Temperate Freshwater Systems Research Articles

Road salt pollution alters sex ratios in emerging mosquito populations

De-icing road salt is a persistent emerging pollutant in temperate freshwater systems, where winter salting is necessary for road and pedestrian safety. Experts argue that road salts may increase salt-tolerant mosquito populations and, potentially, disease transmission in urban areas. Only adult females consume bloodmeals and may carry zoonotic diseases. While there are some species with naturally occurring male-biased sex ratios, it is unclear whether road salt differentially affects male and female mosquitoes to alter sex ratios. We hypothesized that road salts would masculinize emergence sex ratios and decrease female success because females may face higher exposure to stressors during their lengthy juvenile development compared to males. We measured mosquito emergence sex ratios of control (0 g/L added salt) and salt (4.5 g/L added salt) mesocosms in southern Ontario, Canada across the West Nile Virus season (May to October). We found female-biased sex ratios (i.e., <50% male frequency) in both 0 and 4.5 g/L. While mosquito abundance was significantly higher in 4.5 g/L compared to 0 g/L, road salt significantly increased the proportion of emerging males from 32.8% to 40.8% (Negative Binomial Model; Estimate ± SE = 0.283 ± 0.108; P = 0.009); mosquitoes shift their sex ratios from female-biased towards parity (50:50) in response to salt. Our study illustrates the need to evaluate sex-specific abundance in pollution-related mosquito population studies. By showing a shift toward more male mosquitoes emerging in high salinity compared to control treatments, our results suggest that road salts may have the potential to decrease female mosquito success and indirectly reduce disease transmission in cities.

Global analysis of seasonal changes in trematode infection levels reveals weak and variable link to temperature

Seasonal changes in environmental conditions drive phenology, i.e., the annual timing of biological events ranging from the individual to the ecosystem. Phenological patterns and successional abundance cycles have been particularly well studied in temperate freshwater systems, showing strong and predictable synchrony with seasonal changes. However, seasonal successional changes in the abundance of parasites or their infection levels in aquatic hosts have not yet been shown to follow universal patterns. Here, using a compilation of several hundred estimates of spring-to-summer changes in infection by trematodes in their intermediate and definitive hosts, spanning multiple species and habitats, we test for general patterns of seasonal (temperature) driven changes in infection levels. The data include almost as many decreases in infection levels from spring to summer as there are increases, across different host types. Our results reveal that the magnitude of the spring-to-summer change in temperature had a weak positive effect on the concurrent change in prevalence of infection in first intermediate hosts, but no effect on the change in prevalence or abundance of infection in second intermediate or definitive hosts. This was true across habitat types and host taxa, indicating no universal effect of seasonal temperature increase on trematode infections. This surprising variation across systems suggests a predominance of idiosyncratic and species-specific responses in trematode infection levels, at odds with any clear phenological or successional pattern. We discuss possible reasons for the minimal and variable effect of seasonal temperature regimes, and emphasise the challenges this poses for predicting ecosystem responses to future climate change.

Statistical Inferences Applying Non-Parametric Data on Cyanobacterial Investigations: Contributions to Water Quality and New Trends under Global Changes on Portuguese Freshwater Ecosystems.

Cyanobacteria are a bloom-forming ancient group of photosynthetic prokaryotes. A rise in temperature is a major contributor to its massive proliferation, namely on freshwater ecosystems, with social and economic impacts. Thus, reliable and cost-effective tools can permit the fast surveillance and assessment of temperature effects on potentially toxic cyanobacteria distribution and impacts. The occurrence of three potentially toxic cyanobacteria species was assessed on seven sampling points across three sampling years. Moreover, the association between the occurrence of those cyanobacteria species with climate change events was addressed. Here, we combined molecular and statistical methods to study the impacts of temperature on the occurrence of three globally occurring cyanotoxin-producing cyanobacteria species—Microcystis aeruginosa (microcystins), Raphidiopsis raciborskii (cylindrospermopsins and saxitoxins) and Planktothrix agardhii (microcystins and saxitoxins). Samples were collected on seven European temperate freshwater systems located on the North and Centre regions of Portugal, across three distinct sampling years with distinct ranges of air temperature. Data support that M. aeruginosa is still a common inhabitant of Portuguese freshwater ecosystems and a new trend was found on R. raciborskii recent invasion and establishment on the colder north ecosystems of Portugal. Additionally, the highest frequency of detection of both cyanobacteria was associated with warmer years. P. agardhii also revealed a new trend, being reported for the first time on North and Centre Regions of Portugal, however with no statistical relation with air temperature, demonstrating a higher ecological fitness. Distinct profiles of the statistical analysis on the three tested cyanobacteria species contribute to deepen the studies on other species as well as of our analyzed species on a global level. This assessment may help to anticipate possible repercussions on water quality and public health due to most probable alterations on cyanotoxins profile given the ecological fitness established among air temperature and PCR detection of potentially toxic cyanobacteria.

DNA metabarcoding reveals multiple co-occurring species in

Spring diatom blooms dominate the annual cycle of phytoplankton abundance in temperate freshwater systems. Many researchers have questioned whether severe blooms are attributable to a single species and warrant the identification of similar, concurrently occurring organisms. Here, we investigated spring diatom blooms in a temperate freshwater system (Yeongsan River, South Korea) that is thought to predominantly include the diatom Stephanodiscus hantzschii. Water samples were collected from four different sites during the blooms that occurred in March 2015. We analysed physicochemical and biological parameters and examined the species composition of the spring blooms using DNA metabarcoding via pyrosequencing. Our results revealed that several diatom species co-occurred during the blooms: Cyclotella sp. was the most frequently detected, followed by Cyclostephanos dubius and Discostella sp., whereas Stephanodiscus was only detected at two stations with low occurrence. These results suggest the coexistence of many diatoms during spring blooms in the Yeongsan River; however, Cyclotella sp. was responsible for the spring bloom attributed to S. hantzschii. DNA metabarcoding can be a useful tool for resolving species identities in spring diatom blooms in temperate freshwater systems. In addition, the co-occurrence of similar species should be considered when implementing efforts to monitor and control spring blooms.

Controls of Methylmercury Bioaccumulation in Forest Floor Food Webs.

Compared to the extensive research on aquatic ecosystems, very little is known about the sources and trophic transfer of methylmercury (MeHg) in terrestrial ecosystems. In this study, we examine energy flow and trophic structure using stable carbon (δ13C) and nitrogen (δ15N) isotope ratios, respectively, and MeHg levels in basal resources and terrestrial invertebrates from four temperate forest ecosystems. We show that MeHg levels in biota increased significantly ( p < 0.01) with δ13C and δ15N at all sites, implying the importance of both microbially processed diets (with increased δ13C) and trophic level (with increased δ15N) at which organisms feed, on MeHg levels in forest floor biota. The trophic magnification slopes of MeHg (defined as the slope of log10MeHg vs δ15N) for these forest floor food webs (0.20-0.28) were not significantly different ( p > 0.05) from those observed for diverse temperate freshwater systems (0.24 ± 0.07; n = 78), demonstrating for the first time the nearly equivalent efficiencies with which MeHg moves up the food chain in these contrasting ecosystem types. Our results suggest that in situ production of MeHg within the forest floor and efficient biomagnification both elevate MeHg levels in carnivorous invertebrates in temperate forests, which can contribute to significant bioaccumulation of this neurotoxin in terrestrial apex predators.

Small but diverse: larval trematode communities in the small freshwater planorbids Gyraulus albus and Segmentina nitida (Gastropoda: Pulmonata) from the Ruhr River, Germany.

In contrast to the well-studied trematode fauna of lymnaeid snails, only little is known about the role of small planorbid snails as first intermediate hosts for trematodes in temperate freshwater systems. This study aims at closing this gap by assessing the diversity and composition of larval trematode communities in Gyraulus albus and Segmentina nitida in a Central European reservoir system, and by providing an updated comprehensive review of the published trematode records of these snail hosts. A total of 3691 planorbid snails (3270 G. albus; 421 S. nitida) was collected in three consecutive years from four reservoirs of the River Ruhr catchment area in Germany. Gyraulus albus showed a higher overall trematode prevalence (11.7%) and more diverse trematode fauna (12 species) compared to S. nitida, which harboured three species and showed a lower trematode prevalence (1.7%). Altogether, 13 trematode species belonging to four families were identified in both hosts. Seven trematode species encountered in this study represent novel records for these hosts, and/or constitute first records of these larval stages from Germany. Trematode component communities in G. albus were stable across seasons and years, indicating excellent conditions for trematodes in this snail host and the continuous presence of the final hosts of the most dominant trematode species. Overall, this study reveals the importance of small planorbid snails, in particular G. albus, as first intermediate hosts for a species-rich trematode fauna in European freshwater systems, and highlights the parasites' contribution to the ecosystem's biodiversity.

Primary production in nutrient-rich kettle holes and consequences for nutrient and carbon cycling

Kettle holes are often abundant within agriculturally used moraine landscapes. They are highly enriched with nutrients and considered hotspots of carbon turnover. However, data on their primary productivity remain rare. We analysed two kettle holes typical to Germany with common aquatic plant communities during one year. We hypothesised that gross primary production (GPP) rates would be high compared to other temperate freshwater ecosystems, leading to high sediment deposition. Summer GPP rates (4.5–5.1 g C m−2 day−1) were higher than those of most temperate freshwater systems, but GPP rates were reduced by 90% in winter. Macrophytes dominated GPP from May to September with emergent macrophytes accounting for half of the GPP. Periphyton contributed to most of the system GPP throughout the rest of the year. Sediment deposition rates were high and correlated with GPP in one kettle hole. In contrast, due to prolonged periods of anoxia, aerobic sediment mineralisation was low while sediment phosphorus release was significant. Our results suggest that kettle holes have a high potential for carbon burial, provided they do not fully dry up during warm years. Due to their unique features, they should not be automatically grouped with ponds and shallow lakes in global carbon budget estimates.

Differential impact of lytic viruses on the taxonomical resolution of freshwater bacterioplankton community structure

The significance of lytic viral lysis in shaping bacterial communities in temperate freshwater systems is less documented. Here we used Illumina sequencing of 16S rRNA genes to examine bacterial community structure and diversity in relation to variable viral lysis in the euphotic zone of 25 temperate freshwater lakes (French Massif Central). We captured a rich bacterial community that was dominated by a few bacterial classes and operational taxonomic units (OTUs) frequently detected in other freshwater ecosystems. In the investigated lakes with contrasting physico-chemical characteristics, the dominant bacterioplankton community was represented by major taxonomical orders, namely Actinomycetales, Burkholderiales, Sphingobacteriales, Acidimicrobiales, Flavobacteriales and Cytophagales covering about 70% of all sequences. Viral lysis was significantly correlated with the bacterial diversity indices (Chao, Shannon, OTUs) which explained about 33% and 45% of the variation in species diversity and observed richness respectively. Anosim and UniFrac analyses indicated a clear distinction of bacterial community structure among the lakes that exhibited high and low lytic viral infection (FIC) rates. Based on our findings, high FIC (>10%) supported higher species richness, whereas low FIC (<10%) resulted in less diverse community. Our study strongly suggests that lytic activity prevailed over the type of lake ecosystems in shaping bacterioplankton diversity.

Physiological effects of environmentally relevant, multi-day thermal stress on wild juvenile Atlantic salmon (Salmo salar)

The frequency of extreme thermal events in temperate freshwater systems is expected to increase alongside global surface temperature. The Miramichi River, located in eastern Canada, is a prominent Atlantic salmon (Salmo salar) river where water temperatures can exceed the proposed upper thermal limit for the species (~27°C). Current legislation closes the river to recreational angling when water temperatures exceed 20°C for two consecutive nights. We aimed to examine how natural thermal variation, representative of extreme high thermal events, affected the thermal tolerance and physiology of wild, juvenile Atlantic salmon. We acclimated fish to four thermal cycles, characteristic of real-world thermal conditions while varying daily thermal minima (16°C, 18°C, 20°C or 22°C) and diel thermal fluctuation (e.g. Δ5°C-Δ9°C). In each cycling condition, we assessed the role that thermal minima played on the acute thermal tolerance (critical thermal maximum, (CTMax)), physiological (e.g. heat shock protein 70 (HSP70), ubiquitin) and energetic (e.g. hepatic glycogen, blood glucose and lactate) status of juvenile Atlantic salmon throughout repeated thermal cycles. Exposure to 16-21°C significantly increased CTMax (+0.9°C) compared to a stable acclimation temperature (16°C), as did exposure to diel thermal fluctuations of 18-27°C, 20-27°C and 22-27°C, yet repeated exposure provided no further increases in acute thermal tolerance. In comparison to the reference condition (16-21°C), consecutive days of high temperature cycling with different thermal minima resulted in significant increases in HSP70 and ubiquitin, a significant decrease in liver glycogen, and no significant cumulative effect on either blood glucose or lactate. However, comparison between thermally taxed treatments suggested the diel thermal minima had little influence on the physiological or energetic response of juvenile salmon, despite the variable thermal cycling condition. Our results suggest that relatively cooler night temperatures in the summer months may play a limited role in mitigating physiological stress throughout warm diel cycle events.

Phylogeographic Analysis of Blastomyces dermatitidis and Blastomyces gilchristii Reveals an Association with North American Freshwater Drainage Basins

Blastomyces dermatitidis and Blastomyces gilchristii are dimorphic fungal pathogens that cause serious pulmonary and systemic infections in humans. Although their natural habitat is in the environment, little is known about their specific ecologic niche(s). Here, we analyzed 25 microsatellite loci from 169 strains collected from various regions throughout their known endemic range in North America, representing the largest and most geographically diverse collection of isolates studied to date. Genetic analysis of multilocus microsatellite data divided the strains into four populations of B. dermatitidis and four populations of B. gilchristii. B. dermatitidis isolates were recovered from areas throughout North America, while the B. gilchristii strains were restricted to Canada and some northern US states. Furthermore, the populations of both species were associated with major freshwater drainage basins. The four B. dermatitidis populations were partitioned among (1) the Nelson River drainage basin, (2) the St. Lawrence River and northeast Atlantic Ocean Seaboard drainage basins, (3) the Mississippi River System drainage basin, and (4) the Gulf of Mexico Seaboard and southeast Atlantic Ocean Seaboard drainage basins. A similar partitioning of the B. gilchristii populations was observed among the more northerly drainage basins only. These associations suggest that the ecologic niche where the sexual reproduction, growth, and dispersal of B. dermatitidis and B. gilchristii occur is intimately linked to freshwater systems. For most populations, sexual reproduction was rare enough to produce significant linkage disequilibrium among loci but frequent enough that mating-type idiomorphic ratios were not skewed from 1:1. Furthermore, the evolutionary divergence of B. dermatitidis and B. gilchristii was estimated at 1.9 MYA during the Pleistocene epoch. We suggest that repeated glaciations during the Pleistocene period and resulting biotic refugia may have provided the impetus for speciation as theorized for other species associated with temperate freshwater systems.

Assessing age, growth, and reproduction of Alburnus mossulensis and Acanthobrama marmid (Cyprinidae) populations in Karakaya Dam Lake (Turkey)

In total, 626 individuals of Alburnus mossulensis and 586 individuals of Acanthobrama marmid were collected monthly from Karakaya Dam Lake on the upper Euphrates River. The gonadosomatic index, somatic condition, oocyte size, and fecundity were calculated on a monthly basis. Reading of scales indicated that the maximum age was 4+ years for A. mossulensis and A. marmid. The estimated length-weight relationships were W = 0.206 × FL^{2.065} for females and W = 0.119 × FL^{2.138} for males in A. mossulensis, and W = 0.029 × FL^{2.678} for females and W = 0.030 × FL^{2.631} for males in A. marmid. Growth in length equations were L_{t} = 19.6[1 - e^{-0.14(t + 1.39)}] for females and L_{t} = 20.1[1 - e^{-1.40(t + 1.04)}] for males in A. mossulensis and L_{t} = 17.3[1 - e^{-1.37(t + 1.04)}] for females and L_{t} = 16.6[1 - e^{-1.29(t + 1.04)}] for males in A. marmid. This study investigated oocyte size and fecundity for A. mossulensis and A. marmid in Turkey for the first time. The spawning period was between May and August for A. mossulensis and between May and June for A. marmid. These 2 species usually play a key role in the food web of temperate freshwater systems. In addition to water quality, biological data of these 2 species are very important in terms of future water management of the basin of Karakaya Dam Lake.

Environmental actinorhodopsin expression revealed by a new in situ filtration and fixation sampler

Freshwater Actinobacteria are an important and dominant group of bacterioplankton in most temperate freshwater systems. Recently, metagenomic studies discovered rhodopsin-like protein-coding sequences present in Actinobacteria which could be a decisive hint for their success in freshwater ecosystems. We analysed the diversity of actinorhodopsin (ActR) in Lake Stechlin (northern Germany) and assessed the actR expression profile during a diurnal cycle. We obtained 85 positive actR clones which could be subsequently grouped to 17 operational taxonomic units assuming a 90% sequence similarity. The phylogenetic analysis points to a close relationship of all obtained sequences to the acI lineage of Actinobacteria, forming six independent clusters. For the first time, we followed in situ transcription of actR in Lake Stechlin revealing a rather constitutive circadian gene expression. For analysing in situ expression patterns of functional genes in aquatic ecosystems, such as actR, we invented a new in situ filtration and fixation sampler (IFFS). The IFFS enables the representative investigation of microbial transcriptomes in any aquatic ecosystem at all water depths. The IFFS sampler is simple and inexpensive, and we provide all engineering plans for an easy rebuild. Consequently, our IFFS is suitable to reliably study expression of any known functional gene of any aquatic microorganism.

The freshwater shrimp Atyaephyra desmarestii (Millet, 1831) as a bioindicator of hypoxic event effects on temperate freshwater systems

In order to assess the suitability of Atyaephyra desmarestii as a bioindicator of the effects of hypoxic events on temperate freshwater systems, we investigated the respiratory responses of this shrimp to increasing temperatures and progressive hypoxia at two different salinities. This study, based on laboratory measurements, clearly demonstrates that this species has a moderate to poor oxygen regulatory ability and a high sensitivity to hypoxia. The respiratory response of the shrimp to increasing temperatures with increasing MO2 (low thermal regulation in oxygen uptake) was observed within a wide thermal range (15–30°C), although the species seems to be vulnerable to temperatures above 25°C in brackish water. This species copes best with hypoxia in brackish water but only at low to moderate temperatures (T≤20°C). In freshwater, its habitual habitat, the ability of A. desmarestii to oxyregulate seems to be less temperature dependent. These features suggest that the respiratory response of A. desmarestii could be used in short-term stress bioassays to test the consequences of climate change and pollution events which lead to increased hypoxia of aquatic habitats.

The effects of global warming on Daphnia spp. population dynamics: a review

Various species of Daphnia usually play a key role in the food web of temperate freshwater systems. There is much evidence to show that climate change may influence Daphnia population dynamics, consequently altering both predator–prey interactions and the efficiency of algal biomass control in these ecosystems. This review will analyse and discuss the current knowledge on Daphnia responses to climate warming based on an analysis of selected papers. The presented results indicate that warming may have important direct and indirect effects on Daphnia biology and ecology via its influence on their life-history processes (metabolism, growth, reproduction) and the properties of their habitats. The plasticity of daphnids in terms of adaptive responses is generally high and includes phenotypic adaptations and changes in genotypes, although it also depends upon the strength of selection and the available genetic variation. The seasonal timing and magnitude of temperature increases are important for seasonal biomass fluctuations of Daphnia and similarly influence the potential synchrony of daphnids and phytoplankton succession (the timing hypothesis). In light of the most recent studies on this topic, even a minor warming during short but critical seasonal periods can cause factors that disturb Daphnia population dynamics to coincide, which may destabilize lake food webs by decoupling trophic interactions. Both winter and spring are important critical periods for determining future seasonal fluxes of Daphnia spp. and, consequently, the time of the clear-water phase and the occurrence and duration of Daphnia midsummer decline. Winter conditions may also affect the impact of fish predation on daphnids during summer months. However, the effects of global warming on Daphnia population dynamics and on ecosystem functioning are often difficult to predict due to their complexity and the presence of both antagonistic and synergistic drivers. Thus, the diverse responses of daphnids to climate anomalies depend on both biotic (predator abundance and seasonal phytoplankton succession) and abiotic factors (e.g. hydrodynamics, intensity and duration of thermal stratification, trophic state or geomorphology) of lakes, which are directly influenced by weather changes. The analysis and quantification of such complex interactions require the involvement of different kinds of specialists and the development of accurate research approaches, such as molecular genetic methods or mathematical modelling.

Distribution of aerobic anoxygenic phototrophs in temperate freshwater systems

The presence of aerobic anoxygenic phototrophs (AAPs) was recently reported from various marine environments; however, there is little information regarding their distribution in fresh waters. We surveyed a number of freshwater systems in central Europe, by infra-red fluorometry, infra-red epifluorescence microscopy, fluorescence emission spectroscopy and pigment analyses. AAPs were found to be abundant in several oligotrophic and mesotrophic lakes (50-400 ng of bacteriochlorophyll a l(-1), 10-80% of bacterial biomass), while in more eutrophized water bodies they represented a negligible part of the total microbial community (< 1%). The observed freshwater AAPs were morphologically diverse and different from previously observed marine species. Under temperate European climatic conditions, AAP populations undergo strong seasonal changes in terms of both abundance and species composition, with the maximum biomass in summer and the minimum in winter. In the mountain lakes Certovo and Plesné, AAPs contributed more than one half of total bacterial biomass during their summer maximum. These results show that photoheterotrophic bacteria represent an important part of the microbial community in many freshwater systems.

Effect of temperature on development and growth of the raptorial cladoceran Leptodora kindtii under laboratory conditions

Summary1. Leptodora is a key species in many temperate freshwater systems, but so far its role in the food web could not be properly evaluated because detailed information about its secondary production was lacking. As we wanted to estimate the secondary production of Leptodora, we measured its development and growth rates in the laboratory.2. Employing improved methods to estimate growth and instar durations, we cultured Leptodora kindtii in the laboratory at four constant temperatures (15, 17.5, 20 and 25 °C). Growth in length and development times of eggs and instar stages were assessed.3. Growth rates at 15, 17.5 and 20 °C were similar, but at 25 °C growth was distinctly faster. At 17.5 °C we observed seven juvenile instar stages before the first adult instar stage was reached.