Effects of declining calcium availability on the survival,growth and calcium content of a freshwater crayfish,Orconectes virilis

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Effects of dams and their environmental impacts on the genetic diversity and connectivity of freshwater mussel populations in Poyang Lake Basin,China

1. Habitat fragmentation is one of the main threats to biodiversity. Barriers to dispersal caused by anthropogenic habitat alteration may affect phylogeographic patterns in freshwater mussels. Knowledge of the phylogenetic and phylogeographic patterns of unionoids is vital to inform protection of their biodiversity.
2. Here, we assessed influences of dams and their environmental effects on the genetic diversity and population connectivity of a broadly distributed freshwater mussel, Nodularia douglasiae, in Poyang Lake Basin.
3. The results showed high genetic diversity in areas without dams and low genetic diversity in areas with dams. High genetic differentiation and low gene flow were found among the 11 populations. Genetic variation was significantly correlated with dissolved oxygen levels.
4. The observation of low genetic diversity in populations separated by dams indicated that those populations were subjected to genetic erosion and demographic decline because they are disconnected from other populations with higher diversity. High genetic differentiation and low gene flow among the 11 populations could be correlated with anthropogenic habitat alteration.
5. These results indicated that anthropogenic habitat alterations have led to the decline in freshwater mussel diversity. Therefore, we recommend maintaining favourable habitat conditions and connectivity of rivers or lakes, and strengthening study of life histories with host-test experiments to identify potential host fish species to strengthen the knowledge base underpinning freshwater mussel conservation.

     

Role of terrestrial carbon in aquatic UV exposure and photoprotective pigmentation of meiofauna in subarctic lakes

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Revisiting the phylogeography of Asellus aquaticus in Europe: insights into cryptic diversity and spatiotemporal diversification

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Can dispersal buffer against salinity-driven zooplankton community change in Great Plains' lakes?

1. The North American Great Plains contains thousands of lakes that vary in salinity from freshwater to hypersaline. Paleolimnological studies show that salinity levels in these lakes are tightly linked with climate, and current projections point to a more arid future in the region due to natural and anthropogenic climate change, potentially influencing lake salinity.
2. Many zooplankton species are sensitive to changes in salinity, and their position near the base of the aquatic food web makes it important to understand how they might respond to increasing salinity levels. Zooplankton communities in lakes with rising salinity levels may exhibit changes in structure, including a shift toward more salinity-tolerant species and a reduction in abundance, species richness, and diversity. However, it is possible that dispersal of zooplankton among lakes could mitigate such community changes when migrant populations replace sensitive zooplankton with those that are locally adapted to higher salinities.
3. To test if dispersal could reduce salinity-induced changes in zooplankton communities, we ran a field enclosure experiment at a freshwater lake in southern Saskatchewan where we manipulated salinity levels and zooplankton dispersal. We evaluated how salinity and dispersal influenced species identities and relative abundances (community structure) using multivariate statistics and comparing taxonomic and functional compositions among the different treatments (richness, diversity, and evenness).
4. We found that increasing salinity levels in our enclosures above that in our study lake resulted in lower zooplankton abundances and species richness levels, primarily due to the loss of cladoceran species. However, patterns in our multivariate analyses suggested that cladocerans were maintained in enclosures with salinity levels of 2.5 and 5.0 g/L when those enclosures received immigration from nearby lakes.
5. In contrast, our univariate analyses failed to find evidence that immigration affected community structure (richness, diversity, evenness). The lack of significant statistical differences could suggest that dispersal does not have an effect, or it may have been a problem with statistical power, as a power analysis suggested that fairly large effect sizes would have been required to achieve statistical significance.
6. Based on our results, we were unable to reach a definitive conclusion on the role that dispersal might play in buffering zooplankton communities against salinity-driven changes. However, our study provides two important insights for planning future work. First, our power analyses indicated that more replication may be needed given the variability among our experimental enclosures. Second, the patterns in our multivariate analyses suggested that cladocerans could be maintained in lakes undergoing salinity increases if they receive immigration from surrounding lakes with higher salinities. Future work examining how inter- and intraspecific salinity tolerance varies across lakes with a gradient of salinities would be helpful for understanding the role that dispersal might play in buffering against salinity-driven losses of cladoceran zooplankton.

     

Causes of Daphnia midsummer decline in two deep meromictic subalpine lakes

1. Daphnia are key organisms in pelagic food webs, acting as a food resource for fish and predatory zooplankton and regulating phytoplankton through grazing. Its population dynamic follows regular seasonal patterns, with spring peaks followed by summer population declines (midsummer declines, MSDs). Midsummer declines show high inter-annual variation, which has been attributed to different causes. However, the mechanisms controlling the MSD remain poorly understood, especially in deep stratified lakes.
2. We tried to disentangle the factors causing Daphnia MSDs in Lake Lugano and Lake Iseo (in Switzerland and Italy), two deep peri-alpine lakes with similar trophic status and vertical mixing dynamics, characterised by phosphorus accumulation in the hypolimnion and variable mixing during late-winter turnovers.
3. Specifically, we assessed the effects of three different hypothetical pathways according to which: (1) winter air temperature controls MSDs by influencing mixing depth during turnovers and epilimnetic phosphorus replenishment; (2) vernal air temperature influences MSD by accelerating the timing of spring population peak; and (3) summer temperature influences MSDs by increasing fish predation. We assessed the relative strength of these pathways using structural equation modelling on long-term datasets for the two lakes (29 years for Lake Lugano and 19 years for Lake Iseo).
4. Between the hypothesised pathways, the one driven by winter air temperature (through P replenishment) influenced Daphnia abundance in spring in both lakes, but the effects propagated to summer Daphnia abundance only in Lake Lugano. Additionally, summer Daphnia abundance was influenced by the summer air temperature through a positive (although weak) effect. By comparison, vernal air temperature had no detectable effects on summer Daphnia abundance.
5. The results revealed marked differences between the meromictic study lakes and the shallow hypertrophic water bodies that were the focus of previous research on Daphnia MSD, and also between the two study lakes. The influence of epilimnetic P replenishment on the summer Daphnia abundance in Lake Lugano, which was recovering from past eutrophication, may have reflected the greater susceptibility of deep, stratified lakes to P depletion after spring compared to shallow hypertrophic lakes or reservoirs. This effect might not have been detected in Lake Iseo because P was more consistently depleted during the study period (i.e. variance in the predictor was too low to detect an effect).
6. This study highlighted the complexity of the effects of climate variability on Daphnia MSD in deep lakes, showing that the responses can differ even between two neighbouring lakes with similar vertical mixing dynamics and trophic status. At the same time, the results suggest that future increases in winter air temperature, caused by global warming, may cause critically low densities of Daphnia during spring and summer and compromise the ability of zooplankton to control phytoplankton biomass.

     

Experimental evidence that the ecosystem effects of aquatic herbivory by moose and beaver may be contingent on water body type

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Long term vegetation development in Bavarian Mountain Forest ecosystems following natural destruction

Knowledge of the structure and dynamics of Central European virgin forests is very restricted and in many respects hypothetical. Analysis of the development of forest stands influenced by natural disturbances (storm; snow avalanche) is considered to lead to new information about the natural processes involved in virgin (near-nature) forests within a relatively (!) short time span (which, in forests, still counts for decades). National Parks offer areas big enough for such studies, and they guarantee a study period of several decades (or more). This paper presents the first results of vegetation development following natural destruction of the tree layer

in a near-nature spruce forest ecosystem in the Bavarian Forest National Park (Bavaria; Germany) damaged by windfall in August, 1983;

in the Mountain Mixed Forest of the Berchtesgaden National Park (Bavaria; Germany) damaged by a snow slide in January, 1986;

and additionally points from a similar project which deals with windfall areas in 10 managed forests in Bavaria created by the 1990 February storms.

The used permanent plot (transect) method is described. Several aspects of forest vegetation dynamics are discussed against a background of results of the first vegetation record, which is the beginning of a long term permanent plot study.     

Rapid molecular identification of the harmful freshwater dinoflagellate <Emphasis Type="Italic">Peridinium</Emphasis> in various life stages using genus-specific single-cell PCR

Cysts of the freshwater dinoflagellate Peridinium are typically different from vegetative cells in shape and remain largely undescribed. Molecular discrimination of such cysts would be useful to a number of research disciplines. A reliable method for the amplification of ribosomal DNA (rDNA) from Peridinium at different life stages is described. This genotyping strategy relies on whole cell PCR using Peridinium-specific primers designed from available 18S rDNA sequences. Here, we demonstrate the effectiveness of Peridinium-specific PCR for the rapid molecular identification of Peridinium cells in various life stages such as vegetative, planozygote, hypnozygote and cyst.     

The freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> in Bavaria,Germany—Population status,conservation efforts and challenges

The freshwater pearl mussel Margaritifera margaritifera is a highly specialized, sensitive and critically endangered freshwater bivalve with a complex life cycle. An overview on the population status in Bavaria, Germany, one of the species’ main areas of distribution in Central Europe, is presented. Using the example of the freshwater pearl mussel and a Bavarian conservation project for this species, a scheme for the development of site-specific conservation concepts is discussed.     

Host condition and pathogen identity influence bacterial infection survival in the common eastern firefly,Photinus pyralis

1. The degree to which host, pathogen, and environmental characteristics determine fitness outcomes in response to infection across the tree of life is a key question in ecoimmunology. Because infection experiments require large sample sizes and careful controls, studies have generally been limited to lab-adapted organisms.
2. Photinus pyralis is a charismatic firefly that is abundant during its annual summer emergence in the Eastern United States. Here, we assess the importance of host condition, pathogen identity and dose, and pre-infection environment on survival outcomes in response to bacterial infection in wild-caught adult male P. pyralis.
3. Although survival after sterile saline injection was not statistically different from survival of uninjected controls, survival kinetics support sterile saline injection as the most appropriate control.
4. Serratia marcescens and Providencia rettgeri infections increased mortality, especially at high doses. In contrast to fruit fly studies, Providencia sneebia, Pseudomonas aeruginosa, and Enterococcus faecalis infections did not. Infection with higher doses of P. rettgeri had an increased risk of death for fireflies caught later in the season than those captured earlier, but seasonality did not significantly interact with dose to impact mortality with any of the other bacterial species.
5. These results highlight the importance of considering host, pathogen, and environmental factors when investigating infection outcomes in wild-caught, non-model systems. The differences in survival between fireflies and fruit flies emphasise that further studies in a broad array of organisms are needed to explore the diversity of infection responses across the tree of life.

     

Seasonal habitat use indicates that depth may mediate the potential for invasive round goby impacts in inland lakes

1. The round goby (Neogobius melanostomus) is among the fastest-spreading introduced aquatic species in North America and is radiating inland from the Great Lakes into freshwater ecosystems across the landscape. Predicting and managing the impacts of round gobies requires information on the factors influencing their distribution in habitats along the invasion front, yet this information is not available for many recently invaded ecosystems. We evaluated the seasonal habitat use and biomass of round gobies in an inland temperate lake to define the spatiotemporal scope of biological interactions at the leading edge of the round goby invasion.
2. Using novel statistical approaches, we combined hierarchical models that control for imperfect species detection with flexible smooth terms to describe non-linear relationships between round goby abundance and environmental gradients. Subsequently, we generated accurate detection-corrected estimates of the standing stock biomass of round gobies.
3. Our results show seasonally differentiated habitat niches, where suitable round goby habitat in summer months is restricted to shallow depths (<18.4 m) with a mixture of vegetative and mussel cover. We found high round goby biomass of 122 kg/ha in occupied habitats during the summer, with a total lake-wide biomass of 766,000 kg. In winter, round gobies migrate to deep offshore habitats and disperse, dramatically altering their scope for biological interactions with resident aquatic species across summer and winter seasons.
4. The results of this study indicate that the scope of biological interactions in inland lakes may be seasonally variable, with potential for high round goby biomass in shallow lakes or at the periphery of deep lakes in the summer months. Such shallow-water habitats may therefore present higher risk of ecological impacts from round gobies in invaded lentic ecosystems. As round gobies expand inland, consideration of seasonal habitat use will be an important factor in predicting the impacts of this pervasive invader.

     

Homogenisation of water and sediment bacterial communities in a shallow lake (lake Balihe,China)

1. Planktonic and benthic bacterial communities hold central roles in the functioning of freshwater ecosystems and mediate key ecosystem services such as primary production and nutrient remineralisation. Although it is clear that such communities vary in composition both within and between lakes, the environmental factors and processes shaping the diversity and composition of freshwater bacteria are still not fully understood.
2. In order to assess seasonal and spatial variability in lake bacterial communities and identify environmental factors underpinning biogeographical patterns, we performed a large-scale sampling campaign with paired water and sediment sample collection at 18 locations during four seasons in Lake Balihe, a subtropical shallow fish-farming lake in mid-eastern China.
3. Pelagic and benthic bacterial communities were distinctly different in terms of diversity, taxonomic composition and community structure, with Actinobacteria, Bacteroidetes, Cyanobacteria and Alphaproteobacteria dominating lake water, and Acidobacteria, Bacteroidetes, Chloroflexi, Gammaproteobacteria and Deltaproteobacteria dominating sediment. Nevertheless, these two communities had stronger spatial concordance and overlap in taxa during spring and autumn seasons. Together, the main drivers of both the spatial and temporal variations in Lake Balihe bacterial communities were identified as water temperature, turbidity, nitrogen and phosphorus availability, and thermal stratification controlled by wind-mixing and activity of the dense farmed fish populations. Notably, populations affiliated with Firmicutes, known to be abundant in fish gut microbiome, were especially abundant in the summer season and locations where high fish biomass was found, suggesting a potential link between fish gut microbiome and the pelagic bacterial communities.
4. Our findings demonstrated seasonal homogenisation of pelagic and benthic bacterial communities linked to marked shifts in a set of seasonally-driven environmental variables including water temperature and nutrient availability.

     

Acoustic detection and acoustic habitat characterisation of the critically endangered white-bellied heron (Ardea insignis) in Bhutan

1. Growing developmental activities, such as hydropower construction, farm roads, and other human activities, are affecting the critically endangered white-bellied heron (WBH). Out of a known global population of 60, 28 individuals inhabit the river basin area and freshwater lakes and ponds of Bhutan. Several constraints impede continuous monitoring of endangered species, such as the isolated and cryptic nature of the species and the remoteness of its habitat; to date, there are no long-term reference data or techniques implemented for continuous monitoring of this species.
2. In this study, we designed acoustic detection and habitat characterisation methods using long-duration recordings from three habitat areas in Bhutan. Acoustic indices were extracted and used to implement a species-specific call detector and to generate habitat soundscape representations. Using WBH calls annotated in month-long recordings from a known site, a novel indices-based detector was implemented and tested. A total of 960 hr of continuous audio recordings from three habitats in Bhutan were analysed.
3. We found that a species call detector implemented using a combination of acoustic indices (that includes measures of spectral and temporal entropy and different angles of spectral ridges) has a correct detection rate of 81%. Additionally, visual inspection of the species’ acoustic habitat using long-duration false-colour spectrograms enabled qualitative assessment of acoustic habitat structure and other dominant acoustic events.
4. This study proposes a combined approach of species acoustic detection and habitat soundscape analysis for holistic acoustic monitoring of endangered species. As a direct outcome of this work, we documented acoustic reference data on the critically endangered WBH from multiple habitat areas and have analysed its temporal vocalisation patterns across sites.

     

Temporal development of biodiversity of macrophytes in newly established lakes

1. Every year, a vast number of wetlands are constructed to restore ecosystem function and biodiversity, thus counteracting massive historical losses by reclamation to farmland. However, our knowledge of the long-term effects on biodiversity, particularly of large systems such as lakes, is very limited.
2. Our objective was to follow the development of macrophytes over 3–4 decades in 24 new, shallow, eutrophic lakes in order to test the hypotheses that: (1) species richness reaches a maximum after some years and then declines; and (2) species composition changes substantially from small early colonisers to taller, competitive later colonisers, which causes ongoing high β-diversity.
3. A generalised linear mixed-effect model showed that species richness was related to lake size, phosphorus concentration and spatial setting, which are known to influence natural lakes as well. Moreover, species composition and richness were affected by lake age. Species colonised rapidly and richness peaked at an intermediate age and then declined.
4. Temporal species turnover within lakes was high in three lake age groups of ≤10, 11–20 or >20 years since establishment, although lowest after 11–20 years. Species replacement tended to contribute most to β-diversity in the youngest lakes, whereas richness fluctuated in older lakes and appeared to contribute most to temporal turnover there.
5. Early colonisers in ≤10-year-old lakes were commonly replaced by tall canopy-forming species in 11–20-year-old lakes, probably as a result of increasing competition for light and space over time. After 20 years, rootless Ceratophyllum submersum as well as species with floating and emergent leaves became dominant, potentially due to the gradual accumulation of more organic sediment difficult to root and grow in, along with gradually reduced light penetration in the water.
6. Establishing new lakes for biodiversity remains a challenge because of the falling richness and continuous species turnover with lake age, but our results suggest that constructing large, nutrient-poor lakes in species-rich landscapes ensures the best prerequisites for obtaining diverse communities.

     

Amino acids in freshwater food webs: Assessing their variability among taxa,trophic levels,and systems

1. Although the amino acid composition of fishes and some marine invertebrates varies among taxa and systems, similar information is lacking for freshwater invertebrates. The objectives were to characterise and compare the amino acid composition among different aquatic species, dietary habits, and environmental conditions.
2. Benthic macroinvertebrates from different functional feeding groups (FFG), bulk zooplankton, biofilm, and fishes representing 12 families (21 genera or species) were collected from temperate lakes in eastern Canada during the summers of 2013 and 2014. Fifteen protein-bound amino acids, including thiols, were measured in whole invertebrates, biofilm, or fish muscle. We hypothesised that the amino acid composition will differ among species and systems.
3. Multiple discriminant analyses revealed significant differences in the amino acid composition among species—based on varying percentages of cysteine (as cysteic acid) and histidine—and among FFG/trophic designations—based on histidine and lysine—where the primary consumers were more variable than the predators.
4. Overall, the results suggest that patterns were based on phylogenetics, biological characteristics, and the FFG/trophic designations of biota.
5. The within-taxon variability in composition was also related to differences among lakes. Characteristics of their environment, including lake pH and the food web structure (abundance and composition of taxa), probably influenced their dietary habits and amino acid composition of diet.
6. These results expand the currently limited knowledge of the biochemical composition of freshwater biota and provide impetus for further studies on nutritional values in predator-prey relationships, trophic guilds, and the biomagnification of protein-bound contaminants through food webs.

     

Beneath the surface: Application of transparent super absorbent polymer substrates to track faunal activity within the sediment layer

1. Tracking the movement of organisms is a fundamental goal of many ecological studies. Several techniques exist in the study of terrestrial and aquatic fauna; however, to date, the ability to monitor aquatic fauna within the sediment layer efficiently and in multiple dimensions is lacking. Given the importance of subsurface sediments in supporting ecosystem functioning, this inability to observe organism behaviour represents a fundamental gap in our knowledge and limits our capability to holistically characterise the response of freshwater systems to stressors.
2. Here we present an experimental study that employs novel transparent super absorbent polymer substrates (c. 8–12 mm in diameter) in combination with computer vision technology, which enables, for the first time, real-time observation and tracking of organisms within the sediment layer under lotic flow conditions. Use of these substrates allowed the successful extraction of organism trajectories, which enabled the velocity and body orientation of a freshwater amphipod (Gammarus fossarum) in the sediment layer to be calculated in response to a number of vertical hydrological exchange treatments (upwelling, downwelling, and no vertical exchange).
3. Results indicate that under vertical hydrological exchange, a higher proportion of fast velocities (both horizontal and vertical) were recorded for G. fossarum in the sediment layer compared to no vertical exchange (control) conditions. This increase was most marked for upwelling flow exchange. We also observed a change in the body orientation of individuals in the sediment layer from a vertical alignment under no vertical exchange to a more horizontal one under downwelling and more notably upwelling flow exchange. This shift in body position was exacerbated under stronger vertical exchange rates.
4. We identified that following the flow transition of downwelling to upwelling conditions, there was an immediate shift (0–2 min) in both the orientation angle and activity level of individuals. This increased rate of activity was maintained for the individuals' velocity but not for their changing orientation angle. These trends were not apparent within the flow transition of no vertical exchange to downwelling flow.
5. Our new methodological approach enables vital insights into the behaviour of organisms within the sediment layer. Use of super absorbent polymer substrates allows real-time multi-directional tracking of multiple organisms in parallel. We believe the method represents an innovative tool that can be employed to tackle a wide range of ecological questions and thereby improve our mechanistic understanding of ecological responses to biotic and abiotic processes/stressors.

     

Seventy years of changes in the abundance of Danish charophytes

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The influence of iron,siderophores and refractory DOM on cyanobacterial biomass in oligotrophic lakes

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Egestion rates of microplastic fibres in fish scaled to in situ concentration and fish density

1. Microplastics (particles <5 mm) are commonly found in aquatic organisms across taxonomic groups and ecosystems. However, the egestion rate of microplastics from aquatic organisms and how egestion rates compare to other rates of microplastic movement in the environment are sparsely documented.
2. We fed microplastic fibres to round gobies (Neogobius melanostomus), an abundant, invasive species in the Laurentian Great Lakes. We conducted two trials where round gobies were fed microplastic-containing food either a single time (1 day) or every day over 7 days.
3. There was no difference in microplastic egestion rates from the 1 day or 7 day feeding trials, suggesting no impact of duration of exposure on egestion (exponential decay rate = −0.055 [±0.016 SE] and −0.040 [±0.007 SE], respectively). Turnover time of microplastics (i.e., average time from ingestion to egestion) in the gut ranged from 18.2 to 25.0 hr, similar to published values for other freshwater taxa.
4. We also measured microplastics in the digestive tracts of round gobies collected directly from Lake Michigan, U.S.A. Using published values for round goby density and microplastic concentration at the study sites, we calculated areal egestion rate by round gobies (no. particles m^–2 day^–1), and compared it to riverine microplastic export (no. particles m^–2 day^–1). Both area-based rates were of the same order of magnitude, suggesting that round goby egestion could be an important, and potentially overlooked component of microplastic dynamics at the ecosystem scale.
5. Animal egestion is well-known as a major component of nutrient and carbon cycling. However, direct measurements of microplastic fluxes in the environment that include animal egestion rates are uncommon. An ecosystem ecology approach is needed to meet the emerging challenge of generating microplastic budgets for freshwater environments and elsewhere, thereby informing management and mitigation of plastic pollution at a global scale.