6/08/2017  |   11:00 - 11:15   |  306B

SPATIAL VARIATION IN FATTY ACID AND STABLE ISOTOPE SIGNATURES AMONG TROPHIC LEVELS IN LOTIC SYSTEMS Fatty acid and stable isotope signatures allow researchers to better understand food webs. Research in marine systems has indicated that the variance of these biomarkers can exhibit substantial differences across spatial scales, but this type of analysis has not been completed for lotic systems. Our objectives were to evaluate variance structures for fatty acids and stable isotopes (i.e., dC13 and dN15) of target organisms across spatial scales in lotic systems and the implications of this variance on the design and interpretation of trophic studies. Our study focused on sites in large rivers including the Upper Mississippi, Illinois, and St. Croix rivers. Plankton, mussel, caddisfly, bluegill, and gizzard shad samples were collected from mainstem and backwater habitats. PERMANOVA analyses indicated that the highest variation for both isotopes was present at the largest spatial scale for all taxa except plankton dN15. Conversely, the highest variation for fatty acids was present at the smallest spatial scale for all taxa except caddisflies. These data highlight the need to consider the spatial level of highest variance during sample design so that effort is partitioned accordingly.

Andrea Fritts (Primary Presenter/Author), U.S. Geological Survey, afritts@usgs.gov;


Brent Knights ( Co-Presenter/Co-Author), U.S. Geological Survey, bknights@usgs.gov;


Toben Lafrancois ( Co-Presenter/Co-Author), Northland College, tlafrancois@northland.edu ;


William Richardson ( Co-Presenter/Co-Author), U.S. Geological Survey, wrichardson@usgs.gov;


Lynn Bartsch ( Co-Presenter/Co-Author), U.S. Geological Survey, lbartsch@usgs.gov;


Jon Vallazza ( Co-Presenter/Co-Author), U.S. Geological Survey, jvallazza@usgs.gov;


Byron Karns ( Co-Presenter/Co-Author), National Park Service, byron_karns@nps.gov;


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6/08/2017  |   11:15 - 11:30   |  306B

FROM ALGAE TO ALLIGATORS: EXAMINING FOOD WEB STRUCTURE IN FLORIDA SPRING ECOSYSTEMS Many Florida spring-fed rivers have experienced shifts in vegetative community structure and declines in ecosystem health. Once dominated by rooted macrophytes, nuisance macroalgae now proliferates; this shift has been linked to alterations in food web structure and key ecosystem processes. Using stable isotope analysis (SIA) coupled with dietary analyses, we addressed the following questions regarding the role of nuisance algae in the spring food webs: What are the major pathways of energy flow and material transport in Florida spring-river ecosystems? Which consumers forage on nuisance algae and to what degree? Which predators consume algal grazers? In Silver River, a 1st magnitude spring-run river in northcentral Florida, we performed SIA on dominant vegetation types, herbivores, and organisms occupying higher-order trophic levels. Dietary analysis was performed on multiple species of fish and turtles as well as American alligators. Using isotopic mixing model analyses, we estimated the proportional contribution of identifiable resource groups to consumers. Results suggest much of the energy and nutrients sequestered by nuisance algae in this system and likely other Florida spring-run systems circumvents the lotic food web.

James Nifong (Primary Presenter/Author), Kansas State University, jcnifong@ksu.edu;


Tom Frazer ( Co-Presenter/Co-Author), University of Florida, frazer@ufl.edu;


Robert Mattson ( Co-Presenter/Co-Author), St. Johns River Water Management District, RMattson@sjrwmd.com;


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6/08/2017  |   11:30 - 11:45   |  306B

Spatiotemporal consumer aggregation overlaps drive patterns in heterogeneity of ecosystem function Consumers provide simultaneous top down and bottom up controls on stream ecosystem function. The distribution of dense aggregations of consumers may interact with seasonal hydrology to activate mussel beds as control points (hotspots) in the fluxes and composition of elements related to ecosystem functions. To test how the seasonal overlap in the biological processes of sessile and mobile consumers affects ecosystem function, we conducted an eight week mesocosm experiment manipulating the presence of a grazing cyprinid within unionid mussel beds. We measured ammonium uptake, gross primary production, ecosystem respiration, and dissolved organic carbon quantity and composition as response variables. The presence of fish affected the rates and heterogeneity of GPP, ER and ammonium uptake. Consequently, we observed differences in the flux and composition of DOC between mesocosms with and without fish. Mobile fish may be grazing and redistributing nutrients throughout the study system, thereby homogenizing ecosystem functions like GPP, ER and nutrient cycling. Our results suggest that the overlap of different consumer groups may affect the activation and function of mussel beds as ecosystem control points.

Thomas Parr (Primary Presenter/Author), University of Oklahoma, Thomas.parr@ou.edu;


Caryn C. Vaughn ( Co-Presenter/Co-Author), University of Oklahoma, cvaughn@ou.edu;


Keith Gido ( Co-Presenter/Co-Author), Kansas State University, kgido@ksu.edu;


Kiza Gates ( Co-Presenter/Co-Author), Washington Department of Fish and Wildlife, kizagates@gmail.com;


Traci DuBose ( Co-Presenter/Co-Author), University of Oklahoma, tracipopejoy@ou.edu;


Garrett Hopper ( Co-Presenter/Co-Author), Kansas State University, ghopper@ksu.edu;


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6/08/2017  |   11:45 - 12:00   |  306B

LARGE WILDLIFE PROVIDE SIGNIFICANT TERRESTRIAL RESOURCE SUBSIDIES TO AN AFRICAN RIVER FOOD WEB Terrestrial resource subsidies can strongly influence aquatic food webs. In sub-Saharan Africa, large animal migrations are an important driver of subsidy transport. We have been studying the influence of two forms of animal subsidy on the Mara River food web in East Africa. Hippos contribute feces during daily feeding migrations, and wildebeest contribute carcasses from mass drownings during seasonal migrations. These subsides differ in their quantity, quality, timing and duration, which interacts with discharge to influence the river food web. We used stable isotopes to estimate assimilation of basal food web resources by aquatic insects and fish across a range of discharge. We found that hippo feces constitutes a large proportion of fish assimilated C and N (80-90%), particularly during the dry season. Wildebeest soft tissue accounts for up to half of fish assimilated C and N when carcasses are present, but bone biofilm remains an important resource months after carcasses are gone. These data suggest terrestrial resource subsidies from large wildlife may increase secondary production in the Mara River, which could influence the dynamics of the river food web.

Amanda Subalusky (Primary Presenter/Author), University of Florida, asubalusky@ufl.edu;


Christopher Dutton ( Co-Presenter/Co-Author), University of Florida, duttonc@ufl.edu;


Emma Rosi ( Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, rosie@caryinstitute.org;


David Post ( Co-Presenter/Co-Author), Yale University, david.post@yale.edu;


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6/08/2017  |   12:00 - 12:15   |  306B

COUPLING OF ASYNCHRONOUS ENERGY CHANNELS IN SPATIALLY COMPLEX META-FOOD WEBS: TESTING GENERAL THEORY IN RIVERS AND THEIR FLOODPLAINS The science of streams and rivers possesses untapped potential to empirically test general ecological theory. One avenue is evaluating theoretical expectations that certain characteristics of food web complexity promote stability and biodiversity, with the added layer that spatial heterogeneity may facilitate the emergence of such characteristics at meta-food web scales. Recent river and river-floodplain studies have empirically shown that increasing food web complexity and spatial heterogeneity may mediate patterns associated with theoretically stable food webs, such as shifting the distribution of predator-prey interaction strengths toward weaker interactions. However, the mechanisms by which food web patterns and processes thought to impart stability operate in spatially complex and naturally biodiverse ecosystems are poorly understood. We review here theory regarding these relationships, focusing on the role of detrital subsidies and the coupling of asynchronous “fast” and “slow” energy channels in spatially heterogeneous meta-food webs, illustrating why, and proposing a novel approach as to how, river-floodplains may be used to confront this body of theory. Overall, our goal is to spur investigations in rivers and streams that reconcile general theory with empirical observation.

James Paris (Primary Presenter/Author), Stream Ecology Center, Dept. Biological Sciences, Idaho State University, parijame@isu.edu;


Colden Baxter ( Co-Presenter/Co-Author), Idaho State University, baxtcold@isu.edu;


J. Ryan Bellmore ( Co-Presenter/Co-Author), Forest Service, Pacific Northwest Research Station, Juneau, AK, jbellmore@fs.fed.us;


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6/08/2017  |   12:15 - 12:30   |  306B

LIFE ON THE EDGE: DOES FISH MOVEMENT AMONG HABITATS LINK GREAT LAKES COASTAL WETLAND AND NEARSHORE FOOD WEBS? Coastal wetlands of the Laurentian Great Lakes are highly productive ecosystems at the terrestrial-aquatic boundary that support diverse biological communities and provide habitat for 90% of Great Lakes fishes. Nearshore habitats are linked to coastal wetlands by the exchange of materials (e.g., organisms, nutrients, organic matter) through both abiotic and biotic mechanisms. Wetland use by native sport fishes represents a potentially vital linkage that provides energy for economically important coastal fisheries. Using Lake Michigan yellow perch (Perca flavescens) as a model, we investigated use of both coastal wetland and nearshore lake habitats using carbon and nitrogen stable isotopes and otolith microchemistry. Coastal wetland prey are significantly depleted in 13C relative to the nearshore, allowing us to use mixing models to estimate wetland-derived resource use. Perch otolith strontium and barium age signatures suggest intra-population variation in habitat use across life stages. Quantifying the importance of coastal wetlands in supporting recreational fisheries will allow managers to prioritize the conservation and restoration of these areas, many of which have been degraded as a result of land use conversion, invasive species, and pollution.

Katherine O'Reilly (Primary Presenter/Author), Illinois-Indiana Sea Grant, keo@illinois.edu;


James Student ( Co-Presenter/Co-Author), Central Michigan University, stude1jj@cmich.edu;


Christopher Houghton ( Co-Presenter/Co-Author), University of Wisconsin - Green Bay, houghtoc@uwgb.edu;


Patrick Forsythe ( Co-Presenter/Co-Author), University of Wisconsin - Green Bay, forsythp@uwgb.edu;


Gary Lamberti ( Co-Presenter/Co-Author), University of Notre Dame, glambert@nd.edu;


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