Thursday, June 8, 2017
14:00 - 15:45

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14:00 - 14:15: / 306B REVISITING LINDEMAN'S WORK ON CEDAR BOG LAKE USING STABLE ISOTOPES TO STUDY FOOD WEB DYNAMICS

6/08/2017  |   14:00 - 14:15   |  306B

REVISITING LINDEMAN'S WORK ON CEDAR BOG LAKE USING STABLE ISOTOPES TO STUDY FOOD WEB DYNAMICS Since Raymond Lindeman’s pioneering work at Cedar Bog Lake, new techniques for the study of energy flow in aquatic ecosystems have been developed, yet none of these have been applied to this historically and scientifically significant lake. We conducted six sampling events, collecting terrestrial organic matter, within-lake primary producers, zooplankton, aquatic invertebrates, and fish, from spring to fall in the small mesotrophic lake. We utilized bulk stable isotope analyses (D, 13C, 15N) and the Bayesian mixing model framework, MixSIAR, to quantify allochthonous vs. autochthonous nutrient inputs, trace energy sources, determine the trophic position of each species and the overall food chain length, and identify seasonal variations in diet. Preliminary analyses indicate allochthonous inputs are a substantial food resource for some primary consumers, exceeding contributions of attached and planktonic algae and macrophytes by more than half. Our study provides quantification of specific food web pathways described in Lindeman’s seminal research, and preliminary analyses suggest terrestrial subsidies play a more significant role as a basal food resource than Lindeman recognized in his classic diagram.

Alexi Besser (Primary Presenter/Author), University of Minnesota , besse078@umn.edu;


Christy Dolph ( Co-Presenter/Co-Author), University of Minnesota , dolph008@umn.edu;


Jacques Finlay ( Co-Presenter/Co-Author), University of Minnesota, jfinlay@umn.edu;


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14:15 - 14:30: / 306B WATERSHED LAND USE INFLUENCES THE RESOURCE QUALITY AND ELEMENTAL COMPOSITION OF THE RIVERINE MACROPHYTE, PODOSTEMUM CERATOPHYLLUM MICHX.

6/08/2017  |   14:15 - 14:30   |  306B

WATERSHED LAND USE INFLUENCES THE RESOURCE QUALITY AND ELEMENTAL COMPOSITION OF THE RIVERINE MACROPHYTE, PODOSTEMUM CERATOPHYLLUM MICHX. The riverine macrophyte Podostemum ceratophyllum (aka Hornleaf Riverweed) is ecologically important in mid-order rivers in eastern North America. The plant grows attached to stable benthic substrate in fast flowing water where it absorbs nutrients from the water column. Podostemum positively influences invertebrate biomass and is consumed by a variety of riverine fauna, however, little is known about the quality of resources the plant provides to consumers, or how watershed land use is reflected in the elemental composition of the plant. We collected Podostemum from over 60 locations across 11 states between Georgia and Maine. We used optical emission spectroscopy (OES) and isotopic analysis to examine the elemental composition of plant tissue and compared composition to watershed land use using linear mixed modeling. Our data indicate that land use changes elemental ratios and the resource quality of plant tissue. This research provides new insight into benthic resource storage and flux in mid-order eastern North American Rivers.

James Wood (Primary Presenter/Author), University of Georgia, wood@uga.edu;


Mary Freeman ( Co-Presenter/Co-Author), US Geological Survey, mcfreeman@usgs.gov;


Kathy Loftis ( Co-Presenter/Co-Author), University of Georgia, Center for Applied Isotope Studies, Kloftis@uga.edu;


Doug Leasure ( Co-Presenter/Co-Author), University of Georgia, doug.leasure@gmail.com;


Tom Maddox ( Co-Presenter/Co-Author), University of Georgia, Center for Applied Isotope Studies, Tmaddox@uga.edu;


Seth Wenger ( Co-Presenter/Co-Author), University of Georgia, sethwenger@fastmail.fm;


Jon Skaggs ( Co-Presenter/Co-Author), Univeristy of Georgia, jskaggs@uga.edu;


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14:45 - 15:00: / 306B GLACIAL-MELT OVERRIDES LONGITUDIANL PATTERNS IN BASAL RESOURCES AND FOOD WEBS OF APLINE STREAMS

6/08/2017  |   14:45 - 15:00   |  306B

GLACIAL-MELT OVERRIDES LONGITUDIANL PATTERNS IN BASAL RESOURCES AND FOOD WEBS OF APLINE STREAMS Basal resources in stream ecosystems originate either from autochthonous (i.e., within-system) or allochthonous (i.e., external) production. Their quantity and relative proportion depend on location within the stream continuum as well as stream characteristics (e.g., water source from snow/glacial melt) and likely determine food web composition, structure, and production. We studied three catchments with differing degrees of glacial runoff and vegetation cover (alpine prairie to subalpine forest; up-to-downstream) for biofilm, benthic organic matter, and macroinvertebrates. Biofilm chlorophyll-a (chla) was highest in the snowmelt-fed stream and only showed an up-to-downstream increasing pattern in September during the chla-peak (6.13 to 34.19 mg/m2) while streams with glacial influence had generally low chla (<15 mg/m2). Coarse benthic organic matter (CBOM) was also higher in the snowmelt-dominated streams compared to the glacial-fed streams (mean 7 vs 3 g/m2). Macroinvertebrate densities were low in July and August in the glacial-melt influenced streams while the snowmelt dominated streams showed high densities of very small stoneflies. Results suggest that water source rather than upstream to downstream differences in basal resources drive patterns in food webs.

Janine Rüegg (Primary Presenter/Author), École Polytechnique Fédérale de Lausanne, janine.ruegg@epfl.ch;


Tom Battin ( Co-Presenter/Co-Author), Ecole Polytechnique Fédérale de Lausanne, tom.battin@epfl.ch;


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15:00 - 15:15: / 306B REDUCTION IN COMMUNITY BODY SIZE EFFECTS THE STRENGTH OF TROPHIC CASCADES

6/08/2017  |   15:00 - 15:15   |  306B

REDUCTION IN COMMUNITY BODY SIZE EFFECTS THE STRENGTH OF TROPHIC CASCADES Mechanisms that control trophic cascade strength have been predominantly focused on environmental factors or food web linkages, but biotically driven compensatory mechanisms have notbeen as thoroughly explored. A three by two factorial design was used to test the hypothesis that plasticity and range in size frequency distribution of primary consumers influences the effects of top predators on primary producers. Specifically, the effects of planktivorous bluegill (Lepomis macrochirus) on phytoplankton were evaluated with three zooplankton treatments including small zooplankton (Moina micrura), large zooplankton (Dahnia pulex), and a mixture of the two. Bluegill preferentially consumed large zooplankton and reduced zooplankton biomass in all treatments. Phytoplankton chlorophyll a increased among all treatments with fish, but increased more rapidly and to a greater peak concentration in the treatment with Daphnia. Weaker effects in treatments with the small and mixed size zooplankton despite reductions in zooplankton biomass are likely because reduced size corresponds with a higher ratio of production to biomass; trophic response of invertebrates to predation from fish can be simultaneously directional for biomass and homeostatic for production.

Thomas Detmer (Primary Presenter/Author), University of Illinois, tdetmer@illinois.edu;


David Wahl ( Co-Presenter/Co-Author), Illinois Natural History Survey, d-wahl@illinois.edu;


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15:15 - 15:30: / 306B RIPARIAN FOREST STRUCTURE AND STREAM FOOD WEBS

6/08/2017  |   15:15 - 15:30   |  306B

RIPARIAN FOREST STRUCTURE AND STREAM FOOD WEBS Management of stream fish populations focuses on the role of physical habitat heterogeneity in regulating individual and population growth, an approach that assumes food is not limiting or unimportant. This assumption is rarely tested or evaluated despite decades of research showing the fundamental role food plays in regulating individual growth and the carrying capacity of a stream to support fish. Food limitation may be particularly important in forest streams where light and nutrients constrain primary and secondary productivity. Here we examine the linkages between riparian forest structure (e.g. dense 2nd growth stands vs. open old-growth stands), prey availability, and stream salmonid populations during summer low-flow conditions using a combination of experiments and field observations. Multiple lines of evidence support the hypothesis if water temperature is conducive to positive growth, fish populations in Pacific Northwest forest streams are limited by food availability during summer low flows, which is partly determined by riparian forest structure and local habitat conditions.

Peter Kiffney (Primary Presenter/Author), Northwest Fisheries Science Center, peter.kiffney@noaa.gov;


Matthew Kaylor ( Co-Presenter/Co-Author), Oregon State University, matthew.kaylor@oregonstate.edu;


Dana Warren ( Co-Presenter/Co-Author), Oregon State University, dana.warren@oregonstate.edu;


Sean Naman ( Co-Presenter/Co-Author), University of British Columbia , mikaela.imbriani@usu.edu;


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15:30 - 15:45: / 306B ARE ALL RIVERS CREATED EQUAL? DETERMINING HOW FOOD WEB DYNAMICS AFFECT FISH NURSERY HABITAT

6/08/2017  |   15:30 - 15:45   |  306B

ARE ALL RIVERS CREATED EQUAL? DETERMINING HOW FOOD WEB DYNAMICS AFFECT FISH NURSERY HABITAT Estuarine fish nursery areas are managed based on habitat types and water quality. The structure and quality of the planktonic food web may be key to the survival and recruitment of fish. We investigated how differences in lower trophic level food web affected river herring strategic habitat area in Chowan River, N.C. Our objective was to determine how seston and zooplankton fatty acid composition, and zooplankton species composition, would affect larval fish fatty acid composition. The presence of particular fatty acids is linked to larval fish survival. We found differences in the seston and zooplankton fatty acid composition over space and time in Chowan River and three of its tributaries. The zooplankton species composition changed from copepod and cladoceran community to cladoceran community in the tributaries, with higher percentage of copepods in the main stem of Chowan River. The mesozooplankton were higher in EPA and DHA in the main stem, and tributaries had higher levels of EPA and ALA. Differences seen in the seston and zooplankton fatty acid composition can change the growth and fatty acid percent composition of larval river herring.

Deborah Lichti (Primary Presenter/Author), East Carolina University, lichtid12@students.ecu.edu;


Jacques Rinchard ( Co-Presenter/Co-Author), The College of Brockport, State University of New York, jrinchar@brockport.edu;


David Kimmel ( Co-Presenter/Co-Author), NOAA Alaska Fisheries Science Center, david.kimmel@noaa.gov;


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