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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]

Perspectives on the Environmental Implications of Sustainable Hydropower gathers scientific papers from three of the worlds most important hydropower producers to discuss aspects of sustainable hydropower and the means by which it can be studied and achieved. The papers examine the application and use of new technologies and protocols for studying hydropower, adaptive management and the implications and use of long-term data sets for minimizing hydropower impacts on fish populations. The papers include a cross section of biological and hydrological experts. The implicit among country comparisons highlight a number of common hydropower themes, particularly the need to expand from single species studies to include broader consideration of the ecosystem, the importance of maintaining habitat, trait and species diversity and the need for consistently collected long-term data sets. [ABSTRACT FROM AUTHOR]

Sustainable global energy production is back-stopped by hydropower which is responsible for a significant share of the green energy produced worldwide. Hydropower, however, does not come without some environmental impacts but has worked to reduce those impacts. Here, we discuss the historical, legislative, and design configurations of hydropower facilities located in three of the world's most important producers: Brazil, Canada, and Norway. The background is intended to inform the collection of scientific papers from each country aimed at assessing and improving the sustainability of hydropower production that form the core of this special issue on sustainable hydropower. We review the development and key legislative history for hydropower in each country and point out the common backgrounds and interests each nation has in the continued sustainable development of its hydropower resources. [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]

We investigated two inter-related questions: How is the fruit consumption rate affected by fish assembly and how does an increase in fruit production alter fish composition and richness? To answer these questions, we carried out two complementary experiments in a karst tropical stream, Brazil, South America. First, we measured the fish assemblage composition before, during and after the addition of fruit under fruit producing trees. Added fruit increased differentiation of fish between up-stream and down-stream sites over time. Fish composition under fruit-producing trees was distinct from adjacent sites. Second, we set Inga laurina (Fabaceae) fruits on the stream bottom and measured the consumption time. We also analyzed if the fishes that consumed the fruits differed among 41 sites. Fish assemblage structure partially explained the observed consumption rate for the fish assemblages. Our study provides new information on how fruit input and the location of fruiting trees can induce spatial segregation within freshwater fish communities. Our results can help improving management plans for conservation and restoration of headwater streams, including the locations of riparian fruit trees that provide resources and promote hotspots of ecological interactions for freshwater communities. [ABSTRACT FROM AUTHOR]

Fog is an important water input in ecosystems and a carrier of microorganisms, including unicellular pathogens. The aquatic amphibian-killing fungus, Batrachochytrium dendrobatidis (Bd), has a complex transport dynamic. Understanding how the exposure of amphibians to Bd can occur is important for the development of control measurements and for preventing die-offs. Therefore, we tested if the fog water may transport Bd. We collected fog and rainwater in Brazil's Atlantic Forest and experimentally tested if Bd from artificial and natural fog exposures would infect amphibians. We report the first evidence of Bd DNA in fog and corroborate previous data documenting Bd DNA in rainwater. Furthermore, our results indicate that susceptible hosts can be infected and develop lethal chytridiomycosis through the passive transport of Bd live zoospores by the artificial fog. Our results extend the current knowledge about Bd transport pathways between environmental reservoirs. A new short- to medium-range dispersal pathway through fog may explain patterns of pathogen occurrence and opens new avenues of investigation to elucidate exposure mechanisms of direct-developing amphibians to aquatic pathogens. [ABSTRACT FROM AUTHOR]

As human-induced environmental changes reduce niche opportunities from global to local scales, permanent shifts in species traits alter ecosystem processes. Disentangling multiscale mechanisms driving temporal changes in coastal fish biodiversity is thus critical to conservation aims. From seasonal to multiyear periods, we investigated how local environmental variation and landscape features shape temporal beta diversity (abundance-based and trait-based dissimilarities, and their components of replacement and nestedness) per zones in bays and coastal lagoons, Southeastern Brazil. At larger temporal dimensions, unaccounted processes in individual systems influenced primarily taxonomic dissimilarity, whereas functional responses to variation in marine influence varied between types of system and zones. From 2 years to seasons, taxonomic and functional dissimilarities decreased with abundance-based species replacement, and both trait-based components, respectively. Replacement processes were primarily related to marine influence (transparency, salinity, pH, and tidal phase) at larger temporal dimensions, and habitat availability (mangroves and nearby estuaries) and complexity (forest cover and landscape urbanization) in seasons. Seasonal variations in tidal phase (lower) and pH (higher), respectively, promoted taxonomic (abundance gradients) and functional (fish trait loss) nestedness under shorter environmental gradients. Spatial and temporal balances between marine influence, habitat quality, and seascape connectivity drive temporal dissimilarities in coastal fish assemblages. [ABSTRACT FROM AUTHOR]

Several hypotheses try to explain the factors that limit the distribution of tree species in wetlands. Among them, the stress-gradient hypothesis states that interspecific ecological interactions (facilitation and competition) vary inversely across abiotic stress gradients, with facilitation being more common under conditions of high abiotic stress than under more benign conditions. We investigated the effects of ecological interactions on the biomass of two native tree species, Crateva tapia (highly flood-tolerant) and Hura crepitans (low flood tolerant) exposed to different experimental flooding conditions in a greenhouse. Individual and paired plants were submitted for 120 days to four treatments: (1) non-flooding and non-ecological interaction; (2) flooding and non-ecological interaction; (3) non-flooding and ecological interaction; (4): flooded and ecological interaction. Flooding reduced biomass allocation in H. crepitans. C. tapia biomass was reduced by interspecific interaction with H. crepitans. Flood and interspecific ecological interactions together facilitated the accumulation of biomass in H. crepitans. Our results support the stress-gradient hypothesis, showing that in a flooded environment, the species with low tolerance to flooding (H. crepitans) is favored by the presence of other species. Additional tests with other species can confirm whether this is a pattern that helps explain the establishment of tree species in wetlands. [ABSTRACT FROM AUTHOR]

Macrophytes play an important role in maintaining biodiversity. However, little is known about the relationships between different types of macrophytes and the diversity of aquatic communities. The purpose of this study was to determine the relationships between floating and submerged macrophytes and the temporal variation in the taxonomic and functional diversity of phytoplankton in two tropical reservoirs (Cursaí and Cajueiro) located in Northeastern Brazil. A field study was carried out quarterly between November 2018 and November 2019 to analyze the taxonomic (richness, equitability, and Shannon index) and functional (FRic, FEve, and FDiv) diversity indices of phytoplankton in relation to the presence of macrophytes. Taxonomic and functional diversity indices varied over time in sampling sites. Macrophytes had positive effects on taxonomic richness, Shannon index, and FDiv in Cajueiro, and negative effects on the taxonomic equitability and FEve of phytoplankton in Cursaí. Functional diversity of phytoplankton was negatively influenced by water transparency and positively by total dissolved solids, pH, and nitrate in sites with macrophytes, while taxonomic richness was positively influenced by total phosphorus. Our results showed that taxonomic and functional diversity of phytoplankton responded differently to spatial and temporal variation, and species richness, Shannon index and FDiv were related to macrophytes. [ABSTRACT FROM AUTHOR]

We developed the Trophic Diatom Index for Reservoirs (TDIR), the first index proposal for water trophic quality assessment of tropical reservoirs in Brazil. Furthermore, we applied four borrowed diatom indices to compare their performances with TDIR. The proposal development considered a calibration set from surface sediment diatoms (n = 113) from reservoirs ranging from ultraoligotrophic to hypereutrophic. Weighted averaging methods were applied to infer optimum (values) and tolerances for total phosphorous for each diatom species. Indicative values were categorized within the trophic classification for tropical reservoirs, and sensitivity values were classified according to the range of tolerances of diatom species. The TDIR index scores ranged from 1 (ultraoligotrophic) to 6 (hypereutrophic). The TDIR showed good performance for the trophic classification of reservoirs. In contrast, the borrowed diatom indices developed in subtropical rivers underestimated the water quality, whereas the diatom index developed for lakes in temperate regions overestimated the water quality of our reservoirs. Moreover, we calculated new records of indicative values, and some well-cited species had different optimum and tolerances values concerning other well-known studies. TDIR provides an applicable index and contributes as a reliable tool for assessing the water quality and ecological status of tropical reservoirs. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are among the most threatened habitats on Earth, due mainly to anthropogenic pollutants made up of complex mixtures. The Iguaçu River is world famous for the Iguaçu Falls and highlighted by its endemism. Unfortunately, it is considered the second most polluted urban river in Brazil. We aimed to perform an environmental evaluation of Neotropical streams in the Iguaçu River basin, using a multibiomarker approach from a land use and landscape perspective. A set of biomarkers in the fish Psalidodonbifasciatus was analyzed using an Integrated Biomarker Response (IBR) index and correlated with surrounding land uses. Agricultural and urban sites presented more alterations compared to references sites, with elevated protein carbonyls at agricultural sites, increased DNA damage and depletion of glutathione S-transferase at urban sites and decreased glutathione associated with higher histopathological indices at urban and agricultural sites. The IBR shows a consistent increase in negative effects in anthropized areas, with similar values at agricultural and urban sites. The multibiomarker approach, associated with a well-elaborated sample design and a statistical analysis, is an ideal method to obtain more conclusive results about the effects of human activities, revealing the effective result of exposure in the real world. [ABSTRACT FROM AUTHOR]

Even after more than a century of research, the processes underlying species abundance distribution patterns are controversial. Here, we gathered abundance and size (standard length) data of fish species in 54 streams in the Midwest of Brazil to test whether subordinate species abundances (i.e., any species that is not dominant in a community) in each stream are correlated with the absolute size difference between dominant and subordinate species. A negative relationship between these variables would suggest a predominant role of environmental filtering because those species that differ more from the dominant species (the one with the optimum trait value) would become progressively less abundant. On the other hand, a positive relationship would suggest a limit to the similarity as the abundances of subordinate species that differ more from the dominant species would increase. Our results clearly indicated that subordinate species were those that most differed from the dominant species in terms of size. In addition, we found that the subordinate species were larger than the dominant species. Taken together, we infer that environmental filters favoring small body sizes (e.g., shallow water depth and scarcity of large shelters) are the main processes determining species abundance distributions in the streams we studied. [ABSTRACT FROM AUTHOR]

Habitat fragmentation caused by hydroelectric dams has depleted fish populations worldwide. Restocking actions are usually adopted to recover those populations, but hatchery management protocols rarely guarantee the maintenance of genetic diversity and a balanced contribution among captive breeders each generation. Here, a set of 10 microsatellite markers was used to assess the genetic diversity (average allelic richness AR = 10.87 and expected heterozygosity HE = 0.742, respectively) and structuring of Megaleporinus obtusidens, a migratory freshwater fish inhabiting over 2500 km of the São Francisco River in Brazil. Three main genetic clusters were identified in this species across the river basin that could be related to the sharply different climatic and hydrologic regimes from the Upper to the Lower course. A significant reduction (> 50%) in genetic diversity was observed in the broodstock when compared to their wild conspecifics, especially in the allelic richness. The information here presented will aid for management of genetic resources of this species in the São Francisco River taking as reference the genetic clusters identified. Furthermore, the results indicated that restocking is not necessary unless signals of population depletion occurs and, if so, hatchery reproductive protocols should rely on artificial fertilization rather than mass spawning. [ABSTRACT FROM AUTHOR]

Trait-based classifications can efficiently capture species' responses to environmental gradients and their impacts on ecosystem functioning. Thus, the clustering of phytoplankton species into functional groups can improve the understanding of their relationships with the environment and help to predict their response to environmental changes. Accordingly, this study aimed to create habitat templates of Reynolds phytoplankton functional groups (RFGs) in tropical drinking water reservoirs to describe, explain, and predict their occurrence and formation of blooms. We analyzed the structure of RFGs in 10 tropical reservoirs, in humid and semiarid regions of Brazil, and defined their relationships with 10 environmental variables. We designated the habitat template based on niche differentiation, thresholds for the occurrences and bloom formation, cluster analyses, and generalized additive models. We identified 136 species, assembled in 20 RFGs. Six groups of habitat templates were recognized based on environmental conditions and dominant RFGs, usually represented by bloom-forming species of cyanobacteria, dinoflagellates, green algae, and diatoms. The functional groups D, X1, and P presented the most restrictive occurrences, while RFGs M and SN displayed the widest, occurring in almost all sets of conditions. Moreover, salinity was the best predictor of RFGs' biomass (higher R2), followed by depth, soluble reactive phosphorus, irradiance, water transparency, and dissolved inorganic nitrogen. Our approach improves the understanding of how RFGs interact with environmental gradients in tropical reservoirs, helping water managers to adopt sustainable practices to control algal blooms, based on predictions of the future state of dominance. [ABSTRACT FROM AUTHOR]

This study tests if rainfall regime and estuary hydrodynamics affect ecological picocyanobacterial patterns. We statistically related rainfall with picocyanobacteria (flow cytometry) and water quality data from a seven-year-long survey of Guanabara Bay (GB). The quality of GB's water varies spatially, depending on pollution hotspots, tidal influence, and water circulation patterns. It also varies seasonally, depending on the rainfall regime. Our results showed that rainfall regularly makes water quality and microbiology of the inner estuarine regions more like the tributaries' environment. We found that phycocyanin-rich and phycoerythrin-rich picocyanobacterial abundances are associated with riverine and marine waters, respectively. Besides affecting GB's water quality, rainfall governs its picocyanobacterial distribution and ecology. Thus, climate changes may influence the balance of the picocyanobacterial groups in tropical estuaries. Furthermore, the omnipresence of picocyanobacterial groups found in GB, such as Synechococcus and Cyanobium, highlights their ecological role in tropical estuaries, as seen in the open ocean. [ABSTRACT FROM AUTHOR]

In this study, we investigate the main ecological interactions between fouling aquatic organisms (both invasive and native) present in the reservoir of the Governador José Richa hydroelectric plant, located in southern Brazil, and to identify the most suitable period for the interruption of machinery operation for cleaning and maintenance of the hydraulic systems of this plant. A total of 32 experimental plates were fixed to a metallic structure positioned close to the plant's water intake. Three species of invasive fouling were identified in our samples (Limnoperna fortunei [Mollusca], Cordylophora sp., and Hydra sp. [Cnidaria]) and six native taxa belonging to the phyla Protozoa, Ciliophora, Amoebozoa, and Arthropoda. Spring and summer were the seasons with the highest fouling rates, as well as densities of fouling organisms. The highest levels of diversity were recorded during the colder seasons. Several interactions between the organisms were identified, such as mutualism, commensalism, competition, epibiosis, cannibalism, and predation. The data obtained suggest that, from the biological point of view, the most suitable period for machine shutdown destined for the removal of biological fouling in the hydraulic systems of the studied plant is between the end of spring and the beginning of summer. [ABSTRACT FROM AUTHOR]

The flood pulse concept refers to seasonal variation in river water levels promoting landscape spatial heterogeneity, connectivity, and nutrient cycling among nearby environments, in addition to contributing to the ecological functioning of river-floodplain systems. This seasonal variation is inherent to river-floodplain systems and responsible for establishing their natural pattern, as frequently observed in nature. In Brazil, the Upper Parana River and its floodplain constitute a river-floodplain system of interest, where an upstream reservoir cascade has altered the flood regime. This regime has been explored in the past; however, research has focused only on its time-domain. In this study, I sought to analyze the flood pulse in the Upper Paraná River Floodplain through a set of spectral (frequency-domain) and nonlinear analyses using a time-series of water level fluctuations (1968–2017) in the system. In doing so, I believe to bring novel information on this system flood regime in terms of its dynamic invariants. I divided the data into four periods: (i) natural regime period, (ii) transitional period, (iii) dam cascade period, and (iv) Primavera dam period. Spectral analysis demonstrated a decrease in the annual cycle amplitude, reflected in its power spectrum, which indicates a weakening in the difference between flood and drought events. Additionally, nonlinear dynamical analysis revealed a less deterministic and predicable behavior leading to more erratic fluctuations, thus jeopardizing the temporal heterogeneity of the system. Such altered dynamics is harmful for threatening the ability of organisms to harmonize their biological cycles with seasonal phenomena, consequently raising concerns about the maintenance of ecological integrity in the system. [ABSTRACT FROM AUTHOR]

Harmful effects of the toxic cyanobacterium Nodularia spumigena were observed in experimental marine shrimp production ponds in Brazil. Strains of this cyanobacterial species were isolated and cultured, and in the present study, we evaluated the influence of light intensity and the concentration of dissolved inorganic nitrate and phosphate on the growth, toxin concentration, heterocyte formation and akinete germination of N. spumigena. A factorial experiment (3 × 3) was performed to test three light intensities and nutrient concentrations with a reduced nitrate concentration, a reduced phosphate concentration and a nutrient-replete f/2 medium. The influence of light intensity on growth and akinete formation was varied: the highest cell density and chlorophyll a were recorded at the lowest light intensity, while the high light treatment stimulated akinete formation. The availability of phosphate was the main factor favouring the growth of N. spumigena and the formation and germination of akinetes, while the concentration of nodularin per cell was highest under phosphate deficiency. This information is useful in the management of aquaculture ponds and other brackish and marine environments where the goal is to reduce N. spumigena blooms. [ABSTRACT FROM AUTHOR]

The high diversity of fish species found in Brazilian streams has attracted scientific interest in recent years. However, it is not clear how studies have addressed biodiversity knowledge shortfalls. We conducted a scientometric analysis of stream fish studies in Brazil to identify trends and gaps in how objectives, spatial coverage, and biodiversity knowledge shortfalls have been studied. Our review covered 690 articles published between 1981 and 2019, and we found an increase in the number of publications, the spatial scale of studies, and the number of streams studied. We also found biases in the distribution of publications concerning regions, biomes, basins, and biodiversity knowledge shortfalls. The Southeast region, the Paraná River basin, the Atlantic Forest biome, and the Hutchinsonian shortfall contributed to a greater number of studies while the Northeast region, the Pantanal biome, Parnaíba basin, Western Northeast Atlantic basin, and the Prestonian shortfall were less represented. Therefore, to improve our knowledge about stream fish, we recommend new collection efforts in under-sampled regions and new studies focused on filling less-addressed biodiversity knowledge shortfalls. Moreover, we emphasize the importance of standardized sampling protocols, a complete sharing of data, and an increase in scientific collaboration. [ABSTRACT FROM AUTHOR]