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Habitat transitions in living organisms are key innovations often coupled with species diversification after their successful adaptation to new environment. The Cyrenidae is among the most well-known heterodont bivalve groups that have successfully invaded freshwater systems from brackish water environments and display diverse lineage-specific developmental modes. Phylogenetic and molecular clock-based divergence time analyses using 12 complete mitochondrial genome sequences suggest that Cyrenidae species independently colonized freshwater habitats during three distinct spatial and geological periods: one from the American continents approximately in the Early Jurassic and the two others from Australasian/East Asian continents in the Early/Middle Cretaceous and the Paleogene-Neogene boundary, respectively. This study provides significant insight into the temporal and spatial patterns of multiple freshwater invasions, aligning with ancient vicariance events inferred from different geological timelines of plate tectonics. Additionally, mitogenome phylogeny confirms the earlier hypothesis of the repeated parallel evolution of parental care system within this bivalve group. This study shows that the timing and patterns of multiple freshwater invasions and the evolution of parental care systems in the well-known bivalve group Cyrenidae reflect ancient vicariance events driven by plate tectonics. [ABSTRACT FROM AUTHOR]

Although intraspecific trait variation is increasingly recognized as affecting ecosystem processes, few studies have examined the ecological significance of among-population variation in behavioral traits in natural ecosystems. In freshwater habitats, crayfish are consumers that can influence ecosystem structure (e.g., macroinvertebrate communities) and function (e.g., leaf litter breakdown). To test whether crayfish behavioral traits (activity, boldness, and foraging voracity) are major contributors of leaf litter breakdown rates in the field, we collected rusty crayfish (Faxonius rusticus) from eight streams across the midwestern USA and measured behaviors using laboratory assays. At the same streams, we measured breakdown rates of leaf packs that were accessible or inaccessible to crayfish. Our results provide evidence that among-population variation in crayfish boldness and foraging voracity was a strong predictor of leaf litter breakdown rates, even after accounting for commonly appreciated environmental drivers (water temperature and human land use). Our results suggest that less bold rusty populations (i.e., emerged from shelter more slowly) had greater direct impacts on leaf litter breakdown than bold populations (P = 0.001, r2 = 0.85), potentially because leaf packs can be both a shelter and food resource to crayfish. Additionally, we found that foraging voracity was negatively related to breakdown rates in leaf packs that were inaccessible to crayfish (P = 0.025, r2 = 0.60), potentially due to a trophic cascade from crayfish preying on other invertebrates that consume leaf litter. Overall, our results add to the growing evidence that trait variation in animals may be important for understanding freshwater ecosystem functioning. [ABSTRACT FROM AUTHOR]

The present investigation studied the spatial and temporal variation in physicochemical parameters and ciliate community structure at three freshwater sites in Delhi, India. Samples were collected from three freshwater sites, Okhla Bird Sanctuary (OBS), Sanjay Lake (SL) and Raj Ghat (RJ) in alternate months over 1 year, from September 2018 to August 2019. The water at the OBS site exhibited the lowest pH and electrical conductivity, along with the highest concentration of ammonium. The water at RJ was higher in suspended solids, electrical conductivity, and pH than the other two sites. Ciliates belonging to classes Spirotrichea, Oligohymenophorea, and Prostomatea were dominant in these freshwater samples. Maximum ciliate diversity, richness and evenness were observed in the OBS site. The highest diversity was observed during the monsoon and post-monsoon seasons, whilst the lowest was during the winter and summer season. [ABSTRACT FROM AUTHOR]

Odonates are widely considered to be bioindicators of freshwater habitat quality. Somatochlora arctica (Corduliidae) is commonly found across Eurasia, predominantly in North and Central Europe, but in the UK, it has a restricted range and is listed as near threatened despite a large, potential habitat availability. Across their range, larvae are found in Sphagnum-filled bog pools near coniferous woodlands, but detailed data on their habitat requirements are limited and often overlooked in favour of adult surveys which inhibits conservation efforts. This study surveyed three areas across Scotland: Abernethy & Loch Garten National Nature Reserve (NNR), Beinn Eighe NNR and Flanders Moss NNR, to evaluate how different environmental factors per pool (e.g. water depth and chemistry, Sphagnum coverage, woodland distance, etc.) affect the presence of S. arctica larvae. We found a higher occurrence of S. arctica larvae when pools were located close to woodlands (i.e. 0–10 m), and had high coverage of Sphagnum (> 90%). Environmental variables in pools surveyed (i.e. conductivity, water depth, pH and water temperature) had no significant effects on S. arctica presence. Implications for insect conservation: Our results highlight and discuss the importance of nearby woodlands and Sphagnum cover for S. arctica larvae. Future conservation projects should consider the proximity of woodland to current and restored S. arctica sites or promoting expansion of surrounding natural woodland patches to benefit S. arctica and potentially other odonates sharing similar ecological preferences. [ABSTRACT FROM AUTHOR]

Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fish nutrient data are critical for policy development targeting to reduce these problems. Despite this, much of the published studies on nutritional characteristics of fish have focused on marine ecology and there is little information on natural freshwater fish habitats like inland delta areas. This study investigated the nutrient composition of Okavango Delta fishes and their potential contribution to the recommended nutrient intake. Fish species sampled were Clarias ngamensis, Oreochromis andersonii, Schilbe intermedius, Marcusenius altisambesi, Brycinus lateralis, Barbus poechii and Tilapia sparrmanii. The nutrients analyzed were moisture, ash, proteins, Na, K, Ca, Mg, P and Zn. The small fishes (B. lateralis and B. poechii) had higher mineral content; Ca (643–968 mg/100 g), Mg (47–49 mg/100 g) and Zn (2.8–3.6 mg/100 g) compared to the larger species with average mineral content; Ca (73–460 mg/100 g), Mg (23–35 mg/100 g), Zn (1.2–2.9 mg/100 g). The most nutrient-dense species recognized were B. poechii and B. lateralis followed by the large species, M. altisambesi. These species illustrated the potential to contribute 80–121% Ca, 32–47% Mg and 70–150% Zn of the recommended nutrient intake to children (1–9 years), pregnant women and the elderly (65 + years). The study recommends prioritizing small and some large species (M. altisambesi and T. sparrmanii) for polyculture systems, primarily for securing food and nutrition security for local communities. [ABSTRACT FROM AUTHOR]

Freshwater aquatic ecosystems are threatened globally. Biological monitoring is required to deliver rapid and replicable assessment of changes in habitat quality. The Ephemeroptera, Plectoptera, Trichoptera (EPT) index is a globally recognised rapid bioassessment that measures taxa richness of three insect orders whose larvae are considered sensitive to freshwater habitat degradation. South-western Australia contains threatened freshwater ecosystems but has depauperate EPT fauna and high endemism, potentially reducing the capacity of the EPT index to track degradation. This study investigated if EPT species richness, composition or individual species tracked physical or chemical river degradation in three catchments in south-western Australia. We sampled EPT fauna and measured water chemistry, erosion, sedimentation, riparian vegetation cover and instream habitat at 98 sites in the winters of 2007 and 2023. We found 35 EPT taxa across the study area with a median number of species per site of two. EPT species richness had weak positive associations with a composite water quality index and dissolved oxygen and weak negative associations with electrical conductivity and total nitrogen. No association was found between physical and fringing zone degradation measures and EPT species richness. EPT community structure generally did not distinguish between sites with high or low degradation levels. The presence of the mayfly Nyungara bunni tracked salinity, dissolved oxygen and nitrogen levels, but its usefulness as a bioindicator could be limited by its restricted range. This study suggests that the EPT index would need modification or combination with other indices to be a useful rapid bioassessment in south-western Australia. [ABSTRACT FROM AUTHOR]

Chironomidae (Diptera) are one of the most abundant aquatic insects in freshwater habitats and play key roles in aquatic ecosystems. Many studies have assessed chironomid longevity under varying conditions to estimate potential consequences of climate change on longevity. However, these studies did not account for behavioral changes that may affect the ability of chironomids to find a mate or return to the water for oviposition. Longevity estimates may therefore underestimate the effects of climate change on chironomids by neglecting behavior-related fitness losses. To better understand how chironomid behaviors relate to survivorship, we used previously identified behaviors to determine how behavior patterns changed as the chironomid Diamesa mendotae aged. We found that D. mendotae exhibited age-related behaviors that correlated with a decrease in mobility over time. Additionally, behaviors performed early post-collection in D. mendotae adult lifespans were predictive of total chironomid longevity. These findings will help improve estimates of chironomid longevity and our understanding of age-related behaviors in other invertebrates. Improved methods for determining longevity and age-specific fitness-linked behaviors will allow us to better understand climate change's impacts on aquatic insect survival and reproduction, which has broad ramifications for the aquatic ecosystems where they are abundant. [ABSTRACT FROM AUTHOR]

The pond slider (Trachemys scripta) is a major invasive species in freshwater habitats across the world. For decades, the main cause of individuals' occurrences in the wild was the illegal release of pet animals. Recently, as an important component of their management, there has been an increasing focus on their ability to successfully reproduce in the invaded regions. In Romania, the species is reported as widespread in urban wetland environments within major cities, but information about its nesting and potential breeding remains scarce or anecdotal. We surveyed a large population of pond sliders in an artificial urban wetland site in Constanţa, SE Romania, and described their nesting ecology and reproductive output. Although eggs from several nests failed to hatch or were predated, potentially limiting their reproductive success, sliders were found to breed successfully at this site, with 18.6% viable hatchlings recorded. Our study could serve as a baseline for additional targeted surveys and to inform decision-making for successfully managing this invasive species. Although the importation, trading, and breeding of this species are prohibited by EU legislation, active and effective management is now required to address the successful reproduction and further potential spread of T. scripta. [ABSTRACT FROM AUTHOR]

In the context of warming freshwater habitats, protection of Atlantic salmon populations requires an understanding of the effects of temperature on somatic growth during the juvenile life stage. However, quantifying the effect of temperature on growth is challenging given differences among methodologies, metrics of growth, and their underlying assumptions. Using short term studies (2000–2002) in two Canadian populations of wild Atlantic salmon (Margaree and Miramichi rivers), we investigate whether different hierarchical modeling approaches influence the derivation of temperature-growth relationships, by contrasting seasonal growth trajectories (von Bertalanffy; VBGF) to size-at-age data models built with instantaneous growth rates. Size-at-age data analysed seasonally with the VBGF framework failed to detect an effect of temperature, whereas instantaneous growth rates from the same dataset were strongly related to temperature metrics. However, instantaneous growth rates cannot be used to extrapolate predictions into meaningful metrics for fisheries management (e.g., size at the end of the growing season). Nevertheless, we show that size at the end of the growing season can be predicted with VBGF models accounting for site-level variation, which in turn are related to temperature metrics, as observed for instantaneous growth rates. Taken together, these results show that combining these two approaches (size-at-age, growth rates) can circumvent their intrinsic drawbacks and reveal essential ecological patterns that may otherwise remain undetected. In cases where instantaneous growth rates are not available, relating predicted size-at-age from hierarchical VBGF to temperature provides an interesting alternative for detecting subtle environmental effects, even if the VBGF parameters or its residuals are unrelated to temperature metrics. [ABSTRACT FROM AUTHOR]

Exposure to pollutants is a potentially crucial but overlooked driver of population declines in shorebirds along the East Asian-Australasian Flyway. We combined knowledge of moult strategy and life history with a standardised sampling protocol to assess mercury (Hg) contamination in 984 individuals across 33 migratory shorebird species on an intercontinental scale. Over one-third of the samples exceeded toxicity benchmarks. Feather Hg was best explained by moulting region, while habitat preference (coastal obligate vs. non-coastal obligate), the proportion of invertebrates in the diet and foraging stratum (foraging mostly on the surface vs. at depth) also contributed, but were less pronounced. Feather Hg was substantially higher in South China (Mai Po and Leizhou), Australia and the Yellow Sea than in temperate and Arctic breeding ranges. Non-coastal obligate species (Tringa genus) frequently encountered in freshwater habitats were at the highest risk. It is important to continue and expand biomonitoring research to assess how other pollutants might impact shorebirds. Over one-third of the sampled shorebirds along the East Asian-Australasian Flyway are facing Hg risk. Tringa genus in South China was at the highest risk. Feather Hg was best explained by feathers' moulting region, while habitat preference, diet, and foraging stratum were less important. [ABSTRACT FROM AUTHOR]

Monitoring and protecting freshwater habitats are paramount for a sustainable water management perspective. This study investigated potentially toxic elements (PTEs) in the potamic water of the Anday Stream Basin (Türkiye), Black Sea Region, for a hydrological year (from May 2020 to April 2021). Among PTEs, the highest average values were recorded for sodium (Na) at 41.3 mg/L and the lowest for mercury (Hg) at 0.009 μg/L and noted under quality guidelines. The stream was found to be at the level of "Low Heavy Metal Pollution" and "Low Contamination" based on the ecotoxicological risk indices. The highest calculated hazard quotient (HQ) value of 1.21E-02 for Cd was noted in the children via the dermal pathway and the lowest of 6.91E-06 for Fe in adults via the ingestion pathway. Results revealed a higher hazard index (HI) value of 1.50E-02 for Cd to children and the lowest of 1.98E-05 for Fe to adults. As a result of applying agricultural risk indices, the stream showed sodium adsorption ratio values less than 6 and was found to be "Excellent" for agriculture. However, the sodium percentage values were less than 20 and found "Permissible" and the magnesium hazard > 50 and noted as "Unsuitable" for agriculture. Statistical analysis revealed that natural factors mainly attributed to PTE contamination of the Anday Stream Basin. [ABSTRACT FROM AUTHOR]

Information on juvenile alewife use of estuaries is limited on the east coast of North America. In this study, we collected juvenile alewife from the Penobscot River estuary, Maine, and measured stable isotope values from their muscle and liver tissues, which have a low and high turnover rate (respectively). These values were compared to the stable isotope values of preferred prey taxa collected from three distinctly different isotopic habitats within the Penobscot River watershed to estimate the amount of time fish had spent in the estuary. Fish were collected in spring, summer, and autumn in 2013 and 2014 at seven fixed collection sites in the estuary, from four freshwater lakes, and from five bay locations. Based on the δ13C values of muscle and liver tissue, estuarine caught juvenile alewife were assigned to one of the following distinctly different isotopic habitat groups: freshwater transient (recently from freshwater), bay transient (recently from the bay), or estuarine occupant (spent extended time in the estuary). Stable isotope ratios of nitrogen (for all samples) and sulfur (in muscle tissues of a subset of 17 samples) were analyzed to confirm habitat group designations. Bay transients had 37% and 15% higher sulfur and nitrogen isotope ratio values than estuarine occupants and five times more sulfur and almost two times more nitrogen isotope ratio values than freshwater transients. Of 88 juvenile alewife analyzed for carbon isotopes, 32% were identified as estuarine occupants that had spent extended time periods in the estuary, whereas 68% of juvenile alewife had recently moved from bay or freshwater habitats. Mean number of days that juvenile alewife spent in the estuary was highest in spring and declined over time, with more movement occurring in autumn. This result suggests that movement of juvenile alewife between bay and estuary occurs frequently from May to October. Juvenile alewife may use estuarine and nearshore habitats for extended time periods, and migration between estuarine and bay habitats may not follow typical life history strategies. [ABSTRACT FROM AUTHOR]

Ecological and evolutionary transitions offer an excellent opportunity to examine the molecular basis of adaptation. Fishes of the order Beloniformes include needlefishes, flyingfishes, halfbeaks, and allies, and comprise over 200 species occupying a wide array of habitats—from the marine epipelagic zone to tropical rainforest rivers. These fishes also exhibit a diversity of diets, including piscivory, herbivory, and zooplanktivory. We investigated how diet and habitat affected the molecular evolution of cone opsins, which play a key role in bright light and colour vision and are tightly linked to ecology and life history. We analyzed a targeted-capture dataset to reconstruct the evolutionary history of beloniforms and assemble cone opsin sequences. We implemented codon-based clade models of evolution to examine how molecular evolution was affected by habitat and diet. We found high levels of positive selection in medium- and long-wavelength beloniform opsins, with piscivores showing increased positive selection in medium-wavelength opsins and zooplanktivores showing increased positive selection in long-wavelength opsins. In contrast, short-wavelength opsins showed purifying selection. While marine/freshwater habitat transitions have an effect on opsin molecular evolution, we found that diet plays a more important role. Our study suggests that evolutionary transitions along ecological axes produce complex adaptive interactions that affect patterns of selection on genes that underlie vision. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are globally observed in marine as well as freshwater habitats, and laboratory studies have shown that marine organisms can accidentally ingest them. Monitoring the MP ingestion by fish in the environment is very crucial for understanding the risk of consuming MP-contaminated fish for human health. In this study, we investigated MP ingestion in 400 fish individuals from the Veraval Coast, in the state of Gujarat, India. There was 100% MP occurrence in the inedible tissues of fish, and 68% of the analyzed fishes presented MPs in edible tissues. The most dominant MPs based on their size in fishes were 0.05–0.1 mm. One hundred percent presence of only fibres in edible tissue was observed, while in inedible tissue, it was 77%, 20.42% and 2.58% of fibre, fragment and film respectively. The most common MP colour was blue. The predominant polymers were low-density polyethylene (LDPE) followed by polypropylene, high-density polyethylene (HDPE) and polystyrene. This is the first study performed on MPs in marine fishes from this region. Our findings suggest that the abundance of MPs observed in this area is higher than in other states of the country. [ABSTRACT FROM AUTHOR]

The number of invasive species threatening freshwater habitats are increasing globally, and can be accelerated by climate change. Thus, risk assessments of potential invasive species are required for establishing prevention measures, in which quantitative risk assessments provide results objectively. In this study, the invasion risk of largemouth bass (Micropterus salmoides) in four major river basins (the Han, Nakdong, Geum, and Yeongsan) in South Korea was evaluated using an ensemble of species distribution models (SDMs). A weighted ensemble of the SDMs was developed to predict the probability of largemouth bass occurrence in the present (2011–2015) and two future periods: 2050 (2046–2055) and 2080 (2076–2085). The invasion risk of largemouth bass was evaluated using two approaches: relative and absolute risk assessments. Both approaches predicted an increase in Tier 1 (the highest risk) areas under representative concentration pathway (RCP) 4.5; however, a decrease in the areas of concern under RCP 8.5. In particular, the upper streams of the Nakdong and Han river basins are expected to be at risk in the future. In addition, Tier 1 risk areas are predicted to shift northward under both RCP 4.5 and 8.5 scenarios, especially in the Nakdong River Basin. This study provides a quantitative risk assessment tool based on the SDMs for the management of largemouth bass invasion under climate change. [ABSTRACT FROM AUTHOR]

Coastal river systems provide essential habitats for a diversity of fish species that transition marine, estuarine, and freshwater environments to complete their lifecycles. Movement among and within these environments is important to access resources that optimise growth, survival, and reproduction. Knowledge on the movements, including the drivers, underpins management strategies, although this information is often lacking for many species. We used acoustic telemetry to quantify the relative importance of a range of abiotic stimuli in relation to seasonal movement patterns in blue salmon catfish Neoarius graeffei throughout an unregulated coastal river catchment, the Clarence River in northern New South Wales, Australia. Neoarius graeffei continuously occupied the Clarence River system for the duration of the 1-year study and were mostly confined to estuarine reaches, with occasional movement into freshwater habitats. Seasonal differences in habitat occupation were observed, with N. graeffei using habitats close to the river mouth in winter and upstream estuary habitats in spring. Broad-scale movement patterns were influenced by both water temperature and river flow, and high-flow events (> 1.5 m) resulted in short-term changes (~ 10 days) in habitat use. Sex-specific differences in seasonal habitat use were also observed which we hypothesise is linked to contrasting energetic investment in reproduction. The response of N. graeffei to changes in river flow highlights the need for assessment on these impacts for estuarine-dependent species more broadly, in the face of climate change and increased river regulation. [ABSTRACT FROM AUTHOR]

Landscape fragmentation impacts freshwater habitats and their quality, affecting aquatic insect assemblages. Adjacent terrestrial areas are important secondary habitats where amphibiotic insects mature, feed, find mates, and move to locate aquatic breeding habitats. Using a factorial design with 27 small and large ponds within small and large natural patches in an exotic tree plantation-fragmented landscape of South Africa, and odonates as model organisms, we investigated (1) how pond size/natural terrestrial patch size interaction affects odonate diversity patterns versus habitat quality variables, and (2) determined whether anisopterans and zygopterans respond differently to landscape fragmentation. Species richness was similar among ponds. However, odonate abundance was highest in large ponds regardless of natural terrestrial patch size. Zygopteran functional richness and diversity was driven by pond and natural patch size, suggesting that zygopterans are sensitive to landscape fragmentation. In contrast, anisopterans were more resilient to fragmentation and more likely to select suitable habitats following water chemistry and vegetation characteristics. Overall, large ponds were occupied by different odonate assemblages compared to small ponds, and occupancy was strongly associated with mobility traits. These findings emphasize that ponds in both small and large natural terrestrial patches have conservation value. A pondscape that represents various pond sizes is important for maintaining regional odonate diversity. Pond conservation needs to be considered in the wider terrestrial context, which host a range of important secondary habitats. Adjacent natural terrestrial habitats also connect nearby aquatic habitats, which enable insects to move across the landscape in response to natural and artificial drivers. [ABSTRACT FROM AUTHOR]

The surface water is an important habitat for freshwater microorganisms, but there is a lack of understanding of the pattern of microbial diversity and structure in stream continuums of small subtropical forest watersheds. Therefore, this study aimed to understand the variations in microbial diversity and community structure along stream orders (1–5) in the small subtropical forest catchments of the Wuyi Mountains. Using GIS software, 20 streams were chosen and classified into 5 orders. Illumina sequencing was used to analyze the dynamics of microbial communities, along with stream orders and hydro-chemical properties of stream water were also determined. Our results indicated that the bacterial and fungal richness (ACE index) was higher in low-order (1 and 2 orders) streams than in high-order (3, 4, and 5 orders) streams, with the highest value in the order 2 streams (P < 0.05). The water temperature and dissolved oxygen were positively correlated with fungal richness (P < 0.05). The bacterial rare taxa had a significant correlation with the abundance taxa (P < 0.05). The relative abundances of Bacteroidetes, Actinobacteria, and Chytridiomycota microbial phyla were significantly different among different order streams (P < 0.05). Using the neutral community model, we found that the fungal community structure was significantly shaped by hydro-chemical properties, while the bacterial community structure was largely regulated by stochastic processes. Our findings suggest that variations in microbial community structure in subtropical headwaters are largely shaped by the water temperature and dissolved oxygen. [ABSTRACT FROM AUTHOR]

European rivers are disconnected by more than one million man-made barriers that physically limit aquatic species migration and contribute to modification of freshwater habitats. Here, a Conceptual Habitat Alteration Model for Ponding is developed to aid in evaluating the effects of impoundments on fish habitats. Fish communities present in rivers with low human impact and their broad environmental settings enable classification of European rivers into 15 macrohabitat types. These classifications, together with the estimated fish sensitivity to alteration of their habitat are used for assessing the impacts of six main barrier types (dams, weirs, sluices, culverts, fords, and ramps). Our results indicate that over 200,000 km or 10% of previously free-flowing river habitat has been altered due to impoundments. Although they appear less frequently, dams, weirs and sluices cause much more habitat alteration than the other types. Their impact is regionally diverse, which is a function of barrier height, type and density, as well as biogeographical location. This work allows us to foresee what potential environmental gain or loss can be expected with planned barrier management actions in rivers, and to prioritize management actions. European rivers have over a million barriers hindering aquatic species migration and altering freshwater habitats. This study quantifies the spatial extent of upstream fish habitat alteration caused by physical blockage and shows that impoundments have altered 10% or 200,000 km of free-flowing river habitat in Europe. [ABSTRACT FROM AUTHOR]

The East American mudminnow Umbra pygmaea was introduced to Europe a century ago and is now established in at least six European countries. Although considered harmless and with low spread potential, this fish species shows potential to colonise a broad range of habitats due to its wide environmental tolerance. Stomach content analyses were conducted over 3 years to obtain a first insight into this species' diet, which could indicate the potential to alter the biotic composition of recipient ecosystems. The results showed that this fish can potentially have a high impact on insects, fish, and even amphibians through predation. Species distribution models further indicated that environmental conditions of Central European ecoregions are currently a limiting factor for the spread of this species which seems, at least for now, to be driven by anthropogenically driven introductions. Considering the species' potential to be invasive and impact native biota, monitoring of potential spread is recommended. [ABSTRACT FROM AUTHOR]

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]

Ranunculus lingua is an Euro-Siberian vascular plant species of freshwater habitats. Distribution and vegetation preferences of this rare species, which is native to the Slovak flora, have not yet been critically revised. The present paper aimed i) to provide the first complex distribution pattern of this species in Slovakia and ii) to analyse all available vegetation plots with species occurrence in order to elucidate the variability of plant communities. The distribution data were retrieved from herbarium specimens, literature records and field surveys. Our revision suggests that R. lingua was found particularly in the lowland areas of the western, south-western and south-eastern parts of the country. It was very rare in other regions of Slovakia, and several populations have become extinct due to drainage or habitat destruction. New localities of secondary origin were additionally documented in some human-made habitats. The temporal trend showed a strong decrease in the number of localities in natural habitats, mainly in the hilly and mountainous regions of the Western Carpathians from the 1980s to the end of the twentieth century. R. lingua was recorded in both forest and treeless swamp communities. Vegetation analysis revealed numerous records mainly in eutrophic marshes (Phragmito-Magnocaricetea class), willow and alder carrs (Franguletea and Alnetea glutinosae). [ABSTRACT FROM AUTHOR]

The regionally threatened damselfly Sympecma peadisca is one of the few Central European dragonfly species included is considered as Near Threatened in the European Red list. The major threats to this species remain unclear. This species has a unique life history and several adaptations to enabling survival even in semidesert areas, such as overwintering in the adult stage. However, the closely related, more thermophilic species Sympecma fusca has undergone a major range expansion in Europe. Based on data from 129 sites and combining several analytical approaches, I found the following: 1. According to local freshwater conditions, S. paedisca is a typical habitat generalist occupying a wide range of habitats. 2. It requires a wide range of terrestrial habitats to complete its life cycle. 3. An analysis of the land used by both species clearly indicates that both species avoid intensive agricultural areas; however, S. fusca can also occur in suburban areas, where S. paedisca is absent. 4. Projections of the Least Cost Path analysis indicate that the only localities where the species is currently spreading are habitats arising as a consequence of mining activities. The example of S. paedisca is clear evidence of a freshwater species that responds very negatively to the homogenization of the terrestrial environment, even when its natal habitat is not significantly affected. The frequent occurrence of species in postmining areas suggests that species with complex habitat requirements can find suitable secondary habitats where they can prosper in the long term. Implications for insect conservation: Even semi-aquatic groups like damselflies can be very sensitive to gradual changes in surrounding land use. Species with very complex habitat requirements also require comprehensive conservation strategies affecting all habitats utilized by the species. However, the return of some landscape features requires a reduction in the area of production areas in favor of hedgerows and ruderals. Such restoration management requires long-term planning and close cooperation with farmers. [ABSTRACT FROM AUTHOR]

Hydrological (rainy and dry) periods can affect the water quality of lentic ecosystems, which may be useful for understanding their ecological condition in the watershed. Ecological status of various lentic ecosytems (both brackish and freshwater) in the western Mediterranean basin was evaluated by using various diatom metrics throughout rainy (May) and dry (August and October) periods to explain the diatom-stressor interactions using multivariate approaches. Canonical correspondence analysis separated freshwater habitats under the pressures of nitrate and total organic carbon from brackish ecosystems under the pressures of conductivity, nitrite, sulphate, calcium, and copper, which were characterized by different phytoplankton species. Ecological integrations of diatom species varied in the ecosystems throughout rainy and dry periods. Different ecological regional diatom indices were used to find the best index/indices indicating the ecological status of lakes and reservoirs in the basin during the two hydrological periods. The trophic diatom index developed for lakes was not found to be suitable for assessing lentic habitats. European diatom indices generally showed the distinction in the assessment of these ecosystems in the rainy and dry seasons, but others could not. Among the diatom indices, only the trophic index Turkey (TIT) showed a statistically significant correlation with TP. The TIT not only showed degradation of the water quality of ecosystems during the dry season compared to the rainy season, but it has also been successful in distinguishing the ecological conditions of lentic ecosystems. [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]

Dietary information from aquatic organisms is instrumental in predicting biological interactions and understanding ecosystem functionality. In freshwater habitats, generalist fish species can access a diverse array of food sources from multiple food chains. These may include primary photosynthetic production and detritus derived from both oxic and anoxic decomposition. However, the exploitation of anoxic decomposition products by fish remains insufficiently explored. This study examines feeding habits of striped catfish (Pangasianodon hypophthalmus) at both adult and juvenile stages within a tropical reservoir, using stable carbon, nitrogen, and sulfur isotope ratios (δ13C, δ15N, and δ34S, respectively) and fatty acid (FA) analyses. The adult catfish exhibited higher δ15N values compared to primary consumers that feed on primary photosynthetic producers, which suggests ingestion of food sources originating from primary photosynthetic production-based food chains. On the other hand, juvenile catfish demonstrated lower δ15N values than primary consumers, correlating with low δ34S value and large proportions of bacterial FA but contained small proportions of polyunsaturated FA. This implies that juveniles utilize food sources from both anoxic decomposition and primary photosynthetic production-based food chains. Our results indicate that food chains based on anoxic decomposition can indeed contribute to the dietary sources of tropical fish species. [ABSTRACT FROM AUTHOR]

Hydropower plants represent one of the greatest threats for freshwater fish by fragmenting the habitat and avoiding the species dispersal. This type of dispersal barrier is often disregarded when predicting freshwater species distribution due to the complexity in inserting the species dispersal routes, and thus the barriers, into the models. Here, we evaluate the impact of including hydroelectric dams into species distribution models through asymmetrical dispersal predictors on the predicted geographic distribution of freshwater fish species. For this, we used asymmetrical dispersal (i.e., AEM) as predictors for modeling the distribution of 29 native fish species of Tocantins-Araguaia River basin. After that, we included the hydropower power plant (HPP) location into the asymmetrical binary matrix for the AEM construction by removing the connections where the HPP is located, representing the downstream disconnection a dam causes in the fish species dispersal route. Besides having higher predicted accuracy, the models using the HPP information generated more realistic predictions, avoiding overpredictions to areas suitable but limited to the species dispersal due to an anthropic barrier. Furthermore, the predictions including HPPs showed higher loss of species richness and nestedness (i.e., loss of species instead of replacement), especially for the southeastern area which concentrates most planned and built HPPs. Therefore, using dispersal constraints in species distribution models increases the reliability of the predictions by avoiding overpredictions based on premise of complete access by the species to any area that is climatically suitable regardless of dispersal barriers or capacity. In conclusion, in this study, we use a novel method of including dispersal constraints into distribution models through a priori insertion of their location within the asymmetrical dispersal predictors, avoiding a posteriori adjustment of the predicted distribution. [ABSTRACT FROM AUTHOR]

Myxozoans are a unique group of microscopic parasites that infect mainly fishes. These extremely reduced cnidarians are highly diverse and globally distributed in freshwater and marine habitats. Myxozoan diversity dimension is unknown in Mexico, a territory of an extraordinary biological diversity. This study aimed to explore, for the first time, myxozoan parasite diversity from fishes of the Neotropical region of Mexico. We performed a large morphological and molecular screening using host tissues of 22 ornamental and food fish species captured from different localities of Veracruz, Oaxaca and Chiapas. Myxozoan infections were detected in 90% of the fish species, 65% of them had 1 or 2 and 35% had 3 and up to 8 myxozoan species. Forty-one putative new species were identified using SSU rDNA phylogenetic analyses, belonging to two main lineages: polychaete-infecting (5 species) and oligochaete-infecting (36 species) myxozoans; from those we describe 4 new species: Myxidium zapotecus sp. n., Zschokkella guelaguetza sp. n., Ellipsomyxa papantla sp. n. and Myxobolus zoqueus sp. n. Myxozoan detection increased up to 6 × using molecular screening, which represents 3.7 × more species detected than by microscopy. This study demonstrated that Neotropical fishes from Mexico are hosts of a multitude of myxozoans, representing a source of emerging diseases with large implications for economic and conservation reasons. [ABSTRACT FROM AUTHOR]

Habitat coupling, where consumers acquire resources from different habitats, plays an important role in ecosystem functioning. In this study, we provide a global investigation of lake habitat coupling by freshwater fishes between littoral (nearshore) and pelagic (open water) zones and elucidate the extent to which magnitude of coupling varies according to environmental context and consumer traits. We consider the influence of lake factors (surface area, depth, shoreline complexity, and annual temperature), relative trophic position of consumers, fish community species richness, and fish morphological traits on habitat coupling by fishes. Using a worldwide dataset consisting of fish stable isotope values (δ13C and δ15N), we developed an index of habitat coupling, and used Bayesian hierarchical and non-hierarchical beta regressions to estimate the effects of environmental lake context and morphological traits on habitat coupling by fishes. Our results show high rates of habitat coupling among fishes globally with marked taxonomic differences in the magnitude and variation. Habitat coupling was higher in lower elevation lakes and in regions characterized by relatively colder climates, whereas other environmental context factors had little or no effects on habitat coupling. Furthermore, habitat coupling was associated with several locomotion and feeding traits, but independent from species maximum body length. Overall, we highlight the prevalence of multiple resources supporting fish populations and suggest future research identify implications to ecosystem functioning that may result from alterations to habitat coupling by fishes. [ABSTRACT FROM AUTHOR]

World produces 360 million tons of plastic every year, out of which only 7% plastic undergo recycling leaving majority of this waste lying around that get accumulated in the environment, thus posing a serious threat especially in the form of microplastics (MPs) to the large group of organisms on earth. Microplastics have been observed both in freshwater as well as in marine environment; however, recently, the occurrence of MPs in the fresh water that will ultimately lead to pollution in drinking water is emerging as one of the major concern for the scientific community. Till now, relative to the marine environment, the MPs pollution in the fresh water system is not very well understood and still an area of research that needs to be explored in detail. A detailed understanding of the origin, qualification, quantification, hazardous effects, etc. has be established to develop a proper waste management process for the MPs found in fresh water system. This review focuses on the sources, distribution, sampling methods, separation methods, methods of characterization and toxicological effects of microplastics in the freshwater environment. Various factors that affect the transportation and distribution of microplastics in fresh water system are reviewed. It is recommended that a standard protocol must be developed for identification of microplastics for scientific community across the world. The present study will help us to understand the source, transport, and effects of microplastics on the freshwater environment which would thereafter help to standardize the process for quantification and identification of microplastics in the freshwater environment. A combination of methods for the detection and prevention of microplastics in freshwater environment has also been suggested. [ABSTRACT FROM AUTHOR]

Waterbirds depend on a dispersed network of wetlands for their annual life cycle during migration. Climate and land use changes raise new concerns about the sustainability of these habitat networks, as water scarcity triggers ecological and socioeconomic impacts threatening wetland availability and quality. During the migration period, birds can be present in large enough numbers to influence water quality themselves linking them and water management in efforts to conserve habitats for endangered populations. Despite this, the guidelines within laws do not properly account for the annual change of water quality due to natural factors such as the migration periods of birds. Principal component analysis and principal component regression was used to analyze the correlations between the presence of a multitude of migratory waterbird communities and water quality metrics based on a dataset collected over four years in the Dumbrăvița section of the Homoród stream in Transylvania. The results reveal a correlation between the presence and numbers of various bird species and the seasonal changes in water quality. Piscivorous birds tended to increase the phosphorus load, herbivorous waterbirds the nitrogen load, while benthivorous duck species influenced a variety of parameters. The established PCR water quality prediction model showed accurate prediction capabilities for the water quality index of the observed region. For the tested data set, the method provided an R2 value of 0.81 and a mean squared prediction error of 0.17. [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]

The ecological significance of freshwater ecosystems for conservation in the temperate zone has been determined by aquatic biologists using a variety of ecological techniques. One such tool is the Community Conservation Index (CCI), which was primarily developed in Britain but is also recommended for international use. The current study intends to further test the CCI's applicability and its sensitivity in identifying freshwater systems of high conservation importance. The pristine condition of three natural monument (Arinta, Ekor, and Oowu waterfalls) streams was evaluated in this study using the macroinvertebrate metric indicators, and the results were compared with their CCIs. The relative compositions of stress-sensitive species, facultative species, functional feeding guilds (FFGs), and modes of locomotion or microhabitat preference (ML/MP) were selected as the macroinvertebrate metrics. The fauna was dominated by the taxonomic group EPT (Ephemeroptera, Plecoptera, Trichoptera), with the highest EPT-related metrics found at Oowu Waterfalls. Ironically, because a vulnerable species (i.e. Pentaphlebia stahli) is present there, the Ekor Waterfalls, which had the lowest values for the EPT-related metrics, had the highest CCI. Although both the CCI (>20) and macroinvertebrate metrics suggest that the three sites had high conservation value, the CCI proved to be more goal-oriented in determining the conservation value of pristine freshwater ecosystems. In light of the findings of this study, it is recommended that the CCI be utilized in conjunction with macroinvertebrate metric indicators for studies of a similar nature, particularly in Afrotropics' protected and pristine sites that are a potential refuge for rare and threatened species. [ABSTRACT FROM AUTHOR]

Adaptation to one stressor can influence organismal responses to future environmental changes, either to the same or a novel stressor. But there is a lack of research on this topic, particularly in the context of freshwater habitats. Fluctuating salinity and heatwaves that are becoming more frequent and intensified are affecting freshwater ecosystems. We applied an experimental evolution approach to examine the influence of adaptation to elevated salinity on the population's responses to subsequent salt and heat stress. We conducted lab experiments using Daphnia pulicaria cultured from individuals with previous 8-week exposure history to two salinity treatments (6.5 or 350 mg Cl−/L). Iso-female lines with or without prior exposure to elevated salinity were assayed along a salt gradient (18.5 to 1500 mg Cl−/L) or an acute heat gradient treatment (20 to 35 °C). Our results showed that Daphnia survival, fecundity, and body length growth rate declined with increased salt concentration, with survival and fecundity being most sensitive. The treatment group with previous salt exposure history had higher survival and fecundity than the naïve treatment group when treated with salt, without loss of fitness under low-salinity conditions. Daphnia survival and growth rates were reduced in temperatures higher than 30 °C. Despite the fact that the two stressors can induce similar defense mechanisms, previous exposure history to salt did not prevent Daphnia populations from experiencing reduced survival and growth rates under heated conditions. Our work demonstrates that organisms can rapidly adapt to a stressor that protects them from later exposure to increases in this stressor, without a trade-off in fitness under undisturbed conditions, but this evolved tolerance cannot protect them from all levels of this stressor or alleviate damage by a novel one. [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]

Having parts of three freshwater ecoregions, i.e., Oman Mountains, Southwestern Arabian Coast, and Arabian Interior, Oman is considered to have the greatest freshwater biodiversity among the Arabian Peninsula countries. Freshwater habitats and biodiversity of Oman are unique and greatly valued for the crucial role they play in people's survival, as well as that of its native/endemic biota. An obvious starting point and fundamental step to conserve biodiversity and implementing planning management strategies is correct identification and delineating of the taxonomic and conservation units, and their distribution ranges especially endemic and native faunal elements including small, colorful, and mosquito-eating fish species of the genus Aphaniops. Five species of Aphaniops are present in the northern marginal basins of the Indian Ocean, however, there is still a lack of distributional and taxonomic data in many parts, and the species have not been studied yet for their phylogeographic and population structures, which are essential in designing habitat management and conservation plans. This study analyses mitochondrial COI data of Aphaniops samples collected from numerous widespread localities in Oman, a rarely studied area for this group, using a phylogenetic and phylogeographic framework. Our results confirm the presence of two species in Oman, A. kruppi and A. stoliczkanus, revise and suggest wider distributional ranges for both species, and suggest that A. kruppi is represented by two northern and one southern management units, while A. stoliczkanus is divided into two evolutionary units worthy of additional taxonomic evaluation. [ABSTRACT FROM AUTHOR]

Understanding the effects of species invasions on vulnerable freshwater habitats is crucial to protecting those ecosystems. The vermiculated suckermouth sailfin armored catfish, an abundant, invasive grazer in Florida springs and around the world, may interact with native communities in complex ways, including alteration of nutrient availability, which in turn may influence primary production, with cascading effects through the food web. Armored catfish may differ from native fishes in their body nutrient content because of their high proportion of bony material; therefore, increasing densities of armored catfish may shift nutrient availability to primary producers due to their consumption, excretion, and egestion of nutrients. To evaluate this, we measured N:P ratio of catfish tissues compared to the N:P ratios of two abundant native species and found that catfish had a significantly lower body N:P than native species. We also measured the N and P in catfish gut contents and excreta and found that posterior gut (egesta) N:P was significantly higher than anterior gut (ingesta) N:P. Finally, we measured excreted N and P, finding that excreted N:P was high. These data demonstrate that, because high proportions of P are retained in the bodies of invasive armored catfish, they are a P sink and are, therefore, more likely to limit P availability than native fishes in freshwater spring ecosystems both in Florida and worldwide. [ABSTRACT FROM AUTHOR]

Microbial eukaryotes are diverse and ecologically important organisms, yet sampling constraints have hindered the understanding of their distribution and diversity in freshwater ecosystems. Metabarcoding has provided a powerful complement to traditional limnological studies, revealing an unprecedented diversity of protists in freshwater environments. Here, we aim to expand our knowledge of the ecology and diversity of protists in lacustrine ecosystems by targeting the V4 hypervariable region of the 18S rRNA gene in water column, sediment and biofilm samples collected from Sanabria Lake (Spain) and surrounding freshwater ecosystems. Sanabria is a temperate lake, which are relatively understudied by metabarcoding in comparison to alpine and polar lakes. The phylogenetic diversity of microbial eukaryotes detected in Sanabria spans all currently recognized eukaryotic supergroups, with Stramenopiles being the most abundant and diverse supergroup in all sampling sites. Parasitic microeukaryotes account for 21% of the total protist ASVs identified in our study and were dominated by Chytridiomycota, both in terms of richness and abundance, in all sampling sites. Sediments, biofilms and water column samples harbour distinct microbial communities. Phylogenetic placement of poorly assigned and abundant ASVs indicates molecular novelty inside Rhodophyta, Bigyra, early-branching Nucletmycea and Apusomonadida. In addition, we report the first freshwater incidence of the previously exclusively marine genera Abeoforma and Sphaeroforma. Our results contribute to a deeper understanding of microeukaryotic communities in freshwater ecosystems, and provide the first molecular reference for future biomonitoring surveys in Sanabria Lake. [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]

Intensive human exploitation of the Antarctic fur seal (Arctocephalus gazella) in its primary population centre on sub-Antarctic South Georgia, as well as on other sub-Antarctic islands and parts of the South Shetland Islands, in the eighteenth and nineteenth centuries rapidly brought populations to the brink of extinction. The species has now recovered throughout its original distribution. Non-breeding and yearling seals, almost entirely males, from the South Georgia population now disperse in the summer months far more widely and in higher numbers than there is evidence for taking place in the pre-exploitation era. Large numbers now haul out in coastal terrestrial habitats in the South Orkney Islands and also along the north-east and west coast of the Antarctic Peninsula to at least Marguerite Bay. In these previously less- or non-visited areas, the seals cause levels of damage likely never to have been experienced previously to fragile terrestrial habitats through trampling and over-fertilisation, as well as eutrophication of sensitive freshwater ecosystems. This increased area of summer impact is likely to have further synergies with aspects of regional climate change, including reduction in extent and duration of sea ice permitting seals access farther south, and changes in krill abundance and distribution. The extent and conservation value of terrestrial habitats and biodiversity now threatened by fur seal distribution expansion, and the multiple anthropogenic factors acting in synergy both historically and to the present day, present a new and as yet unaddressed challenge to the agencies charged with ensuring the protection and conservation of Antarctica's unique ecosystems. [ABSTRACT FROM AUTHOR]

Plastic wastes in the environment ultimately reach to the aquatic habitats and become available to aquatic organisms. The pathway of microplastic in aquatic ecosystem is very less investigated specially in freshwater. There have been evidences of MPs ingestion by freshwater biota but the fate of these MPs further in the food chain is unexplored. Thus, we reviewed the status of MPs in freshwater biota and tried to compare the studies to merge the available information, concepts, and perspectives in order to draw a conclusion on bioaccumulation potential, trophic transfer possibilities, biomagnification, and trends of ingesting MPs by the biota. In this review, the previously available information about MPs in aquatic biota is arranged, analyzed, and interpreted to understand all possible routes of MPs in freshwater habitats. The review further provides a better understanding about the lack of information and research gaps that are needed to be explored to develop a solution to the problem of MPs in near future. [ABSTRACT FROM AUTHOR]

Ultrasmall algae have attracted the attention of biologists investigating the basic mechanisms underlying living systems. Their potential as effective organisms for producing useful substances is also of interest in bioindustry. Although genomic information is indispensable for elucidating metabolism and promoting molecular breeding, many ultrasmall algae remain genetically uncharacterized. Here, we present the nuclear genome sequence of an ultrasmall green alga of freshwater habitats, Medakamo hakoo. Evolutionary analyses suggest that this species belongs to a new genus within the class Trebouxiophyceae. Sequencing analyses revealed that its genome, comprising 15.8 Mbp and 7629 genes, is among the smallest known genomes in the Viridiplantae. Its genome has relatively few genes associated with genetic information processing, basal transcription factors, and RNA transport. Comparative analyses revealed that 1263 orthogroups were shared among 15 ultrasmall algae from distinct phylogenetic lineages. The shared gene sets will enable identification of genes essential for algal metabolism and cellular functions. Multi-omic and evolutionary analyses of the ultrasmall green algae, Medakomo hakoo, suggest that it might belong to a new genus within the class Trebouxiophyceae and provide further insight into the essential genes for microalgae. [ABSTRACT FROM AUTHOR]

It has been well documented that periphyton communities play a key role in primary productivity, nutrient cycling, and food web interactions. However, a worldwide overview of research on the key themes, current situation, and major trends within the field is lacking. In this study, we applied the machine learning technique (latent Dirichlet allocation, LDA) to analyze the abstracts of 6690 publications related to periphyton from 1991 to 2020 based on the Web of Science database. The relative frequency of classical and basic research on periphyton related to colonization, biomass, growth rate, and habitats has been clearly decreasing. The increasing trends of research on periphyton are embodied in the periphyton function in freshwater ecosystems (e.g., application as ecological indicators, function in the removal of nutrients, and application in paleolimnology), the research at macroscales (e.g., spatial–temporal variation, and functional and taxonomic diversity), and the anthropogenic themes (e.g., climate warming, response to multiple stressors, and land use type). The keyword and title analysis showed that the periphyton studies are concentrated mainly on diatom aspects, especially with respect to streams relative to lakes. The thematic space based on non-metric multidimensional scaling (NMDS) showed that the classical themes such as growth rate, colonization, and environmental factors (e.g., multiple stressors and climate warming) were most linked to other research themes. We proposed that future trends in the periphyton should focus on the function of periphyton in lakes and their response to multiple environmental pressures with the increasingly extensive eutrophication in lakes and the increasingly significant change in the climate. [ABSTRACT FROM AUTHOR]

Neotropical freshwater stingrays (subfamily Potamotrygoninae) are carnivorous bottom feeder batoids widely distributed in most river basins of South America. They represent the unique extant group of elasmobranchs that evolved to live exclusively in freshwater environments. These species are exploited either by commercial fisheries (e.g., for food or ornamental industry) or by indigenous communities allocated along with their natural range. Restrictive life history characteristics coupled with habitat degradation make Potamotrygoninae species highly vulnerable to human impacts and highlight the necessity of studies to inform basic biological aspects, from ecology to genetics, to guide their conservation and clarify the molecular basis of adaptation to the freshwater environment. We used available and newly assembled Potamotrygon spp. mitogenomes to perform a comparative investigation of their molecular evolution. A phylogenetic estimation using the mitogenome of Potamotrygon falkneri and other Elasmobranchii supports monophyly for Potamotrygonidae and indicates a close relationship to Dasyatidae. A synteny analysis comprising 3 Potamotrygon and other 51 batoids revealed a highly conserved mitogenomic context. We detected various amino acid sites under positive selection exclusively in Potamotrygon spp., within the sequences of ND4, ND5, ND6, and COXII genes. Positively selected mutational events in key genes of energetic metabolism may be related to the physiological adaptation of Potamotrygon spp. during the ancient incursion into freshwater. This broad comparative mitogenomic study provides novel insights into the evolutionary history of neotropical freshwater stingrays and their relatives and stands out as a valuable resource to aid in current and future research on elasmobranch molecular evolution. [ABSTRACT FROM AUTHOR]

Identifying and quantifying global change impacts on biotic and abiotic components of ecosystems is critical to promote an effective adaptation that increases the success of conservation strategies. To achieve this goal, global and regional assessment efforts require certain degree of harmonization on local monitoring programs to establish relevant comparisons at different spatio-temporal scales. Otherwise, the lack of harmonization might hinder the detection and assessment on the effects of human impacts. In this work we have compiled information on freshwater monitoring programs located in areas of intensive research and conservation interest: International Long Term Ecological Research (ILTER) nodes and mountain National Parks. We aimed at evaluating the quality and robustness of these programs to assess the impact of global change, addressing from the worldwide to the European and Spanish national scale. Results highlighted that freshwater monitoring programs lack a common strategy to monitor these ecosystems. Even at the continental and national scales, contrasting strategies and level of detail have been historically applied. Water quality, habitat and biodiversity are more commonly monitored than community structure and ecosystem functioning. Monitoring efforts on the Spanish Mountain National parks indicated differences on the targeted aquatic ecosystems. Rivers and lakes received a higher attention, while mires were rarely considered. Our results provide evidence that greater efforts should be directed towards constructing a coordinated strategy to monitor freshwater ecosystems at national, continental, and global scales. This strategy should involve a shared backbone of biophysical and biogeochemical variables for each habitat type on agreed protocols that are implemented across regions and administrative borders. Achieving this will support a substantial advance on the ecological research to further delineate proper conservation strategies to face the challenges imposed by global change. [ABSTRACT FROM AUTHOR]

The European eel is a facultative catadromous species, meaning that it can skip the freshwater phase or move between marine and freshwater habitats during its continental life stage. Otolith microchemistry, used to determine the habitat use of eel or its salinity history, requires the sacrifice of animals. In this context, blood-based gene expression may represent a non-lethal alternative. In this work, we tested the ability of blood transcriptional profiling to identify the different salinity-habitat histories of European eel. Eels collected from different locations in Norway were classified through otolith microchemistry as freshwater residents (FWR), seawater residents (SWR) or inter-habitat shifters (IHS). We detected 3451 differentially expressed genes from blood by comparing FWR and SWR groups, and then used that subset of genes in a machine learning approach (i.e., random forest) to the extended FWR, SWR, and IHS group. Random forest correctly classified 100% of FWR and SWR and 83% of the IHS using a minimum of 30 genes. The implementation of this non-lethal approach may replace otolith-based microchemistry analysis for the general assessment of life-history tactics in European eels. Overall, this approach is promising for the replacement or reduction of other lethal analyses in determining certain fish traits. [ABSTRACT FROM AUTHOR]

In an increasingly urbanized world, there is a need to study urban areas as their own class of ecosystems as well as assess the impacts of anthropogenic impacts on biodiversity. However, collecting a sufficient number of species observations to estimate patterns of biodiversity in a city can be costly. Here we investigated the use of community science-based data on species occurrences, combined with species distribution models (SDMs), built using MaxEnt and remotely-sensed measures of the environment, to predict the distribution of a number of species across the urban environment of Los Angeles. By selecting species with the most accurate SDMs, and then summarizing these by class, we were able to produce two species richness models (SRMs) to predict biodiversity patterns for species in the class Aves and Magnoliopsida and how they respond to a variety of natural and anthropogenic environmental gradients. We found that species considered native to Los Angeles tend to have significantly more accurate SDMs than their non-native counterparts. For all species considered in this study we found environmental variables describing anthropogenic activities, such as housing density and alterations to land cover, tend to be more influential than natural factors, such as terrain and proximity to freshwater, in shaping SDMs. Using a random forest model we found our SRMs could account for approximately 54% and 62% of the predicted variation in species richness for species in the classes Aves and Magnoliopsida respectively. Using community science-based species occurrences, SRMs can be used to model patterns of urban biodiversity and assess the roles of environmental factors in shaping them. [ABSTRACT FROM AUTHOR]

Many flatfish species are partially euryhaline, such as the Pacific sanddab which spawn and feed in highly dynamic estuaries ranging from seawater to near freshwater. With the rapid increase in saltwater invasion of freshwater habitats, it is very likely that in these estuaries, flatfish will be exposed to increasing levels of dissolved organic carbon (DOC) of freshwater origin at a range of salinities. As salinity fluctuations often coincide with changes in DOC concentration, two natural freshwater DOCs [Luther Marsh (LM, allochthonous) and Lake Ontario (LO, autochthonous) were investigated at salinities of 30 and 7.5 ppt. Optical characterization of the two natural DOC sources indicate salinity-dependent differences in their physicochemistry. LO and LM DOCs, as well as three model compounds [tannic acid (TA), sodium dodecyl sulfate (SDS) and bovine serum albumin (BSA)] representing key chemical moieties of DOC, were used to evaluate physiological effects on sanddabs. In the absence of added DOC, an acute decrease in salinity resulted in an increase in diffusive water flux (a proxy for transcellular water permeability), ammonia excretion and a change in TEP from positive (inside) to negative (inside). The effects of DOC (10 mg C L-1) were salinity and source-dependent, with generally more pronounced effects at 30 than 7.5 ppt, and greater potency of LM relative to LO. Both LM DOC and SDS increased diffusive water flux at 30 ppt but only SDS had an effect at 7.5 ppt. TA decreased ammonia excretion at 7.5 ppt. LO DOC decreased urea-N excretion at both salinities whereas the stimulatory effect of BSA occurred only at 30 ppt. Likewise, the effects of LM DOC and BSA to reduce TEP were present at 30 ppt but not 7.5 ppt. None of the treatments affected oxygen consumption rates. Our results demonstrate that DOCs and salinity interact to alter key physiological processes in marine flatfish, reflecting changes in both gill function and the physicochemistry of DOCs between 30 and 7.5 ppt. [ABSTRACT FROM AUTHOR]

Humans and ecosystems are deeply connected to, and through, the hydrological cycle. However, impacts of hydrological change on social and ecological systems are infrequently evaluated together at the global scale. Here, we focus on the potential for social and ecological impacts from freshwater stress and storage loss. We find basins with existing freshwater stress are drying (losing storage) disproportionately, exacerbating the challenges facing the water stressed versus non-stressed basins of the world. We map the global gradient in social-ecological vulnerability to freshwater stress and storage loss and identify hotspot basins for prioritization (n = 168). These most-vulnerable basins encompass over 1.5 billion people, 17% of global food crop production, 13% of global gross domestic product, and hundreds of significant wetlands. There are thus substantial social and ecological benefits to reducing vulnerability in hotspot basins, which can be achieved through hydro-diplomacy, social adaptive capacity building, and integrated water resources management practices. This work identifies the world's most vulnerable basins to social and ecological impacts from freshwater stress and storage loss: a set of 168 hotspot basins for global prioritization that encompass 1.5 billion people, 17% of global food crops, 13% of global GDP, and hundreds of significant wetlands. [ABSTRACT FROM AUTHOR]