Impacts of reduced Lepidurus arcticus availability on brown trout life history traits in a mountain reservoir
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Aquatic Sciences
RESEARCH ARTICLE
Impacts of reduced Lepidurus arcticus availability on brown trout life history traits in a mountain reservoir Hanna‑Kaisa Lakka1,2 · Antti P. Eloranta1,3 · Trygve Hesthagen3 · Randi Saksgård3 · Michael Power4 Received: 3 December 2019 / Accepted: 19 August 2020 © The Author(s) 2020
Abstract Lepidurus arcticus (the Arctic tadpole shrimp) is a vulnerable keystone species in Arctic and alpine water bodies where its occurrence and population size may influence the viability and life history traits of resident salmonids. Using data from a Norwegian mountain hydropower reservoir, Aursjoen, we illustrate how reduced availability of L. arcticus as prey resulted in the reduced condition, growth and delayed maturation of resident brown trout (Salmo trutta). We further link changes in the relative abundance of L. arcticus as prey to changing reservoir conditions, e.g. water level changes in the spring period, thereby establishing an indirect link between reservoir operation regimes and brown trout population traits. While no evidence for decreased brown trout survival was found, the results indicate that alternative brown trout prey resources, i.e. the small chydorid cladoceran Eurycercus lamellatus, do not appear to have successfully offset the caloric loss from reduced consumption of large-sized L. arcticus. Although the fundamental explanation for the observed L. arcticus collapse remains largely unknown, the present findings provide strong evidence that this vulnerable crustacean species can affect the abundance, viability and life history traits of valued resident salmonid populations in oligotrophic alpine lakes and reservoirs exposed to climate- and hydropower-driven changes in water levels and temperature. Keywords Branchiopoda · crustaceans · hydropower reservoir · keystone species · nutrition · prey availability
Introduction Improved understanding of relationships between abundance of keystone invertebrate species and life history traits of their predators would facilitate better management and mitigation of biodiversity loss in alpine and high-latitude freshwater ecosystems (Lento et al. 2019). In lakes hosting Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00027-020-00751-x) contains supplementary material, which is available to authorized users. * Hanna‑Kaisa Lakka hanna‑[email protected] 1
Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
2
Department of Natural History, NTNU University Museum, Norwegian University of Science and Technology, Trondheim, Norway
3
Department of Aquatic Ecology, Norwegian Institute for Nature Research (NINA), Trondheim, Norway
4
Department of Biology, University of Waterloo, Waterloo, ON, Canada
salmonid fishes, large-sized crustacean species commonly act as keystone species due to their omnivorous diet and high importance for fish nutrition (Sømme 1934; Borgstrøm et al. 1985; MacNeil et al. 1999). Although large-sized crust
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