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  • 1
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    Towards a better understanding of microbial carbon flux in the sea (2011)
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    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2008. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 53 (2008): 21-38, doi:10.3354/ame01230.
    Description: We now have a relatively good idea of how bulk microbial processes shape the cycling of organic matter and nutrients in the sea. The advent of the molecular biology era in microbial ecology has resulted in advanced knowledge about the diversity of marine microorganisms, suggesting that we might have reached a high level of understanding of carbon fluxes in the oceans. However, it is becoming increasingly clear that there are large gaps in the understanding of the role of bacteria in regulating carbon fluxes. These gaps may result from methodological as well as conceptual limitations. For example, should bacterial production be measured in the light? Can bacterial production conversion factors be predicted, and how are they affected by loss of tracers through respiration? Is it true that respiration is relatively constant compared to production? How can accurate measures of bacterial growth efficiency be obtained? In this paper, we discuss whether such questions could (or should) be addressed. Ongoing genome analyses are rapidly widening our understanding of possible metabolic pathways and cellular adaptations used by marine bacteria in their quest for resources and struggle for survival (e.g. utilization of light, acquisition of nutrients, predator avoidance, etc.). Further, analyses of the identity of bacteria using molecular markers (e.g. subgroups of Bacteria and Archaea) combined with activity tracers might bring knowledge to a higher level. Since bacterial growth (and thereby consumption of DOC and inorganic nutrients) is likely regulated differently in different bacteria, it will be critical to learn about the life strategies of the key bacterial species to achieve a comprehensive understanding of bacterial regulation of C fluxes. Finally, some processes known to occur in the microbial food web are hardly ever characterized and are not represented in current food web models. We discuss these issues and offer specific comments and advice for future research agendas.
    Description: Our work was supported by the following grants: NSF grant 0217282 (H.D.), Spanish MEC grant MODIVUS (J.M.G.), the Swedish Science Council (J.P.), the IEO time-series RADIALES programme (X.A.G.M.), the Earth and Life Science Division of the Dutch Science Foundation, ARCHIMEDES project, #835.20.023 (G.J.H.).
    Keywords: Carbon flux ; Microbial ecology ; Ocean ; Bacteria ; Protists ; Light ; Genomics ; Chemoautotrophy ; Models
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Microzooplankton grazing along the Western Antarctic Peninsula (2013)
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    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2013. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 70 (2013): 215-232, doi:10.3354/ame01655.
    Description: The significance of microzooplankton as grazers in pelagic ecosystems has been established, yet relatively few studies of microzooplankton grazing, compared to that of macrozooplankton, have been conducted in the Southern Ocean. We report phytoplankton and bacterial growth and grazing mortality rates along the Western Antarctic Peninsula (WAP), a region of rapid climate change. Growth and grazing rates were determined by dilution experiments at select stations along the WAP in January of 2009 to 2011 and in the nearshore waters near Palmer Station in February and March 2011. Microzooplankton exerted higher grazing pressure on bacteria compared to phytoplankton along the WAP and also selectively grazed on smaller phytoplankton (picoautotrophs and nanophytoplankton) and on the more actively growing (high nucleic acid) bacterial cells. Among all phytoplankton size classes, growth rates ranged from undetectable (i.e. not significant; NS) to 0.99 d-1, grazing mortality rates were NS to 0.56 d-1, and microzooplankton removed 〈100% of daily phytoplankton production in all but one experiment. For high and low nucleic acid content bacteria, growth rates were NS to 0.95 d-1, and grazing mortality rates were NS to 0.43 d-1; microzooplankton often removed 〉100% of daily bacterial production. There was a significant (albeit weak) exponential relationship between temperature and phytoplankton mortality, although the range of experimental temperatures was small. The present study provides a reference point of microzooplankton grazing impact along the WAP in the summer and contributes valuable information to studies modeling the flow of carbon through the WAP food web, improving our ability to predict climate-induced changes in the WAP ecosystem.
    Description: The Palmer LTER is supported by National Science Foundation award ANT-0823101 from the Division of Polar Programs Antarctic Organisms and Ecosystems Program. Additional funding to support the participation of L.M.G. on a Palmer LTER cruise was provided by A. G. ‘Casey’ Duplantier Jr. and the 1st Advantage Federal Credit Union of Newport News, Virginia, USA.
    Keywords: Microzooplankton ; Protozoa ; Grazing ; Western Antarctic Peninsula ; Southern Ocean ; Climate
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  • 3
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    Marine bacterial, archaeal and eukaryotic diversity and community structure on the continental shelf of the western Antarctic Peninsula (2014)
    Inter-Research
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    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2014. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 73 (2014): 107-121, doi:10.3354/ame01703.
    Description: The classic view of polar ocean foodwebs emphasizes large predators sustained by energy and material flow through short, efficient diatom-krill-predator food chains. Bacterial activity is generally low in cold polar waters compared to that at lower latitudes. This view appears to be changing, with new studies of microbial foodwebs in Arctic and Antarctic oceans. We characterized bacterial, archaeal, and eukaryotic community diversity and composition from 2 depths (near surface and below the euphotic zone) at 4 sites, including the inshore and offshore, and north and south corners of a sampling grid along the western coast of the Antarctic Peninsula (WAP). We detected up to 2-fold higher richness in microbial eukaryotes at surface and deep inshore northern stations as compared to southern stations, but offshore northern and southern stations revealed either no trend or higher richness at depth in the south. In contrast, bacterial and archaeal richness showed no significant differences either inshore or offshore at northern versus southern extents, but did vary with depth. Archaea were virtually absent in summer surface waters, but were present in summer deep and winter surface samples. Overall, winter bacterial and archaeal assemblages most closely resembled summer sub-euphotic zone assemblages, reflecting well-established seasonal patterns of water column turnover and stratification that result in an isolated layer of ‘winter water’ below the euphotic zone. Inter-domain heterotroph-phototroph interactions were evident from network analysis. The WAP is among the most rapidly warming regions on earth. Our results provide a baseline against which future change in microbial communities may be assessed.
    Description: Funding was provided by NSF DEB- 0717390 to L.A.Z. (MIRADA-LTERS) and NSF Awards OPP- 0217282 and 0823101 (Palmer LTER) from the Antarctic Organisms and Ecosystems Program to H.W.D.
    Keywords: Antarctica ; MIRADA-LTERS ; Palmer LTER ; Pyrosequencing ; V6 ; V9 ; Microbial oceanography
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  • 4
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    Microbial services : challenges for microbial ecologists in a changing world (2011)
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    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2008. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 53 (2008): 13-19, doi:10.3354/ame01220.
    Description: Bacteria, archaea and other microbes have dominated most biogeochemical processes on Earth for 〉99% of the history of life, but within the past few decades anthropogenic activity has usurped their dominance. Human activity now impacts every ecosystem on the planet, necessitating a new socio-ecological view of ecosystem processes that incorporates human perceptions, responses, activities and ideas into ecology. The concept of ecosystem services is an important link between ecosystem processes and the social sphere. These include the provisioning, regulating, cultural and supporting benefits that ecosystems provide to enhance human well-being. Many ecosystem services are provided by microbes, initiating the concept of microbial services to society—an idea long appreciated by microbial ecologists. Experimental studies of the biodiversity–ecosystem function relationship emphasizing microbial functions are inconclusive, with increasing diversity sometimes being observed to enhance function, while at other times the opposite relationship has been found. A specific function addressing the role of bacteria in helping or hindering carbon storage in the deep ocean in response to iron fertilization is similarly uncertain. Bacteria respond positively to mesoscale iron additions in many cases, but in doing so, may retard carbon storage by decomposing sinking particles. Human exploitation of microbial services to enhance planetary sustainability must be based on focused studies of microbial processes in a human-dominated world.
    Description: The work for this manuscript was supported in part by NSF OPP 0217282.
    Keywords: Ecosystem services ; Microbial services ; Microbial diversity function ; Sustainability ; Iron fertilization
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  • 5
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    Response of a summertime Antarctic marine ­bacterial community to glucose and ammonium enrichment (2011)
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    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2011. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 64: 205-220, doi:10.3354/ame01519.
    Description: Along the western Antarctic Peninsula, marine bacterioplankton respond to the spring phytoplankton bloom with increases in abundance, production and growth rates, and a seasonal succession in bacterial community composition (BCC). We investigated the response of the bacterial community to experimental additions of glucose and ammonium, alone or in combination, incubated in replicate carboys (each: 50 l) over 10 d in November 2006. Changes in bulk properties (abundance, production rates) in the incubations resembled observations in the nearshore environment over 8 seasons (2001 to 2002 through 2008 to 2009) at Palmer Stn (64.8°S, 64.1°W). Changes in bulk properties and BCC in ammonium-amended carboys were small relative to controls, compared to the glucose-amended treatments. The BCC in Day 0 and Day 10 controls and ammonium treatments were 〉72% similar when assessed by denaturing-gradient gel electrophoresis (DGGE), length heterogeneity polymerase chain reaction (LH-PCR) and capillary electrophoresis single-strand conformation polymorphism (CE-SSCP) fingerprinting techniques. Bacterial abundance increased 2- to 10-fold and leucine incorporation rates increased 2- to 30-fold in the glucose treatments over 6 d. The BCC in carboys receiving glucose (with or without ammonium) remained 〉60% similar to that in Day 0 controls at 6 d and evolved to 〈20% similar to that in Day 0 controls after 10 d incubation. The increases in bacterial production rates, and the changes in BCC, suggest that selection for glucose-utilizing bacteria was slow under the ambient environmental conditions. The results suggest that organic carbon enrichment is a major factor influencing the observed winter-to-summer increase in bacterial abundance and activity. In contrast, the BCC was relatively robust, changing little until after repeated additions of glucose and prolonged (~10 d) incubation.
    Description: H.W.D. and A.E.M. were supported by US NSF grants ANT-0632278 and ANT- 0632389, respectively. This research was partly supported by NSF OPP-0217282 (Palmer LTER). J.F.G. was supported by the Institut Français pour la Recherche et la Technologie Polaires (IFRTP).
    Keywords: Antarctica ; Bacterial community composition ; Bioassay ; Marine bacterioplankton
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  • 6
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    Carbon fluxes and pelagic ecosystem dynamics near two western Antarctic Peninsula Adélie penguin colonies : an inverse model approach (2013)
    Inter-Research
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Ecology Progress Series 492 (2013): 253-272, doi:10.3354/meps10534.
    Description: An inverse food-web model for the western Antarctic Peninsula (WAP) pelagic food web was constrained with data from Palmer Long Term Ecological Research (PAL-LTER) project annual austral summer sampling cruises. Model solutions were generated for 2 regions with Adélie penguin Pygoscelis adeliae colonies presenting different population trends (a northern and a southern colony) for a 12 yr period (1995-2006). Counter to the standard paradigm, comparisons of carbon flow through bacteria, microzooplankton, and krill showed that the diatom-krill-top predator food chain is not the dominant pathway for organic carbon exchanges. The food web is more complex, including significant contributions by microzooplankton and the microbial loop. Using both inverse model results and network indices, it appears that in the northern WAP the food web is dominated by the microbial food web, with a temporal trend toward its increasing importance. The dominant pathway for the southern WAP food web varies from year to year, with no detectable temporal trend toward dominance of microzooplankton versus krill. In addition, sensitivity analyses indicated that the northern colony of Adélie penguins, whose population size has been declining over the past 35 yr, appears to have sufficient krill during summer to sustain its basic metabolic needs and rear chicks, suggesting the importance of other processes in regulating the Adélie population decline.
    Description: We acknowledge support from the National Science Foundation, Office of Polar Programs, Award 0823101 (Antarctic Organisms and Ecosystems Program) to Palmer LTER.
    Keywords: Inverse model ; Food web ; Antarctica ; Microzooplankton ; Krill ; Ecosystem state change ; Climate change
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  • 7
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    Oceanic heterotrophic bacterial nutrition by semilabile DOM as revealed by data assimilative modeling (2011)
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    Publication Date: 2022-05-26
    Description: Author Posting. © Inter-Research, 2010. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 60 (2010): 273-287, doi:10.3354/ame01427.
    Description: Previous studies have focused on the role of labile dissolved organic matter (DOM) (defined as turnover time of ~1 d) in supporting heterotrophic bacterial production, but have mostly neglected semilabile DOM (defined as turnover time of ~100 to 1000 d) as a potential substrate for heterotrophic bacterial growth. To test the hypothesis that semilabile DOM supports substantial amounts of heterotrophic bacterial production in the open ocean, we constructed a 1-dimensional epipelagic ecosystem model and applied it to 3 open ocean sites: the Arabian Sea, Equatorial Pacific and Station ALOHA in the North Pacific Subtropical Gyre. The model tracks carbon, nitrogen and phosphorus with flexible stoichiometry. This study used a large number of observations, including measurements of heterotrophic bacterial production rates and standing stocks, and DOM concentration data, to rigorously test and constrain model output. Data assimilation was successfully applied to optimize the model parameters and resulted in simultaneous representation of observed nitrate, phosphate, phytoplankton and zooplankton biomass, primary production, heterotrophic bacterial biomass and production, DOM, and suspended and sinking particulate organic matter. Across the 3 ocean ecosystems examined, the data assimilation suggests semilabile DOM may support 17 to 40% of heterotrophic bacterial carbon demand. In an experiment where bacteria only utilize labile DOM, and with more of the DOM production assigned to labile DOM, the model poorly represented the observations. These results suggest that semilabile DOM may play an important role in sustaining heterotrophic bacterial growth in diverse regions of the open ocean.
    Description: Y.W.L. was supported by fellowships from the Virginia Institute of Marine Sciences and Marine Biological Laboratory as well as NSF Grants OPP-0217282 and 0823101 to H.W.D. and VIMS and MBL, respectively. M.A.M.F.’s participation was supported in part by a grant from the NASA Ocean Biology and Biogeochemistry program (NNX07AF70G), S.C.D.’s participation was supported by an NSF grant to the Center for Microbial Oceanography, Research and Education (CMORE), NSF EF-0424599, and M.J.C. was supported in part by NSF grants EF-0424599 (C-MORE) and OCE 0425363.
    Keywords: Heterotrophic bacteria ; Semilabile dissolved organic matter ; Marine ecosystem model ; Data assimilation
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  • 8
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    Effect of continental shelf canyons on phytoplankton biomass and community composition along the western Antarctic Peninsula (2015)
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Ecology Progress Series 524 (2015): 11-26, doi:10.3354/meps11189.
    Description: The western Antarctic Peninsula is experiencing dramatic climate change as warm, wet conditions expand poleward and interact with local physics and topography, causing differential regional effects on the marine ecosystem. At local scales, deep troughs (or canyons) bisect the continental shelf and act as conduits for warm Upper Circumpolar Deep Water, with reduced seasonal sea ice coverage, and provide a reservoir of macro- and micronutrients. Shoreward of many canyon heads are Adélie penguin breeding colonies; it is hypothesized that these locations reflect improved or more predictable access to higher biological productivity overlying the canyons. To synoptically assess the potential impacts of regional bathymetry on the marine ecosystem, 4 major canyons were identified along a latitudinal gradient west of the Antarctic Peninsula using a high-resolution bathymetric database. Biological-physical dynamics above and adjacent to canyons were compared using in situ pigments and satellite-derived sea surface temperature, sea ice and ocean color variables, including chlorophyll a (chl a) and fucoxanthin derived semi-empirically from remote sensing reflectance. Canyons exhibited higher sea surface temperature and reduced sea ice coverage relative to adjacent shelf areas. In situ and satellite-derived pigment patterns indicated increased total phytoplankton and diatom biomass over the canyons (by up to 22 and 35%, respectively), as well as increases in diatom relative abundance (fucoxanthin:chl a). While regional heterogeneity is apparent, canyons appear to support a phytoplankton community that is conducive to both grazing by krill and enhanced vertical export, although it cannot compensate for decreased biomass and diatom relative abundance during low sea ice conditions.
    Description: We acknowledge support from the National Aeronautics and Space Administration Ocean Bio - logy and Biogeochemistry Program (NNX14AL86G) and the National Science Foundation Polar Programs awards 0823101 (Antarctic Organisms and Ecosystems Program) and 1440435 (Antarctic Integrated System Science) to the Palmer LTER program.
    Keywords: Western Antarctic Peninsula ; Canyons ; Phytoplankton ; Diatoms ; Remote sensing ; Adélie penguin habitat ; Sea ice
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  • 9
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    Total and phytoplankton mediated bottom-up control of bacterioplankton change with temperature in NE Atlantic shelf waters (2011)
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    Publication Date: 2022-05-26
    Description: Author Posting. © Inter-Research, 2010. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 58 (2010): 229-239, doi:10.3354/ame01374.
    Description: The regulation of heterotrophic bacterial growth by resource supply (bottom-up control) was temperature-dependent in our analysis of data obtained during 2006 in the euphotic layer of the southern Bay of Biscay (NE Atlantic) continental shelf. The dataset was split into 2 subgroups using 16°C as the boundary between warm and cool waters based on differences in associated physico-chemical conditions, e.g. inorganic nutrient limitation at higher temperatures. The linear regressions between bacterial biomass (BB) and leucine incorporation rates (LIR) were significantly positive in both temperature regimes, thus indicating similar total bottom-up control, albeit with a slightly higher slope in warm waters (0.33 vs. 0.22). However, the relationship of LIR with phytoplankton biomass (chl a), which is an indicator of bottom-up control that is mediated by phytoplankton, was only significant in waters below 16°C. The analysis of bimonthly variations in the BB-LIR and LIR-chl a correlations indicated that the strength of total bottom-up control significantly increased while the role of phytoplankton in supplying DOM to bacteria diminished with mean temperatures over the 12 to 19°C range, suggesting a seasonal switch in the major source of substrates used by bacteria. We show that the abundance of cells with relatively high nucleic acid content (HNA), which are hypothesized to be the most active ones, was positively associated with bacterial production and specific growth rates in cool but not in warm conditions. These results suggest that HNA bacteria are good predictors of bulk activity and production in temperate ecosystems only when the community relies principally on phytoplankton substrates for growth and metabolism.
    Description: X.A.G.M. was partially supported by a sabbatical grant at the MBL from the Spanish Ministry of Education and Science (MEC) and A.C.-D. received an FPI research training predoctoral fellowhip. This work was supported by the time-series project RADIALES from the Instituto Espanol de Oceanografia (IEO).
    Keywords: Bacterioplankton ; Bottom-up control ; Temperature ; Bacterial biomass ; Bacterial activity ; Phytoplankton ; Coastal waters
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