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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Mar. Sci. | doi: 10.3389/fmars.2019.00508

The Importance of Mesozooplankton Diel Vertical Migration for Sustaining a Mesopelagic Food Web

 Thomas B. Kelly1, 2*, Peter C. Davison3, Ralf Goericke3, Michael R. Landry3,  Mark Ohman4 and  Michael R. Stukel2, 5
  • 1Dept. of Earth, Ocean & Atmospheric Sciences, Florida State University, United States
  • 2Center for Ocean Atmospheric Prediction Studies, Florida State University, United States
  • 3Integrative Oceanography Division, Scripps Institution of Oceanography, University of California, United States
  • 4Integrative Oceanography Division, Scripps Institution of Oceanography, University of California, San Diego, United States
  • 5Department of Earth, Ocean, and Atmospheric Science, Florida State University, United States

We used extensive ecological and biogeochemical measurements obtained from quasi-Lagrangian experiments during two California Current Ecosystem Long-Term Ecosystem Research cruises to analyze carbon fluxes between the epipelagic and mesopelagic zones using a linear inverse ecosystem model (LIEM). Measurement constraints on the model include 14C primary productivity, dilution-based microzooplankton grazing rates, gut pigment-based mesozooplankton grazing rates (on multiple zooplankton size classes), 234Th:238U disequilibrium and sediment trap measured carbon export, and metabolic requirements of micronekton, zooplankton, and bacteria. A likelihood approach (Markov Chain Monte Carlo) was used to estimate the resulting flow uncertainties from a sample of potential flux networks. Results highlight the importance of mesozooplankton active transport (i.e., diel vertical migration) for supplying the carbon demand of mesopelagic organisms and sequestering carbon dioxide from the atmosphere. In nine water parcels ranging from a coastal bloom to offshore oligotrophic conditions, mesozooplankton active transport accounted for 18% - 84% (median: 42%) of the total carbon supply to the mesopelagic, with gravitational settling of POC (12% - 55%; median: 37%) and subduction (2% - 32%; median: 14%) providing the majority of the remainder. Vertically migrating zooplankton contributed to downward carbon flux through respiration and excretion at depth and via consumption loses to predatory zooplankton and mesopelagic fish (e.g. myctophids and gonostomatids). Sensitivity analyses showed that the results of the LIEM were robust to changes in nekton metabolic demands, rates of bacterial production, and mesozooplankton gross growth efficiency. This analysis suggests that prior estimates of zooplankton active transport based on conservative estimates of standard (rather than active) metabolism should be revisited.

Keywords: biological carbon pump, export production, DVM, LIEM, inverse model, carbon export, ecosystem model, active transport

Received: 29 Mar 2019; Accepted: 31 Jul 2019.

Copyright: © 2019 Kelly, Davison, Goericke, Landry, Ohman and Stukel. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mr. Thomas B. Kelly, Florida State University, Dept. of Earth, Ocean & Atmospheric Sciences, Tallahassee, United States, tbk14@fsu.edu