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Global climate change threatens the integrity of freshwater ecosystems across the globe. At higher latitudes these ecosystems are experiencing the highest rates of temperature increase related to climate change. Freshwater invertebrate communities are important sources of food for fishes and bioindicators helping us understand the health of entire ecosystems. Our research is part of a larger experiment which aims to artificially warm an arctic lake by 2-4 ⁰C, to try and determine the impact of rising temperatures on lake food webs and ecosystem function. Our objectives were to calculate benthic macroinvertebrate densities in two arctic lakes, Fog1 and Fog3 (one control and one reference), compare between these lakes as a function of abiotic and biotic differences, and assess whether these macroinvertebrate densities have responded to increases in lake warming. Using standard protocols, we analyzed benthic samples from 2016-2019 taken using an Ekman dredge from lake depths between 0-4 meters. We classified each taxon into four main groups: Diptera, Mollusca, zooplankton, and other aquatic macroinvertebrates and calculated the densities of each group (number/m2). Densities varied greatly from year to year, ranging from 609 organisms/meter2 to 20,391 organisms/ meter2. We observed a very large increase in “other aquatic macroinvertebrates” group in Fog1 (warmed lake) in 2018, comprised mostly of Hydracarina (mites) and including some unique Trichopterans and Annelids. While the densities of benthic macroinvertebrates ranged greatly across lakes and years, we did not observe a definitive trend in response to experimental warming (some groups increased one year but decreased the next and vice versa). In future work, we will explore the metabolic preferences of those taxonomic groups that may have responded to warming, as well as potential top down (e.g., fish predation) pressures on benthic macroinvertebrates.

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