title: Dr first_name: Evelyn middle_name: B last_name: Sherr organization: COAS, Oregon State University email: sherre@coas.oregonstate.edu mailing_address: COAS-OSU104 Ocean Admin Bldg city: Corvallis state_province: OR postal_code: 97331-5503 country: USA phone: 541-737-4369 fax: 541-7372064 additional_investigators: 1 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: PROJECT SUMMARY A central goal of the Shelf-Basin Interactions (SBI)program is to understand the processes affecting carbon trans-formations 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 mesozooplankton 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 icrozooplankton, 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 cycl ing of carbon in arctic shelves and basin systems. We propose participation in the four process cruises of the SBI Phase II program. The planned cruise 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 (standing 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 mesozoo-plankton 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 to the impacts of changing ice cover and hydrographic parameters on biogeochemical fluxes.? This project will provide rate measurements for microzooplankton and mesozooplankton grazing and 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: Microzooplankton grazing and phytoplankton growth via dilution assays data_set_summary: Microzooplankton grazing impact on phytoplankton was assessed using the Landry-Hassett dilution technique in the western Arctic Ocean during spring and summer 2002 and 2004. Forty experiments were completed in a region encompassing productive shelf regions of the Chukchi Sea, mesotrophic slope regions of the Beaufort Sea off the North Slope of Alaska, and oligotrophic deep water sites in the Canada Basin. Grazing and growth rates found in this study were low compared to rates reported in other major geographic regions of the world ocean. data_format: MS Excel 5.1.2600 (2003) worksheet data_structure: Data column headers SBI Cruise, date, SBI station location, SBI Station number, Lat oN, Long oW, Bottom depth (m), Sample depth (m), Sample temperature (oC), Sample nitrate concentration (uM), Initial chl-a concentration (ug/liter), Experiment incubation light level (% Io), dilution assay growth rate (u/day),dilution assay grazing rate (g/day), Dillution slope regression r statistic, fraction of growth grazed parameters: chlorophyll-a, phytoplankton growth rate, microzooplankton grazing rate collection_methods: Water for grazing experiments was collected using 30 liter Niskin bottles at a subset of stations occupied during four SBI process cruises in 2002 and 2004 along established transects from shelf to open basin: along Barrow Canyon, off the northern coast of Alaska east of Point Barrow, east of Hanna Shoals and west of Hanna Shoals in the Chukchi Sea. A total of 40 dilution experiments were completed (Sherr et al. submitted). Except for the first experiment, only one depth was selected for each experiment. Sampling for dilution experiments was coordinated with sampling for primary productivity assays and for mesozooplankton grazing experiments (Campbell et al., submitted). Dilution experiments were carried out following the protocol of Landry (1993). All carboys, bottles, and tubing used in setting up dilution assays were pre-soaked in 10% HCl and thoroughly rinsed with deionized water. Nitex gloves were worn during experimental set-up. Water for the dilution assays was collected in 30-liter Niskin bottles at a pre-determined depth, either the Chl-a maximum or a depth in the upper mixed layer, usually at the 5% or 15% light level, corresponding to a depth sampled for phytoplankton production. Seawater was gently transferred into 50 liter carboys through silicon tubing with 200 µm Nitex mesh pouches zip-tied to the ends to screen out larger grazers; care was taken to keep the mesh pouches below the water surface and to avoid bubbles in the tubing as the carboys were filled. The 200 µm screened water was used as whole seawater (WSW) in setting up the dilution series. After collection of seawater, all other preparation steps were carried out in a temperature-controlled environmental chamber set at -1 oC under dim light (approximately 0.1 % of incident light). For dilutions, particle-free seawater was prepared by gravity filtration through a Pall 0.2 µm filter that was presoaked in 10% HCl and thoroughly rinsed with deionized water. Five to seven liters of seawater were passed through the 0.2 µm filter before beginning collection of particle free water for the dilutions. Experimental bottles were filled within two to three hours of sample collection. Particle free water was added to 2 liter polycarbonate bottles using a set of bottles of known volume to yield replicate treatments of 100%, 80%, 60%, 40%, and 20% and 8% or 12% WSW. To avoid nutrient limitation due to decreased rate of nutrient recycling in the higher dilutions, ammonium nitrate and sodium phosphate were added to experimental bottles to yield concentrations of 5 µM N and 0.25 µm P. Replicate WSW treatments without added nutrients were also included in most of the dilution experiments. A carboy filled with WSW was gently mixed for several minutes using a plexiglass rod with a small plexiglass disc attached to the end. Then, while the carboy continued to be gently mixed, WSW was siphoned out of the carboy to fill the experimental bottles and an additional 2 liter bottle for initial samples. Parafilm was placed on top of each bottle prior to securing the cap, in order to mini mize air bubbles in the bottles, since protist cells can lyse in contact with air (Gifford, 1988). The experimental bottles were placed into plexiglass cylinders covered with combinations of neutral density grey, Scrim, and blue plastic film to mimic in situ light intensity and quality. One light level was chosen for each experiment, depending on the water depth at which the sample was collected. The cylinders were secured in on-deck incubators cooled with flowing surface seawater, which ranged in temperature from -1 oC to 6 oC depending on the season and location in the SBI sampling region. In 2002 the duration of dilution experiments was 60 to 75 hours. In 2004 a shorter incubation time of approximately 48 hours for experiments was used, since results from the 2002 field season suggested that 2 day incubations would yield adequate growth and grazing rates , and a shorter time minimized potential for temperature variation during the incubation. In 6 experiments in which there were problems with the seawater flow to the incubators, or in which the ship was expected to t ravel through water masses of varying surface temperature during an experiment, dilution experiment bottles were incubated at constant temperature in the dark in either the -1 oC environmental chamber or in a walk-in refrigerator set at 2 oC. Initial samples were taken from WSW samples for determination of chlorophyll-a concentration, for flow cytometric analysis of phytoplankton cell abundance, light scattering properties, and fluorescence, and for microscopic enumeration of microzooplankton abundance, biomass, and general taxonomic composition. At the end of the dilution incubations, final samples were taken from each bottle for Chl-a concentration and for flow cytometric analysis of phytoplankton. Depending on the initial phytoplankton concentration and dilution, from 25 to 500 ml replicate or triplicate subsamples from each bottle were filtered for chlorophyll-a determination. Depending on the phytoplankton concentration, from 25 ml to 150 ml quadruplicate volumes were settled onto GFF filters in dim light. The filters were extracted in 6 ml of 90% acetone in 13 x 100 mm glass culture tubes at -20 oC for 18 to 24 hours. At the end of the extraction period, the filter was carefully removed from each tube, and the chlorophyll-a concentration determined using a calibrated Turner Designs fluorometer. A solid chlorophyll standard was used to check for fluorometer drift at the beginning of each reading of Chl-a samples. Phytoplankton growth and grazing rates were calculated from dilution by change in chlorophyll-a concentration corrected for change in cell-specific fluorescence determined via flow cytometry. Initial Chl-a concentrations in the dilutions were estimated from WSW Chl-a concentrations and the known dilution. Phytoplankton realized growth rates were calculated for each experimental bottle using a logistic growth model based on initial and final Chl-a concentrations. Regression statistics of the plots of fraction of WSW versus realized growth rate were used to estimate µ (y-intercept), the intrinsic growth rate of the phytoplankton with no grazing mortality, and g (slope), the microzooplankton grazing rate, both in units of day-1 (Landry 1993). In a few cases, there was non- linearity in the regression slopes in which increase in realized growth rate of phytoplankton was only observed in dilution treatments of < 60%. For these plots, regressions to determine µ and g were based on 8.2%, 20%, and 40% dilution bottle data. Estimates of daily phytoplankton growth and grazing loss in terms of carbon biomass were made using the logistic equation, based on the dilution growth and grazing rates, initial Chl-a concentrations and a C:Chl-a ratio of 30 (Sherr et al., 2003). collection_period_start: 20020510 collection_period_end: 20040817 seasonal_measurements: spring and summer temporal_resolution: twice weekly study_location: Western Arctic Ocean geog_coordinates: 67 oN to 73 oN; -152oW to -168 oW spatial_resolution: upper 50 m of water column, several to 10's of km resolution in sampling station locations refs_about_data: References cited: Campbell, R.G., E. B. Sherr, C. J. Ashjian, S. Plourde, B. F. Sherr, V. Hill, D. A. Stockwell. Mesozooplankton prey preference and grazing impact in the Western Arctic Ocean. Deep-Sea Research II, submitted Jan 2007. Landry, M.R. 1993. Estimating rates of growth and grazing mortality of phytoplankton by the dilution method, p. 715-722. In Kemp, P.F., Sherr, B.F., Sherr, E.B. and Cole J.J. (eds.), Handbook of Methods in Aquatic Microbial Ecology. Lewis Publ., Boca Raton, FL. Sherr, E.B., Sherr, B.F., Wheeler, P.A., Thompson, K. 2003. Temporal and spatial variation in stocks of autotrophic and heterotrophic microbes in the upper water column of the central Arctic Ocean. Deep-Sea Research I 50, 557-571. refs_using_data: Sherr, E.B., Sherr, B.F., Hartz, A.J. Microzooplankton grazing impact in the Western Arctic Ocean. Deep-Sea Research II, submitted Nov-2006. related_URLs: http://bioloc.coas.oregonstate.edu/SherrLab/Arcticresearch.html http://bioloc.coas.oregonstate.edu/SherrLab/Microplankton%20ima ges.html transfer_medium: How about as an email attachment?, data_volume_mb: 0.096 agree: Agree first_name0: Barry last_name0: Sherr middle_initial0: F organization0: COAS-Oregon State University data_usage: grid_description: tech_contact_middle_name: tech_contact_email: tech_contact_fax: tech_contact_title: tech_contact_postal_code: tech_contact_first_name: tech_contact_state_province: tech_contact_last_name: tech_contact_organization: development_machine: tech_contact_phone: temporal_coverage_start: tech_contact_city: processing_algorithm: release_date: additional_info: tech_contact_country: temporal_coverage_end: tech_contact_mailing_address: ip:67.189.8.137