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

Rii, Yoshimi M.; Karl, David M.; Church, Matthew J.

doi:10.3354/meps11954

Cited by 55 publications

(55 citation statements)

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“…)—have a substantial role in C cycling of the Northwest Atlantic Ocean. Similar results have been found in the North and South Pacific and Atlantic gyres (Jardillier et al ; Grob et al ; Rii et al , b ). The important role of P‐Euk in the oligotrophic ocean C cycling is likely due to their larger cell biovolume relative to picocyanobacteria.…”

Section: Discussionsupporting

confidence: 88%

“…Answering these questions is fundamental to understand marine ecosystem functioning and to predict how the marine environment will respond to global climate changes (Worden et al ). Although the abundance, distribution, and ecological roles of marine protists have been the focus of many studies (Ohtsuka et al ), there is still much to be learned, particularly for the smaller sized eukaryotes (i.e., picoeukaryotes [< 2–3 μ m] and nanoeukaryotes [2–20 μ m], hereafter designated as small eukaryotes) that are increasingly being recognized as important to oceanic C cycling as primary producers and consumers (Massana et al ; Cuvelier et al ; Grob et al ; Massana ; Hartmann et al ; Worden et al ; Rii et al , b ). Despite recent progress in the examination of marine protists using modern molecular tools, major gaps remain in our understanding of these understudied eukaryotic microorganisms, particularly in comparison to marine prokaryotes (Caron et al ; Keeling and Campo ).…”

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confidence: 99%

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Small pigmented eukaryotes play a major role in carbon cycling in the P‐depleted western subtropical North Atlantic, which may be supported by mixotrophy

Duhamel

Kim

Sprung

et al. 2019

Limnology & Oceanography

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We found that in the phosphate (PO4)‐depleted western subtropical North Atlantic Ocean, small‐sized pigmented eukaryotes (P‐Euk; < 5 μm) play a central role in the carbon (C) cycling. Although P‐Euk were only ~ 5% of the microbial phytoplankton cell abundance, they represented at least two thirds of the microbial phytoplankton C biomass and fixed more CO2 than picocyanobacteria, accounting for roughly half of the volumetric CO2 fixation by the microbial phytoplankton, or a third of the total primary production. Cell‐specific PO4 assimilation rates of P‐Euk and nonpigmented eukaryotes (NP‐Euk; < 5 μm) were generally higher than of picocyanobacteria. However, when normalized to biovolumes, picocyanobacteria assimilated roughly four times more PO4 than small eukaryotes, indicating different strategies to cope with PO4 limitation. Our results underline an imbalance in the CO2 : PO4 uptake rate ratios, which may be explained by phagotrophic predation providing mixotrophic protists with their largest source of PO4. 18S rDNA amplicon sequence analyses suggested that P‐Euk was dominated by members of green algae and dinoflagellates, the latter group commonly mixotrophic, whereas marine alveolates were the dominant NP‐Euk. Bacterivory by P‐Euk (0.9 ± 0.3 bacteria P‐Euk−1 h−1) was comparable to values previously measured in the central North Atlantic, indicating that small mixotrophic eukaryotes likely exhibit similar predatory pressure on bacteria. Interestingly, bacterivory rates were reduced when PO4 was added during experimental incubations, indicating that feeding rate by P‐Euk is regulated by PO4 availability. This may be in response to the higher cost associated with assimilating PO4 by phagocytosis compared to osmotrophy.

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Section: Discussionsupporting

confidence: 88%

mentioning

confidence: 99%

Small pigmented eukaryotes play a major role in carbon cycling in the P‐depleted western subtropical North Atlantic, which may be supported by mixotrophy

Duhamel

Kim

Sprung

et al. 2019

Limnology & Oceanography

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“…The same phenomenon has been reported along biogeochemical conditions in the North Atlantic (Partensky et al, 1996;Zubkov et al, 2000), as well as the southeastern Pacific (Grob et al, 2007a;Rii et al, 2016b). By contrast, sites with comparatively limited seasonal variability, like station ALOHA in the North Pacific subtropical gyre, have shown consistently high ratios of Prochlorococcus to Synechococcus year-round (Rii et al, 2016a), while studies of nitraterich eutrophic regions often report the complete exclusion of Prochlorococcus by Synechococcus and eukaryotic populations (Sherr et al, 2005;Zubkov et al, 2007). The high relative abundance of Prochlorococcus at LDB compared to sites with similar Chl a concentrations may be due to having captured the bloom in decay (de Verneil et al, 2017), with nutrients having been largely depleted at the time of measurement and relative Prochlorococcus abundances returning to levels more representative of the WTSP.…”

Section: Distribution Of Pigments and Photo Acclimation In Different supporting

confidence: 76%

“…Especially over the last 10 years, molecular methodologies have allowed for the characterization of these groups at the taxon or species level, revealing enormous diversity across all trophic levels of marine microbial communities and identifying numerous ecotypes occupying distinct ecological niches (Carlson et al, 2007;Venter et al, 2004). More recently, environmental sequencing has revealed a surprising diversity of small-sized PPE and new eukaryotic lineages continue to be discovered and characterized (Kashtan et al, 2014;Kim et al, 2016;Lepère et al, 2009;Rii et al, 2016a), while also revealing the importance of viruses in regulating phytoplankton communities (Brum et al, 2015;Huang et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Microbial community structure in the western tropical South Pacific

2018

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Abstract. Oligotrophic regions play a central role in global biogeochemical cycles, with microbial communities in these areas representing an important term in global carbon budgets. While the general structure of microbial communities has been well documented in the global ocean, some remote regions such as the western tropical South Pacific (WTSP) remain fundamentally unexplored. Moreover, the biotic and abiotic factors constraining microbial abundances and distribution remain not well resolved. In this study, we quantified the spatial (vertical and horizontal) distribution of major microbial plankton groups along a transect through the WTSP during the austral summer of 2015, capturing important autotrophic and heterotrophic assemblages including cytometrically determined abundances of non-pigmented protists (also called flagellates). Using environmental parameters (e.g., nutrients and light availability) as well as statistical analyses, we estimated the role of bottom-up and top-down controls in constraining the structure of the WTSP microbial communities in biogeochemically distinct regions. At the most general level, we found a "typical tropical structure", characterized by a shallow mixed layer, a clear deep chlorophyll maximum at all sampling sites, and a deep nitracline. Prochlorococcus was especially abundant along the transect, accounting for 68 ± 10.6 % of depth-integrated phytoplankton biomass. Despite their relatively low abundances, picophytoeukaryotes (PPE) accounted for up to 26 ± 11.6 % of depth-integrated phytoplankton biomass, while Synechococcus accounted for only 6 ± 6.9 %. Our results show that the microbial community structure of the WTSP is typical of highly stratified regions, and underline the significant contribution to total biomass by PPE populations. Strong relationships between N 2 fixation rates and plankton abundances demonstrate the central role of N 2 fixation in regulating ecosystem processes in the WTSP, while comparative analyses of abundance data suggest microbial community structure to be increasingly regulated by bottom-up processes under nutrient limitation, possibly in response to shifts in abundances of high nucleic acid bacteria (HNA).

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“…The same phenomenon has been reported along biogeochemical conditions in the North Atlantic (Partensky et al, 1996;Zubkov et al, 2000), as well as the South East Pacific (Grob et al, 2007a;Rii et al, 2016b). By contrast, sites with comparatively limited seasonal variability, like Station ALOHA in the North Pacific subtropical gyre, have shown consistently high ratios of Prochlorococcus to Synechococcus ratios year-round (Rii et al, 2016a), while studies of nitrate-rich eutrophic regions often report the complete ex-20 clusion of Prochlorococcus by Synechococcus and eukaryotic populations (Sherr et al, 2005;Zubkov et al, 2007).…”

mentioning

confidence: 81%

Microbial community structure in the Western Tropical South Pacific

Bock¹,

Wambeke²,

Dion³

et al. 2018

Preprint

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Accounting for 40 percent of the earth's surface, oligotrophic regions play an important role in global biogeochemical cycles, with microbial communities in these areas representing an important term in global carbon budgets. While the general structure of microbial communities has been well documented in the global ocean, some remote regions such as the Western Tropical South Pacific (WTSP), remain fundamentally unexplored. Moreover, the biotic and abiotic factors constraining micro-15 bial abundances and distribution remain not-well resolved. In this study, we quantified the spatial (vertical and horizontal) distribution of major microbial plankton groups along a transect through the WTSP during the austral summer of 2015, capturing important autotrophic and heterotrophic assemblages including cytometrically determined abundances of non-pigmented protists (also called flagellates). Using environmental parameters (e.g. nutrients and light availability) as well as statistical analyses, we estimated the role of bottom-up and top-down controls in constraining the structure of the WTSP microbial communities in bio-20 geochemically distinct regions. At the most general level, we found a "typical tropical structure," characterized by high abundances of Prochlorococcus at the surface, a clear deep chlorophyll maximum at all sampling sites, and a deep nitracline. Despite their relatively low abundances, picophytoeukaryotes (PPE) accounted for up to half of depth-integrated phytoplankton biomass in the lower euphotic zone. While present at all stations, Synechococcus accounted for only 2 % and 4 % of total phytoplankton abundance and biomass, respectively. Our results show that the microbial community structure of the WTSP is typical of highly 25 stratified regions, and underline the significant contribution to total biomass by PPE populations. Strong relationships between N 2 fixation rates and plankton abundances demonstrate the central role of N 2 fixation in regulating ecosystem processes in the WTSP, while comparative analyses of abundance data suggest microbial community structure to be increasingly regulated by bottom-up processes under nutrient limitation, possibly in response to shifts in abundances of high nucleic acid bacteria (HNA).

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

Cited by 55 publications

References 75 publications

Small pigmented eukaryotes play a major role in carbon cycling in the P‐depleted western subtropical North Atlantic, which may be supported by mixotrophy

Small pigmented eukaryotes play a major role in carbon cycling in the P‐depleted western subtropical North Atlantic, which may be supported by mixotrophy

Microbial community structure in the western tropical South Pacific

Microbial community structure in the Western Tropical South Pacific

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