While the fishery on the Peruvian anchovy in the northern Humboldt Current upwelling system off Peru (HUS) is the world’s largest single-species fishery, the primary production is not the largest leading to a paradoxical 5–10 times higher fishery yield in the HUS compared to other eastern boundary upwelling systems. It is not fully understood how the food web can sustain this exceptional trophic transfer efficiency and how it relates to upwelling and light intensities. The relationship between upwelling intensity and productivity is also not sufficiently understood to predict the effect of climate change on the ecosystem. A mismatch between upwelling intensity and phytoplankton productivity proposed by Messié and Chavez (2015) suggests that while upwelling is highest in winter, primary productivity peaks in summer. To test the hypothesis that light causes the out-of-phase observations, and to improve our understanding of trophic processes controlling productivity in the HUS, we simulated winter low light and summer high light conditions during a 35-day mesocosm experiment 6 km off-shore from Callao/Lima during austral summer 2020. Natural plankton was enclosed in 9 mesocosms (KOSMOS, GEOMAR Kiel) and five levels of upwelling intensities were simulated by adding nutrient-rich deep water (0%, 15%, 30%, 45% and 60%). We present the first comprehensive data from this experiment, on the pelagic food-web structure, trophic interactions and role of the micro- and mesozooplankton in overall trophic transfer efficiency to fish. 

Primary Presenter: Jens Nejstgaard, IGB Leibniz-Institute of Freshwater Ecology and Inland Fisheries (jens.nejstgaard@igb-berlin.de)

Authors:

Jens Nejstgaard, IGB Leibniz Institute of Freshwater Ecology and Inland Fisheries, Germany  (jens.nejstgaard@igb-berlin.de)

Stella Berger, IGB Leibniz Institute of Freshwater Ecology and Inland Fisheries, Germany   (stella.berger@igb-berlin.de)

Silvan Goldenberg, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany  (sgoldenberg@geomar.de)

Sven Katzenmeier, Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau, Germany  (katzenme@rptu.de)

Megan Gross, Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau, Germany  (megross@rptu.de)

Silke Lischka, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany and Department of Computer Science, Christian-Albrechts-Universität zu Kiel, Germany  (slischka@geomar.de)