Freshwater Microbial Eukaryotic Core Communities, Open-Water and Under-Ice Specialists in Southern Victoria Island Lakes (Ekaluktutiak, NU, Canada)

Abstract

Across much of the Arctic, lakes and ponds dominate the landscape. Starting in late September, the lakes are covered in ice, with ice persisting well into June or early July. In summer, the lakes are highly productive, supporting waterfowl and fish populations. However, little is known about the diversity and ecology of microscopic life in the lakes that influence biogeochemical cycles and contribute to ecosystem services. Even less is known about the prevalence of species that are characteristic of the seasons or whether some species persist year-round under both ice cover and summer open-water conditions. To begin to address these knowledge gaps, we sampled 10 morphometrically diverse lakes in the region of Ekaluktutiak (Cambridge Bay), on southern Victoria Island (NU, Canada). We focused on Greiner Lake, the lakes connected to it, isolated ponds, and two nearby larger lakes outside the Greiner watershed. The largest lakes sampled were Tahiryuaq (Ferguson Lake) and the nearby Spawning Lake, which support commercial sea-run Arctic char (Salvelinus alpinus) fisheries. Samples for nucleic acids were collected from the lakes along with limnological metadata. Microbial eukaryotes were identified with high-throughput amplicon sequencing targeting the V4 region of the 18S rRNA gene. Ciliates, dinoflagellates, chrysophytes, and cryptophytes dominated the lake assemblages. A Bray–Curtis dissimilarity matrix separated communities into under-ice and open-water clusters, with additional separation by superficial lake area. In all, 133 operational taxonomic units (OTUs) occurred either in all under-ice or all open-water samples and were considered “core” microbial species or ecotypes. These were further characterized as seasonal indicators. Ten of the OTUs were characteristic of all lakes and all seasons sampled. Eight of these were cryptophytes, suggesting diverse functional capacity within the lineage. The core open-water indicators were mostly chrysophytes, with a few ciliates and uncharacterized Cercozoa, suggesting that summer communities are mixotrophic with contributions by heterotrophic taxa. The core under-ice indicators included a dozen ciliates along with chrysophytes, cryptomonads, and dinoflagellates, indicating a more heterotrophic community augmented by mixotrophic taxa in winter.

Arctic cyanobacterial mat community diversity decreases with latitude across the Canadian Arctic

“…In keeping with sensitivity to external conditions, distinct eukaryotic communities were identified between annual winter and summer conditions in Arctic lakes (Bock et al 2014 ) and ponds (Simon et al. 2015 , Potvin et al 2022 ).…”

Linking Groundwater to Surface Discharge Ecosystems: Archaeal, Bacterial, and Eukaryotic Community Diversity and Structure in Quebec (Canada)

“…However, there are many studies on microeukaryote communities in surface freshwater habitats, in lakes and rivers. Mostly phytoplankton, ciliates, dinoflagellates, and algae are found in surface water surveys [ 26 , 27 , 28 ], while fungi, Metazoa, Ciliophora, Cercozoa, and Amoebozoa are detected in groundwater studies [ 12 , 29 , 30 ]. The higher species richness in surface habitats is likely linked to the presence of sunlight and photosynthetic microorganisms which are absent in the dark subsurface ecosystems driven by chemosynthesis, as well as higher organic matter availability in surface systems given the direct link to terrestrial matter [ 31 , 32 ].…”

Diverse winter communities and biogeochemical cycling potential in the under-ice microbial plankton of a subarctic river-to-sea continuum

“…Winter under-ice pelagic microbial communities can differ markedly from those in summer open-water conditions ( 4 , 5 ), with some microbial taxa that excel during winter, while others decrease their activity or enter into dormancy. Seasonal changes in bacterial communities can vary according to lifestyle, with evidence that free-living planktonic bacteria may have greater temporal stability and lower dissimilarity between seasons than particle-associated bacteria ( 6 , 7 ).…”