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Marine Ecology Progress Series

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MEPS 717:107-126 (2023)  -  DOI:

Effects of migrating mesopelagic fishes on the biological carbon pump

Dag L. Aksnes1,*, Anita S. Løtvedt1, Christian Lindemann1, Maria Ll. Calleja2, Xosé Anxelu G. Morán3, Stein Kaarvedt4, T. Frede Thingstad1

1Department of Biological Sciences, University of Bergen, 5020 Bergen, Norway
2Max Planck Institute for Chemistry, 55128 Mainz, Germany
3Instituto Español de Oceanografia, 33212 Gijón, Spain
4Department of Biosciences, University of Oslo, 0316 Oslo, Norway
*Corresponding author:

ABSTRACT: Mesopelagic fishes and invertebrates contribute to the biological carbon pump (BCP) through direct and indirect effects on the gravitational, diffusive, and migrant (active) fluxes. Here, we analyzed the effect of these organisms on total carbon export and sequestration using an idealized depth-resolved food-web model. We constrained a baseline scenario with observations from the Red Sea where mesopelagic fishes perform extensive diel vertical migration (DVM), presumably making them particularly important in carbon export. Our results are consistent with previous studies suggesting that mesopelagic fishes fuel a hotspot of heterotrophic activity in the mesopelagic zone of the Red Sea. While the supply of new nutrients to the euphotic zone is of first order in framing total carbon export and sequestration, we found 2 modulating effects of fish DVM. First, DVM enhances carbon sequestration because active carbon flux attenuates less than the gravitational and diffusive fluxes, and also because migrators fuel the gravitational flux deep into the mesopelagic zone. Secondly, through microbial food-web cascades, fish predation affects the relative contribution of the active and the passive fluxes with non-linear, less intuitive consequences for carbon export and sequestration. These food-web cascades involve a surprisingly large variation in the depth of the euphotic zone that is associated with a ‘diatom nutrient trap’ at the bottom of the euphotic zone.

KEY WORDS: Diel vertical migration · DVM · Fish · Microbial food web · Cascade · Carbon flux · Subtropical ocean · Red Sea

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Cite this article as: Aksnes DL, Løtvedt AS, Lindemann C, Calleja ML, Morán XAG, Kaarvedt S, Thingstad TF (2023) Effects of migrating mesopelagic fishes on the biological carbon pump. Mar Ecol Prog Ser 717:107-126.

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