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SFS Annual Meeting

Thursday, June 6, 2024
15:30 - 17:00

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C25 Food Webs

15:30 - 15:45 | Independence Ballroom D | CAN TROPHIC FLEXIBILITY MITIGATE SHIFTING HABITAT AND COMMUNITY STRUCTURE FOR A CLIMATE-SENSITIVE FISH?

6/06/2024  |   15:30 - 15:45   |  Independence Ballroom D

Can trophic flexibility mitigate shifting habitat and community structure for a climate-sensitive fish? Global climate change is expected to have broad consequences in aquatic ecosystems. In lakes, climate change is expected to alter resource availability and community structure. Abiotic habitat template shifts may affect characteristics of primary productivity as well as fish and invertebrate community structures, in turn affecting overall food webs. Arctic Charr, Salvelinus alpinus, are a cold-water salmonid distributed throughout high latitudes of the northern hemisphere. Although Arctic Charr frequently dominate arctic and subarctic lakes, they are considered poor competitors in high diversity systems. Populations within Maine, the southernmost edge of their range, may be particularly vulnerable to climate warming. However, Arctic Charr can exhibit extreme resource polymorphism and occupy many trophic roles, which may help them to avoid interspecific competition and mitigate climate change impacts associated with shifting resource availability. Using environmental sampling and stable isotope analyses we evaluated trophic structure and limnological characteristics (e.g., temperature, pH, dissolved oxygen, light attenuation) of three Maine lakes with Arctic Charr populations to determine how abiotic conditions and community structure influence the trophic niches occupied by Arctic Charr and co-occurring fishes. Carbon and nitrogen stable isotope analysis is being conducted on 13 species of fishes as well as benthic invertebrates, zooplankton, and primary production. Long term results of this project are intended to inform modeling of Arctic Charr trophic responses under a variety of climate change scenarios, improving our understanding of the long-term viability of this and other cold-water adapted vulnerable species.

Glenn Schumacher (Primary Presenter/Author), University of Maine, glenn.schumacher@maine.edu;

Christina A. Murphy (Co-Presenter/Co-Author), U.S. Geological Survey, Maine Cooperative Fish and Wildlife Research Unit, Orono, ME, christina.murphy@maine.edu;

Nathan Furey (Co-Presenter/Co-Author), University of New Hampshire, Nathan.Furey@unh.edu;

Michael Kinnison (Co-Presenter/Co-Author), University of Maine, mkinnison@maine.edu;

15:45 - 16:00 | Independence Ballroom D | EFFECTS OF A RANGE-SHIFTING CADDISFLY ON HIGH-ELEVATION FOOD WEBS

6/06/2024  |   15:45 - 16:00   |  Independence Ballroom D

Effects of a range-shifting caddisfly on high-elevation food webs Species are moving pole-ward in latitude and upslope in elevation in response to climate change. Understanding the impact that these species range shifts are having on recipient food webs and ecosystems will be critical for predicting ongoing change. In subalpine ponds in the Rocky Mountains of Colorado, a new species of over-wintering detritivorous caddisfly, Nemotaulius hostilis, first appeared in 2016 and had a huge population boom in 2021 following two mild winters. Long-term (30+ years) knowledge on salamander and benthic invertebrate food webs in this system provides us with the unique opportunity to determine if this new species would increase bottom-up food resources for top-predator salamanders, compete with other resident detritivores, and alter rates and timing of ecosystem processes such as detritus decomposition. After two years of surveying the food-web and ecosystem impacts, we found a positive effect of the new species on salamanders, little evidence of competition with local detritivores, and little to no influence on detritus breakdown rates over fall and winter when N. hostilis larvae are active. Thus, this new species appears to be facilitating new trophic pathways in this relatively species poor subalpine ecosystem, with little to no negative impacts on local species. Given species range shifts into high elevation or latitude systems often augment resident diversity and functional traits, we suggest positive outcomes such as facilitation or bottom-up resource transfer may be common, and may outweigh negative impacts on residents via competition and predation.

Amanda Klemmer (Primary Presenter/Author), University of Maine, amanda.klemmer@maine.edu;

Howard Whiteman (Co-Presenter/Co-Author), Murray State University, hwhiteman@murraystate.edu;

Ava Ardito (Co-Presenter/Co-Author), University of Maine, ava.ardito@maine.edu;

Jared Balik (Co-Presenter/Co-Author), Western Colorado University, jbalik@western.edu;

Parker Bausman (Co-Presenter/Co-Author), University of Maine , parker.bausman@maine.edu;

Lucy Crayton (Co-Presenter/Co-Author), Warren Wilson College, lcrayton.f20@warren-wilson.edu;

Elliot Johnston (Co-Presenter/Co-Author), Tetra Tech, elliot.johnston@tetratech.com;

Destiny Thorndike (Co-Presenter/Co-Author), University of Maine , destiny.thorndike@maine.edu;

Scott Thomas (Co-Presenter/Co-Author), Murray State, scott06thomas@gmail.com;

Susan Washko (Co-Presenter/Co-Author), Western Colorado University, swashko@western.edu;

Hamish Greig (Co-Presenter/Co-Author), University of Maine, hamish.greig@maine.edu;

16:00 - 16:15 | Independence Ballroom D | SHRIMPLY THE BEST: THE FOOD-WEB ROLE OF FRESHWATER DECAPODS DURING PROLONGED HIGH FLOW EVENTS.

6/06/2024  |   16:00 - 16:15   |  Independence Ballroom D

SHRIMPLY THE BEST: THE FOOD-WEB ROLE OF FRESHWATER DECAPODS DURING PROLONGED HIGH FLOW EVENTS. Flood pulses play a crucial role in the food-web processes of rivers by providing lateral connectivity between floodplains and the main channel of rivers. Inundated floodplains are hotspots of high-quality autochthonous resources that contain essential biomolecules such as long-chain polyunsaturated fatty acids for consumers. However, in Australia’s Murray Darling Basin, intensive water management has reduced the frequency of overbank flows. To assess the potential food-web implications, we analyzed the fatty acid composition of basal resources and omnivorous decapods as key consumers during an overbank flow event in a floodplain river. We hypothesized that omnivorous decapods would be able to take advantage of this influx of high-quality resources. We found that the concentration of basal resources like detritus and biofilm as well as decapod biomass increased during the over-bank flow. During flooding, the total proportion of EPA, ARA and DHA fatty-acids (associated autochthonous sources) within of decapod tissues was greater than the total proportion of LIN and ALA fatty-acids (associated with allochthonous carbon sources). This suggests that decapods are preferentially utilizing and incorporating the higher-quality fatty-acids in floodplain autochthonous resources during flooding. Changes in the frequency of flood pulses may alter secondary productivity by decapods, with likely implications for higher trophic levels as they are important prey resources for large fish and waterbirds. This knowledge could be used to inform environmental flow management, highlighting the importance of periodic floodplain inundation for riverine food-webs.

Alana Cormican (Primary Presenter/Author), Centre for Applied Water Science, University of Canberra, alana.cormican@canberra.edu.au;

Kishor Maharjan (Co-Presenter/Co-Author), Centre for Applied Water Science, University of Canberra, Kishor.Maharjan@canberra.edu.au;

Paul McInerney (Co-Presenter/Co-Author), CSIRO, paul.mcinerney@csiro.au;

Jason Thiem (Co-Presenter/Co-Author), NSW Department of Primary Industries, Fisheries, jason.thiem@dpi.nsw.gov.au;

Ross M. Thompson (Co-Presenter/Co-Author), Centre for Applied Water Science, University of Canberra, ross.thompson@canberra.edu.au;

Darren P. Giling (Co-Presenter/Co-Author), Centre for Applied Water Science, University of Canberra, darren.giling@canberra.edu.au;

16:15 - 16:30 | Independence Ballroom D | METHANE MUNCHIES: UNRAVELLING THE GAS-TRONOMIC DELIGHTS OF RIVERS

6/06/2024  |   16:15 - 16:30   |  Independence Ballroom D

METHANE MUNCHIES: UNRAVELLING THE GAS-TRONOMIC DELIGHTS OF RIVERS All organisms require a source of carbon to grow and reproduce, whether it’s CO2 used by autotrophic organisms, or complex organic carbon obtained by animals from their diets. Dominant paradigms of freshwater ecology provide theoretical frameworks for two primary sources of carbon: autochthonous carbon of algal origin and allochthonous carbon from terrestrial vascular plants. An additional, less studied, pathway for carbon to enter rivers is as methane. Methane is produced in small quantities via methanogenesis by anaerobic methanogenic archaea, yet because rivers are generally well oxygenated, it’s not usually a significant contributor to carbon budgets. However, methane may also enter rivers via seeps where underground deposits connect to the surface via fissures and fractures. Here, we explored the contribution of methane to food webs in the Condamine River (Queensland, Australia) by comparing ?13C values of animals and their foods from reaches rich in dissolved thermogenic methane with reaches where methane concentrations were at background levels. Within thermogenic methane seep zones, we found evidence that methane serves as the principal basal carbon source for food webs. Additionally, we demonstrate the persistence of methane–derived carbon across multiple trophic levels of the ecosystem. Our findings establish the prevalence of a thermogenic methane–methanotrophic bacteria–primary consumer pathway and underscore its significance as the dominant energy conduit in rivers with high concentrations of dissolved methane.

Paul McInerney (Primary Presenter/Author), CSIRO, Paul.Mcinerney@csiro.au;

Gavin Rees (Co-Presenter/Co-Author), CSIRO Land and Water, gavin.rees@csiro.au;

Ben Wolfenden (Co-Presenter/Co-Author), N/A, Benjamin.Wolfenden@environment.nsw.gov.au;

Daryl Nielsen (Co-Presenter/Co-Author), CSIRO, Daryl.Nielsen@csiro.au;

16:30 - 16:45 | Independence Ballroom D | FOOD WEBS OF AGRICULTURAL STREAMS ARE LESS COMPLEX BUT NOT LESS EFFICIENT

6/06/2024  |   16:30 - 16:45   |  Independence Ballroom D

Food webs of agricultural streams are less complex but not less efficient The expansion and intensification of agricultural land use and the associated deforestation, eutrophication and modification of habitat heterogeneity remain the most important stressors to stream ecosystems worldwide. Their effects on biodiversity and community composition are well described, but we lack comparative knowledge about the effects of agriculture on the topology of and energy fluxes in food webs. We combined stable isotope-derived dietary proportions with quantifications of ecosystem production to calculate food chain length, complexity and trophic transfer efficiency (TTE) of the green (biofilm) and brown (terrestrial POM) food chain in two forested and two agricultural streams. Food web complexity was lower, and food chains were shorter in agricultural than in forested streams. There was a shift in basal resources from tPOM to biofilm in agricultural streams, and TTE of the brown and green pathway decreased with increasing trophic positions in agricultural streams. However, the remarkably high TTE of primary consumers in agricultural streams compensated for the loss of green and brown fluxes to higher trophic levels. We attribute the observed food web effects to the release of primary consumers from top-down pressure, as predator production was lower in agricultural than in forested streams. We discuss if the inverse relationship between food web complexity and TTE is a peculiarity of highly modified freshwater ecosystems.

Mario Brauns (Primary Presenter/Author), Helmholtz Centre for Environmental Research - UFZ, mario.brauns@ufz.de;

Romy Wild (Co-Presenter/Co-Author), Technical University of Munich, romy.wild@tum.de;