title: Dr first_name: Evelyn last_name: Sherr organization: COAS-Oregon State University email: sherre@coas.oregonstate.edu mailing_address: 104 Ocean Admin Bldg city: Corvallis state_province: OR postal_code: 97331-5503 country: USA phone: 541-737-4369 fax: 541-737-2064 project_or_program: SBI grant_number: 0124892-OPP grant_title: COLLABORATIVE RESEARCH: Mesozooplankton-Microbial Food Web Interactions in Western Arctic Shelf and Basin Regions prop_summary: A central goal of the Shelf-Basin Interactions (SBI) program is to understand the processes affecting carbon transformations and fluxes within and between Arctic shelf and basin ecosystems, and how climate change might impact these processes. The cycling of carbon in Arctic shelf and basin habitats depends on the structure and functioning of the food webs of these regions. In the pelagial, both micro- and meso- zooplankton are significant consumers of primary production. The partitioning of primary production between the fractions remaining in the water column or sedimenting to the benthos (where organic matter is less available for export from the shelf) can be greatly affected by the relative grazing rates of microzooplankton versus mesozooplankton herbivores. Microzooplankton grazing dampens export flux, while mesozooplankton grazing enhances it. The primary focus of our proposed collaborative project is an analysis of the impact of microzooplankton and mesoz ooplankton grazers on the fluxes and exchanges of carbon within the oceanic waters of the Canada Basin and the shelf waters of the Chukchi/Beaufort Seas. We will use standard methods and experimental protocols to determine the standing stocks and size structures of microzooplankton, phytoplankton, and mesozooplankton assemblages, to measure growth (microzooplankton) and reproduction (mesozooplankton) rates, to measure grazing rates of heterotrophic protists and dominant mesozooplankton in the two regions, and to identify mesozooplankton that are sentinel species of Arctic change. Our collaborative study will explicitly address trophic linkages previously unexplored in this region of the Arctic. We hypothesize that changing ecosystem structure, such as might occur during climate change, will alter the role of these trophic interactions in the utilization and cycling of carbon in arctic shelves and basin systems. We propose participation in the four process cruises of the SBI Phase II program. The plannedcruise schedules of May-June and July-August will permit us to work in contrasting scenarios of ice cover, and importance of ice algae versus phytoplankton in primary production, during early summer compared to late summer. Since we plan a comparison of the phytoplankton - microzooplankton - mesozooplankton trophic coupling in shelf versus basin systems, we will carry out a full set of analyses (sta nding stock determinations and rate measurements) at a number of stations in both basin and shelf regions of the SBI-II study area. Abundances and rate measures will be combined to determine relative mesozooplankton and microzooplankton grazing impacts. The research proposed here addresses major objectives of the SBI-II program: ?Assessment of relative importance of top-down as compared to bottom-up controls over pelagic-benthic coupling and carbon partitioning among different trophic levels? and ?Assessment of food web changes consequent o the impacts of changing ice cover and hydrographic parameters on biogeochemical fluxes.? This project will provide rate measurements for microzooplankton and mesozooplankton grazing ad reproduction, parameters that were identified as high priority for the seasonal process cruises in the SBI Phase II Implementation Plan. We will fully collaborate with, and make our data available to, other SBI investigators. data_set_title: SBI Flow Cytometric data on bacteria and phytoplankton data_set_summary: SHERR SBI Flow Cytometry data for a subset of Primary Production cast profiles in the upper 50 m of the water column 1)2002 data includes abundances of heterotrophic bacterial cells: total, high nucleic acid, and low nucleic acid, < ~5 um eukaryotic phototrophic cells, and > ~5 um eukaryotic phototrophic cells, which were mainly diatoms 2)2004 data includes abundances of coccoid cyanobacteria, < ~5 um eukaryotic phototrophic cells, and > ~5 um eukaryotic phototrophic cells, which were mainly diatoms data_format: MS Excel 5.1 worksheet data_structure: Column headers: Date of collection, station location,SBI station number, N Lat, W Long, Bottom depth (m), Sampling depth (m), Sample light level (percent incident light), Total bacteria (105 cells/ml), High nucleic acid (HNA) bacteria (105 cells/ml), Low nucleic acid (LNA) bacteria (105 cells/ml), Coccoid cyanobacteria (103 cells/ml), small photosynthetic eukaryotes (Peuk, 103 cells/ml), big phytoplankton cells mainly diatoms (103 cells/ml) parameters: bacteria and phytoplankton abundance in cells per ml collection_methods: 3 ml aliquots of each sample were pipetted into 4 ml cryovials and preserved with 0.2% (w/v) final concentration of freshly made paraformaldehyde. The samples were gently mixed and let sit in the dark at room temperature for 10 minutes before quick-freezing and storage in liquid nitrogen. On return of samples to the lab, the cryovials were stored at -80 oC until flow cytometric analysis was performed. Duplicate subsamples of seawater for nutrient analyses were collected in acid-washed NalgeneTM 60 ml HDPE bottles and immediately frozen at -20 oC for nutrient analysis. Flow cytometric analysis of cell abundances: In the laboratory, samples were thawed and kept on ice in a dark container until run on a Becton-Dickinson FACSCaliber flow cytometer with a 488 nm laser. For enumeration of small sized phytoplankton, 500 μl subsamples were processed as described in Sherr et al. (2005). Populations of coccoid cyanobacteria (Synechococcus or SYN), of small photosynthetic eukaryotes (PEUK), and of larger photosynthetic eukaryotes were distinguished by differences in fluorescence in orange (cyanobacteria), in red (eukaryotic phytoplankton) wavelengths and in side scatter properties. We have previously determined that 75% to 85% of the red-fluorescing cells in the PEUK region of our cytograms are < 5 μm in size (Sherr et al. 2005). For heterotrophic bacteria, 250 μl subsamples were diluted with 250 μl of DiW, and stained with SYBR Green I and potassium citrate for 15 min, following the protocol of Marie et al. (1997) (details in Sherr 2006). Bacterial counts were made during a three minute sample run at low flow rate. Regions were established in cytograms of side scatter and green fluorescence to define bacterial cells with high nucleic acid content (HNA) and low nucleic content (LNA). The cytogram for each sample was individually inspected, and HNA and LNA regions manually moved to conform to the appropriate areas of the bacterial dot-plot. Mean cell-specific SYBR fluorescence was obtained for total bacteria and for HNA and LNA cells, along with abundance of cells within each group. Logical gating in Becton-Dickinson Cell Quest software was used to exclude coccoid cyanobacteria when they occurred, based on orange fluorescence, from the abundance counts of heterotrophic bacteria. Each subsample was spiked immediately before processing with a known amount of either 3.0 μm (for phytoplankton) or 1.0 μm (for bacteria) Polysciences Fluoresbrite yellow-green beads from respective stock solutions of beads that had been precalibrated with Becton-Dickinson True-Count beads. The number of beads enumerated in each sample run was used to accurately determine the sample volume processed and thus the abundances of SYN, PEUK, and bacteria. collection_period_start: 20020510 collection_period_end: 20040814 seasonal_measurements: spring and summer temporal_resolution: once or twice per week study_location: Western Arctic Ocean geog_coordinates: 67oN - 74oN, 151oW - 169oW spatial_resolution: upper 50 m of water column, several km to 10s of km refs_about_data: Sherr, E.B., Sherr, B.F., Wheeler, P.A. 2005. Distribution of coccoid cyanobacteria and small eukaryotic phytoplankton in the upwelling ecosystem off the Oregon coast during 2001 and 2002. Deep-Sea Research II 52:317-330 Sherr E.B., Sherr B.F., Longnecker K. 2006. Distribution of bacterial abundance and cell-specific nucleic acid content in the Northeast Pacific Ocean. 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