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Interaction between microbial assemblages around the South Shetland Islands (Antarctica)

Autor García Muñoz, Cristina ; Lubián, Luis M. ; García, Carlos M.; Sangrà, Pablo
Palabras clave Clusters
Flow cytometry
Microbial assemblages
South Shetland Islands
Fecha de publicación abr-2012
Citación IPY 2012 Conference (2012)
ResumenA comparative analysis of heterotrophic bacteria, phytoplankton and nanograzers distribution in Drake passage (a region where data are scarce) and Bransfield Strait (Antarctic Ocean) was made by using flow citometry during COUPLING cruise (January 2010). This cruise was focused on the analysis of physical-biological coupling at the mesoscale range, studying hydrodynamics, water attributes and plankton structure around the South Shetland Islands (SSI). An improvement of the understanding of microbial system in the context of the carbon flux in polar regions is crucial, as climate chan ge may have the fastest impact in these areas. In the present work, we describe the spatial distribution of the different assemblages that make up the microbial community. We grouped the st ations based on the depth integrated abundances using cluster anal ysis. Physical features and nutr ients concentrations were related to the clusters found. Two bacterial subpopulations were discriminated after SYTO-13 staining based on their different green fluorescence (FL1) signal: low nucleic acid content (LNA) and high nucleic acid content (HNA). Total bacterial numbers varied from 0.21 to 4.21 x10 5 Cells/mL, HNA comprised 56.8 % (± 7.6) of all bacteria. Four groups of eukaryotic autotrophic cells and a pool of nanoheterotrophs were detected using the wide angle light scatter signal (SSC) and orange and red fluorescence (FL2 and FL3, respectively). These groups had different distributions in the Drake Passage, around the SSI platform, in the Bransfield Strait and in the Antarctic Sound. In this latter area the microplankton (>20 m) size fraction predominated, reaching also the highest Chl a concentrations. The only phytoplankton group present in all stations was “ Nano medium ” (5.2 μm mean Equivalent Spherical Diameter (ESD)) being also the most abundant (5.3 x10 11 ( Cells/m 2 )). This group represented 75.9% of the total integrated phytoplankton ( Cells/m 2 ) below 20 μm. HNA and LNA bacteria subpopulations differed in the response of SSC to environmental factors. SSC-HNA decreased strongly with depth and varied along the study area while no similar trends were observed for the LNA subpopulation. LNA shows better correlations with the main phytoplankton groups (“ Nano medium ” and “ Nano large ” (8.9 μm mean ESD)) and Chl a concentration (2-20 μm). Vertical profiles of microbial abundances along the ma in transect revealed a decoupled distribution of HNA being located below the phytoplankton assemblages. Three clusters of stations were identified in a north-south gradient of species pr esence / absence. Temperature, salinity and silicate concentration were significantly different between clusters. Also mesoscale structures (i.e. fronts, stratified areas) modulate the distribution of the plankton in specific sites. In conclusion, during the austral summer of 2010 around the SSI, different stages in the successional microbial community were being carried out simultaneously, due to the different physicochemical characteristics at each station and the succession between blooming and senescent scenarios. Our study highlights that piecing together both HNA and LNA bacteria as total bacterioplankton and all phytoplankton groups without discriminating the different populations, could lead to misinterpretation of the antarctic microbial loop.
Descripción Trabajo presentado en la IPY 2012 Conference (From Knowledge to Action), celebrada en montreal del 22 al 27 de abril de 2012.
URI http://hdl.handle.net/10261/110145
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