Woods Hole Oceanographic Institution

Julie Rose

» Microzooplankton grazing and algal blooms in the Ross Sea

» Breaking open the black boxes of marine microbial communities

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This work is being done in conjunction with the CORSACS program, funded by the Office of Polar Programs at the National Science Foundation. For more information, please go to (Mak Saito)

Microzooplankton grazing and algal blooms in the Ross Sea: interactive effects of temperature, carbon dioxide and phytoplankton community composition

David Hutchins, Jack DiTullio, Rob Dunbar, Peter Lee, Maeve Lohan, Mak Saito, Peter Sedwick, Walker Smith, Philippe Tortell

A long range goal of much of my research is exploring how microbial community structure and food web dynamics and their associated biogeochemical cycles are affected by changes in parameters such as temperature, CO2 and iron. As this a complicated and dynamic issue, my research necessarily combines theoretical, laboratory and field methods. For instance, by compiling and interpreting published data on the effect of temperature on growth rates of phototrophic protists, heterotrophic protists and copepods (Rose and Caron 2007, Limnology and Oceanography 52(2)) I discovered that temperature may in part regulate the ability of heterotrophic organisms to control the formation of algal blooms in the present day ocean. Thus future increases in temperature predicted by climate change models may affect not only growth rates of individual plankton taxa, but also have impacts on the dynamics among trophic levels of microbial communities. I have complemented this theoretical work with field and laboratory work examining the effects of temperature on growth and grazing using cultures of Antarctic heterotrophic protists. This established baseline information about these organisms, while allowing observation of larger-scale trends in temperature response through comparison to published information for temperate congeners. Currently I am expanding this work with further field studies, examining changes in temperature, CO2, iron and light on mixed plankton assemblages in the Ross Sea, Antarctica. In particular, I am interested in the effects of future increased temperature on microalgal and bacterial grazing in polar regions. I am also interested in how increased temperature affects relationships among trophic levels within the microbial food web, since my recent literature review predicts a different temperature response between heterotrophic and phototrophic microorganisms. This work is highly collaborative in nature, and has involved trace metal chemists, photochemists, biogeochemists and phytoplankton ecologists. We have been able to document changes in biomass, community structure, photosynthetic parameters, food web dynamics and nutrient cycling within shipboard incubations using both traditional ?growout? experiments as well as novel continuous-culture-style experiments using natural plankton assemblages. This collaborative work is ongoing, but early results suggest that both individual and interactive effects among these variables may have major impacts on plankton communities.

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