Recent climate warming favours more specialized cladoceran taxa in western Canadian Arctic lakes
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AIM: Shifts in the distribution of freshwater algal communities as a result of climate‐related limnological changes are well documented; however, impacts on higher trophic levels have received less attention. For example, little is known about how Cladocera (Crustacea, Branchiopoda), often dominant invertebrates and key ecological indicators, have responded to recent warming on broad spatial and temporal scales. Here, we use lake sediment records to test the hypothesis that recent, intensive warming in the western Canadian Arctic has resulted in consistent shifts in the composition of cladoceran assemblages. LOCATION: Small, first‐order lakes in the Mackenzie Delta region of the western Canadian Arctic. METHODS: Sediment cores representing the recent past (approximately 150–200 years) were obtained from five lakes spanning a strong climatic gradient. Subfossil remains of Cladocera were identified and enumerated and overall primary production was inferred using spectroscopic techniques. The habitat preferences and feeding strategy of each taxon were compared. Detrended canonical correspondence analysis was used to estimate compositional turnover since 1850, and compared with that of three cladoceran assemblages from Nova Scotia, to place high‐latitude changes in context. RESULTS: Cladoceran assemblage changes occurred coincident with the timing of known regional warming and were strongly linked to estimated changes in primary production. In the northern and deepest lakes, an increase in the planktonic, filter‐feeding taxon Bosmina spp. coincided with a decrease in the generalist littoral taxa Chydorus cf. brevilabris and Alona circumfimbriata. In the more southern lakes, an increase in macrophyte‐associated scrapers Acroperus harpae and Eurycercus spp. occurred concurrently with decreases in generalist taxa. In one lake, an increase in another specialist, an obligate mud‐dwelling taxon, was observed. MAIN CONCLUSIONS: In the western Canadian Arctic, warming has resulted in an increase in cladoceran taxa occupying more specialized feeding and habitat niches. Generalist taxa capable of occupying multiple habitats and employing diverse feeding strategies have been systematically replaced by more specialist species. This response is analogous to what has been inferred for algal communities across the Northern Hemisphere, and represents the first evidence of consistent cladoceran changes to recent climate warming in high‐latitude regions.
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