skip to main content

Attention:

The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Thursday, October 10 until 2:00 AM ET on Friday, October 11 due to maintenance. We apologize for the inconvenience.


Title: Quantifying Per-Cell Chlorophyll a in Natural Picophytoplankton Populations Using Fluorescence-Activated Cell Sorting
Marine phytoplankton play a central role in global biogeochemical cycling, carbon export, and the overall functioning of marine ecosystems. While chlorophyll a (Chl a ) is widely used as a proxy for phytoplankton biomass, identifying the proportion of Chl a attributable to different phytoplankton groups remains a major challenge in oceanography, especially for the picophytoplankton groups that often represent the majority of phytoplankton biomass in the open ocean. We describe a method for measuring picophytoplankton per-cell Chl a in field samples using fluorescence-activated cell sorting followed by solvent-based Chl a extraction and fluorescence quantification. Applying this method to surface samples from the Gulf of Mexico, we determined per-cell Chl a to be 0.24 ± 0.07, 0.6 ± 0.33, and 26.36 ± 20.9 fg Chl a cell -1 for Prochlorococcus , Synechococcus , and PPE, respectively (mean ± SD). Measurements of per-cell Chl a using this method are precise to within 1.7, 2.1, and 3.1% for Prochlorococcus , Synechococcus , and PPE, respectively. We demonstrate that this approach can be used to obtain estimates of group-specific Chl a for Prochlorococcus , Synechococcus , and picophytoeukaryotes, the latter two of which cannot be captured by existing methods. We also demonstrate that measurements of per-cell Chl a made using this method in field samples are sufficiently precise to capture relationships between per-cell Chl a and cytometer red fluorescence, providing a bridge between biomass estimates from cell counts and bulk measurements of total Chl a .  more » « less
Award ID(s):
1458070 1737240 1737078
NSF-PAR ID:
10331660
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Frontiers in Marine Science
Volume:
9
ISSN:
2296-7745
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The 2014–2015 warm anomaly (aka “the Blob”), the largest of periodic and intensifying marine heat wave (MHW) perturbations in the northeast Pacific, may provide some insight about the future warmer ocean. Here, we use mixed‐layer carbon estimates for total phytoplankton, major size classes and functional groups from 45 CalCOFI cruises to: (1) compare 2014–2015 MHW impacts in the southern California Current System to baseline estimates from 2004 to 2013 and (2) to test a space‐for‐time exchange hypothesis that links biomass structure to variability of nitracline depth (NCD). Seasonal and inshore‐offshore analyses from nine stations revealed almost uniform 2°C MHW warming extending 700 km seaward, fourfold to sixfold declines in nitrate concentration and 18‐m deeper NCDs. Phytoplankton C decreased 16–21% compared to 45–65% for Chla, with the threefold difference due to altered C : Chla. Among size classes, percent composition of nanoplankton decreased and picophytoplankton increased, driven by higherProchlorococcusbiomass, whileSynechococcusand picoeukaryotes generally declined. Diatom and dinoflagellate C decreased in both onshore and offshore waters. Seasonally, the MHW delayed the normal winter refresh of surface nitrate, resulting in depressed stocks of total phytoplankton and nanoplankton,Synechococcusand picoeukaryotes during winter. Consistent with the space‐for‐time hypothesis, biomass variations for baseline and MHW cruises followed similar (not significantly different) slope relationships to NCD. All biomass components, exceptProchlorococcus, were negatively related to NCD, and community biomass structure realigned according to regression slopes differences with NCD variability. Empirically derived biomass‐NCD relationships could be useful for calibrating models that explore future food‐web impacts in this coastal upwelling system.

     
    more » « less
  2. Abstract

    Nitrogen (N) is a limiting nutrient in vast regions of the world’s oceans, yet the sources of N available to various phytoplankton groups remain poorly understood. In this study, we investigated inorganic carbon (C) fixation rates and nitrate (NO3−), ammonium (NH4+) and urea uptake rates at the single cell level in photosynthetic pico-eukaryotes (PPE) and the cyanobacteria Prochlorococcus and Synechococcus. To that end, we used dual 15N and 13C-labeled incubation assays coupled to flow cytometry cell sorting and nanoSIMS analysis on samples collected in the North Pacific Subtropical Gyre (NPSG) and in the California Current System (CCS). Based on these analyses, we found that photosynthetic growth rates (based on C fixation) of PPE were higher in the CCS than in the NSPG, while the opposite was observed for Prochlorococcus. Reduced forms of N (NH4+ and urea) accounted for the majority of N acquisition for all the groups studied. NO3− represented a reduced fraction of total N uptake in all groups but was higher in PPE (17.4 ± 11.2% on average) than in Prochlorococcus and Synechococcus (4.5 ± 6.5 and 2.9 ± 2.1% on average, respectively). This may in part explain the contrasting biogeography of these picoplankton groups. Moreover, single cell analyses reveal that cell-to-cell heterogeneity within picoplankton groups was significantly greater for NO3− uptake than for C fixation and NH4+ uptake. We hypothesize that cellular heterogeneity in NO3− uptake within groups facilitates adaptation to the fluctuating availability of NO3− in the environment.

     
    more » « less
  3. Abstract

    Climate change is projected to modify the physical and chemical environment of the ocean, but the quantitative impact on the distribution of phytoplankton groups is unclear. Most Earth System Models (ESMs) predict future declines of phytoplankton in low latitude waters, contradicting observations showing that picophytoplankton can reach high abundance in warm waters. Here, we used a historic and three climate scenarios along with quantitative niche models to projectProchlorococcus,Synechococcus, and picoeukaryotic phytoplankton distributions for the year 2100. First, we found global responses with up to 50% and 9% increase forProchlorococcusandSynechococcusabundances, respectively, and 8% decrease for picoeukaryotic phytoplankton. All groups increased in abundance at low latitude, andSynechococcusand picoeukaryotic phytoplankton showed bands of decreases and increases in mid‐ and high‐latitudes, respectively.Prochlorococcustemporal trends were consistent among ESMs and increased with the strength of the scenario, whileSynechococcusand picoeukaryotic phytoplankton showed mixed results. Second, we evaluated sources of uncertainty associated to future projections. The anthropogenic uncertainty, associated to climate scenarios, increased with time and was relevant forProchlorococcus. The environmental and biological uncertainty, associated to ESMs and niche models, respectively, represented the largest fraction but differed among lineages. Quantifying uncertainties is key because the predicted differences in the future distribution and abundance can have large‐scale consequences on ocean ecosystem functioning.

     
    more » « less
  4. Abstract

    The Hawaii Ocean Time‐series (HOT) at Station ALOHA (22.75°N, 158°W) in the North Pacific Subtropical Gyre (NPSG) serves as a critical vantage point for observing plankton biomass production and its ecological implications. However, the HOT program's near‐monthly sampling frequency does not capture shorter time scale variability in phytoplankton populations. To address this gap, we deployed the SeaFlow flow cytometer for continuous monitoring during HOT cruises from 2014 to 2021. This approach allowed us to examine variations in the surface abundance and cell carbon content of specific phytoplankton groups: the cyanobacteriaProchlorococcus,Synechococcus, andCrocosphaeraas well as a range of small eukaryotic phytoplankton ( 5 μm). Our data showed that daily to monthly variability inProchlorococcusandSynechococcusabundance matches seasonal and interannual variability, while small eukaryotic phytoplankton andCrocosphaerashowed the highest seasonal and interannual fluctuations. The study also found that eukaryotic phytoplankton andCrocosphaerahad higher median cellular growth rates (0.076 and , respectively) compared toProchlorococcusandSynechococcus(0.037 and , respectively). These variances in abundance and growth rates indicate that shifts in the community structure significantly impact primary productivity in the NPSG. Our results underscore the importance of daily to monthly phytoplankton dynamics in ecosystem function and carbon cycling.

     
    more » « less
  5. Abstract

    Marine picophytoplankton is the most abundant photosynthetic group on Earth; however, it is still underrepresented in dynamic ecosystem models. Major constraints for understanding its role in the ecosystem at a global scale are sparse data and lack of a baseline description of its distribution. Here, we present three datasets to assess the global abundance of the principal groups of picophytoplankton,Prochlorococcus,Synechococcus, and picoeukaryotic phytoplankton: (1) a compilation of 109,045 field observations with ancillary environmental data, (2) a global monthly climatology of 1° grids from 0 to 200 m, and (3) four climate scenarios projections, from the Coupled Model Intercomparison Project 5, spanning years 1901 to 2100. Together this set of observational and modeled data can improve our understanding of the role of picophytoplankton in the global ecosystem.

     
    more » « less