Mountain lakes contain a unique assemblage of crustacean zooplankton species. Fishless alpine lakes are typically dominated by the large calanoid copepod Hesperodiaptomus arcticus and large melanic Daphnia. These species are highly responsive to the effects of climate change due to their sensitivity to environmental variables like temperature, turbidity, and chromophoric dissolved organic matter. Our zooplankton work centers around five different themes. Diel vertical migration Overholt, E.P., K.C. Rose, C.E. Williamson, J.M. Fischer, N.A. Cabrol. 2016. Behavioral responses of freshwater calanoid copepods to the presence of ultraviolet radiation: avoidance and attraction. Journal of Plankton Research 38: 16-26. Fischer, J.M., M.H. Olson, N. Theodore*, C.E. Williamson, K. C. Rose, and J. Hwang*. 2015. Diel vertical migration of copepods in mountain lakes: the changing role of ultraviolet radiation across a transparency gradient. Limnology and Oceanography 60: 252-262. Leach, T.H., C.E. Williamson, N. Theodore*, J.M. Fischer, and M.H. Olson. 2015. The role of ultraviolet radiation in the diel vertical migration of zooplankton: an experimental test of the transparency-regulator hypothesis. Journal of Plankton Research 37: 886-896. Community ecology Loewen, C.J.G., A. L. Strecker, G.L. Larson, A. Vogel, J.M. Fischer, and R.D. Vinebrooke. 2018. Macroecological driver of zooplankton communities across the mountains of western North America. Ecography DOI 10.1111/ecog.03817. Fischer, J.M., M.H. Olson, C.E. Williamson, J.C. Everhart*, P.J. Hogan, J.A. Mack, K.C. Rose, J.E. Saros, J.R. Stone, R.D. Vinebrooke. 2011. Implications of climate change for Daphnia in alpine lakes: predictions from long-term dynamics, spatial distribution, and a short-term experiment. Hydrobiologia 676: 263-277. Phenology Luke Groff’s Honors Thesis Project (2019) Cannibalistic copepod caper: the effects of a changing environment on zooplankton phenology Climate change can modify normal seasonal patterns in ecosystems and, consequently, affect important life cycle events of organisms. This study investigates an unusual phenological pattern in the copepod Hesperodiaptomus arcticus in Opabin Lake, a glacially-fed system in the Canadian Rocky Mountains. This project built on the findings of Haley Plante ’17 who demonstrated a striking biennial oscillation between exclusively adult stages and exclusively juvenile stages in H. arcticus and hypothesized that this pattern was a result of a two-year life cycle and cannibalism in the nutrient poor lake. To test this hypothesis, I performed a microcosm experiment and compared body sizes of H. arcticus across my study systems. I also utilized stable isotope analysis to assess the trophic position of adults relative to juveniles in Opabin and Zigadenus (where cycling occurs) in comparison to Annette (no cycling) and Moraine (no cycling) and adults relative to Leptodiaptomus tyrelli (a small food item for H. arcticus) in Redoubt. Results from these analyses provided preliminary support for the cannibalism hypothesis. Additionally, by adding life stage data for four additional lakes as well as updating previously analyzed lakes to include summer 2017 and 2018, I observed dampening of the cycling pattern in Opabin and hypothesized that this dampening could be caused by warming lake temperatures, earlier spring ice-off, reduced turbidity, and increased phytoplankton abundances. Biogeography Fischer, J.M., M.H. Olson, C.E. Williamson, J.C. Everhart*, P.J. Hogan, J.A. Mack, K.C. Rose, J.E. Saros, J.R. Stone, R.D. Vinebrooke. 2011. Implications of climate change for Daphnia in alpine lakes: predictions from long-term dynamics, spatial distribution, and a short-term experiment. Hydrobiologia 676: 263-277. Colleen Lawlor’s Independent Study Project (2019) Distribution and abundance of Daphnia in Canadian Rocky Mountain lakes Patterns of spatial distribution among communities of organisms are affected by many different ecological variables. The distribution of Daphnia, a freshwater lake-dwelling zooplankton and a model organism for studying environmental change, exhibits an interesting yet poorly understood pattern in the Canadian Rocky Mountains for three reasons: (1) its dependence on ecological variables is unclear, (2) it is complicated by discordance between traditional morphological species identifications and more recent genetic ones, and (3) community structures are constantly changing due to continual hybridization and dispersal of the different species, which in this region include D. pulex, D. pulicaria, and D. middendorffiana. This study aims to resolve some of the uncertainty regarding Daphnia distribution in Canadian Rocky Mountain lakes by comparing DNA sequence data of the mitochondrial NADH dehydrogenase subunit 5 (ND5) locus from individuals isolated from fourteen lakes with varying ecological characteristics. Data from these ND5 sequences suggest that Daphnia in the Canadian Rockies are distributed primarily based on geographic location rather than environmental conditions. Although these results contradict many studies that indicate significant effects of ecological variables on Daphnia populations and distribution, additional research including a larger set of study lakes and additional genetic loci may generate results that are more consistent with these former studies as well as valuable insights into the spatial distribution of Daphnia species in the Canadian Rockies and beyond. Parasites Ruby Fries ‘20 and Maddie Flemming ‘21 are investigating ellobiopsid parasites on alpine zooplankton. The goal of their work is to describe the spatial and temporal patterns of parasite prevalence.