, and their role in the marine food web. Body size is the master trait, however zooplankton exhibit vast diversity in other important functional traits, such as predator-prey mass ratio (PPMR) and body composition. Energy transfer through the marine food web depends on these traits, so to better understand the role of zooplankton in marine ecosystems any realistic representation of the zooplankton must incorporate this diversity. In this thesis, I use recent developments in size spectrum modelling, coupled with the extensive literature on zooplankton physiology and size-based feeding characteristics, to explore the structure of the zooplankton community across the global ocean, and their role in mediating energy from phytoplankton to fish.We begin by reviewing the development of size spectrum modelling, particularly focusing on the last 10 years and the recent innovations in size spectrum modelling. In particular, we review the development of functional size spectrum modelling, which allows size spectrum models to resolve multiple groups by their functional traits, and how this has been used for various higher trophic level groups, especially fish. The focus on fish means that the unique dynamics of the plankton have been overlooked in these models. We use the functional size spectrum framework to demonstrate how changes in the size-based feeding behaviour of the zooplankton community affects the productivity of higher trophic levels, and their resilience to fishing pressure: the higher the PPMR of the zooplankton community, the more productive and resilient the fish community. However, higher zooplankton PPMR also increases the temporal variability of the zooplankton and fish communities.The most common modelling assumption with respect to the zooplankton community is that its composition does not change across environmental gradients. However, there is strong evidence that the composition of the zooplankton community is not static, but varies across the global ocean, and this will have implications for how energy moves from phytoplankton to fish. We explore the role of functional traits in structuring the zooplankton community across the global ocean. We develop a functional size spectrum model of the marine ecosystem, which resolves the body size ranges, size-based feeding characteristics and carbon content of nine of the most abundant zooplankton groups (heterotrophic flagellates and ciliates, larvaceans, omnivorous and carnivorous copepods, chaetognaths, euphausiids, salps and jellyfish). Zooplankton community composition emerges from the model across global environmental gradients, based on the functional traits of the nine groups. Across the global ocean, the emergent distributions of the zooplankton community broadly agreed with empirical observation and theory. Heterotrophic flagellates and ciliates, salps, larvaceans, carnivorous copepods and chaetognaths were a larger component of zooplankton biomass in oligotrophic waters, omnivorous copepods were prevalent everywhere, and euphausiids and jellyfish dominated the zooplankton in eutrophic waters.Traditionally, eutrophic systems are hypothesised to be more efficient at transferring energy from phytoplankton to fish, compared to oligotrophic systems. We use the zooplankton- resolved functional size spectrum model to test this hypothesis, and assess the role of zooplankton composition in mediating transfer efficiency from phytoplankton to fish. Changes in the composition of the zooplankton lead to eutrophic waters supporting three times more fish biomass per unit phytoplankton, compared to oligotrophic waters. However, we also found that salps and larvaceans – despite their low carbon content – were critical in oligotrophic waters, providing a direct energy pathway from the small pico-phytoplankton which dominates in oligotrophic regions, to planktivorous fish. Without salps and larvaceans, total fish biomass was up to 50% lower in oligotrophic waters, and 17% lower across the global ocean.The work presented here demonstrates the power of the functional traits to explain global patterns in the zooplankton community. The zooplankton-resolved size spectrum model developed here is a step forward in trait-based modelling, and our understanding of the role of zooplankton in the marine ecosystem.

© 2017 Everett, Baird, Buchanan, Bulman, Davies, Downie, Griffiths, Heneghan, Kloser, Laiolo, Lara-Lopez, Lozano-Montes, Matear, McEnnulty, Robson, Rochester, Skerratt, Smith, Strzelecki, Suthers, Swadling, van Ruth and Richardson. Zooplankton are the intermediate trophic level between phytoplankton and fish, and are an important component of carbon and nutrient cycles, accounting for a large proportion of the energy transfer to pelagic fishes and the deep ocean. Given zooplankton's importance, models need to adequately represent zooplankton dynamics. A major obstacle, though, is the lack of model assessment. Here we try and stimulate the assessment of zooplankton in models by filling three gaps. The first is that many zooplankton observationalists are unfamiliar with the biogeochemical, ecosystem, size-based and individual-based models that have zooplankton functional groups, so we describe their primary uses and how each typically represents zooplankton. The second gap is that many modelers are unaware of the zooplankton data that are available, and are unaccustomed to the different zooplankton sampling systems, so we describe the main sampling platforms and discuss their strengths and weaknesses for model assessment. Filling these gaps in our understanding of models and observations provides the necessary context to address the last gap-a blueprint for model assessment of zooplankton. We detail two ways that zooplankton biomass/abundance observations can be used to assess models: data wrangling that transforms observations to be more similar to model output; and observation models that transform model outputs to be more like observations. We hope that this review will encourage greater assessment of zooplankton in models and ultimately improve the representation of their dynamics.

The evidence for an equal distribution of biomass from bacteria to whales has led to development of size-spectrum models that represent the dynamics of the marine ecosystem using size rather than species identity. Recent advances have improved the realism of the fish component of the size-spectrum, but these often assume that small fish feed on an aggregated plankton size-spectrum, without any explicit representation of zooplankton dynamics. In these models, small zooplankton are grouped with phytoplankton as a resource for larval fish, and large zooplankton are parameterized as small fish. Here we investigate the impact of resolving zooplankton and their feeding traits in a dynamic size-spectrum model. First, we compare a base model, where zooplankton are parameterized as smaller fish, to a model that includes zooplankton-specific feeding parameters. Second, we evaluate how the parameterization of zooplankton feeding characteristics, specifically the predator-prey mass ratio (PPMR), assimilation efficiency and feeding kernel width, affects the productivity and stability of the fish community. Finally, we compare how feeding characteristics of different zooplankton functional groups mediate increases in primary production and fishing pressure. Incorporating zooplankton-specific feeding parameters increased productivity of the fish community, but also changed the dynamics of the entire system from a stable to an oscillating steady-state. The inclusion of zooplankton feeding characteristics mediated a trade-off between the productivity and resilience of the fish community, and its stability. Fish communities with increased productivity and lower stability were supported by zooplankton with a larger PPMR and a narrower feeding kernel – specialized herbivores. In contrast, fish communities that were stable had lower productivity, and were supported by zooplankton with a lower PPMR and a wider feeding kernel – generalist carnivores. Herbivorous zooplankton communities were more efficient at mediating increases in primary production, and supported fish communities more resilient to fishing. Our results illustrate that zooplankton are not just a static food source for larger organisms, nor can they be resolved as very small fish. The unique feeding characteristics of zooplankton have enormous implications for the dynamics of marine ecosystems, and their representation is of critical importance in size-spectrum models, and end-to-end ecosystem models more broadly.

Unidad de excelencia María de Maeztu MdM-2015-0552 Climate change is a complex global issue that is driving countless shifts in the structure and function of marine ecosystems. To better understand these shifts, many processes need to be considered, yet they are often approached from incompatible perspectives. This article reviews one relatively simple, integrated perspective: the abundance-size spectrum. We introduce the topic with a brief review of some of the ways climate change is expected to impact the marine ecosystem according to complex numerical models while acknowledging the limits to understanding posed by complex models. We then review how the size spectrum offers a simple conceptual alternative, given its regular power law size-frequency distribution when viewed on sufficiently broad scales. We further explore how anticipated physical aspects of climate change might manifest themselves through changes in the elevation, slope and regularity of the size spectrum, exposing mechanistic questions about integrated ecosystem structure, as well as how organism physiology and ecological interactions respond to multiple climatic stressors. Despite its application by ecosystem modellers and fisheries scientists, the size spectrum perspective is not widely used as a tool for monitoring ecosystem adaptation to climate change, providing a major opportunity for further research. Given the millions of species living in the global ocean, their diverse life strategies and inter-relationships, and the multiple dimensions of anthropogenic stressors, it can be extremely challenging to grasp the overall impact of climate change on marine ecosystems. In spite of this great complexity, observations have shown that ecosystem size structures tend to be highly regular, with many small and few large individuals, decreasing in abundance with size according to a simple power law distribution. This simple power law relationship is known as the abundance-size spectrum. The size spectrum encompasses all species and has long been known to be among the most robust large-scale regularities in aquatic ecology. As such, it provides a unique lens through which to integrate biotic changes from multiple aspects of climatic change. Below, we review the physical, biogeochemical and ecological impacts projected by complex numerical models for the remainder of this century, as an illustration of current expectations. We then turn to the size spectrum as a more intuitive, readily grasped framework that provides a bird's eye view of the ecosystem and helps to simplify the expectations, as well as revealing shortfalls in mechanistic understanding.