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  • 1
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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
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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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
    Repository Name: Woods Hole Open Access Server
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  • 3
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    A simplified age-stage model for copepod population dynamics (2012)
    Inter-Research
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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 Marine Ecology Progress Series 360 (2008): 179-187, doi:10.3354/meps07314.
    Description: Complex 3D biological-physical models are becoming widely used in marine and freshwater ecology. These models are highly valued synthesizing tools because they provide insights into complex dynamics that are difficult to understand using purely empirical methods or theoretical analytical models. Of particular interest has been the incorporation of concentration-based copepod population dynamics into 3D physical transport models. These physical models typically have large numbers of grid points and therefore require a simplified biological model. However, concentration-based copepod models have used a fine resolution age-stage structure to prevent artificially short generation times, known as numerical ‘diffusion.’ This increased resolution has precluded use of age-stage structured copepod models in 3D physical models due to computational constraints. In this paper, we describe a new method, which tracks the mean age of each life stage instead of using age classes within each stage. We then compare this model to previous age-stage structured models. A probability model is developed with the molting rate derived from the mean age of the population and the probability density function (PDF) of molting. The effects of temperature and mortality on copepod population dynamics are also discussed. The mean-age method effectively removes the numerical diffusion problem and reproduces observed median development times (MDTs) without the need for a high-resolution age-stage structure. Thus, it is well-suited for finding solutions of concentration-based zooplankton models in complex biological-physical models.
    Description: This work was supported by US GLOBEC NOAA grant NA17RJ1223.
    Description: 2013-05-22
    Keywords: Plankton ; Copepods ; Modeling ; Marine ecology ; Oceanography ; Limnology ; Methodology ; Mean age
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Whale distribution in relation to prey abundance and oceanographic processes in shelf waters of the Western Antarctic Peninsula (2011)
    Inter-Research
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    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2006. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 317 (2006): 297-310, doi:10.3354/meps317297.
    Description: The Western Antarctic Peninsula (WAP) is a biologically rich area supporting large standing stocks of krill and top predators (including whales, seals and seabirds). Physical forcing greatly affects productivity, recruitment, survival and distribution of krill in this area. In turn, such interactions are likely to affect the distribution of baleen whales. The Southern Ocean GLOBEC research program aims to explore the relationships and interactions between the environment, krill and predators around Marguerite Bay (WAP) in autumn 2001 and 2002. Bathymetric and environmental variables including acoustic backscattering as an indicator of prey abundance were used to model whale distribution patterns. We used an iterative approach employing (1) classification and regression tree (CART) models to identify oceanographic and ecological variables contributing to variability in humpback Megaptera novaeangliae and minke Balaenoptera acutorstrata whale distribution, and (2) generalized additive models (GAMs) to elucidate functional ecological relationships between these variables and whale distribution. The CART models indicated that the cetacean distribution was tightly coupled with zooplankton acoustic volume backscatter in the upper (25 to 100 m), and middle (100 to 300 m) portions of the water column. Whale distribution was also related to distance from the ice edge and bathymetric slope. The GAMs indicated a persistent, strong, positive relationship between increasing zooplankton volume and whale relative abundance. Furthermore, there was a lower limit for averaged acoustic volume backscatter of zooplankton below which the relationship between whales and prey was not significant. The GAMs also supported an annual relationship between whale distribution, distance from the ice edge and bathymetric slope, suggesting that these are important features for aggregating prey. Our results demonstrate that during the 2 yr study, whales were consistently and predictably associated with the distribution of zooplankton. Thus, humpback and minke whales may be able to locate physical features and oceanographic processes that enhance prey aggregation.
    Description: Resources for this project were provided by the National Science Foundation Office of Polar Programs grant OPP-9910307 and the International Whaling Commission. This work represents a portion of A.S.F.’s dissertation, funded by a Duke University Marine Laboratory Fellowship.
    Keywords: Whale distribution ; Zooplankton ; Ice edge ; Antarctica ; SO GLOBEC ; CART ; GAM
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Mixotrophy : a widespread and important ecological strategy for planktonic and sea-ice nanoflagellates in the Ross Sea, Antarctica (2011)
    Inter-Research
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    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2009. 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 54 (2009): 269-277, doi:10.3354/ame01276.
    Description: Mixotrophic nanoflagellates (MNF) were quantified in plankton and sea ice of the Ross Sea, Antarctica, during austral spring. Tracer experiments using fluorescently labeled bacteria (FLB) were conducted to enumerate MNF and determine their contribution to total chloroplastidic and total bacterivorous nanoflagellates. Absolute abundances of MNF were typically 〈200 ml–1 in plankton assemblages south of the Polar Front, but they comprised 8 to 42% and 3 to 25% of bacterivorous nanoflagellates in the water column and ice cores, respectively. Moreover, they represented up to 10% of all chloroplastidic nanoflagellates in the water column when the prymnesiophyte Phaeocystis antarctica was blooming (up to 23% if P. antarctica, which did not ingest FLB, was excluded from calculations). In ice cores, MNF comprised 5 to 10% of chloroplastidic nanoflagellates. The highest proportions of MNF were found in some surface water samples and in plankton assemblages beneath ice, suggesting a potentially large effect as bacterial grazers in those locations. This study is the first to report abundances and distributions of mixotrophic flagellates in the Southern Ocean. The presence of MNF in every ice and water sample examined suggests that mixotrophy is an important alternative dietary strategy in this region.
    Description: This work was supported by NSF grant OPP-0125833 to D.A.C. and R.J.G.
    Keywords: Ross Sea ; Antarctica ; Mixotrophy ; Mixotrophic nanoflagellates ; Bacterivory ; Plankton ; Sea ice ; Fluorescently labeled bacteria
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Response of a summertime Antarctic marine ­bacterial community to glucose and ammonium enrichment (2011)
    Inter-Research
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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
    Repository Name: Woods Hole Open Access Server
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