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Although ostracods are important components in aquatic ecosystems, little is known about their microbiomes. Here, we analyzed the microbiomes of the putative ancient asexual ostracod species, Darwinula stevensoni, in three natural populations from different freshwater habitats in the UK, Belgium, and Spain. We applied high-throughput amplicon sequencing approaches to analyze the V3–V4 part of the bacterial 16S rRNA region. We tested for host-specific microbiomes by comparing bacterial assemblages of ostracods with those of sediment and water samples from the same locations. Around 2,200 Amplicon Sequence Variants (ASVs) were identified from ostracod samples with universal primers and 1,700 ASVs with endosymbiotic-specific primers, illustrating a high microbiome diversity in D. stevensoni. Most bacterial taxa were unique to the microbiome of D. stevensoni as compared to other freshwater invertebrates and to non-marine ostracods. Alpha diversity of ostracod microbiomes did not differ significantly between the three populations, but PERMANOVA detected significant differences in bacterial compositions. Microbiomes varied highly among ostracod specimens from the same population. Possible factors shaping ostracod microbiomes could be latitude, food, age, and environmental variables. Preliminary functionality analyses showed that Darwinula-specific microbiomes contribute to lipid, carbohydrate, nucleotide, and amino acid metabolic processes and the synthesis of co-factors and vitamins. [ABSTRACT FROM AUTHOR]

Dispersal is a main determinant of community assembly. Landscape configurations of rivers, lakes, or ponds are often independently considered in this framework. However, these systems share species conforming to a waterscape with different environments coupled by dispersal. While empirical results support a main role of this coupling on biodiversity organization, it is difficult to assess its importance at large geographic scales. Using a theoretical approach, we quantified the potential role of dispersal through different freshwater ecosystems of the United Kingdom and Ireland on biogeographic diversity patterns. We implemented a coalescent model considering 11,131 communities connected by distance-dependent dispersal and with species that have different performances for recruitment in three different aquatic habitats. Biogeographic diversity patterns were estimated for each habitat alone or for the whole waterscape combining ephemeral, temporal, and permanent waters. The results indicated that the coupling between different types of environments fostered local diversity, in a magnitude that increased from the ephemeral to permanent waters and from poorer to richer communities. Furthermore, a strong spatial structure in the potential effect of dispersal among different freshwater environments was observed, indicating that freshwater biogeography was likely determined by the connection among freshwater ecosystems to a larger extent than previously thought. [ABSTRACT FROM AUTHOR]

The strength of trophic and non-trophic interactions in predator–prey dynamics may be modified by predator density/diversity and prey size characteristics. In aquatic environments, multi-dimensional scaling of search areas (water depth and surface area) may mediate interactions among predators, with implications for prey risk. Here, we used a comparative functional response (FR) approach to investigate the effects of search area, predator composition and prey size on the strength of trophic and non-trophic interactions in freshwater habitats. A model system comprising two predatory notonectids (Anisops breddini and Anisops sardeus) was examined consuming four larval instar prey of Culex quinquefasciatus mosquitoes at nine different arena sizes, consisting of three crossed levels of surface area and water depth. Type II FRs were most common among predator groups, with 2nd instar prey consumed the most overall. Here, A. sardeus exhibited significantly higher feeding rates as compared to A. breddini, particularly in shallow waters. Non-trophic interactions in conspecific A. breddini and heterospecific pairs were mostly negative, indicating reduced prey risk. Further, predator–predator antagonisms were most pronounced in the heterospecific pairs. Strength of trophic and non-trophic interactions is thus dependent on complex interplays between the characteristics of predator–prey participants in combination with environmental heterogeneities. [ABSTRACT FROM AUTHOR]

Microplastics are considered the major pollutant of the Anthropocene. This study presents a retrospective examination of the literature to characterize microplastic research in marine and freshwater habitats and to explore the interconnections among the topics uncovered. After automated text mining, topic modeling was carried out to track the evolution of research topics in peer-reviewed articles on microplastics published from January 2010 to May 2021. The literature analysis suggested a total of 15 topics. The most representative terms in topics related exclusively to marine habitats were similar and differed from those in the topics related to both marine and freshwater habitats. The observed patterns in the popularity of the topics uncovered suggest that several topics have tended to increase in prevalence over time. However, no topic had high popularity, and only two topics were considered "cold," i.e., there was a drop in prevalence over time. The topics that had the largest research gaps on average across all topics were also among the most specific, those describing the key themes of certain manuscripts. This type of literature analysis is increasingly necessary so that the scientific knowledge available can be useful in the search for solutions to the environmental problems of today's society. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) has seen a massive increase in application in freshwater systems with a concurrent growth in protocol developments and a drive to gain a better understanding of the 'ecology' of eDNA. This raises the question of whether we are currently still in an early, developmental phase of eDNA-based assessments or already transitioning into a more applied stage for biomonitoring. I conducted a systematic literature review on 381 eDNA-focused studies in freshwater systems targeting macro-organisms over the last 5 years, assessing study goals, methods, target systems and taxa and study design aspects. The results show an increase of biomonitoring-focused studies throughout the years, while the fraction of studies investigating the 'ecology' of eDNA decreased. The application of metabarcoding significantly increased while studies applying qPCRs tentatively declined. A geographic inequality was observed concerning study numbers and study goals biased towards the global North. Descriptive studies increased, but the fraction of in-field studies and studies applying eDNA and conventional methods combined revealed no trend. These results show a shift towards application-focused work for eDNA-based assessments but also reveal this field to still be developing. In this transitional phase, practitioners need to ensure consistency and data comparability for long-term monitoring programmes. [ABSTRACT FROM AUTHOR]

In the western US, freshwater mussels (Order Unionida) contribute valuable ecosystem functions to riverine systems, yet have declined across their range following widespread degradation of freshwater habitat and parallel declines in salmonids, host fish for larval western pearlshell mussels (Margaritifera falcata). The status of M. falcata populations is of particular conservation interest in isolated coastal watersheds given unique freshwater mussel-host fish relationships. To understand M. falcata population ecology in Oregon's coastal watersheds, we analyzed stream survey data on presence/absence of mussels collected over a recent eleven-year period, explored co-varying habitat characteristics, and summarized mussel distribution and host fish co-occurrence. We also collected M. falcata and compared condition indices among eight locations. Naïve occupancy in surveyed areas was 12.3%, about half of predicted occupancy (ψ = 0.24, CI 0.19–0.31) based on modeling repeated visits over a ten year assumed closed period. Mussel occupancy was correlated with reach-scale habitat variables, and the probability of mussel observations was positively correlated with presence of coho (Oncorhynchus kisutch) salmon. Condition varied significantly among locations. Spatial relationships between existing mussel distribution, host species, and habitat variables answer questions about coastal freshwater mussel populations, as well as serve to identify priorities for further research and population assessment. [ABSTRACT FROM AUTHOR]

In this study, we explored the association between land use and fish species richness on 52 coastal lagoons in Southeast and South Brazil. We measured the proportion of agriculture and urbanization around lagoons over 26 years and used the coefficient of variation (CV) as a surrogate of the temporal land cover variability. We compiled species occurrences from primary data, from the literature and from museum records, and assigned each recorded species to different habitat use groups: benthic/bottom or water column, and littoral or limnetic zones. In the Southeast, where most lagoons are subject to marine influence, richness was negatively associated to agriculture and positively associated to urbanization. In the South, where freshwater lagoons predominate, richness was negatively associated to urbanization and positively associated to agriculture. The results suggest that fish communities from freshwater coastal lagoons are more sensitive to land use than brackish lagoons. Differently from brackish lagoons, that are colonized by both freshwater and marine species, freshwater lagoons rely on neighboring lagoons as species donors. However, this apparent resilience of the brackish lagoons must be regarded with caution, since the increase in marine connections due to artificial sandbar openings may impair freshwater species with time. [ABSTRACT FROM AUTHOR]

Our study incorporates high-resolution, multivariate ecological niche modeling (ENM) to test whether two putative state-threatened mussel species in East Texas (Fusconaia askewi and F. lananensis) are ecologically differentiated. We forecasted suitable habitat to identify any differences in the taxa's habitat associations, using a total of 60 environmental layers comprising climate, soil, and hydrology in a multivariate framework. We found the two species were not ecologically different, consistent with other work (e.g., morphology and genetics) suggesting that they are synonymous. We synonymized the two to make an ENM that was then ground truthed by sampling 25 novel sites throughout East Texas. Our ENM significantly distinguished suitable from unsuitable habitat for these sites, identifying five new records. We compared model evaluation metrics using the original data versus the ground-truthed data, and we found that some metrics were more reliable than others. The verified ecological niche modeling approach that we present here can be applied in other studies in riverine environments and has particular relevance to conservation science. [ABSTRACT FROM AUTHOR]

Invasive freshwater species are reported to have tolerance of salinity stress that allows them colonizing new sites in estuaries. Pomacea canaliculata, a gastropod that disperses from its native freshwater habitats to penetrate estuarine environments in invaded regions has raised considerable concern. Previous studies indicated P. canaliculata can survive a short period of exposure at certain environmental salinity. However, salinity tolerance of snails remains unknown in context of a possible long-term acclimation that may further facilitate dispersal into estuaries. Here, in a laboratory experiment, juvenile snails were first exposed to four different levels of pre-acclimation salinity (0, 2, 4 or 6 psu) for 30 days randomly. Snails in each level of pre-acclimation salinity were then transferred to five salinity treatments (8, 10, 12, 14 and 16 psu) separately, with three replicates for each salinity stressor. Pomacea canaliculata pre-acclimated in low salinity environments could survive at least 5 days when exposed to salinities less than 12 psu, with the maximum body weight gains rate (WG, 30.369 ± 1.418%) and specific growth rate (SGR, 1.326 ± 0.032% d−1). Half of the snails pre-acclimated at 6 psu survived over 25–31 days when exposed to a stressor of 8 psu. The upper limit of pre-acclimation (6 psu) was optimal for post-adaptation of P. canaliculata to stressful saline environments (from 8 to 16 psu). We determined the salinity stress tolerances of the invasive P. canaliculata and examined the effects of salinity pre-acclimation on its survival and growth. The results on enhanced salinity tolerance of P. canaliculata through gradual acclimation is of particular importance to brackish environments (e.g. alkaline lakes, mangrove habitats) of tropical and subtropical coasts. Given the high adaptability of P. canaliculata and its potential threats, early detection and management strategies should urgently be implemented in these regions. [ABSTRACT FROM AUTHOR]

Rock pools are ephemeral freshwater habitats characterized by their small size, well-defined boundaries, and periodic desiccation, making them ideal model systems to answer numerous ecological questions. Although there are numerous studies on rock pool fauna around the world, tardigrades have only rarely been recorded. We conducted the first tardigrade-focused study on rock pools by quantitatively extracting and classifying them from rock pools in the Italian Apennines. Rock pools were divided into three types, based on maximum duration of their inundation period. Following the patterns usually observed with rock pool invertebrates, we tested the hypothesis that desiccation has a negative effect on prevalence, abundance, and diversity of tardigrades, and thus could alter the trophic structure of their communities. In contrast to what is commonly found for other animal groups in the same type of habitat, we found that tardigrades were more diverse and prevalent in shallower, more desiccation prone, rock pools. Moreover, the trophic structure of tardigrade communities was different among the different pool types. Lastly, we also provide DNA barcodes of the most commonly found taxa. Ultimately, our study demonstrates that tardigrade communities in rock pools provide a valuable model system for the study of abiotic factors influencing meiofauna communities. [ABSTRACT FROM AUTHOR]

In this study, we present a new method to compare the distribution of knowledge regarding the biodiversity of a taxa with the distribution of environments inhabited by that taxa, in order to identify the main geographical gaps in biodiversity knowledge. We compared the geographical distribution of studies describing freshwater fish assemblages in Argentina with the distribution of freshwater bodies, delimiting priority areas that require additional sampling effort in order to achieve a more balanced understanding of this taxa's diversity throughout the country. Our results show a substantial geographical bias in the distribution of knowledge regarding freshwater fish assemblages in Argentina, with most of the studies concentrating on a few areas of the country. Many sectors appear as undersampled, and most of the country has been studied only recently, after many sites have undergone severe impact by anthropic activities. The absence of fish assemblages descriptions previous to habitat changes in these sites considerably limits our capacity to understand changes in biodiversity that anthropic habitat modifications might have generated or even the ones they are generating now. We show the areas of Argentina where freshwater fish diversity needs to be studied most urgently based on the distribution of freshwater habitats. [ABSTRACT FROM AUTHOR]

Metacommunity ecology provides a basis for understanding how ecological communities are assembled. Metacommunity theory can be applied to assess the effects of anthropogenic disturbance on freshwater communities. However, few studies have examined how species-specific responses to environmental covariates can generate broader patterns in freshwater metacommunities. I determined occupancy patterns in an amphibian metacommunity to identify important predictors of reproduction at wetland sites. I conducted surveys at 49 wetlands for tadpoles with fish traps and dip netting in an urbanising region in southeastern Australia. The larvae of seven frog species were detected. There were negative relationships between the probabilities of reproduction at a site and the relative abundance of the eastern mosquitofish (Gambusia holbrooki) and wetland electrical conductivity. There was a positive relationship between tadpole occupancy and the proportion of accessible habitat within 1000 m of a site, a measure of the combined effects of roads and habitat amount. These results highlight the negative effect of predatory Gambusia on frog communities and illustrate the importance of the species-sorting and mass-effect perspectives of metacommunity theory at multiple spatial scales. Habitat restoration projects for amphibians should remove exotic fish or prevent their establishment in managed wetlands and maintain habitat connectivity to facilitate dispersal. [ABSTRACT FROM AUTHOR]

The functional roles of freshwater mussels (Unionida) in tropical systems are poorly understood. We quantified the effects of mussel filtration, excretion and deposition in three anthropogenic tropical systems, i.e. a man-made lake, abandoned mining pool and rice paddy channel. Sinanodonta cf. woodiana (non-native) was present at all three sites, whilst Pilsbryoconcha compressa (native) was present in the channel only. Clearance rates, biodeposition rates and effects on suspended algal pigment and dissolved nutrient concentrations were quantified in controlled, replicated experiments in laboratory tanks with water from original habitats. Clearance rates were generally low and did not explain the high biodeposition rates observed. A considerable proportion of the natural diet of these populations may therefore consist of material that was not available in tanks, i.e. benthic or deposited algae. Deposition rates in lake and channel populations exceeded published rates from temperate and Mediterranean habitats, presumably due to prevalence of non-palatable material and/or higher metabolic rates in tropical systems. The presence of S. cf. woodiana but not P. compressa led to a strong increase in total ammonia nitrogen concentrations and N:P ratios, exceeding estimations from other systems. This study suggests that freshwater mussels play different functional roles in anthropogenic tropical habitats than in temperate systems. [ABSTRACT FROM AUTHOR]

Molluscs are among the most diverse and widespread animal groups in freshwater habitats. Unfortunately, like most freshwater taxa, they are decreasing dramatically and are now among the most threatened animals on Earth, with many species already extinct or on the brink of extinction. Here, we review our current knowledge on the biodiversity and conservation of freshwater molluscs using the concept of knowledge shortfalls. We focus on seven previously proposed key shortfalls to review and analyse existing knowledge gaps relating to (1) taxonomy, the Linnean Shortfall; (2) distribution, the Wallacean Shortfall; (3) abundance and population dynamics, the Prestonian Shortfall: (4) evolution, the Darwinian Shortfall; (5) abiotic tolerances, the Hutchinsonian Shortfall; (6) traits, the Raunkiaeran Shortfall; and (7) biotic interactions, the Eltonian Shortfall. In addition, we address a new shortfall, which relates to the application and effectiveness of conservation measures, including assessments, methods, funding, and policies, the Ostromian Shortfall. Based on our review, we provide recommendations and suggest pathways to overcome these existing shortfalls. This work also introduces the articles in this special issue of Hydrobiologia, which represent key contributions to the First International Freshwater Mollusk Conservation Society Meeting held in Verbania, Italy, in 2018. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity can determine the performance of exotic plants in environmental disturbance. Aquatic plants can adapt to the stress caused by water level fluctuations in the water level, water depth, or substrate nutrients through phenotypic plasticity. The high-potential invasiveness of Myriophyllum aquaticum in riparian wetlands may be associated with its growth and phenotypic plasticity. The interactive effects of fluctuations in the water level, water depth, and substrate nutrients on the growth performance of M. aquaticum were evaluated. We performed two two-factorial experiments to evaluate the effects of (i) frequency and amplitude of water level fluctuations and (ii) water depth and substrate nutrients on the performance of M. aquaticum. The results indicated that in the first experiment, low fluctuation frequency with a ± 20 cm amplitude significantly increased the value of all growth traits (except for total length of lateral branches). Regardless of fluctuation frequency, relative to a ± 60 cm amplitude and a static water level, the maximum values of total biomass, plant height, relative growth rate, and total length of lateral branches existed in moderate fluctuation amplitudes (± 20 cm, ± 40 cm). In the second experiment, the growth performance of M. aquaticum decreased with increasing water depth from 25 cm to 75 cm. High nutrient substrate significantly increased all growth traits (except for chlorophyll content) in water depths of 25 and 50 cm. Above all, M. aquaticum has optimal growth performance in response to low fluctuation frequency, moderate fluctuation amplitudes (± 20 cm, ± 40 cm), and high nutrient substrate in shallow water (water depth lower than 75 cm). These results indicate that M. aquaticum has a high-potential invasiveness in shallow water and with low disturbance of freshwater habitats. [ABSTRACT FROM AUTHOR]

Seabird colonies influence ecosystems by releasing high concentrations of nutrients, metals, and contaminants via their wastes. Here, we examined seven lentic waterbodies impacted by two major colonies of Leach's Storm-petrel (Hydrobates leucorhous), six from Baccalieu Island, Newfoundland and Labrador with ~ 1.95 million breeding pairs, and another from Grand Colombier Island, St. Pierre and Miquelon with ~ 200,000 breeding pairs. In comparison to nearby study sites not influenced by seabirds, we recorded more acidic pH, elevated specific conductance, and higher concentrations of dissolved organic carbon, total nitrogen, and total phosphorus in the seabird-influenced sites. The storm-petrels also significantly increased the metal concentrations of Co, Cu, Fe, Li, Nb, Ni, Sn, Sr, and Ti relative to reference sites. In the most highly affected ponds, the concentrations of Cd, Cu, and Fe exceeded Canadian Water Quality Guidelines for the Protection of Aquatic Life, implicating seabirds as biovectors of environmental contamination. Together, our data highlight the importance of seabirds, and likely other colonial organisms, as influential vectors that can strongly impact aquatic ecosystem chemistry and biota. [ABSTRACT FROM AUTHOR]

Shallow freshwater ecosystems are structurally complex with different, highly-coupled habitats: the pelagic, the within-macrophyte-meadow, and the benthic. Submerged macrophyte meadows support benthic microorganisms and provide the trophic network with non-trophic relationships. Multi-interaction network analysis disentangles how these systems respond to changes in global-change-related factors. We examined whether (i) populations' responses to such disturbances are habitat-dependent, and (ii) if whole-community configurations are different. We performed an indoor-mesocosm experiment ("control" plus two disturbed scenarios: enhanced ultraviolet radiation (UVR) or temperature), recreating shallow freshwater ecosystems. We assessed the population-nodes' carbon biomass, their resistance and resilience to the disturbances, and global- and node-scale structural parameters of the multi-interaction network. Under the UVR-scenario, the phytoplankton C-biomass (from pelagic and within-meadow habitats) was significantly the highest, with mixotrophs dominating. Warming favoured macrophyte growth and significantly increased the network's size and nestedness, with zooplanktonic herbivores playing a connector role. The within-meadow and benthic habitats' nodes were highly influential for the network, whatever the scenario. The benthic nodes were the most resistant to the disturbances. Therefore, a phytoplankton- and a macrophyte-dominated configuration was attained under UVR and warming scenarios, respectively. The macrophyte meadows, and the community linked to them, were pivotal in the achievement of these contrasting configurations. [ABSTRACT FROM AUTHOR]

Microscopic animals (also referred to as meiofauna) in freshwater habitats include several common, abundant and species-rich phyla, whose patterns of diversity are poorly known. Several approaches using DNA sequence data can be used to improve our knowledge on their biodiversity. In this review, we focus on studies using DNA data for taxonomy, and for environmental studies through metabarcoding on freshwater meiofauna. The results of the literature survey reveal that the use of DNA data is still rather limited. We screen the available literature on the topic and analyse the details of the current use and choices of the methods in freshwater meiofauna, the potential problems and limitations, and the flawed parts that still need to be improved. We conclude the review with a perspective on the still unexploited potentials in future applications to address biodiversity shortfalls in species diversity and taxonomy, and in the ecological and biogeographical patterns of species distribution. [ABSTRACT FROM AUTHOR]

Extreme climatic events, such as heat waves, may induce changes in nutrient acquisition by omnivorous ectotherms. Likely modulated by the intensity, frequency and duration of these events, dietary shifts during heat waves may threaten the stability of freshwaters. We investigated the effects of heat wave duration on diet assimilation and life-history traits of the freshwater gastropod Radix balthica. We compared the magnitude of the effects of a short (1 week) and a long heat wave (7 weeks) on the assimilation of animal- and plant-based diets, measuring performance in terms of growth rate and reproduction. We hypothesized that heat waves should increase the proportion of plant material assimilated on the mixed diet and change the performance of snails on the animal and plant-based diets. Both heat waves increased the assimilation of plant material on the mixed diet and growth rate, with minor negative effects on reproduction. However, responses were disproportional to heat wave duration, as the short heat wave elicited swift and relatively stronger responses. Our findings showcase the role of phenotypic plasticity in aiding ectotherms to cope with increased thermal stress and acclimate. Temporarily changing the strength of trophic interactions, heat waves may alter community dynamics in freshwater habitats. [ABSTRACT FROM AUTHOR]

We present a comprehensive survey of the scientific literature pertaining to non-indigenous and invasive zooplankton published across the first decades of the twenty-first century (i.e., 2000–2018). We provide a concise summary of the manner in which the scientific community has allocated its efforts to this issue in recent decades, and to illuminate trends that emerge from the literature. Our search yielded 620 publications encompassing 139 invasive zooplankton species, with invasive zooplankton reported from every region of the planet—including the Arctic and Antarctic. Most taxa were reported in a small number of publications, with the majority being mentioned in only a single paper. In contrast, approximately half of the surveyed publications concerned just four species: Bythotrephes longimanus, Mnemioposis leidyi, Cercopagis pengoi, and Daphnia lumholtzi. Our survey reveals strong geographic patterns among the literature, with most publications arising from economically developed western nations. We found that the majority of publications pertained to holoplanktonic organisms from freshwater habitats, especially from the North American Great Lakes. Based on these results, we present several recommendations for future research topics that may hold considerable opportunity for growth in our understanding of the invasion process. [ABSTRACT FROM AUTHOR]

Freshwater mollusc diversity has repeatedly been found to peak in lowland stagnant waters, which are highly exposed to human-made degradation and the spread of non-native species. Despite the increasing loss of these habitats, little is known about the main predictors of their mollusc diversity patterns. Therefore, we aimed to determine the environmental drivers of mollusc assemblage variation between and within sites by sampling 62 water bodies in the Dyje River floodplain (south-eastern Czechia). We measured 14 environmental variables, categorized as site-specific or plot-specific. Species richness and abundances were analysed by GLM and GEE; species compositional variance was assessed by NMDS and db-RDA ordinations. Mollusc species richness, ranging between 0 and 15 species per site, and abundance sharply decreased towards high trophy sites, with the chlorophyll-a concentration and water pH highly correlated with species counts. Species compositional variation was driven mainly by water trophy and the quality of organic detritus. Site heterogeneity turned out to significantly control local assemblages of molluscs, while the presence of individual species seemed to be filtered by site trophy and the shoreline length. Thus, to maintain high regional diversity of aquatic molluscs in lowland agricultural landscapes, the presence of low trophy sites seems to be essential. [ABSTRACT FROM AUTHOR]

Many freshwater habitats are subject to change through time. Specifically, natural flow regimes are substantially modified by not only seasonal climatic change, but also anthropogenic activity. Consequently, freshwater organisms are exposed to variable flow, potentially altering their behaviour and subsequently parasite transmission amongst social hosts. Here, we investigate the effects of flow conditions on the shoaling behaviour of Trinidadian guppies (Poecilia reticulata), and the resulting transmission of a directly transmitted ectoparasite, Gyrodactylus turnbulli. Shoals exposed to continuous flow exhibited significantly greater G. turnbulli peak intensities and abundance when compared to fish subjected to interrupted, but not no-flow conditions. Parasite transmission rate was greater in shoals exposed to interrupted flow, resulting in parasites becoming more distributed amongst shoal members and thus reducing mean intensity in comparison to continuous flow shoals. Furthermore, as prevalence increased, the distance between shoaling conspecifics increased at greater rates in interrupted and no-flow conditions compared to continuous flow: indicating that in the absence of flowing water, parasitism has a greater effect on shoaling decisions. This data highlights how fish behaviourally respond to variable flow conditions and the implications for parasite transmission. [ABSTRACT FROM AUTHOR]

Freshwater ecosystem function within agricultural landscapes may be altered by differences in processing of organic matter (OM) detritus entering freshwater habitats. We compared litter breakdown rates between crop residues; maize, cotton and soybean, and native riparian species: willow oak, American sycamore and cottonwood from inundated remnant river meander channels located within the Lower Mississippi River Basin (LMRB). Litter breakdown varied among the six species with the highest and lowest breakdown rates represented by crop (X¯k day−1 = 0.007-0.011) and riparian species (X¯k day−1 = 0.003-0.005), respectively. OM nutrient concentration varied widely across the six species. OM C:N ratios declined with time for all species except cotton. Temporal patterns in C:P ratios varied among crop residues but initially increased before declining for all three riparian species. Riparian OM breakdown rates were more negatively related to increasing C:N ratios of OM at the end of the study compared to crop species. Historic shifts in landscape-scale OM sources from diverse bottomland tree assemblages to crop residues has likely altered LMRB bayou and oxbow ecosystems by shifting both the timing and lability of OM pulses and decreasing long-term storage of OM, an important habitat and food resource for aquatic communities. [ABSTRACT FROM AUTHOR]

The distribution pattern of benthic meiofauna in freshwater ecosystems reflects a trade-off between residences in the high-risk, but productive, sediment surface versus the safer, but physiologically harsher, conditions deeper in the sediment. In this study, we used field enclosures and exclosures in a natural freshwater pond to investigate the effects of the juvenile common carp (Cyprinus carpio) on the distribution patterns of meiofaunal assemblages. Carp fed voraciously on meiofauna, reducing within few days the density and biomass of nematodes, oligochaetes, and microcrustaceans but not of rotifers, in the upper (0-2 cm) as well as deeper (2-4 cm) sediment layers. However, fish predation had less impact on the populations of nematodes and oligochaetes in the deeper sediment than in the surface sediment, as evidenced by reductions of 65 versus 80%, respectively. An analysis of the gut contents of carp indicated a high degree of omnivory, including the frequent consumption of meiofaunal organisms and also demonstrated the importance of meiobenthic invertebrates as prey for juvenile bottom-feeding fishes. [ABSTRACT FROM AUTHOR]

Where biodiversity conservation and environmental preservation are significant concerns, rapid assessment and monitoring of the colonization and spread of non-native species are essential for timely decision-making and response. We developed and evaluated the adequacy of a rapid assessment protocol (RAP) for detecting non-native fish species in 74 Eastern Brazilian lakes. The RAP consists of a single field day employing two surveyors to conduct interviews with local sport fishers, visual surveys of fish, angling with lures, and gillnetting. We compared our results with those from separate, intense, large sampling effort (LSE) field surveys. Despite requiring less than 1/100th of the field effort, the RAP was able to detect the presence of most non-native fish species that were reported in the same lakes by LSE surveys. Information from local sport fishers was invaluable, particularly for detecting species that were in low abundance, but was not available for lakes within a forest preserve area. Non-native introductions commonly lead to rapid and widespread invasion and adverse effects on native biota. Our results strongly suggest that the RAP could function as a cost-effective tool for efficiently assessing the presence of non-native fishes in lakes and monitoring their colonization and spread over large geographic areas. [ABSTRACT FROM AUTHOR]

The Brazilian Environmental Ministry (MMA) released a report in 2016 listing 163 non-native species into Brazilian inland waters. Reservoirs are among the freshwater habitats most frequently associated with the release of non-native species. Therefore, the aim of the present study was to evaluate the occurrence and distribution of the non-native species listed by the MMA, in large Brazilian reservoirs (≥ 30 km2). Further, we have tested the hypothesis that beta diversity of non-native species within reservoirs from the same basin is lower than those among reservoirs from distinct basins. A literature search was performed for 70 Brazilian reservoirs, resulting in the records of 91 non-native species. Reservoirs from the Paraná basin showed the highest number of occurrences, with 33 non-native species recorded only in the Itaipu reservoir. Beta diversity of non-native species showed higher variability among reservoirs from different basins than those within the same basin. Some basins were also distinguished by their composition of non-native species, as supported by the IndVal index. Non-native species were widespread along Brazilian reservoirs, and their distribution can be even higher than reported. [ABSTRACT FROM AUTHOR]

Megalonaias is the most geographically widespread genus of the subfamily Ambleminae and is distributed across much of the eastern half of North America, from Minnesota to Nicaragua. Despite the large geographic distribution, the species-level diversity of Megalonaias is quite depauperate (2 spp.), suggesting the genus may not be constrained by the same physical, ecological, or physiological barriers that limit dispersal in many other amblemines. However, this hypothesis is contingent on the assumption that the current taxonomy of Megalonaias accurately reflects its evolutionary history, which remains incompletely understood due to the marginalization of Mesoamerican populations in systematic research. Using one mitochondrial (COI) and one nuclear marker (ITS1) sequenced from 41 individuals distributed across both the Nearctic and Mesoamerican ecoregions, we set out to better understand the species boundaries and genetic diversity within Megalonaias. The reconstructed molecular phylogeny and the observed genetic diversity suggests that Megalonaias is a monotypic genus and that Megalonaias nickliniana, currently considered a federally endangered species, is not a valid species. These results are discussed in the context of their systematic and conservation implications, as well as how the unusual life history strategy of Megalonaias may be influencing its molecular diversity. [ABSTRACT FROM AUTHOR]

Despite the increasing number of studies on use of a functional diversity approach in community ecology, minimal information is available on functional traits of zooplankton in tropical and subtropical freshwater systems. The versatility of functional-trait-based approaches helps provide insight into many ecological processes in freshwater communities. We aim to provide baseline information on functional traits for tropical and subtropical Cladocera. Data on functional traits were gathered using published and unpublished data from Asia. The functional traits were chosen based on data availability and importance to the region's ecological conditions. Ten traits were chosen based on these criteria: two feeding, one reproductive, six survival, and one growth. Clustering of species showed possible unique and overlapping ecological roles and the impact of traits on the possible competition between and coexistence of species. Principal component analysis revealed tradeoffs between functional traits, where species that are heavily correlated with reproductive and growth traits do not usually have good survival traits and vice versa. These results can be used for further investigations on use of functional diversity and comparison of cladoceran communities, and provide additional insight into competition and coexistence within and structure of zooplankton communities across a wide range of ecological gradients. [ABSTRACT FROM AUTHOR]

The introduction and spread of aquatic invasive species constitutes a global epidemic that continues to homogenize the world's aquatic flora and fauna. Species invasions are occurring at an unprecedented scale, yet few centrally organized distributional databases can accurately display location information used to prioritize management efforts within a watershed, region, or political boundary. For particularly harmful groups of invaders such as some freshwater invertebrates, one consequence is that predictive power is limited because current invasion patterns are unknown. We used the Nonindigenous Aquatic Species database of the US Geological Survey to determine current hotspots of invertebrate invasion in the US and compared those patterns with better-documented fish invasions. Invasive freshwater invertebrates were densely clustered in the Laurentian Great Lakes region compared to invasive fish that were concentrated in Florida and the Southwest. However, temporal patterns of fish and invertebrate invasions did not significantly differ. Ballast water was the most important source of invertebrate introductions, whereas fish were more often introduced by stocking, aquaculture, and aquarium release. A centralized database of current species distributions, ideally at the global scale, would greatly inform prevention and mitigation efforts for harmful species invasions. [ABSTRACT FROM AUTHOR]

Due to an unfortunate mistake during the production process, the inset map in Fig. 1a is missing. The original article has been corrected and the correct display of Fig. 1 is also published here. [ABSTRACT FROM AUTHOR]

This review discusses the main developments in the systematics of coccoid green algae over the last three decades. The relationships of key groups of planktonic coccoid green algae are shown in the phylogenetic trees of Chlorophyceae and Trebouxiophyceae. The trees clearly show that the morphology of these algae do not adequately reflect their phylogenetic position. Different phylogenetic species can be hidden under one and the same morphotype. As most of the genera have a polyphyletic origin, they are in need of a systematic re-evaluation. Species classification using the phylogenetic species concept resulted in the establishment of new genera with smaller numbers of species and the description of new species that are not distinguishable by light microscopy. An overview of genera is given in tables and the revised designations of species as contained in the harmonized taxon list of the European Water Framework Directive lists is provided. In this transitional phase from an artificial to a more natural systematics of algae, field biologists and ecologists as well as molecular biologists must strengthen their interdisciplinary cooperation. The alignment of eco-functional groups of algae with true species identities using the barcoding conception will provide a better understanding of the interaction between organisms and their environment. [ABSTRACT FROM AUTHOR]

The 'All Taxa Biodiversity Inventories' (ATBIs) project coordinated by the European Distributed Institute of Taxonomy (EDIT) aims to achieve a baseline biodiversity assessment of flora and fauna in those regions characterized by a lack of knowledge and a high potential for biodiversity. Within the framework of the ATBIs, the aim of this study was to analyse the diatom flora and ecology of a complex of freshwater ecosystems in the Maritime Alps Natural Park (Italy), designated as a Special area of Conservation under the European Habitat Directive. We sampled epilithic and epiphytic diatoms in different habitats in 24 sites: shallow lake, springs, and streams. Our analysis resulted in a list of 138 diatom taxa, highlighting the great biodiversity and the complex structure of the investigated diatom communities. The taxa list included a wide range of uncommon species, including some recorded for the first time in North-Western Italy. Among the different habitats the highest level of diversity was found in the more lentic waters, in particular in limnocrene springs. These results show that the diatom communities of pristine and undisturbed high-mountain environments are rich and complex, despite the severe environmental conditions. [ABSTRACT FROM AUTHOR]

The aragonite shells of 55 mollusc specimens from the late Early and early Middle Miocene of two palaeolakes of the Dinaride Lake System (DLS) are analysed for their δO and δC signatures. The data set has a bimodal distribution with a prominent peak between −3 and −4‰ for both isotopes and a second much weaker peak at more depleted values of c. −9 to −7‰. Taxa with 'heavy' values are interpreted to represent the inhabitants of the shores or shallow areas of the lake. Depleted values are attributed to species preferring freshwater habitats of springs or small rivulets, thus representing the freshwater end-member. The overall rather high values in both stable isotopes result from a combination of evaporation effects and the influx of already isotopically heavy freshwater from the karstic catchment area. Thus, the DLS is interpreted as a closed freshwater system without marine influence but with enough contribution of freshwater to keep the oxygen values close to −5‰. Mean lake surface water temperatures, based on the δO values, excluding the freshwater end-member taxa, range around roughly 19-21°C. Despite the problems in calculating these temperatures, the values are in agreement with mean annual air temperatures deduced from the palaeobotanic record by applying the Coexistence Approach method. The seasonal range was around 10-11°C and is mainly recorded in shells from lake settings. Taxa with freshwater end-member signatures lack this range due to the more stable temperature regime and less fluctuating dissolved inorganic carbon (DIC) pool. Congeneric species from the same stratigraphic horizon often display discrete but different isotope signatures. This fact suggests habitat segregation and might be a major factor for sympatric speciation and the endemic radiation within the mollusc fauna of the DLS. [ABSTRACT FROM AUTHOR]

Identifying the factors influencing the settlement of European eel ( Anguilla anguilla) juveniles in continental habitats is crucial to designing effective management and conservation measures for this endangered species. A long-term data series (1993-2008) of European eel and European catfish ( Silurus glanis) abundance in a freshwater canal of the Camargue water system (southern France), along with parallel data on water salinity and glass eel abundance in the adjacent Vaccarès lagoon, was analysed to identify the possible causes of decline in eel abundance observed in the canal during the last two decades. A model including glass eel recruitment and catfish abundance as covariates explained 78% of the observed variation in eel settlement success. Results suggest that (1) salinity does not play a significant role in determining the fraction of eels moving from the brackish lagoon to the canal; (2) density dependence affects settlement success, possibly through a reduction of juvenile survival in the adjacent lagoon; and (3) catfish abundance is negatively correlated with eel settlement. We discuss this latter point in terms of possible predation of catfish upon eels and/or inter-specific competition between the two species. [ABSTRACT FROM AUTHOR]

Studies of cyanobacterial nostocacean taxa are important to the global scientific community, mainly because a significant number of beneficial strains that belong to the order Nostocales fix atmospheric nitrogen, thus contributing to the fertility of agricultural soils worldwide, while others behave as nuisance microorganisms in aquatic ecosystems due to their involvement in toxic bloom events. However, in spite of their ecological importance and environmental concerns, their identification and taxonomy are still problematic and doubtful, often being based on current morphological and physiological studies, which generate confusing classification systems and usually vary under different conditions. Therefore, the present research aimed to investigate through a polyphasic approach differences in morphological, biochemical and genotypic features of three nostocacean cyanobacterial strains isolated from central-western Portuguese shallow freshwater bodies. Morphometric, genetic ( 16S rRNA, nifH and hetR fragments) and biochemical (fatty acid methyl ester; FAME profiles) data were used to characterize the strains. Morphological analysis and sequencing of 16S rRNA fragments showed that the strains belonged to Anabaena cylindrica (UTAD_A212), Aphanizomenon gracile (UADFA16) and Nostoc muscorum (UTAD_N213) species. These strains showed clear distinct morphological and genetic features, allowing easy allocation to their respective genera. The same happened by using partial sequences of hetR and nifH genes, in spite of the scarcity of deposited sequences. Biochemical characterization showed that the FAME profiles obtained were consistent with both morphological and molecular analyses. It was suggested that the ratio of monounsaturated to polyunsaturated FAMEs, together with the unsaturation index, could be used as genus-specific chemotaxonomic biomarkers. [ABSTRACT FROM AUTHOR]

There is evidence of an ongoing alteration of the flow regime owing to climate change forcing, which has resulted in substantial increases in the frequency and magnitude of extreme events such as floods and droughts. Such changes in the flow regime may have major implications in freshwater ecosystems and, in particular, in the organic carbon dynamics in semiarid stream ecosystems. Much is known about the role of extreme flow events on structuring stream ecosystems, but few studies explored the effects of extreme flow events magnitude, timing, and sequence on stream ecosystems. To assess the effect of extreme events on stream organic C dynamics, a simple and flexible modeling approach was applied to simulate the organic carbon dynamics in a simplified river reach. The river reach model was initially calibrated and tested using long-term data for stream water velocity and amount of organic carbon in sediment. After that, multiple scenarios differing in the extreme flow events (floods and droughts) sequence and magnitude were used to simulate the effects of possible flow regime changes on the stream organic carbon dynamics. Initial expectations were that: (i) an increase in the magnitude or frequency of extreme flow events would reduce the amount of organic carbon respired within the simulated river reach, and (ii) relationship between the timings of the extreme flow events and of the litterfall input would influence considerably the effects of the extreme flow events. Results pointed out that: (i) the amount of processed carbon respect the amount entering the ecosystem was affected by extreme events such floods and droughts, but the relevance of those events differed along the year, with a maximal effect during the litterfall period; (ii) extreme event timing rather than the magnitude was more relevant to the stream organic carbon dynamics; and (iii) the amount of respired carbon in the ecosystem could be amplified or reduced depending on event sequence. Increasing awareness of the role of inland waters in the global carbon cycle and the shaping role of hydrology on the stream organic carbon dynamics stress the need to better quantify carbon fluxes and the hydrological controls on these fluxes. [ABSTRACT FROM AUTHOR]

lien aquatic plant species have had spectacular success in invading New Zealand's freshwaters. Their continued introduction has resulted in few water bodies retaining their natural or original indigenous aquatic vegetation, and associated adverse changes, such as reduced biodiversity and amenity values are well known. This highlights the need to accurately assess aquatic plant species that are already in the country and those outside for their potential to have a negative impact on New Zealand's lakes and waterways. The study presented in this paper describes an approach to evaluating the invasive weed potential of Hydrilla verticillata (L.f.) Royle compared with Elodea canadensis Michx. under flowing water conditions. The two species were planted in combination and alone, and in a sheltered or exposed position relative to the direction of the water flow. Over the 2-year study, two different waterflow rates were used (0.1 and 0.2 m/s) which represented the gauged flows from a stream of interest that contains E. canadensis and flows from a H. verticillata infested lake. H. verticillata was competitive compared with E. canadensis and able to persist and thrive in the presence of E. canadensis in both exposed and sheltered habitats. These results corroborate observations from other countries of H. verticillata growing in flowing waters and highlight the significant threat posed by H. verticillata to streams and waterways in New Zealand. [ABSTRACT FROM AUTHOR]