Microbial community structure at the U.S.-Joint Global Ocean Flux Study Station ALOHA: Inverse methods for estimating biochemical indicator ratios

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 N2 fixation rates and plankton abundances demonstrate the central role of N2 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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Defining marine microbial biomes from environmental and dispersal filtered metapopulations

10.1101/141077 ◽

2017 ◽

Author(s):

Markus V. Lindh

Keyword(s):

Community Structure ◽

Microbial Community ◽

Microbial Community Structure ◽

Spatial Scales ◽

Dispersal Limitation ◽

Global Ocean ◽

Microbial Populations ◽

Microbial Biogeography ◽

Metapopulation Theory ◽

Mock Communities

SummaryEnergy and matter fluxes essential for all life1 are modulated by spatial and temporal shifts in microbial community structure resulting from environmental and dispersal filtering2,3, emphasizing the continued need to characterize microbial biogeography4,5. Yet, application of metapopulation theory, traditionally used in general ecology for understanding shifts in biogeographical patterns among macroorganisms, has not been tested extensively for defining marine microbial populations filtered by environmental conditions and dispersal limitation at global ocean scales. Here we show, from applying metapopulation theory on two major global ocean datasets6,7, that microbial populations exhibit core- and satellite distributions with cosmopolitan compared to geographically restricted distributions of populations. We found significant bimodal occupancy-frequency patterns (the different number of species occupying different number of patches) at varying spatial scales, where shifts from bimodal to unimodal patterns indicated environmental and dispersal filtering. Such bimodal occupancy-frequency patterns were validated in Longhurst’s classical biogeographical framework and in silico where observed bimodal patterns often aligned with specific biomes and provinces described by Longhurst and where found to be non-random in randomized datasets and mock communities. Taken together, our results show that application of metapopulation theory provides a framework for determining distinct microbial biomes maintained by environmental and dispersal filtering.

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Microbial community structure in the Western Tropical South Pacific

10.5194/bg-2017-562 ◽

2018 ◽

Cited By ~ 5

Author(s):

Nicholas Bock ◽

France Van Wambeke ◽

Moïra Dion ◽

Solange Duhamel

Keyword(s):

Community Structure ◽

Microbial Community ◽

Microbial Communities ◽

Microbial Community Structure ◽

N2 Fixation ◽

South Pacific ◽

Global Ocean ◽

General Level ◽

Bottom Up

Abstract. 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 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 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 stratified regions, and underline the significant contribution to total biomass by PPE populations. Strong relationships between N2 fixation rates and plankton abundances demonstrate the central role of N2 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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