Permafrost thaw lakes and ponds as habitats for abundant rotifer populations

Abstract

Thermokarst lakes and ponds were sampled across a range of permafrost landscapes in subarctic Québec (Nunavik, Canada) to compare their rotifer and other zooplankton characteristics with a set of rock-basin lakes and ponds in the region. A total of 24 rotifer species were identified, with an average of seven taxa per waterbody. Rotifer abundance was an order of magnitude higher in the thaw ponds than in rock-basin waters. In some thaw ponds, rotifers accounted for >50% of the total zooplankton biomass, but for <10% in all of the rock-basin waters. Neither α-nor β-diversity was significantly different between the two waterbody types. Grazing experiments with microspheres (0.5-6 μm diameter) showed that medium-sized particles (2-3 μm) were preferred to smaller and larger particles; clearance rates were <0.05% of the water column per day, implying that the rotifer populations were unlikely to be bottom-up limited by food availability. Rotifer abundance was negatively correlated with cladoceran densities, suggesting possible interference effects. Chaoborus larvae were also present and may exert a top-down control. Thermokarst ponds are currently favorable environments for rotifers, but the rapid change they have begun to experience brings uncertainty about their ongoing capacity to sustain these prolific communities.Key words: diversity, permafrost, rotifers, thermokarst, zooplankton.Résumé : Des lacs et des mares thermokarstiques ont fait l'objet de prélèvement d'échan-tillons dans divers paysages de pergélisol à travers le Québec subarctique (Nunavik, Canada), afin de comparer les caractéristiques de leurs rotifères et autres zooplanctons, et ce, à un ensemble de lacs et de mares d'ombilic glaciaire dans la région. On a identifié un total de 24 espèces de rotifères, avec une moyenne de sept taxons par plan d'eau. L'abondance de rotifères était d'un ordre de grandeur plus élevé dans les mares de fonte que dans les eaux d'ombilic glaciaire. Dans quelques mares de fonte, les rotifères représentaient >50% de l'ensemble de la biomasse du zooplancton, mais elles en représentaient <10% dans toutes les eaux d'ombilic glaciaire. Ni la diversité α ni β ne se distinguait sensiblement entre les deux types de plan d'eau. Des expériences de broutage avec des microsphères (0,5 à 6 μm de diamètre) ont montré que les particules de taille moyenne (2-3 μm) étaient préférées comparativement aux plus petites et aux grandes particules; les taux d'élimination étaient <0,05% de la colonne d'eau par jour, ce qui laisse entendre qu'il était peu probable que les populations de rotifères subissent une limitation ascendante en raison de la disponibilité alimentaire. L'abondance de rotifères était négativement corrélée avec les densités de cladocères, suggérant des effets d'interférence possibles. Des larves Chaoborus étaient aussi pré-sentes et pouvaient exercer un contrôle descendant. Les mares thermokarstiques sont For personal use only.actuellement des environnements propices aux rotifères, mais le changement rapide que ces env...

Increasing dominance of terrigenous organic matter in circumpolar freshwaters due to permafrost thaw

“…Due to the fractionation during methanogenesis, methane has more negative δ 13 C values and can be metabolized by methanotrophic bacteria, which then enter the food web (Bastviken et al ). Mixotrophic algae constitute a major fraction of the total phytoplankton community growing in the thaw ponds of the region (Bégin and Vincent ) and could rely on the methanotrophic bacteria as an energy source, explaining the more depleted δ 13 C signature of the phytoplankton. Given the extreme shallowness (< 1 m) and the absence of stratification in bedrock and tundra ponds, the benthic source was an important contributor to DOM, likely resulting from the resuspension of decomposed benthic materials (Evans ) and by diffusion of benthic carbon exudates to the water column (Rautio et al ; Rodríguez et al ).…”

Increased risk of cyanobacterial blooms in northern high‐latitude lakes through climate warming and phosphorus enrichment

“…While abiotic factors (DOC, pH, conductivity) accounted for most of the variability in bacterial community structure (Crevecoeur, Vincent, Comte, & Lovejoy, ), they had only limited explanatory power for phytoplankton community structure. These waters are known to host abundant zooplankton populations, including cladocerans and diverse rotifers (Bégin & Vincent, ), and it is likely that these have a strong top down influence on phytoplankton species composition, as observed in other aquatic ecosystems (Hessen & Kaartvedt, ). However, future changes in the physicochemical environment are likely to exceed the natural variability observed here, and could drive shifts in phytoplankton community composition that are not evident from the relatively weak correlative relationships in our taxonomic survey.…”

“…planktonicum observed in our experiment is of particular concern for water quality in that many species of Dolichospermum are known to produce neurotoxins (Li, Dreher, & Li, ), and D. planktonicum also produces a microcystin‐like liver toxin (Bruno, Barbini, Pierdominici, Serse, & Ioppolo, ). Extracts of D. planktonicum have strong inhibitory effects on the growth and reproduction of rotifers and cladocerans (Barrios, Nandini, & Sarma, ), two zooplankton groups in the food web of permafrost thaw lakes (Abramova et al., ; Bégin & Vincent, ). The stimulation of picocyanobacteria by P enrichment would likely compound the stresses imposed on the zooplankton, given that subarctic picoplankton appear to be a poor quality food source for cladocerans in these thaw lakes (Przytulska, Bartosiewicz, Rautio, Dufresne, & Vincent, ).…”

Chlorovirus and myovirus diversity in permafrost thaw ponds

“…Viruses are intracellular obligate parasites and therefore their dynamics are inextricably linked to those of their hosts. The diversity of Bacteria (Comte et al 2016a,b), Archaea (Crevecoeur et al 2015(Crevecoeur et al , 2016 and protists (Przytulska et al 2016, Bégin & Vincent 2017, the presumptive primary hosts of the subarctic thermokarst viruses, has recently been characterized in several Québec subarctic ponds. Crevecoeur et al (2015) reported that the largest differences in bacterial diversity were between the 2 permafrost landscape types (palsa vs. lithalsa), and Comte et al (2016b) concluded that the composition of these communities appears to be primarily determined by environmental filtering and dispersal limitation.…”