6/06/2017  |   14:00 - 14:15   |  306C

PATTERNS OF MACROINVERTEBRATE COMMUNITY COMPOSITION AND PRODUCTION ACROSS A NATURAL STREAM TEMPERATURE GRADIENT As global temperatures increase, it is critical that we understand (a) how warming may alter structure of ecological communities and (b) how such changes may impact ecosystem functions such as the flux of energy through food webs. Predicting these responses is challenging because of difficulties in isolating temperature from other environmental variables and in scaling short-term and species-level responses to longer timescales and higher levels of organization. Here, we exploit a natural temperature gradient (5-30°C) within a small geographical area to quantify the influence of temperature on invertebrate assemblage structure and production in six Icelandic streams. We show that temperature acts as a strong filter on community structure as well as on the phenology and evenness of invertebrate production. Dominant energy fluxes shifted from chironomid taxa in cold streams to gastropods and simuliids in warmer ecosystems. Community-level production exhibited strong seasonality in response to light, even in streams that maintain similar temperatures year-round. Our results provide a unique assessment of the relationship between temperature and community secondary production and the potential response of stream ecosystem function to climate warming.

James Junker (Primary Presenter/Author), University of North Texas, james.junker1@gmail.com;


Wyatt Cross ( Co-Presenter/Co-Author), Montana State University, wyatt.cross@montana.edu ;


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


James Hood ( Co-Presenter/Co-Author), The Ohio State University, hood.211@osu.edu;


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


Gisli Mar Gislason ( Co-Presenter/Co-Author), University of Iceland, gmg@hi.is;


Daniel Nelson ( Co-Presenter/Co-Author), University of Oklahoma, dnelson12@crimson.ua.edu;


Jón S. Ólafsson ( Co-Presenter/Co-Author), Marine and Freshwater Research Institute, Iceland, jon.s.olafsson@hafogvatn.is;


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6/06/2017  |   14:15 - 14:30   |  306C

WHY A MAYFLY CLOEON DIPTERUM (EPHEMEROPTERA: BAETIDAE) GETS SMALLER AS TEMPERATURES WARM Larvae of the multivoltine mayfly Cloeon dipterum were reared from egg hatch to adult at 10 constant water temperatures ranging from 12.1° to 33.5°C. Median larval development time ranged from 13.5 to 110 d. Survivorship was greatest between 16° and 25°C (averaging about 85%) and declined to zero at 33.5°C. Thresholds for growth and development were 10.0° and 10.7°C, respectively. C. dipterum followed the “temperature size rule (TSR), with adult females being ~5X larger at 12.1° than at 31.7°C. We hypothesize that TSR is due to developmental rates increasing substantially faster than growth rates as test temperature increased toward the lethal limit. Respirometry data showed that aerobic metabolism at chronically lethal temperatures remained substantial and that as temperatures increased, so did metabolic maintenance costs for supporting higher body mass. We used our data to test the “oxygen- and capacity-limited thermal tolerance” hypothesis and results indicate that it may be more suited to explain acute thermal limits than chronic thermal limits which are more ecologically relevant. Our study suggests that C. dipterum has the potential to complete up to 5 generations per year at mid-latitudes in eastern North America.

Bernard Sweeney (POC,Primary Presenter), Stroud Water Research Center, sweeney@stroudcenter.org;


David Funk ( Co-Presenter/Co-Author), Stroud Water Research Centrer, dfunk@stoudcenter.org;


Allison Camp ( Co-Presenter/Co-Author), North Carolina State University, aacamp@ncsu.edu;


David Buchwalter ( Co-Presenter/Co-Author), North Carolina State University, david_buchwalter@ncsu.edu;


John Jackson ( Co-Presenter/Co-Author), Stroud Water Research Center, jkjackson@stroudcenter.org;


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6/06/2017  |   14:30 - 14:45   |  306C

LETHAL AND SUBLETHAL RESPONSES OF 2 BAETID MAYFLIES EXPOSED TO CONSTANT AND VARIABLE TEMPERATURE EXTREMES Thermal effects on aquatic insect performance (survival, growth rate, development times, body size, fecundity) are well known, but the effects of diel (vs constant) temperature regimes on thermal limits for performance remain poorly understood. Laboratory experiments involved whole life cycle rearing (1st instar to adult) of two baetid mayfly species ( Neocloeon triangulifer and Cloeon dipterum ) in 6 different temperature regimes (range 14-30°C, with constant ±0.1°C or with diel cycle of ±2.5°C ). These are multivoltine species that overwinter as larvae. Responses to 18 and 22°C were nearly identical between constant and variable temperature regimes for both species. However, at 14°C, development time and degree-days to complete development were less, and development rate, growth rate and intrinsic rate of increase (r) greater at variable compared with constant. At or near the warmest temperatures (26 and 28°), performance in the variable temperature treatment generally declined relative to constant (e.g., development time and degree days were greater in the variable temperature treatment). Thus, a ±2.5° diel temperature fluctuation significantly affected mayfly performance at the cool and warm end of the thermal range.

John Jackson (Primary Presenter/Author), Stroud Water Research Center, jkjackson@stroudcenter.org;


David Funk ( Co-Presenter/Co-Author), Stroud Water Research Centrer, dfunk@stoudcenter.org;


Bernard Sweeney ( Co-Presenter/Co-Author), Stroud Water Research Center, sweeney@stroudcenter.org;


David Buchwalter ( Co-Presenter/Co-Author), North Carolina State University, david_buchwalter@ncsu.edu;


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6/06/2017  |   14:45 - 15:00   |  306C

GENE EXPRESSION AND METABOLOMICS REVEAL PHYSIOLOGICAL MECHANISMS UNDERLYING THERMAL EFFECTS IN MAYFLY NEOCLOEN TRIANGULIFER Temperature dictates the performance and distributions of aquatic insects. Life history data show that the mayfly Neocloen triangulifer generally follows the temperature size rule, with faster growth rate, smaller body size and less fecundity at warmer temperatures. However, the physiological mechanisms underlying thermal effects remains unclear. Here we attempted to link physiological processes to life history outcomes in N. triangulifer by studying gene expression and metabolomics. We reared N. triangulifer at different static temperatures (22-30°C, 2°C interval) from hatching eggs to mature larvae. Larvae fail to reach adulthood when reared at 30°C.We found no change in hypoxia responsive genes in larvae exposed to thermal stress. Metabolomics data showed decrease of several lipids and acylcarnitines in larvae, suggesting thermal stress largely acts upon bioenergetic pathways. We also observed an increase in tissue histamines, which may indicate larvae likely reduce food intake at upper thermal limits. Collectively, these data suggest that rather than oxygen limitation, energetic challenges and metabolic maintenance costs more likely underlie the observed response of life history to temperature.

Hsuan Chou (Primary Presenter/Author), North Carolina State University, hchou2@ncsu.edu;


Wimal Pathmasiri ( Co-Presenter/Co-Author), RTI International, wpathmasiri@rti.org ;


Susan Sumner ( Co-Presenter/Co-Author), University of North Carolina at Chapel Hill, susan_sumner@unc.edu ;


David Funk ( Co-Presenter/Co-Author), Stroud Water Research Centrer, dfunk@stoudcenter.org;


John Jackson ( Co-Presenter/Co-Author), Stroud Water Research Center, jkjackson@stroudcenter.org;


Bernard Sweeney ( Co-Presenter/Co-Author), Stroud Water Research Center, sweeney@stroudcenter.org;


David Buchwalter ( Co-Presenter/Co-Author), North Carolina State University, david_buchwalter@ncsu.edu;


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6/06/2017  |   15:00 - 15:15   |  306C

ECOSYSTEM METABOLISM APPARENT TEMPERATURE SENSITIVITY VARIES ACROSS A SUB-ALPINE STREAM NETWORK Ecosystem metabolism defines the autotrophic and heterotrophic energetics within an ecosystem. Water temperature drives, in part, both ecosystem respiration (ER) and gross primary production (GPP). We estimated daily fluxes of ecosystem metabolism in 15 streams for 12 to 18 months across a 254-km2 sub-alpine network in Austria. To study the sensitivity of ecosystem metabolism to temperature, we quantified apparent temperature sensitivity for GPP and ER as described by Arrhenius kinetics. Network-wide ER activation energy (AE) was lower (<0.60 eV) than the expected range for metabolism kinetics, varying 2-fold across individual sub-catchments. Network-wide AE for GPP was 3-fold greater than predicted based on metabolism kinetics alone and varied across sub-catchments from 0.2 to 1.8 eV. This variability in AE of ER and GPP within a single stream network indicated that individual streams likely would respond differently to changing environmental conditions, dependent on local factors such as organic matter quality and nutrient resources. Despite the variability of AE for ecosystem metabolism across the network, ER AE was negatively correlated with GPP AE, indicating a close coupling of these metabolic processes.

Amber Ulseth (Primary Presenter/Author), Sam Houston State University, amber.ulseth@epfl.ch;


Gabriel Singer ( Co-Presenter/Co-Author), University of Innsbruck, gabriel.singer@uibk.ac.at;


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


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6/06/2017  |   15:15 - 15:30   |  306C

LONG-TERM SEDIMENTATION FROM PERMAFROST DEGRADATION DECREASES BENTHIC MACROINVERTEBRATE DRIFT DENSITIES IN ARCTIC STREAMS Retrogressive thaw slumps (RTS), landscape features formed from permafrost degradation, are increasing in size and frequency in the western Canadian Arctic. The debris from RTS flows into nearby stream systems, greatly changing the physical and chemical properties of the stream, however, little is known about the biological impacts of this abiotic disturbance regime. Disturbances in streams can increase benthic macroinvertebrate (BMI) drift, and decrease BMI abundance in impacted stream reaches. This study investigated the influence of RTS disturbances on BMI drift. Sites were sampled upstream and downstream of RTS. Grab samples and sediment traps were used to assess the physical and chemical conditions of stream sites and BMIs were collected using drift nets. Drift density was assessed over a gradient of sedimentation using regressions. There was an unexpected decrease in BMI drift densities with as sedimentation increased, but proportional drift, which corrected for abundance of BMIs collected from the benthos, increased along a sedimentation gradient. This study showed that drift densities can decrease in chronically-impacted streams due to depleted local populations, opposite to what is generally found in the literature.

Brianna Levenstein (Primary Presenter/Author), Canadian Rivers Institute, Department of Biology, University of New Brunwsick, brianna.levenstein@unb.ca;


Jennifer Lento ( Co-Presenter/Co-Author), Canadian Rivers Institute, Department of Biology, University of New Brunswick, jlento@gmail.com;


Joseph M. Culp ( Co-Presenter/Co-Author), Environment and Climate Change Canada and Canadian Rivers Institute, Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5, joseph.culp@canada.ca;


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