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Adaptation to different ecological niches is considered one of the main drivers of species diversification, also in cryptic species complexes, notwithstanding their morphological stasis. We here review all the published information on ecological differentiation within cryptic species complexes within the phylum Rotifera. We found 177 instances of cryptic species identified genetically, published in 101 papers. Only a subset of the papers contained available information on ecological differences and only for two of the 54 known complexes, namely Brachionus calyciflorus s.l. and Brachionus plicatilis s.l., sufficient data were available for analyses of ecological differences. For the B. calyciflorus complex, B. fernandoi consistently occurred at a significantly lower temperature than the other species in the complex; no differences were found for other environmental variables. For the B. plicatilis complex, B. paranguensis occurred in waters with higher pH than the other species; no differences were found for other environmental variables. These results, even if preliminary and based on scattered information, reveal that adaptation to different ecological niches exists also between closely related species. Our aim is to showcase this interesting field of research spurring further detailed studies to focus on the mechanisms of ecological speciation using rotifer cryptic species as a model system. [ABSTRACT FROM AUTHOR]

The feeding upon large animals—even larger than the predator—by benthic cnidarians has been reported from many ecosystems but never exhaustively studied to date. By reviewing 38 papers on this topic, this review aims to recap the observations on the predatory behaviour of polyps, to establish feeding plasticity boundaries and to understand the contribute of this trophic strategy to the benthic–pelagic coupling. The reviewed documents published increasingly during the last two decades mostly reported observations on heterotrophic Anthozoa in shallow ecosystems collected through photo/video records. The main prey items are represented by gelatinous zooplankton and echinoderms. The lexical discordance in the considered papers highlights the need to standardize the terminology to describe the feeding behaviour of benthic Cnidaria, opportunistic and characterized by a strong plasticity. Given the importance of large prey in cnidarian trophism, we proposed an unambiguous terminology that will help the online search of literature and address future studies. We suggest identifying micro-predation (predator/prey size ratio ≥ 5:1) and macro-predation (predator/prey size ratio is ≤ 1:1) as distinct feeding modalities, because the capture of large prey involves peculiar movements of polyps, such as stretching and retracting of column and tentacles to pull the prey towards the mouth. [ABSTRACT FROM AUTHOR]

Most information on rotifers living in lake sands comes from the 1930s, when the first reports on this subject by Jerzy Wiszniewski appeared. After some decline in the interest in lake psammon in the following years, research on lake psammon returned in the last decade of the twentieth century. The last comprehensive review of ecology of psammon Rotifera was included in the excellent 1998 publication by Schmid-Araya on Rotifera in interstitial sediments. More than 20 papers have been published since that time. So far, research conducted almost exclusively in the northern hemisphere have dealt with issues related to distribution of rotifers, their species structure and diversity as well as to their relation to abiotic and biotic factors. The aim of the present study was to collect all available information on psammon rotifers, assess the shortcomings in our knowledge and fill these gaps with the results of some of my recent research. The results of the study show that the species richness of this group in geographical terms is still unknown. It means we also do not know the level of endemism among the psammon rotifers. The role of psammon rotifers in benthic food webs is another issue requiring research. [ABSTRACT FROM AUTHOR]

Studies on zooplankton in lakes, ponds, and rivers have always received more attention, while zooplankton from streams remains understudied worldwide. Therefore, the role of zooplankton in neotropical stream functioning is still poorly understood. In order to remedy this situation, we aimed to answer the following questions: (1) How many papers have been published on the zooplankton from Brazilian streams? (2) In which hydrographic regions were these studies conducted? (3) Are there specific patterns of zooplankton species occurrence in neotropical streams? (4) What are the main types of studies and what are the main environmental factors influencing zooplankton in streams? In order to answer these questions, we performed a systematic review of indexed scientific papers. We indeed observed a paucity of studies on zooplankton in Brazilian streams. But despite the low number of studies (24), many species (276 taxa) were reported from seven Brazilian hydrographic regions. The species composition showed great variability within the hydrographic regions and fourteen environmental variables (physical, chemical, and spatial), which can represent environmental filters and influence dispersion processes, were related to zooplankton occurrences. These bibliographic data helped to clarify patterns in species composition and community structure of zooplankton in these streams. More studies are needed to further investigate the role of zooplankton in neotropical streams, which can help to develop conservation strategies. [ABSTRACT FROM AUTHOR]

This paper introduces and summarises the main outcomes of the 19th workshop of the International Association for Phytoplankton Taxonomy and Ecology held in Tiszafüred, Hungary, Tisza Balneum Hotel, from 23 to 30 September 2022. The selected theme of the workshop was "Trait-Based Approaches in Micro-Algal Ecology". The discussions presented during the workshop sessions resulted in the 18 articles contained in this Special Issue. There are 6 main thematic aspects developed by the participants: 1. Shape and size: are these traits easy to measure? 2. Spatial scales: when and where to look for microalgae? 3. Climate and extremes of ecological gradients: hot topics of this century. 4. Metaphyton and metaphytic habitats: life beyond plankton and benthos. 5. Microalgae in water management: phycology in practice. 6. Traditional and new methods: perspectives and comments. Trait-based approaches in microalgae ecology, although requiring further investigation and methodological development, represent a valid tool for refining the analysis of environmental variability in aquatic ecosystems. The papers presented in this Special Issue demonstrate that these approaches are extremely useful not only in the study of planktic algae but constitute a thoughtful method for the analysis of benthic and metaphytic microalgae in a wide variety of aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of phytoplankton assemblages in various and variable aquatic ecosystems is of paramount importance, given the strategic supporting services offered by these organisms. Such knowledge is implicitly based on the analysis of the realized niche of the different populations, i.e. of the sets of conditions within which populations show a positive growth. The range of phytoplankton morphological traits variability is evolutionarily selected to maximize the ecological performance of species while they are entrained in the spectrum of turbulent flows. In addition, most phytoplankton species exhibit high morphological plasticity that can further optimize their performance under reduced environmental variability. Although this plasticity is well known, it is seldom considered in phytoplankton studies. Morphological analysis could therefore be used as a tool to estimate the environmental variability within which a species can persist and, ultimately, the niche width of phytoplankton populations. This opinion paper tries to answer the questions: to what extent can the morphological variability of phytoplankton offer a synthesis of the environmental variability of aquatic ecosystems?. Do the morphological traits contain sufficient information to describe the width of the realized niche of phytoplankton species? What can we do to fill eventual gaps in our knowledge? [ABSTRACT FROM AUTHOR]

Invasion of non-native fishes threatens freshwater biodiversity worldwide. Yet, detailed estimates of population demography for invasive species, such as population size and body size, are rarely integrated in evaluating aquatic community responses. Our study capitalised on detailed brook trout population demographic data collected for a replicated whole lake ecosystem experiment involving experimental harvesting of exotic brook trout in nine mountain lakes. We applied environmental DNA (eDNA) metabarcoding and morphological taxonomy to examine the response of crustacean zooplankton and macroinvertebrate communities to gradients in brook trout effective density and lake elevation. Density-dependent effects of brook trout on crustacean zooplankton and macroinvertebrate communities were detected even decades after their first introductions (between 1926 & 1980). However, they were moderated by environmental factors such as elevation, lake maximum depth and dissolved organic carbon. Elevation was important in structuring crustacean zooplankton and macroinvertebrate community composition. While there were differences in explanatory variables when describing communities characterized by eDNA metabarcoding and morphological taxonomy, the principal environmental factors that structured the communities were similar. Our paper highlights persisting density-dependent impacts of exotic trout on invertebrate communities even decades after first introduction, and it considers the conservation implications for lake restoration. [ABSTRACT FROM AUTHOR]

The application of modern molecular methods and phylogenetic approaches saw an explosion in cyanobacterial taxonomy in the first two decades of the twenty-first century. The relative ease of description of new taxa and the pressure to publish a high number of scientific papers has created apparent confusion. The situation is particularly complicated for ecologically oriented limnological research and practical hydrobiologists especially have numerous criticisms of this trend. On closer observation, however, the situation is not as tragic as it first appears. More than a thousand new species have been discovered or renamed and only 18 percent are freshwater planktonic species, which garner the most interest in routine analyses. Most new taxa are described from terrestrial habitats. Despite the increase in studies from tropical areas, most of the new species are from the temperate zone, which probably does not account for the reality. Significant advances in modern taxonomy are visible mainly for the trichal types, but other groups such as the pleurocapsal species are considerably less studied. In this article I try to show that, despite all the difficulties and limitations, it is not necessary to consider these rapid changes as a complication in common cyanobacteriological research. [ABSTRACT FROM AUTHOR]

This document is a preface to a special issue of the journal Hydrobiologia on the topic of stream ecology and environmental gradients. The preface explains that human activities have fragmented natural landscapes, leading to changes in environmental gradients and a decline in biodiversity. The document highlights the importance of understanding the effects of environmental gradients on aquatic communities and ecosystem services. The special issue includes 10 papers from authors of various nationalities, focusing on the effects of land use, vegetation cover, water pollution, and other disturbances on diatoms, macroinvertebrates, and fish communities. The studies demonstrate that environmental gradients can alter water quality, habitat availability, and the structure and composition of aquatic communities. The document concludes by expressing gratitude to the reviewers and authors who contributed to the special issue. [Extracted from the article]

The text is a preface to a special issue of the journal Hydrobiologia, titled "Trait-Based Approaches in Micro-Algal Ecology." The preface provides an overview of the 19th workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP), which focused on trait-based approaches in micro-algal ecology. The workshop brought together scientists and students from various countries to discuss ecological topics and practice species identification. The preface also mentions the history of the IAP workshops and the special issue's dedication to Colin S. Reynolds, a prominent phytoplankton ecologist. The special issue includes a selection of review and research papers covering a wide range of spatial and temporal scales and aquatic habitats. The authors express gratitude to the referees, editorial staff, and workshop participants. [Extracted from the article]

This correction notice addresses errors in a previously published article titled "Effect of Mississippi River discharge plume on temporal and spatial variability of toxic cyanobacteria in an oligohaline estuary." The errors involve the calculation of flushing times using a specific equation, which resulted in incorrect values being reported in the original article. The correction provides the accurate flushing times associated with the spillway openings in 2019. Despite the correction, the overall conclusion of the article remains unchanged, highlighting the significant impact of spillway openings on flushing times. The corrected values align more closely with predictions from numerical modeling. [Extracted from the article]

Stygobionts, namely animals with strong adaptations to subterranean environments that are unable to complete their life cycles outside groundwater, can be observed in spring ecotones, but their occurrence is generally considered accidental. The aim of this paper is to assess if stygobiont occurrence in springs is linked to specific environmental conditions or if it is random, irrespective of their features. For three years, we surveyed 59 spring sites recording the occurrence of vertebrate and invertebrate stygobiont species and assessing if spring features were related to their distribution. Moreover, we recorded the escape reactions of two easily identifiable stygobiont species. We detected six taxa usually considered as strictly stygobiont based on their troglomorphic features. Two of them were quite widespread: the salamander Proteus anguinus and the shrimp Troglocaris planinensis. Environmental characteristics were significantly related to the distribution of stygobionts. Hydroperiod and occurrence of flooding were the factors that played the strongest role in affecting occurrence. Our study suggests that the occurrence of stygobionts in springs is linked to specific habitat features rather than being a random mechanism and that the exploitation of ecotones can be important for the lifecycle of some species usually assumed to be strictly associated to caves. [ABSTRACT FROM AUTHOR]

Anthropic structures have been deployed in aquatic environments for the most variable purposes. Here, we review the use of artificial aquatic habitats (AAHs) worldwide through a systematic and comprehensive search of peer-reviewed literature. We aimed to synthesize the knowledge on the subject, identify gaps, and propose new perspectives for future research. In total, 460 peer-reviewed papers from 1972 to mid-2016 were included in our systematic review. Field studies carried out in marine temperate environments were predominant, whereas fewer efforts have been made in marine tropical and freshwater ecosystems. Experimental habitats made of concrete were the most common artificial structures. Visual census was the most used sampling method, and there was a dominance of short-term (< 12 months) and shallow waters (< 5 m depth) studies. Fish was the most studied group (18%), whereas tunicates encompassed the large proportion of non-native species associated with AAHs (32.9%). Although idealized for the promotion of biodiversity, AAHs have been serving as stepping stones for non-native invasive species, facilitating biotic homogenization by increasing the connectivity of hard-bottom systems. The scarcity of studies in coastal tropical and freshwater ecosystems, as well as the efforts with reduced temporal scales and restricted depths, calls for future research to better understand the role of artificial habitats, especially in climate change scenarios. In this sense, we provide a conceptual framework exploring major issues regarding AAHs, including biodiversity status, ecosystem services, and climate change, in order to guide future research and assist conservation measures. [ABSTRACT FROM AUTHOR]

Exceptional resistance to dehydration allows species of bdelloid rotifers to tolerate desiccation stress in unpredictable habitats. The roles of exogenous and endogenous factors in resistance to short-term dehydration were investigated in Rotaria rotatoria to better understand this capacity among bdelloid rotifers. As the dehydration period was increased and the relative humidity (RH) was reduced, the proportion of rotifers active after the dehydration period decreased. The RH and dehydration period substantially influenced the recovery rate of R. rotatoria under rehydration for 1 h but had less effect under 12-h or 24-h rehydration treatment. The recovery rate was lower in rotifers subjected to a long dehydration period and short rehydration time, but improved by shortening the dehydration period and extending the rehydration treatment. Strain ZJ27 showed higher survivability than strain HX8, appropriate to their habitat near the sea in a region where drought and tropical rainstorms are frequent. Accordingly, species or strains originating from different climate regions and habitats will have experienced different frequencies of desiccation over their adaptive evolutionary history, resulting in varying levels of resistance among species. In addition, RH is shown to be a key factor in resistance to desiccation. [ABSTRACT FROM AUTHOR]

Zooplankton indicators based on rotifers (TSIROT) and an indicator based on Secchi disk visibility (TSISD) were used to assess trophic state changes in artificial, slow-flowing, and stagnant canal waters. The study was conducted in the summers of 2019, 2021, and 2022 in the Bydgoszcz Canal and the Noteć Canal (Poland). Water samples were taken from five sites once in the month of July and once in August. In terms of the species number and density, rotifers dominated among zooplankton (at almost all sites), which reflected the high trophic state. Our results showed statistically significant correlations between TSIROT and TSISD as well as between the individual indicators TSIROT1 (Rotifer numbers), TSIROT2 (Rotifer biomass), TSIROT3 (bacterivorous numbers of rotifers), TSIROT6 (rotifers indicating high trophic state), and TSISD. According to our study, the presented indices most likely determine the trends between TSIROT cumulative and TSISD in the studied canals. Similarly to previous studies performed on lakes and small reservoirs, zooplankton constituted a useful indicator of trophic state. It seems that, for stagnant and slowly flowing waters of canals such as the Bydgoszcz Canal and the Noteć Canal, the method of zooplankton trophic status indicators based on rotifers may be applied. [ABSTRACT FROM AUTHOR]

Most species of Keratella possess dome-shaped, dorsal plates comprising a network of polyhedral units (facets), delineated by slightly raised ridges. The arrangement of facets define a species' facet pattern (FP), with the resulting structure resembling a geodesic dome. Researchers have sorted species into categories based on their FPs, but those have not been analyzed. Additionally, while a strong lorica has been suggested to protect Keratella from predatory attack or other actions causing blunt force trauma (BFT), we know little of how that occurs. Thus, in our study we tested two hypotheses. (1) There is support for categorizing Keratella species into unique groupings based on their FPs. (2) FPs provide resistance to physical stresses. To test that hypothesis we used the structural analysis software SkyCiv©. Our results indicate support for four FP categories. Additionally, the SkyCiv analysis provided preliminary 'proof-of-concept' that Keratella FPs have a functional significance: i.e., adding or subtracting facets in our model was followed by a change in predicted structural reliability. We posit that FPs are adaptations protecting Keratella from fractures to the lorica that may result from BFT incurred during predatory attack by copepods or while caught within the branchial chambers of daphnids. [ABSTRACT FROM AUTHOR]

Differences between peak-season and off-season dry mass, organic matter mass, and both concentrations and pools (standing stocks) of ash, N, P, K, Ca, Mg and Na were investigated in the rhizosphere soil, and live and dead aboveground plant biomass at 14 sites hosting 4 plant community types in the littoral zone of a eutrophic ancient shallow reservoir of about 5 km2 area, the Rožmberk fishpond (S. Bohemia, CZ). Comparisons between the peak-season and off-season data and several stoichiometric relations calculated from them provided an insight into the mineral nutrient economy of the examined types of the fishpond littoral vegetation. It is rooted in relatively nutrient-poor sandy soil, but differently enriched with nutrients contained in either the percolating fishpond water, or that of springs located at the landward edge of the littoral zone. The degree of eutrophication of our sampling sites and their vegetation thus seem to be positively correlated with the degree of contact of the plants´ rhizosphere with the nutrient-richer fishpond or spring water. [ABSTRACT FROM AUTHOR]

Low-order streams and riparian wetlands are important contributors to the drainage network in the landscape. However, there has been little research into the nature of these ecosystems in Brazil. Our estimates show that riparian wetlands of low-order streams and other small associated wetlands cover at least 25% of the forested part of the Amazon basin and about 10% of the Cerrado region. Information on the semi-arid Caatinga is lacking, but ~ 3% of the area may be occupied by riparian wetlands and other small wetland types, many of which are periodically dry. Riparian vegetation includes a very large richness in tree species. The amount and species richness of herbaceous plants depend on light availability. In-streams of the semi-arid region of Brazil, hydrophytes are restricted by unpredictable flash floods and periodic drought. Aquatic food webs are largely based on the organic matter produced by the riparian vegetation. Large-scale agriculture and cattle ranching pose a serious threat to riparian wetlands, their biodiversity, and their function as a buffer in the hydrological cycle of the landscape. A nation-wide screening program would provide a more detailed picture and allow the elaboration of a national conservation and restoration program for the Brazilian riparia. [ABSTRACT FROM AUTHOR]

As a result of a field trip in 1980 to the monsoonal wetland of the Keoladeo National Park, India, which was organized by Dr. Brij Gopal, a study of the vegetation dynamics of this wetland was initiated. The original hypothesis for this study was that the seasonal vegetation changes caused by the annual summer monsoon was a compressed habitat cycle. Habitat cycles are a characteristic of prairie potholes in North America. Habitat cycles are the result of wet–dry cycles that last from 5 to 25 years during which the vegetation of a pothole changes from dense emergent vegetation (dry years) to open water with only submerged vegetation (wet years). In retrospect, our field studies were not consistent with our hypothesis. The increase in water level caused by the monsoon was not large enough to kill the emergent vegetation, as happens during prolonged high-water years in prairie potholes. However, both wetland types have significant seed banks that allow their plant species to survive adverse conditions. We now believe that the vegetation dynamics of monsoonal wetlands are best described as seasonal shifts between a wet marsh phase when the wetland is flooded and a dry grassland phase when it is not. [ABSTRACT FROM AUTHOR]

Seedlings of two species of mangroves, Bruguiera gymnorrhiza and Rhizophora apiculata, were monitored for 8 years on the Pacific island of Kosrae, Federated States of Micronesia, to determine the effects of canopy cover and hydrogeomorphic zone on long-term survival and growth. Annual rainfall is high with little seasonality. Study plots with seedling subplots were in fringe, riverine, and interior hydrogeomorphic zones along four small rivers. The height of each seedling was measured each year and was designated each time as being under an open, partially closed, or closed canopy. Growth rates of both species were slow, and no seedling that was newly established during the study became a sapling (2 m). Many seedlings stopped growing for long periods of time. Bruguiera seedlings were more numerous than Rhizophora seedlings. They grew faster than Rhizophora seedlings except in riverine zones. Predicted growth rates of Bruguiera were fastest under an open canopy and slowest under a closed canopy, but Rhizophora was not affected by canopy status. Overall mortality rates for the two species were similar, averaging 36% year−1. El-Niño-Southern Oscillation events did not affect growth or mortality but may have caused some defoliation. [ABSTRACT FROM AUTHOR]

Salinity control, nutrient additions, and sediment supply were directly or indirectly the rationale for a $220 million coastal wetland restoration project (Davis Pond River Diversion) that began in 2002. We sampled Mississippi River water going in and out of the receiving basin from 1999 to 2018 to understand why wetland loss increased after it began. There was a reduction in inorganic sediments, nitrogen (N), and phosphorus (P) concentrations within the ponding area of 77%, 39% and 34%, respectively, which is similar to that in other wetlands. But the average sediment accumulation of 0.6 mm year−1 inadequately balances the present-day 5.6 mm year−1 sea level rise or the 7.9 ± 0.13 mm year−1 accretion rates in these organic soils. Nutrients added likely reduced live belowground biomass and soil strength, and increased decomposition of the organic matter necessary to sustain elevations. The eutrophication of the downstream aquatic system from the diversion, principally by P additions, increased Chl a concentrations to a category of 'poor' water quality. We conclude that this diversion, if continued, will be a negative influence on wetland area and will eutrophy the estuary. It is a case history example for understanding the potential effects arising from proposed river diversions. [ABSTRACT FROM AUTHOR]

The bioturbation potential of three freshwater operculate snails, Filopaludina bengalensis, Gabbia orcula and Melanoides tuberculata, was compared, using water column depth and sediment surface area as the explanatory variables. Assessment of nutrient fluxes from sediment to overlying water was estimated in glass microcosms, that varied in height (tall, medium, short) and base (narrow, wide), resulting in six habitat conditions. In course of movement and grazing, all the three snail species modified surface architecture of the sediment. Besides, the snails modulated NOXˉ (NO2ˉ-N + NO3ˉ-N), NH4+-N and PO43−-P concentrations and other parameters (TDS, conductivity) of the water column in significantly varying proportions. Snail-induced changes in the rate of nutrient flux were highest for F. bengalensis. Periphytic chlorophyll-a concentration was reduced in all snail-treated microcosms compared to the control. Grazing, scraping and movement of snails on sediment facilitated the release of the nutrients in a species-specific manner depending on sediment surface area and water column depth of the microcosm. Apparently, snails may be useful in mobilizing the sediment content in freshwater lakes and ponds, facilitating ecosystem processes. [ABSTRACT FROM AUTHOR]

Despite advances in phytoplankton ecology through functional approaches, little is known about functional traits highlighting metacommunity processes. Our aim was to highlight and compare the influence of spatial and local environmental factors in a phytoplankton metacommunity, in a subtropical shallow lake system, based on taxonomic composition and different functional trait measures. Environmental filtering significantly explained metacommunity variation in most approaches. The spatial signal found could be interpreted as mass effects, given the scale of the present study, and was also a significantly driver of community variability. Among the functional measures, Morphology-Based Functional Groups revealed a stronger influence of the pure environmental component. Although the taxonomic approach helped capture variability in the local environment in a reliable way, it also showed the highest residual variance. Phytoplankton volume significantly captured both local and spatial processes under low residual variance, which may make it a promising functional trait for metacommunity studies. Our findings demonstrated that the drivers of phytoplankton metacommunity may be differently captured by taxonomic and functional measures, so that the approaches can eventually give more or less weight to the environmental and/or spatial signals. We thus recommend the use of taxonomic and functional approaches in metacommunity studies in a complementary way. [ABSTRACT FROM AUTHOR]

Long-term ecological research of deep Lake Mondsee covers over more than six decades of phytoplankton observation. According to our study, phytoplankton groups of various phenological traits are suitable to address the impact of two major environmental stressors: nutrient surplus by eutrophication from 1968 to 1998 and warming by climate change. Here, we focus on phytoplankton biovolume, phytoplankton assemblage structure, net changes rates, and phytoplankton biodiversity. Biweekly net change-dependent persistence of phytoplankton assemblages followed a dome-shaped relationship of observations. A short-term persistence of taxonomic traits along weeks is predominant and contributes to the structural stabilization of phytoplankton assemblages. This short-term persistence is interpreted by the benefit of lifetime adjustment of phytoplankton organisms. The long-term development phytoplankton structure is discussed as an alignment of organisms over generations. Single key taxa, as Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis &Komárek 1988, which are omnipotent players in phytoplankton assemblages and occur during different environmental scenarios in the long-term, are most suitable for long-term ecological research. Our findings interpret that phytoplankton taxa are excellent organisms to track the impact of environmental constraints due to their short generation time (1), their lifetime adjustment (2), and the re-occurrence in the long-term over generations (3). [ABSTRACT FROM AUTHOR]

In 2019, phytoplankton and environmental parameters were analysed monthly during the growing season from April to September at 26 sampling sites in the Danube and 10 additional sampling sites in the main tributaries as part of the Joint Danube Survey 4, organised by the ICPDR. Our results showed that both phytoplankton biomass and composition follow the River Continuum Concept on free-flowing sections, but also responds to hydromorphological changes where the largest dam Iron Gate represents the largest interruption of the river and the phytoplankton continuum. Besides longitudinal interruption, water residence time was the most important factor for phytoplankton composition, while nutrients were less relevant. The low phytoplankton biomass and its composition in the Danube support the oligotrophication trend, but this one-year study could not confirm it with certainty. Phytoplankton is the most important autotrophic component in the Upper and Middle Danube, where environmental conditions do not support the optimal growth of other river flora. The predominant FGs coda were A, C and D as a typical potamoplankton component, while the codon TB occurs throughout the Danube but is more prominent in the Upper reach and other river sections with higher discharge events. [ABSTRACT FROM AUTHOR]

In phytoplankton ecology the shape of microalgae appears predominantly as a categorical variable. Using shape-realistic 3D models of 220 microalgae we proposed and calculated six shape metrics and tested how these relate to each other and to the size of the microalgae. We found that some of the metrics are more sensitive to elongation, while others are related to multicellularity. We found a linear relationship between shape measures and the greatest axial linear dimensions of the microalgae. Our findings suggest that there is an evolutionary trade-off between the shape and size of the microalgae. It is important to stress that we found that surface area to volume ratio of the microalgae are hyperbolic functions of the length and volume for each shape. In our study, we demonstrated that the proposed shape metrics serve as suitable quantitative traits, and help to understand better how simple shapes evolved to more complex outlines. [ABSTRACT FROM AUTHOR]

Diverse macrovegetation can provide heterogeneous habitats for benthic diatoms. The removal of macrophytes as direct plant control, however, can be considered as a threat, which can even lead to remarkable microhabitat alterations. Lake Tisza (Hungary) has a high nature conservation value, but it is also an important recreation centre, which is why very delicate water management is necessary including vegetation thinning. Here, we studied the importance of microhabitat heterogeneity (emergent, submerged and floating macrophytes) in maintaining diverse periphytic diatom assemblages. We hypothesized that the substrate type has greater influencing role on the composition and diversity of diatoms than the lake heterogeneity related to basins. We also assumed that floating vegetation hosts the most different and least diverse diatom assemblages. Our results mostly proved these hypotheses. Heterogeneous assemblages were formed on the different substrates (support hypothesis), however, the basin level differences were also detected (reject hypothesis). Our results also highlighted, that macrophyte species with lesser morphological complexity hosted the least diverse periphytic assemblages (support hypothesis). However, many unique and red list taxa were found on floating plants (reject hypothesis). These findings emphasize the key role of microhabitat complexity in maintaining diverse and healthy functioning of microbial assemblages in a multi-purpose reservoir. [ABSTRACT FROM AUTHOR]

Phytoplankton is one of the five biological quality elements used to assess the ecological status of lakes within the Water Framework Directive. Classical morphological Utermöhl method and eDNA metabarcoding by Ilumina sequencing the hypervariable V9 region of the eukaryotic SSU rRNA gene were used to analyse the qualitative and quantitative composition of the phytoplankton and compared at the taxonomic and FG level to highlight advantages and disadvantages of eDNA metabarcoding method over classical microscopy. Samples were collected from April to September in seven Croatian natural karst lakes. Cluster analysis based on the Bray–Curtis similarity of taxa biomass (microscopy) and number of sequences (eDNA metabarcoding) clearly separated lakes showing that eDNA metabarcoding is sensitive to species change. Overlap at the species level between methods was found primarily in the taxa of Cryptophyta, Miozoa, and Ochrophyta, while some very common taxa of Bacillariophyta, Charophyta, and Chlorophyta identified by microscopy were not detected by eDNA metabarcoding, possibly due to incompleteness of the reference databases. At a higher organizational level, the results showed poor overlap of taxonomic and functional group composition and poor comparability of relative biomass to relative number of sequences, indicating the need to complete reference databases and standardize quantification to further develop eDNA metabarcoding for ecological status assessment. [ABSTRACT FROM AUTHOR]

In contrast to pelagic and benthic realms of the aquatic ecosystems, studies on the metaphytic habitats remain underrepresented in the literature. However, this realm may have a potential impact on composition and diversity of the open water assemblages through metacommunity processes (source-sink dynamics, mass-effect) especially in small ponds with extended littoral zone. Using a limnocorral experiment we studied how metaphyton affects diversity and composition of open water phytoplankton in a small eutrophic pond in the vegetation period. The three habitats (metaphyton, isolated and non-isolated open water) showed considerable differences in their taxa and functional group composition. Abundance-based diversity measures did not reveal remarkable differences among the assemblages of the three habitats. However, taxonomic and functional richness of the metaphyton and the non-isolated part of the pelagial significantly exceeded that of the limnocorral. Incidence-based similarity index values also showed closer resemblance of the metaphyton and plankton samples compared to that of the limnocorral. In the case of several functional groups, their functional redundancy in the metaphyton exceeded that in the open water areas. These results suggest that the metaphyton provides a refuge for several euplanktic elements that survive in the littoral and occasionally enrich the phytoplankton of the open water areas, representing that a within–lake metacommunity processes shape the composition and functioning of the open water areas in standing waters. [ABSTRACT FROM AUTHOR]

Climate change is affecting the global hydrological cycle, causing drastic changes in precipitation patterns. Extreme climatic events are becoming more frequent and intense than in the past, leading to water-level fluctuations and affecting aquatic ecosystems. Semiarid regions are very susceptible to changing climate. We analyzed a 10 years dataset from a tropical semiarid reservoir during extreme hydrological events (heavy rains and prolonged drought), and evaluated phytoplankton functional responses to environmental conditions. We found, as hypothesized, that phytoplankton functional structure change in a temporal scale due to water–volume fluctuation induced by the rainfall pattern. Depth and inorganic material acted as environmental filters selecting phytoplankton groups. High water level seems to improve water quality and low water level worsen it. Colonial and filamentous cyanobacteria dominate the wet period; however, it may have a critical threshold during severe periods of drought, which will lead to dominance of groups well adapted to low light conditions and with mixotrophic metabolism. Phytoplankton functional approaches can simplify phytoplankton identification and reflect better the environmental conditions than the taxonomic approach. Therefore, these approaches can help to understand the shifts in aquatic ecosystems under extreme hydrological events and predict functional response of phytoplankton being an important tool to water management and conservation. [ABSTRACT FROM AUTHOR]

We re-examined the effects of acidification on Scandinavian freshwater lakes using paleolimnological reconstructions focused on subfossil chironomids. Our study showed a widespread shift in chironomid community composition occurring at around 1960 and corresponding with the maximum fallout of anthropogenic SO42− deposition. Results also showed that taxonomic turn-over was higher in chironomid records from nitrogen-limited lakes, likely due to the cumulative effects of acidification and eutrophication driven by atmospheric nitrogen deposition. Despite strong evidence of chemical recovery from acidification, all lake records failed to show a return to pre-acidified community compositions and most chironomid communities instead continue to follow the trajectories triggered by acidification. We hypothesized that when SO42− deposition started to decrease after 1980, a period also marked by rapid environmental and climatic changes, the influence of pH and/or other acidification-related variables in structuring chironomid community became less important, thus, giving more relative importance to other drivers, such as brownification and climatic processes. Results, therefore, suggest the key role of acidification in shaping the response of chironomid communities to future environmental changes. Future paleolimnological studies will contribute to better manage aquatic ecosystems recovering from acidification worldwide by allowing managers to quantify the efficacy of different management actions taken to mitigate acidification as well as to redefine appropriate restoration targets. [ABSTRACT FROM AUTHOR]

Seasonal variations of floating-leaved macrophyte Nuphar lutea chlorophyll content were studied in lakes with different water quality. The aim was to investigate whether chlorophyll content of the plants could be used as an indicator of brownification. The relationship between chlorophyll a and b (CHL a:b) of the petioles decreased with increasing water colour. The relationship between CHL a:b and turbidity was less clear. The sum concentration of chlorophyll a and b of the petioles did not respond to water colour consistently. The strong effect of water colour on petiole CHL a:b was probably due to the effect of colour on the attenuation of short-wavelength light. CHL b absorbs short-wavelength light more effectively than CHL a. To maximize the harvesting of short-wavelength light, macrophytes increase their CHL b concentration relative to CHL a. The results suggested that petiole CHL a:b of N. lutea can be used as an indicator of brownification. High phytoplankton biomass may, however, disturb the relationship between water colour and CHL a:b. Therefore, the most reliable results are obtained by sampling several times during the growing season. The floating leaves cannot be recommended as brownification indicators because the relationship between their CHL content and water colour is weak. [ABSTRACT FROM AUTHOR]

Pikeperch (Sander lucioperca Linnaeus, 1758) is a wide-ranged percid predator fish characterised by a great ecological value in the Eurasian freshwater and brackish ecosystems. It is also one of the most famous fish species of Lake Balaton (Hungary), where a unique (genetically separated) pikeperch stock lives. However, until now, no detailed information was available about the pikeperch population genetic structure in Lake Balaton. In the present study, the population genetic structure of the pikeperch assemblages in the lake was revealed by using microsatellite markers. Commercial fishery and angler catch data going back more than 100 years verified that the pikeperch has always been a key element of Lake Balaton's fish stock utilization. Results of genetic data analyses showed that the pikeperch in the Lake Balaton forms a metapopulation system, in which only the westward stocks show certain separation. Moreover, it seems that the exploitation and mass fish kills that happened in the 1960s and 1970s may have had only a slight impact on the population genetic structure of Balaton pikeperch stocks. The information about genetic features and utilization changes of pikeperch stocks can help to develop area-specific management plans and ensure the long-term survival of this carnivore fish species characteristic of Lake Balaton. [ABSTRACT FROM AUTHOR]

Population growth and increasing production demands threaten the highly diverse Andean freshwater ecosystems. Biological indicators constitute a valuable tool for evaluating the ecological quality of freshwater ecosystems under different pressures. Diatom and macroinvertebrate assemblages are the most used bioindicators to assess water pollution, whereby these biotic groups occupy the first and second trophic levels and respond to habitat pollution. Several studies have explored the response of these communities to water pollution in other regions, but no studies have examined their performance in Andean rivers. In this context, this research aimed to evaluate the responses and relationships of both groups of bioindicators in the Upper Guayllabamba basin. We collected macroinvertebrate and diatom samples from nine sites in this basin during the dry and wet seasons, calculated trophic indices for both groups, and related them to environmental characteristics. The results indicated that both bioindicators were sensitive to changes in land use and nutrients. Epilithic diatoms were more sensitive to changes in water chemistry and macroinvertebrates to changes in fluvial habitat and land use. The index based on macroinvertebrates better-detected changes in quality classes between sites and seasons. Therefore, both indices gave complementary information, and their joint use seems suitable in Andean streams. [ABSTRACT FROM AUTHOR]

Fish as bioindicators are a widely used tool for environmental monitoring of freshwater ecosystems worldwide. However, its adaptation to temperate Neotropical streams constitutes a challenge due to the presence of pauperised ichthyofauna with high tolerance to environmental degradation. We designed, evaluated, and validated an Index of Biotic Integrity (IBI) that uses fish as bioindicators of the ecological integrity of streams of the Pampa Plain, Argentina. An integral characterization of the environmental conditions (water quality, habitat structure, and riparian condition) and fish assemblages were performed in 17 study sites (natural grasslands, urban, and livestock reaches). The IBI was designed with 10 metrics and showed to be sensitive to different environmental conditions due to significant differences between study sites and land uses. The IBI also showed to be responsive due to its significant associations with water quality, habitat structure variables, and some multimetric indexes. Moreover, when validated against a recently fish database, it demonstrated to be sensitive for use in other temperate streams exposed to similar environmental conditions. An integral environmental assessment as the one designed can lead to optimized strategies for the management and conservation of these fragile ecosystems. [ABSTRACT FROM AUTHOR]

The advance of deforestation impacts freshwater ecosystems and, consequently, the environmental heterogeneity and associated biodiversity. Our objective was to examine the effect of deforestation on environmental heterogeneity (EH), species richness (SR), and functional richness (FRic) and the role of EH in the abundance of species and functional groups of stream fish. We analyzed 71 streams of the Acará-Capim basin, eastern Amazon. We used path analysis to assess whether land-use types influence the predominant vegetation cover and channel characteristics, and their indirect effect on EH, SR, and FRic. Taxa indicator threshold analysis was used to assess whether fish species and functional groups act as bioindicators of EH and percentage of forest in total catchment (PFTC). The higher percentage of secondary forest in total catchment (PSFTC) favored herbaceous understory plants and SR. The largest amount of sediments and higher PSFTC negatively influenced EH. FRic was not influenced by any of the variables. Species with high swimming ability that belong to the trophic guilds piscivores and invertivores, are associated with high values of EH and PFTC. Our results may be useful for riparian forest restoration projects, as we show which variables increase or decrease EH and demonstrate how bioindicators respond to this. [ABSTRACT FROM AUTHOR]

Yellowstone cutthroat trout inhabiting Yellowstone Lake have declined substantially over the past 25 years as a result of predation by invasive lake trout, the presence of whirling disease, and periods of persistent drought. We used otolith microchemistry to assess whether cutthroat trout recruitment patterns have changed in response to these environmental stressors. Though water chemistry variation among the 22 sampled spawning tributaries was low, we identified 9 distinct spawning stream clusters. Random forest models were developed for assessing relative recruitment, yielding a high classification accuracy of 84.4% for known-origin cutthroat trout fry otoliths and 79.0% for simulated otolith signatures based on water chemistry. Proportion of recruitment varied significantly between pre- and post-stressor samples (X2 = 15.40, P = 0.03). The majority of pre- (0.84) and post-stressor (0.77) recruitment occurred in the same three stream clusters, but there was a notable decrease in recruitment in streams with high whirling disease prevalence, and a notable increase from the tributary cluster without whirling disease and with low lake trout predation risk. Conservation efforts should be focused on protecting important spawning tributaries and improving cutthroat trout recruitment in spawning streams that in the past likely contributed much greater numbers of fish. [ABSTRACT FROM AUTHOR]

The effectiveness of constructed wetlands (CWs) created to improve water quality has been demonstrated. However, their role in enhancing biodiversity, such as in plankton communities, is still understudied. To assess this, we analysed, over two years, the plankton of three structurally different CWs which are intermediaries between low-quality waters and a protected Mediterranean wetland (Albufera de València Natural Park). We estimated the alpha-diversity of each CW and the beta-diversity among their different sectors. In two CWs, the diversity decreased as water flowed from the Inlet (a species mix from anthropically disturbed environments) to the Outlet, due to natural assembly processes. In the other CW, as it received water dominated by a few species, the emerging assemblages increased the diversity. Moreover, comparing the three CWs, the most divergent communities were those in the outlets (due to the emergence of exclusive species, biovolume differences, etc.). Therefore, they contributed to beta-diversity as they acted as generators of communities, which were characterized by the loss of cyanobacteria and chlorophytes, the dominance of large copepods or cladocerans and the presence of unshared species. We emphasize the importance of having structurally and functionally different CWs to enhance biodiversity and improve biological water quality in natural parks. [ABSTRACT FROM AUTHOR]

Rodríguez-Rey and Whittaker (Hydrobiologia 850:2089–2100, 2023, https://doi.org/10.1007/s10750-023-05220-8) recently investigated the ecological niche of lumpfish (Cyclopterus lumpus) in the Atlantic Ocean using species distribution models. They utilise occurrence records of lumpfish from the Global Biodiversity Information Facility (GBIF) and environmental data extracted from Bio-ORACLE v2.0. A premise of their analysis is that that the GBIF data reflects the relative distribution of lumpfish in the North Atlantic. However, this assumption does not hold true, as evident from the geographic imbalance observed between the GBIF samples and the data obtained from commercial fisheries for lumpfish, as well as fish surveys conducted across the North Atlantic. There is also a concern that only 11% of the individuals listed in the dataset overlapped with the time period from when environmental parameters were estimated (2000–2014). Comparing the suitability index calculated using output from the species distribution models raises concerns about its reliability as it conflicts with the actual distribution of lumpfish from survey data in the eastern Atlantic. This conflict suggests serious problems with the model, and any projections into the future should be treated with caution. [ABSTRACT FROM AUTHOR]

We tracked locations of three fish species in two bays with differing hydrology in SW Florida in 2018–2020 to test the hypotheses about fish residency, movements, and environmental variables. Due to extensive watershed modification, one bay receives less freshwater and the other receives more relative to natural conditions. Home range duration differed for gray snapper (54 ± 6 days), red drum (132 ± 39), and goliath grouper (226 ± 63). Distances between relocation movements were similar for gray snapper and red drum (~ 1.2 km), but farther for goliath grouper (2.3 ± 0.3 km). Relocations were primarily seaward for gray snapper (83%) but varied for the other species. Home range duration related to age for goliath grouper (< 100 days for 1–1.5-year-olds, 300–425 days for 4–4.5-year-olds). Generalized additive models marginally related probability of gray snapper relocating to salinity and temperature whereas relocations of the other species occurred during all environmental conditions. Movement simulations lacking environmental cues produced similar emigration patterns as observed in tagged fish. Overall, results suggest that movements here are not strongly linked to environmental conditions, will be resilient to watershed restoration that should moderate salinity, and have implications for understanding the impacts of localized depletion due to recreational fishing. [ABSTRACT FROM AUTHOR]

Since the 1980s, the freshwater apple snails, Pomacea canaliculata, Pomacea maculata, and their hybrid, have been introduced into a wide range of freshwater ecosystems in tropical to temperate regions. Although P. canaliculata has become established in temperate East Asia, P. maculata and the hybrid are rarely found in this region. To evaluate the risk of P. maculata and the hybrid particularly as rice pests in temperate regions, we compared growth rate, winter survival rate, and feeding efficiency on rice seedlings of these snails with P. canaliculata. When P. maculata and P. canaliculata hatchlings were reared under laboratory or field conditions, the adult P. maculata had larger shells than adult P. canaliculata. Neither P. maculata nor F1 hybrids could survive winter in a simulated drained paddy field, and only a few individuals of P. maculata and F1 hybrids overwintered successfully in freshwater. Pomacea maculata juveniles fed on rice seedlings at the highest rate at temperatures above 27°C. These results suggest that P. maculata becomes a serious rice pest in temperate region as P. canaliculata once it is introduced from warmer regions under global warming. Further biological examination of P. maculata is needed to evaluate the risk of this snail in detail. [ABSTRACT FROM AUTHOR]

The human-mediated transfers of tilapia for aquaculture as a panacea for food insecurity in Africa have led to unprecedented and irreversible impacts on native ichthyofaunal biodiversity. Though aquaculture has been pointed to as the main gateway to species introductions in the Pangani system, formal documentation on how it has contributed to such colonization is anecdotal. The present study aimed to genetically identify, update the list of introduced tilapia taxa, and authenticate if aquaculture is the main gateway to their widespread. We genetically identified non-native tilapias from the Pangani Catchment and aquaculture facilities by genotyping partial Mitochondrial DNA Control region. Molecular analyses depicted the Pangani Catchment to be exclusively inhabited by six non-native tilapiine taxa, particularly Oreochromis niloticus, Oreochromis leucostictus, Coptodon rendalli, Oreochromis esculentus, Oreochromis spilurus, and Oreochromis urolepis hornorum. Oreochromis niloticus, O. leucostictus, and C. rendalli were also predominant in aquaculture and shared haplotypes with their counterparts from the Pangani Catchment. We identified commercial strains of O. niloticus that also shared haplotypes between the two systems. Such haplotype sharing proves aquaculture is the gateway to introducing non-native tilapias into the Pangani Catchment. Thus, fish farming in the region should adhere to regional and international legislation to prevent future spillage. [ABSTRACT FROM AUTHOR]

In the Mediterranean, one of the main reasons for discarding commercial species is when fishers catch fish smaller than the minimum conservation reference size (MCRS). In reality though, other drivers that vary by country/region have greater impact on the discarding process. A notable illustration of the coexistence of different motives is the Greek bottom trawl fishery. Present work focused on the spatial analysis of discards of three commercial species subjected to MCRS with low market price and often discarded independent of their size (i.e., Trachurus trachurus, Parapenaeus longirostris, Sardina pilchardus). To model and map the spatial distribution of species discards, hierarchical Bayesian spatial models were utilized employing discards dependence on environmental inputs. Further information was gained, by calculating the spatial overlap between the spatial distribution of species discards and their known nurseries. Results showed that S. pilchardus discards had the highest estimated values in shallower waters, whereas T. trachurus and P. longirostris discards were distributed over greater depths. Only a small portion of species nurseries and discard grounds coincided, verifying that the reasons behind discarding were market-driven. Area-specific and species-specific management is essential to reduce discards, since local market demand and fishing restrictions have an impact on the discarding process. [ABSTRACT FROM AUTHOR]

Goose and swan populations have increased concurrently with environmental degradation of wetlands, such as eutrophication, vegetation losses, and decrease in biodiversity. An important question is whether geese and swans contribute to such changes or if they instead benefit from them. We collected data from 37 wetlands in southern Sweden April − July 2021 to study relationships between geese, swans and other waterbird guilds, macrophytes, invertebrates, as well as physical and water chemistry variables. Neither goose nor swan abundance was negatively correlated with other trophic levels (abundance, richness, or cover). On the contrary, goose or swan abundances were positively related to abundances of surface and benthic feeding waterbirds, cover of specific macrophytes, and to invertebrate richness and abundance. Moreover, invertebrates (number of taxa or abundance) were positively associated with abundance of several waterbird guilds and total phosphorous with surface feeders, whereas water colour was positively (surface feeders) or negatively (benthic feeders) related. We conclude that waterbirds are more abundant in productive wetlands and that geese and swans do not show clear deleterious effects on other trophic levels included in this study. However, patterns may be masked at the species level, which should be addressed in further studies, complemented with experimental studies of grazing impact. [ABSTRACT FROM AUTHOR]