MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 600:41-53 (2018) - DOI: https://doi.org/10.3354/meps12643 Mixing regime-dependent causality between phytoplankton and bacteria in the subtropical North Atlantic Ocean ecosystem Hyewon Kim1,3,*, Dong Eun Lee2, Hugh W. Ducklow1 1Division of Biology and Paleo Environment, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA 2Division of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA 3Present address: Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA *Corresponding author: hk8m@virginia.edu ABSTRACT: Ever since marine heterotrophic bacteria were understood to mediate carbon fluxes to upper trophic levels via the microbial loop, quantifying the coupling between bacteria and phytoplankton has been one of the main priorities for marine microbiologists. The complex nature of phytoplankton-bacterial interactions may lead to nonlinear and regime-dependent coupling, for which conventional statistical approaches such as cross-correlation provide an incomplete picture of the dynamics. Here, we employed a nonlinear method for detecting causality, called convergent cross mapping (CCM), to examine a causal linkage between phytoplankton (primary production) and bacteria (bacterial production) at the Bermuda Atlantic Time-series Study (BATS) site. First, we verified the robustness of our CCM models with synthetic time series output from the Fasham-Ducklow-McKelvie ecosystem model. Initially, we hypothesized a strong bi-directional causal link between phytoplankton and bacteria due to the importance of the microbial loop at BATS. However, the results from our CCM models highlight that phytoplankton-bacterial causal coupling depends on seasonally distinct mixing regimes. While there was no evidence for bi-directional causality between phytoplankton and bacteria during the mixing period, moderate unidirectional causality of bacteria on phytoplankton was detected during the stratification period. Our study reveals causal associations between the 2 major microbial loop processes, for which better quantification is needed to improve our understanding of carbon cycling and export via microbial food webs. KEY WORDS: Convergent cross mapping · CCM · Bermuda Atlantic Time-series Study · BATS · Primary production · Bacterial production · Sargasso Sea Full text in pdf format Supplementary material PreviousNextCite this article as: Kim H, Lee DE, Ducklow HW (2018) Mixing regime-dependent causality between phytoplankton and bacteria in the subtropical North Atlantic Ocean ecosystem. Mar Ecol Prog Ser 600:41-53. https://doi.org/10.3354/meps12643 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 600. Online publication date: July 30, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.