Browsing by Author "Takacs-Vesbach, Cristina"

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McMurdo Dry Valley lake edge ‘moats’: the ecological intersection between terrestrial and aquatic polar desert habitats
(Cambridge University Press, 2024-04) Stone, Michael S.; Devlin, Shawn P.; Hawes, Ian; Welch, Kathleen; Gooseff, Michael N.; Takacs-Vesbach, Cristina; Morgan-Kiss, Rachael; Adams, Bryon J.; Barrett, J. E.; Priscu, John C.; Doran, Peter T.
Aquatic ecosystems - lakes, ponds and streams - are hotspots of biodiversity in the cold and arid environment of Continental Antarctica. Environmental change is expected to increasingly alter Antarctic aquatic ecosystems and modify the physical characteristics and interactions within the habitats that they support. Here, we describe physical and biological features of the peripheral ‘moat’ of a closed-basin Antarctic lake. These moats mediate connectivity amongst streams, lake and soils. We highlight the cyclical moat transition from a frozen winter state to an active open-water summer system, through refreeze as winter returns. Summer melting begins at the lakebed, initially creating an ice-constrained lens of liquid water in November, which swiftly progresses upwards, creating open water in December. Conversely, freezing progresses slowly from the water surface downwards, with water at 1 m bottom depth remaining liquid until May. Moats support productive, diverse benthic communities that are taxonomically distinct from those under the adjacent permanent lake ice. We show how ion ratios suggest that summer exchange occurs amongst moats, streams, soils and sub-ice lake water, perhaps facilitated by within-moat density-driven convection. Moats occupy a small but dynamic area of lake habitat, are disproportionately affected by recent lake-level rises and may thus be particularly vulnerable to hydrological change.
Microbial Community Dynamics in Two Polar Extremes: The Lakes of the McMurdo Dry Valleys and the West Antarctic Peninsula Marine Ecosystem
(2016-10) Bowman, Jeff S.; Oceanog, La Jolla; Vick-Majors, Trista J.; Morgan-Kiss, Rachael M.; Takacs-Vesbach, Cristina; Ducklow, Hugh W.; Priscu, John C.
The Palmer and McMurdo LTER (Long Term Ecological Research) sites represent climatic and trophic extremes on the Antarctic continent. Despite these differences, the microbial components of the McMurdo lake and Palmer marine ecosystems share fundamental characteristics, including the production of organic carbon via autotrophy and its assimilation via heterotrophy. We leveraged 20+ years of observations at the Palmer and McMurdo LTERs to identify key differences in microbial ecosystem dynamics between these sites. Although the relationships between fundamental biological parameters, including autotrophy and heterotrophy, are different between these sites, recent climate events have influenced the coupling of these parameters. We hypothesize that for the lakes of the McMurdo LTER, decoupling is largely driven by physical processes, whereas in the coastal Antarctic, it is largely driven by biological processes. We combined this hypothesis with a new analysis of microbial community and metabolic structure to develop novel conceptual microbial food-web models.
Niche specialization of bacteria in permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica
(2017-04) Kwon, Miye; Kim, Mincheol; Takacs-Vesbach, Cristina; Lee, Jaejin; Hong, Soon Gyu; Kim, Sang Jong; Priscu, John C.; Kim, Ok-Sun
Perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are chemically stratified with depth and have distinct biological gradients. Despite long-term research on these unique environments, data on the structure of the microbial communities in the water columns of these lakes are scarce. Here, we examined bacterial diversity in five ice-covered Antarctic lakes by 16S rRNA gene-based pyrosequencing. Distinct communities were present in each lake, reflecting the unique biogeochemical characteristics of these environments. Further, certain bacterial lineages were confined exclusively to specific depths within each lake. For example, candidate division WM88 occurred solely at a depth of 15 m in Lake Fryxell, whereas unknown lineages of Chlorobi were found only at a depth of 18 m in Lake Miers, and two distinct classes of Firmicutes inhabited East and West Lobe Bonney at depths of 30 m. Redundancy analysis revealed that community variation of bacterioplankton could be explained by the distinct conditions of each lake and depth; in particular, assemblages from layers beneath the chemocline had biogeochemical associations that differed from those in the upper layers. These patterns of community composition may represent bacterial adaptations to the extreme and unique biogeochemical gradients of ice-covered lakes in the McMurdo Dry Valleys.