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Biogeosciences An interactive open-access journal of the European Geosciences Union
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In this study we use a regional biogeochemical model of the Eastern Tropical South Pacific Ocean to implicitly simulate the effect that fluctuations in populations of small pelagic fish, such as anchovy and sardine, may have on the biogeochemistry of the Northern Humboldt Current System. To do so, we vary the zooplankton mortality in the model, under the assumption that these fishes eat zooplankton. We also evaluate the model for the first time against mesozooplankton observations.
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https://doi.org/10.5194/bg-2020-417
https://doi.org/10.5194/bg-2020-417

  09 Dec 2020

09 Dec 2020

Review status: this preprint is currently under review for the journal BG.

Zooplankton mortality effects on the plankton community of the Northern Humboldt Current System: Sensitivity of a regional biogeochemical model

Mariana Hill Cruz1, Iris Kriest1, Yonss Saranga José1, Rainer Kiko2, Helena Hauss1,3, and Andreas Oschlies1,3 Mariana Hill Cruz et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
  • 2Sorbonne Université, Laboratoire d'Océanographie de Villefranche-sur-mer, France
  • 3Christian-Albrechts-University Kiel, Germany

Abstract. Small pelagic fish off the coast of Peru in the Eastern Tropical South Pacific (ETSP) support around 10 % of the global fish catches. Their stocks fluctuate interannually due to environmental variability which can be exacerbated by fishing pressure. Because these fish are planktivorous, any change in fish abundance may directly affect the plankton and the biogeochemical system.

To investigate the potential effects of variability in small pelagic fish populations on lower trophic levels, we used a coupled physical-biogeochemical model to build scenarios for the ETSP and compare these against an already published reference simulation. The scenarios mimic changes in fish predation by either increasing or decreasing mortality of the model's large and small zooplankton compartments.

The results revealed that large zooplankton was the main driver of the response of the community. Its concentration increased under low mortality conditions and its prey, small zooplankton and large phytoplankton, decreased. The response was opposite, but weaker, in the high mortality scenarios. This asymmetric behaviour can be explained by the different ecological roles of large, omnivorous zooplankton, and small zooplankton, which in the model is strictly herbivorous. The response of small zooplankton depended on the antagonistic effects of mortality changes as well as the grazing pressure by large zooplankton. The results of this study provide a first insight on how the plankton ecosystem might respond if variations in fish populations were modelled explicitly.

Mariana Hill Cruz et al.

 
Status: open (until 31 Jan 2021)
Status: open (until 31 Jan 2021)
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Mariana Hill Cruz et al.

Mariana Hill Cruz et al.

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Short summary
In this study we use a regional biogeochemical model of the Eastern Tropical South Pacific Ocean to implicitly simulate the effect that fluctuations in populations of small pelagic fish, such as anchovy and sardine, may have on the biogeochemistry of the Northern Humboldt Current System. To do so, we vary the zooplankton mortality in the model, under the assumption that these fishes eat zooplankton. We also evaluate the model for the first time against mesozooplankton observations.
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