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  • 1
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    When an ecological regime shift is really just stochastic noise (2013)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 110 (2013): 2438–2439, doi:10.1073/pnas.1222736110.
    Description: Populations of marine species wax and wane over time and space reflecting environmental forcing, biological dynamics, and in some cases human perturbations such as fishing, habitat destruction and climate change. The growing availability of multi‐decadal observational records opens new windows on how ocean ecosystems function, but the analysis and interpretation of such long time-­‐series also requires new mathematical tools and conceptual models. Population time-­‐ series often show strong variations at decadal time‐scales, and a central question is whether this arises from non‐linear biological processes or simply tracking of external physical variability. Borrowing from climate research, Di Lorenzo and Ohman develop a novel approach for deciphering links between physical forcing and biological response, using as a test case time‐series of marine zooplankton abundances off the coast of California.
    Description: The authors gratefully acknowledge support from the U.S. National Science Foundation through the Palmer Long Term Ecological Research (LTER) project (http://pal.lternet.edu/) (NSF OPP-­‐0823101).
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 2
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    Comparing food web structures and dynamics across a suite of global marine ecosystem models (2015)
    Elsevier
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecological Modelling 261-262 (2013): 43–57, doi:10.1016/j.ecolmodel.2013.04.006.
    Description: Dynamic Green Ocean Models (DGOMs) include different sets of Plankton Functional Types (PFTs) and equations, thus different interactions and food webs. Using four DGOMs (CCSM-BEC, PISCES, NEMURO and PlankTOM5) we explore how predator–prey interactions influence food web dynamics. Using each model's equations and biomass output, interaction strengths (direct and specific) were calculated and the role of zooplankton in modeled food webs examined. In CCSM-BEC the single size-class adaptive zooplankton preys on different phytoplankton groups according to prey availability and food preferences, resulting in a strong top-down control. In PISCES the micro- and meso-zooplankton groups compete for food resources, grazing phytoplankton depending on their availability in a mixture of bottom-up and top-down control. In NEMURO macrozooplankton controls the biomass of other zooplankton PFTs and defines the structure of the food web with a strong top-down control within the zooplankton. In PlankTOM5, competition and predation between micro- and meso-zooplankton along with strong preferences for nanophytoplankton and diatoms, respectively, leads to their mutual exclusion with a mixture of bottom-up and top-down control of the plankton community composition. In each model, the grazing pressure of the zooplankton PFTs and the way it is exerted on their preys may result in the food web dynamics and structure of the model to diverge from the one that was intended when designing the model. Our approach shows that the food web dynamics, in particular the strength of the predator–prey interactions, are driven by the choice of parameters and more specifically the food preferences. Consequently, our findings stress the importance of equation and parameter choice as they define interactions between PFTs and overall food web dynamics (competition, bottom-up or top-down effects). Also, the differences in the simulated food-webs between different models highlight the gap of knowledge for zooplankton rates and predator–prey interactions. In particular, concerted effort is needed to identify the key growth and loss parameters and interactions and quantify them with targeted laboratory experiments in order to bring our understanding of zooplankton at a similar level to phytoplankton.
    Description: This work was supported with funding from Palmer LTER (NSF OPP-0823101) and C-MORE (NSF EF-0424599).
    Keywords: Dynamic Green Ocean Model ; Plankton Functional Types ; Zooplankton ; Food web dynamic ; Predator–prey interactions
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    West Antarctic Peninsula : an ice-dependent coastal marine ecosystem in transition (2013)
    The Oceanography Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2013. This article is posted here by permission of The Oceanography Society] for personal use, not for redistribution. The definitive version was published in Oceanography 26, no. 3 (2013): 190–203, doi:10.5670/oceanog.2013.62.
    Description: The extent, duration, and seasonality of sea ice and glacial discharge strongly influence Antarctic marine ecosystems. Most organisms' life cycles in this region are attuned to ice seasonality. The annual retreat and melting of sea ice in the austral spring stratifies the upper ocean, triggering large phytoplankton blooms. The magnitude of the blooms is proportional to the winter extent of ice cover, which can act as a barrier to wind mixing. Antarctic krill, one of the most abundant metazoan populations on Earth, consume phytoplankton blooms dominated by large diatoms. Krill, in turn, support a large biomass of predators, including penguins, seals, and whales. Human activity has altered even these remote ecosystems. The western Antarctic Peninsula region has warmed by 7°C over the past 50 years, and sea ice duration has declined by almost 100 days since 1978, causing a decrease in phytoplankton productivity in the northern peninsula region. Besides climate change, Antarctic marine systems have been greatly altered by harvesting of the great whales and now krill. It is unclear to what extent the ecosystems we observe today differ from the pristine state.
    Description: Palmer LTER is supported by National Science Foundation grant ANT-0823101. Amsler was supported by NSF ANT- 0838773 and ANT-1041022. RaTS is a component of the Polar Oceans research program, funded by the British Antarctic Survey.
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Responses of summer phytoplankton biomass to changes in top-down forcing : insights from comparative modelling (2018)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Ecological Modelling 376 (2018): 54-67, doi:10.1016/j.ecolmodel.2018.03.003.
    Description: The present study describes the responses of summer phytoplankton biomass to changes in top-down forcing (expressed as zooplankton mortality) in three ecosystems (the North Sea, the Baltic Sea and the Nordic Seas) across different 3D ecosystem models. In each of the model set-ups, we applied the same changes in the magnitude of mortality (±20%) of the highest trophic zooplankton level (Z1). Model results showed overall dampened responses of phytoplankton relative to Z1 biomass. Phytoplankton responses varied depending on the food web structure and trophic coupling represented in the models. Hence, a priori model assumptions were found to influence cascades and pathways in model estimates and, thus, become highly relevant when examining ecosystem pressures such as fishing and climate change. Especially, the different roles and parameterizations of additional zooplankton groups grazed by Z1, and their importance for the outcome, emphasized the need for better calibration data. Spatial variability was high within each model indicating that physics (hydrodynamics and temperature) and nutrient dynamics also play vital roles for ecosystem responses to top-down effects. In conclusion, the model comparison indicated that changes in top-down forcing in combination with the modelled food-web structure affect summer phytoplankton biomass and, thereby, indirectly influence water quality of the systems.
    Description: The work was supported by the EU grant “Vectors of Change in Oceans and Seas, Marine Life, Impact and Economic Sectors” (Vectors, FP7/2010-2013) and The Danish Council for Strategic Research to the project “Integrated Management of Agriculture, Fishery, Environment and Economy” (IMAGE, grant no. 09-067259).
    Keywords: Plankton functional types ; Trophic cascades ; Zooplankton mortality ; Phytoplankton ; Ensemble modelling
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 5
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    Carbon fluxes and pelagic ecosystem dynamics near two western Antarctic Peninsula Adélie penguin colonies : an inverse model approach (2013)
    Inter-Research
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Ecology Progress Series 492 (2013): 253-272, doi:10.3354/meps10534.
    Description: An inverse food-web model for the western Antarctic Peninsula (WAP) pelagic food web was constrained with data from Palmer Long Term Ecological Research (PAL-LTER) project annual austral summer sampling cruises. Model solutions were generated for 2 regions with Adélie penguin Pygoscelis adeliae colonies presenting different population trends (a northern and a southern colony) for a 12 yr period (1995-2006). Counter to the standard paradigm, comparisons of carbon flow through bacteria, microzooplankton, and krill showed that the diatom-krill-top predator food chain is not the dominant pathway for organic carbon exchanges. The food web is more complex, including significant contributions by microzooplankton and the microbial loop. Using both inverse model results and network indices, it appears that in the northern WAP the food web is dominated by the microbial food web, with a temporal trend toward its increasing importance. The dominant pathway for the southern WAP food web varies from year to year, with no detectable temporal trend toward dominance of microzooplankton versus krill. In addition, sensitivity analyses indicated that the northern colony of Adélie penguins, whose population size has been declining over the past 35 yr, appears to have sufficient krill during summer to sustain its basic metabolic needs and rear chicks, suggesting the importance of other processes in regulating the Adélie population decline.
    Description: We acknowledge support from the National Science Foundation, Office of Polar Programs, Award 0823101 (Antarctic Organisms and Ecosystems Program) to Palmer LTER.
    Keywords: Inverse model ; Food web ; Antarctica ; Microzooplankton ; Krill ; Ecosystem state change ; Climate change
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Phytoplankton competition during the spring bloom in four plankton functional type models (2014)
    Copernicus Publications on behalf of the European Geosciences Union
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 10 (2013); 6833-6850, doi:10.5194/bg-10-6833-2013.
    Description: We investigated the mechanisms of phytoplankton competition during the spring bloom, one of the most dramatic seasonal events in lower-trophic-level ecosystems, in four state-of-the-art plankton functional type (PFT) models: PISCES, NEMURO, PlankTOM5 and CCSM-BEC. In particular, we investigated the relative importance of different ecophysiological processes on the determination of the community structure, focusing both on the bottom-up and the top-down controls. The models reasonably reproduced the observed global distribution and seasonal variation of phytoplankton biomass. The fraction of diatoms with respect to the total phytoplankton biomass increases with the magnitude of the spring bloom in all models. However, the governing mechanisms differ between models, despite the fact that current PFT models represent ecophysiological processes using the same types of parameterizations. The increasing trend in the percentage of diatoms with increasing bloom magnitude is mainly caused by a stronger nutrient dependence of diatom growth compared to nanophytoplankton (bottom-up control). The difference in the maximum growth rate plays an important role in NEMURO and PlankTOM5 and determines the absolute values of the percentage of diatoms during the bloom. In CCSM-BEC, the light dependency of growth plays an important role in the North Atlantic and the Southern Ocean. The grazing pressure by zooplankton (top-down control), however, strongly contributes to the dominance of diatoms in PISCES and CCSM-BEC. The regional differences in the percentage of diatoms in PlankTOM5 are mainly determined by top-down control. These differences in the mechanisms suggest that the response of marine ecosystems to climate change could significantly differ among models, even if the present-day ecosystem is reproduced to a similar degree of confidence. For further understanding of plankton competition and for the prediction of future change in marine ecosystems, it is important to understand the relative differences in each physiological rate and life history rate in the bottom-up and the top-down controls between PFTs.
    Description: T. Hashioka, Y. Yamanaka and T. Hirata, were supported by the Grant-in-Aid for the Global COE Program from MEXT, by the Global Environment Research Fund (S-5) from the Ministry of the Environment and by the Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation from JSPS. S. Doney, I. Lima and S. Sailley acknowledge support from C-MORE (NSF EF-0424599).
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Global assessment of ocean carbon export by combining satellite observations and food-web models (2014)
    John Wiley & Sons
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 28 (2014): 181-196, doi:10.1002/2013GB004743.
    Description: The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of ~6 Pg C yr−1. Global export estimates show small variation (typically 〈 10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean's biological pump.
    Description: D.A.S. and K.O.B. acknowledge support from the National Aeronautics and Space Administration (NNX11AF63G). S.C.D. and S.F.S. acknowledge support from the National Science Foundation through the Center for Microbial Oceanography: Research and Education (C-MORE) (NSF EF-0424599).
    Description: 2014-09-10
    Keywords: Carbon cycle ; Biological pump ; Carbon export ; Remote sensing ; Food webs
    Repository Name: Woods Hole Open Access Server
    Type: Article
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