Metabolic impacts of climate change on marine ecosystems : Implications for fish communities and fisheries

Unidad de excelencia María de Maeztu MdM-2015-0552Aim:Climate change will reshape marine ecosystems over the 21st century through diverse and complex mechanisms that are difficult to assess quantitatively. Here, we characterize expectations for how marine community biomass will respond to the energetic consequences of changes in primary production and temperature-dependent metabolic rates, under a range of fishing/conservation scenarios. Location: Global ocean. Time period: 1950-2100.Major taxa studied: Commercially harvested marine ectotherms ('fish'). Methods: We use a size-structured macroecological model of the marine ecosystem, coupled with a catch model that allows for calibration with global historical data and simulation of fishing. We examine the four energetic mechanisms that, within the model framework, determine the community response to climate change: net primary production, phytoplankton cell size, and the temperature dependencies of growth and natural mortality. Results: Climate change decreases the modelled global fish community biomass by as much as 30% by 2100. This results from a diminished energy supply to upper trophic levels as photosynthesis becomes more nutrient limited and phytoplankton cells shrink, and from a temperature-driven increase of natural mortality that, together, overwhelm the effect of accelerated somatic growth rates. Ocean circulation changes drive regional variations of primary production, producing patterns of winners and losers that largely compensate each other when averaged globally, whereas decreasing phytoplankton size drives weaker but more uniformly negative changes. The climate impacts are similar across the range of conservation scenarios but are slightly amplified in the strong conservation scenarios owing to the greater role of natural mortality. Main conclusions: The spatial pattern of climate impacts is mostly determined by changes in primary production. The overall decline of community biomass is attributed to a temperature-driven increase of natural mortality, alongside an overall decrease in phytoplankton size, despite faster somatic growth. Our results highlight the importance of the competition between accelerated growth and mortality in a warming ocean

Estimating global biomass and biogeochemical cycling of marine fish with and without fishing

Unidad de excelencia María de Maeztu CEX2019-000940-MThe biomass and biogeochemical roles of fish in the ocean are ecologically important but poorly known. Here, we use a data-constrained marine ecosystem model to provide a first-order estimate of the historical reduction of fish biomass due to fishing and the associated change in biogeochemical cycling rates. The pre-exploitation global biomass of exploited fish (10 g to 100 kg) was 3.3 ± 0.5 Gt, cycling roughly 2% of global primary production (9.4 ± 1.6 Gt year−1) and producing 10% of surface biological export. Particulate organic matter produced by exploited fish drove roughly 10% of the oxygen consumption and biological carbon storage at depth. By the 1990s, biomass and cycling rates had been reduced by nearly half, suggesting that the biogeochemical impact of fisheries has been comparable to that of anthropogenic climate change. Our results highlight the importance of developing a better mechanistic understanding of how fish alter ocean biogeochemistry

Global ensemble projections reveal trophic amplification of ocean biomass declines with climate change

While the physical dimensions of climate change are now routinely assessed through multimodel intercomparisons, projected impacts on the global ocean ecosystem generally rely on individual models with a specific set of assumptions. To address these single-model limitations, we present standardized ensemble projections from six global marine ecosystem models forced with two Earth system models and four emission scenarios with and without fishing. We derive average biomass trends and associated uncertainties across the marine food web. Without fishing, mean global animal biomass decreased by 5% (±4% SD) under low emissions and 17% (±11% SD) under high emissions by 2100, with an average 5% decline for every 1 °C of warming. Projected biomass declines were primarily driven by increasing temperature and decreasing primary production, and were more pronounced at higher trophic levels, a process known as trophic amplification. Fishing did not substantially alter the effects of climate change. Considerable regional variation featured strong biomass increases at high latitudes and decreases at middle to low latitudes, with good model agreement on the direction of change but variable magnitude. Uncertainties due to variations in marine ecosystem and Earth system models were similar. Ensemble projections performed well compared with empirical data, emphasizing the benefits of multimodel inference to project future outcomes. Our results indicate that global ocean animal biomass consistently declines with climate change, and that these impacts are amplified at higher trophic levels. Next steps for model development include dynamic scenarios of fishing, cumulative human impacts, and the effects of management measures on future ocean biomass trends

ECMO for COVID-19 patients in Europe and Israel

Since March 15th, 2020, 177 centres from Europe and Israel have joined the study, routinely reporting on the ECMO support they provide to COVID-19 patients. The mean annual number of cases treated with ECMO in the participating centres before the pandemic (2019) was 55. The number of COVID-19 patients has increased rapidly each week reaching 1531 treated patients as of September 14th. The greatest number of cases has been reported from France (n = 385), UK (n = 193), Germany (n = 176), Spain (n = 166), and Italy (n = 136) .The mean age of treated patients was 52.6 years (range 16–80), 79% were male. The ECMO configuration used was VV in 91% of cases, VA in 5% and other in 4%. The mean PaO2 before ECMO implantation was 65 mmHg. The mean duration of ECMO support thus far has been 18 days and the mean ICU length of stay of these patients was 33 days. As of the 14th September, overall 841 patients have been weaned from ECMO support, 601 died during ECMO support, 71 died after withdrawal of ECMO, 79 are still receiving ECMO support and for 10 patients status n.a. . Our preliminary data suggest that patients placed on ECMO with severe refractory respiratory or cardiac failure secondary to COVID-19 have a reasonable (55%) chance of survival. Further extensive data analysis is expected to provide invaluable information on the demographics, severity of illness, indications and different ECMO management strategies in these patients

Formulation, General Features and Global Calibration of a Bioenergetically-Constrained Fishery Model.

Human exploitation of marine resources is profoundly altering marine ecosystems, while climate change is expected to further impact commercially-harvested fish and other species. Although the global fishery is a highly complex system with many unpredictable aspects, the bioenergetic limits on fish production and the response of fishing effort to profit are both relatively tractable, and are sure to play important roles. Here we describe a generalized, coupled biological-economic model of the global marine fishery that represents both of these aspects in a unified framework, the BiOeconomic mArine Trophic Size-spectrum (BOATS) model. BOATS predicts fish production according to size spectra as a function of net primary production and temperature, and dynamically determines harvest spectra from the biomass density and interactive, prognostic fishing effort. Within this framework, the equilibrium fish biomass is determined by the economic forcings of catchability, ex-vessel price and cost per unit effort, while the peak harvest depends on the ecosystem parameters. Comparison of a large ensemble of idealized simulations with observational databases, focusing on historical biomass and peak harvests, allows us to narrow the range of several uncertain ecosystem parameters, rule out most parameter combinations, and select an optimal ensemble of model variants. Compared to the prior distributions, model variants with lower values of the mortality rate, trophic efficiency, and allometric constant agree better with observations. For most acceptable parameter combinations, natural mortality rates are more strongly affected by temperature than growth rates, suggesting different sensitivities of these processes to climate change. These results highlight the utility of adopting large-scale, aggregated data constraints to reduce model parameter uncertainties and to better predict the response of fisheries to human behaviour and climate change

Metabolic impacts of climate change on marine ecosystems : Implications for fish communities and fisheries

Unidad de excelencia María de Maeztu MdM-2015-0552Aim:Climate change will reshape marine ecosystems over the 21st century through diverse and complex mechanisms that are difficult to assess quantitatively. Here, we characterize expectations for how marine community biomass will respond to the energetic consequences of changes in primary production and temperature-dependent metabolic rates, under a range of fishing/conservation scenarios. Location: Global ocean. Time period: 1950-2100.Major taxa studied: Commercially harvested marine ectotherms ('fish'). Methods: We use a size-structured macroecological model of the marine ecosystem, coupled with a catch model that allows for calibration with global historical data and simulation of fishing. We examine the four energetic mechanisms that, within the model framework, determine the community response to climate change: net primary production, phytoplankton cell size, and the temperature dependencies of growth and natural mortality. Results: Climate change decreases the modelled global fish community biomass by as much as 30% by 2100. This results from a diminished energy supply to upper trophic levels as photosynthesis becomes more nutrient limited and phytoplankton cells shrink, and from a temperature-driven increase of natural mortality that, together, overwhelm the effect of accelerated somatic growth rates. Ocean circulation changes drive regional variations of primary production, producing patterns of winners and losers that largely compensate each other when averaged globally, whereas decreasing phytoplankton size drives weaker but more uniformly negative changes. The climate impacts are similar across the range of conservation scenarios but are slightly amplified in the strong conservation scenarios owing to the greater role of natural mortality. Main conclusions: The spatial pattern of climate impacts is mostly determined by changes in primary production. The overall decline of community biomass is attributed to a temperature-driven increase of natural mortality, alongside an overall decrease in phytoplankton size, despite faster somatic growth. Our results highlight the importance of the competition between accelerated growth and mortality in a warming ocean

Methane and Environmental Change during the Paleocene-Eocene Thermal Maximum (PETM): Modeling the PETM Onset as a Two-stage Event

An atmospheric CH4 box model coupled to a global carbon cycle box model is used to constrain the carbon emission associated with the PETM and assess the role of CH4 during this event. A range of atmospheric and oceanic emission scenarios representing different amounts, rates, and isotopic signatures of emitted carbon are used to model the PETM onset. The first 3 kyr of the onset, a pre-isotope excursion stage, is simulated by the atmospheric release of 900 to 1100 Pg C CH4 with a delta C-13 of -22 to - 30 %. For a global average warming of 3 deg C, a release of CO2 to the ocean and CH4 to the atmosphere totalling 900 to 1400 Pg C, with a delta C-13 of -50 to -60%, simulates the subsequent 1 -kyr isotope excursion stage. To explain the observations, the carbon must have been released over at most 500 years. The first stage results cannot be associated with any known PETM hypothesis. However, the second stage results are consistent with a methane hydrate source. More than a single source of carbon is required to explain the PETM onset

Metabolic impacts of climate change on marine fish communities and fisheries - Dataset and figure plot script

Here we provide the MATLAB functions, model forcing data (net primary production and temperature), and model output required to generate the figures and perform calculations from the manuscript "Metabolic impacts of climate change on marine fish communities and fisheries", which is currently in submission as a research article. The figures plot script (plot_figures_climate_fish_deconstruction.m) is written in MATLAB version R2012a

Formulation, General Features and Global Calibration of a Bioenergetically-Constrained Fishery Model

<div><p>Human exploitation of marine resources is profoundly altering marine ecosystems, while climate change is expected to further impact commercially-harvested fish and other species. Although the global fishery is a highly complex system with many unpredictable aspects, the bioenergetic limits on fish production and the response of fishing effort to profit are both relatively tractable, and are sure to play important roles. Here we describe a generalized, coupled biological-economic model of the global marine fishery that represents both of these aspects in a unified framework, the BiOeconomic mArine Trophic Size-spectrum (BOATS) model. BOATS predicts fish production according to size spectra as a function of net primary production and temperature, and dynamically determines harvest spectra from the biomass density and interactive, prognostic fishing effort. Within this framework, the equilibrium fish biomass is determined by the economic forcings of catchability, ex-vessel price and cost per unit effort, while the peak harvest depends on the ecosystem parameters. Comparison of a large ensemble of idealized simulations with observational databases, focusing on historical biomass and peak harvests, allows us to narrow the range of several uncertain ecosystem parameters, rule out most parameter combinations, and select an optimal ensemble of model variants. Compared to the prior distributions, model variants with lower values of the mortality rate, trophic efficiency, and allometric constant agree better with observations. For most acceptable parameter combinations, natural mortality rates are more strongly affected by temperature than growth rates, suggesting different sensitivities of these processes to climate change. These results highlight the utility of adopting large-scale, aggregated data constraints to reduce model parameter uncertainties and to better predict the response of fisheries to human behaviour and climate change.</p></div