SFS Annual Meeting

6/03/2024  |   13:30 - 13:45   |  Salon 3/4

EVIDENCE OF WINTER STARVATION OF BENTHIC MACROINVERTEBRATES ALONG A THERMAL GRADIENT OF ARCTIC SPRING-STREAMS Perennially flowing spring-fed streams in arctic Alaska provide winter habitat for benthic macroinvertebrates when all other stream habitats freeze. The temperatures of these streams stay relatively constant despite 24 hours of sunlight in summer and little or no light during winter. Such uncoupling of temperature and light regimes provides a unique opportunity to assess the effects of annual light-cycles independent of temperature. Previous investigations at one of our study sites, Ivishak Spring, found consumer carbon-limitation in winter as metabolic demand exceeded net primary production. Here we ask whether higher water temperatures exacerbate the severity of carbon-limitation driving starvation and corresponding changes in consumer tissue stoichiometry. Annual cycles in the body composition of macroinvertebrates from five spring streams (mean annual temperature range: 1-12?) were assessed with semi-monthly samples from June 2022 to May 2023. We measured whole-body percent carbon (C), nitrogen (N) and phosphorus (P), ?13C, ?15N, and total lipid content of three insect taxa: Isoperla petersoni (Plecoptera: Perlodidae), Ecclisomyia conspersa (Trichoptera: Limnephilidae) and Chironomidae (Diptera). Preliminary analyses show Isoperla petersoni and Chironomidae C:N and C:P declined through winter. Isoperla increased in ?13C and ?15N in the winter, while Chironomidae decreased. Further analyses are ongoing (data on E. conspera and total lipid content of all taxa). We anticipate that findings from our study will contribute to the understanding of light-temperature interactions in controlling compensatory physiological mechanisms that reduce the scope of winter C-limitation in these unique arctic ecosystems.

Annie G. Blalock (Primary Presenter/Author), The University of Alabama, agblalock@crimson.ua.edu;

Tori A. Hebert (Co-Presenter/Co-Author), The University of Alabama, tahebert@crimson.ua.edu;

Carla L. Atkinson (Co-Presenter/Co-Author), The University of Alabama, carla.l.atkinson@ua.edu;

Jonathan P. Benstead (Co-Presenter/Co-Author), The University of Alabama, jbenstead@ua.edu;

Alexander D. Huryn (Co-Presenter/Co-Author), The University of Alabama, huryn@ua.edu;

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6/03/2024  |   13:45 - 14:00   |  Salon 3/4

TO WHAT EXTENT TO TEMPERATURE AND LIGHT AVAILABILITY AFFECT METABOLISM OF A GROUNDWATER-DOMINATED RIVER? In aquatic ecosystems, temperature and light are primary drivers of ecosystem metabolism. However, light availability and temperature are seasonally generally synchronous outside of the tropics, making it difficult to assess the independent influence of either of these drivers on ecosystem metabolism. We assessed the effects of seasonal variation in light availability on gross primary production (GPP) and ecosystem respiration (ER), macrophyte community dynamics, and autotrophic metabolism in a physicochemically stable groundwater-dominated river with high perennial macrophyte biomass across a single year. Using high-resolution drone imagery and field measurements, seasonal macrophyte biovolume (m3) was measured across four reaches of varying anthropogenic activity. Seasonal GPP, respiration (R), and net primary production (NPP) were measured at the reach scale and for three macrophyte species and plastic plant analogues of increasing morphological complexity to determine how plant morphology influenced macrophyte metabolism and epiphytes. GPP and ER in the upper San Marcos River very high when compared to the literature and were correlated with seasonal light availability, indicating autotrophic respiration as the main contributor to ER. Reach-scale macrophyte biovolume were controlled by human recreational activity, not seasonal light availability. Macrophyte and epiphyte metabolism were different across seasons and plant morphotypes, with the highest rates of epiphyte GPP and R occurring on structurally complex macrophytes. Our results indicate that ecosystem metabolism in thermally stable groundwater rivers is largely driven by light limitation of autotrophic biomass and that disturbance from human activity has the capacity to override this interaction.

Weston Nowlin (Primary Presenter/Author), Texas State University, wn11@txstate.edu;

Matthew Stehle (Co-Presenter/Co-Author), Texas State University, mrs239@txstate.edu;

Todd Swannack (Co-Presenter/Co-Author), UNITED STATES ARMY ENGINEER RESEARCH AND DEVELOPMENT CENTER, Todd.M.Swannack@erdc.dren.mil;

Benjamin Schwartz (Co-Presenter/Co-Author), Department of Biology, Texas State University, San Marcos, Tx., bs37@txstate.edu;

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