Temporal and vertical variability in picophytoplankton primary productivity in the North Pacific Subtropical Gyre

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 562:1-18 (2016) - DOI: https://doi.org/10.3354/meps11954 FEATURE ARTICLE Temporal and vertical variability in picophytoplankton primary productivity in the North Pacific Subtropical Gyre Yoshimi M. Rii1,2,*, David M. Karl1,2, Matthew J. Church1,2,3 1Department of Oceanography, University of Hawai'i at Mãnoa, Honolulu, HI 96822, USA 2Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawai'i at Mãnoa, Honolulu, HI 96822, USA 3Present address: Flathead Lake Biological Station, University of Montana, Polson, MT 59860, USA *Corresponding author: shimi@hawaii.edu ABSTRACT: Picophytoplankton (≤3 µm) are major contributors to plankton biomass and primary productivity in the subtropical oceans. We examined vertical and temporal variability of picophytoplankton primary productivity at near-monthly time scales (May 2012–May 2013) in the North Pacific Subtropical Gyre (NPSG) based on filter size-fractionated and flow cytometric sorting of radiolabeled (14C) picoplankton cells. Primary productivity by picophytoplankton comprised ~68 to 83% of total (>0.2 µm) particulate 14C-based productivity, and was lowest between September and December and highest between March and August. Group-specific rates of production by Prochlorococcus, Synechococcus, and photosynthetic picoeukaryotes (PPE) averaged ~39, ~2, and ~11% of the total 14C-productivity, respectively. Average cell-specific rates of production by PPE (15.2 fmol C cell-1 d-1) were 25- to 90-fold greater than Prochlorococcus (0.36 fmol C cell-1 d-1) and Synechococcus (1.56 fmol C cell-1 d-1). Prochlorococcus dominated (61-78%) the summed picophytoplankton biomass, while PPE and Synechococcus contributed 21-36% and 2-8%, respectively. Rates of production normalized to biomass were nearly equivalent amongst Prochlorococcus, Synechococcus, and PPE, averaging 0.6, 0.5, and 0.4 d-1, respectively. Over our study period, Prochlorococcus and PPE production varied 4- to 5-fold, while biomass varied ~3-fold. In contrast, Synechococcus production varied ~30-fold, with peak rates in March 2013 accompanied by ~13-fold increase in biomass. Combined, our results provide evidence for rapid growth by picophytoplankton in this persistently low-nutrient ecosystem, highlighting the importance of cell loss processes responsible for mediating organic matter cycling in the euphotic zone of the NPSG. KEY WORDS: Picoplankton · 14C primary production · Picophytoplankton · Picoeukaryotes · Prochlorococcus · Synechococcus · Flow cytometry · Time series · North Pacific Full text in pdf format Information about this Feature Article NextCite this article as: Rii YM, Karl DM, Church MJ (2016) Temporal and vertical variability in picophytoplankton primary productivity in the North Pacific Subtropical Gyre. Mar Ecol Prog Ser 562:1-18. https://doi.org/10.3354/meps11954 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 562. Online publication date: December 29, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.