Preprints
https://doi.org/10.5194/bg-2022-157
https://doi.org/10.5194/bg-2022-157
 
20 Jul 2022
20 Jul 2022
Status: a revised version of this preprint is currently under review for the journal BG.

Zooplankton community succession and trophic links during a mesocosm experiment in the coastal upwelling off Callao Bay (Peru)

Patricia Ayón Dejo1, Elda Luz Pinedo Arteaga1, Anna Schukat2, Jan Taucher3, Rainer Kiko3,4, Helena Hauss3,5, Sabrina Dorschner2, Wilhelm Hagen2, Mariona Segura-Noguera6, and Silke Lischka3,5 Patricia Ayón Dejo et al.
  • 1Instituto del Mar del Perú (IMARPE), Dirección General de Investigaciones en Oceanografía y Cambio Climático, Callao, Perú
  • 2University of Bremen, BreMarE Bremen Marine Ecology, Marine Zoology, Bremen, Germany
  • 3GEOMAR Helmholtz Centre for Ocean Research Kiel, Biological Oceanography, Kiel, Germany
  • 4Laboratoire d’Océanographie de Villefranche-sur-Mer, Sorbonne Université, Villefranche-sur-Mer, France
  • 5Department of Computer Science, Christian Albrechts University Kiel, Kiel, Germany
  • 6Institut de Ciències del Mar (ICM_CSIC), Barcelona, Spain

Abstract. The Humboldt Current Upwelling System (HUS) is the most productive eastern boundary upwelling system (EBU) in terms of fisheries yield on the planet. EBUs are considered hotspots of climate change with predicted expansion of mesopelagic oxygen minimum zones (OMZs) and related changes in frequency and intensity of upwelling of nutrient-rich/oxygen-low deep-water. To increase our mechanistic understanding of how upwelling impacts on plankton communities and trophic links, we investigated mesozooplankton community succession as well as gut fluorescence, fatty acid and elemental compositions (C, N, O, P), and stable isotope (δ13C, δ15N) ratios of dominant meso- and microzooplankton representatives in a mesocosm setup off Callao (Peru) after simulated upwelling with OMZ water from two different locations and N:P signatures. An oxycline between 5 and 15 m with hypoxic conditions below ~10 m (<50 μL-1) persisted in the mesocosms throughout the experiment. No treatment effects became apparent in the mesozooplankton community composition, but differences in nutrient concentrations established through OMZ water additions were negligible. Copepods and polychaete larvae dominated in terms of abundance and biomass. Development and reproduction of the dominant copepod genera Paracalanus spp., Hemicyclops sp., Acartia sp., and Oncaea sp. was hindered as evident from accumulation of adult copepodids but largely missing nauplii. Failed hatching of nauplii in the hypoxic bottom layer of the mesocosms and poor nutritional condition of copepods suggested from very low gut fluorescence and fatty acid compositions most likely explains the retarded copepod development. Correlation analysis revealed no particular trophic relations between dominant copepods and phytoplankton groups. Possibly particulate organic matter with relatively high C:N ratio was a major diet of copepods. C:N ratios of copepods (pooled and species-specific for Paracalanus spp., Hemicyclops sp.) and polychaetes ranged between 4.8–5.8 and 4.2–4.3, respectively. Stable isotope signatures of copepods varied over time but not between treatments. δ15N was comparatively high (~13–17 ‰) potentially because the injected OMZ source water was enriched in δ15N as a result of anoxic conditions. Elemental ratios of dinoflagellates deviated strongly from the Redfield ratio. We conclude, that intensification and increased frequency of upwelling and expanding/shoaling OMZs could severely impact population dynamics and reproductive success of zooplankton communities and, thus, the pelagic food web of the HUS.

Patricia Ayón Dejo et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-157', Anonymous Referee #1, 12 Aug 2022
    • AC1: 'Reply on RC1', S. Lischka, 20 Sep 2022
  • CC1: 'Comment on bg-2022-157', Joshua Stone, 23 Aug 2022
    • AC2: 'Reply on RC2', S. Lischka, 20 Sep 2022
  • RC2: 'Comment on bg-2022-157', Joshua Stone, 24 Aug 2022
    • AC2: 'Reply on RC2', S. Lischka, 20 Sep 2022

Patricia Ayón Dejo et al.

Patricia Ayón Dejo et al.

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Short summary
Ocean upwelling regions are highly productive. With ocean warming, severe changes in upwelling frequency and/or intensity and expansion of accompanying oxygen minimum zones are projected. In a field experiment off Peru, we investigated how different upwelling intensities affect the pelagic food web and found failed reproduction of dominant zooplankton. Therefore, changes projected could severely impact reproductive success of zooplankton communities and the pelagic food web in upwelling regions.
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