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We aimed to understand how the environmental variability produced by water parameters, land use, and land cover in small streams affects aquatic hyphomycete and invertebrate assemblages associated with leaf litter. Land use and land cover were quantified in the drainage area of streams located in the subtropical portion of the Atlantic Forest. We incubated Nectandra megapotamica leaves in streams and, after 30 days, collected decomposing litter to analyze associated aquatic hyphomycetes and invertebrates. Dissolved oxygen was associated with the distribution of aquatic hyphomycetes. On the other hand, 4,068 aquatic invertebrates were found, assigned into five functional feeding groups (FFG). Native vegetation and water temperature were the variables responsible for structuring the invertebrate assemblages associated with detritus. Native vegetation, dissolved oxygen, and total dissolved nitrogen were responsible for the structuring of FFGs. Streams that showed high rates of agriculture and urbanization in the drainage area showed low leaf mass loss. Our study demonstrated that the presence of anthropic uses and reduced native vegetation in the drainage area affected the assemblages of aquatic hyphomycetes and shredders, which are key players in the process of leaf decomposition in streams. [ABSTRACT FROM AUTHOR]

Temporal variation in limnological characteristics favors an increase in aquatic macrophyte diversity in Neotropical riverine environments. We assessed temporal and environmental variability in the aquatic macrophyte community in riverine environments of the Tapajós river basin, southern Amazonia, Brazil. Hydroperiod, type of riverine environment, limnological variables, and surrounding woody vegetation were found to influence aquatic macrophyte richness, cover, and dry and fresh biomass. A total of 98 species from 68 genera and 40 families were recorded. The greatest observed richness in streams was during the dry period. Richness, cover, and biomass were greater in lagoons and rivers during rising water and flood hydroperiods. Amphibious and emergent species had higher biomass in flood and receding water hydroperiods. Higher richness, cover, and fresh biomass were mostly related to electrical conductivity. Suspended and dissolved solids reduced species richness in all environments. Greater tree abundance in the surrounding vegetation was associated with higher macrophyte richness in streams and with macrophyte cover and biomass in rivers. The aquatic macrophyte community in southern Amazonia is subject to variation in riverine ecosystem type, tree composition and structure in surrounding vegetation, hydroperiod (temporal variation), and limnological parameters (environmental/temporal variation). [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]

Eucalyptus afforestation may affect stream ecosystems, but the magnitude of these effects on water quality and biota in subtropical lowland streams is little understood. We evaluated the potential effects of Eucalyptus afforestation on water quality and macroinvertebrate assemblage. Water quality parameters and macroinvertebrate assemblages were sampled in summer and winter in 30 streams covering an afforestation gradient (from 0.05 to 96% of the catchment area) and tested their relationship. We analyzed the taxa density distribution in afforestation and water parameters using the Thresholds Indicator Taxa Analyses (TITAN). Nutrient concentrations, conductivity, and total dissolved solids showed positive responses to the increase of afforestation, but the responses varied among seasons. Macroinvertebrate metrics showed negative (Ephemeroptera-Trichoptera-Plecoptera (EPT), sensitive families, scrapers), and positive (Chironominae, Oligochaeta) responses to the afforestation. Densities of sensitive taxa (mostly EPT) decrease with an increase in Eucalyptus afforestation, which is also related to water quality and possibly to habitat changes attributed to afforestation management. The use of water quality parameters in combination with macroinvertebrates assemblage contributes to managing these streams under catchment afforestation. [ABSTRACT FROM AUTHOR]

Heavily modified water bodies (HMWB) have been seriously affected by human activities and natural processes promoting their imbalance, and impacting their functioning and biodiversity. This study explores a new approach of monitoring and assessing water quality in Mediterranean reservoirs using phytoplankton communities across a disturbance gradient, according to water framework directive. Phytoplankton and environmental data were sampled in 34 reservoirs over 8 years. Two types of reservoirs were analyzed: Type1 "run-of-river reservoirs" (located in the main rivers, with a low residence time); and Type2 "true reservoirs" (located in tributaries, with high residence time). The transition from deeper and colder reservoirs (reference sites) to shallow and warmer (impaired sites) was clear in Type2, correlated to organic pollution and mineral gradients. Impaired sites from both types showed a higher richness of tolerant taxa. Principal response curve (PRC) provided a concise summary of phytoplankton temporal dynamics and assessed ecosystem health for Mediterranean HMWBs. PRC will provide a powerful tool for environmental quality assessment and be incorporated into monitoring and assessment programs. This approach can help policymakers to manage natural capital to achieve multiple objectives, mainly increasing ecosystem services, and improve readability and interpretation of spatial patterns in temporal changes. [ABSTRACT FROM AUTHOR]

Climatic and hydrological variation is of utmost importance in regions of the globe facing water scarcity and river intermittency (e.g. areas under Mediterranean influence). The main aim of this study was to compare the macroinvertebrate community structure and its bioindicator value (i.e. waterbody ecological status) in streams from three Portuguese regions (Regions C, N and S), representing distinct climatic features and water availability scenarios. Results showed that, overall, sampling sites differed in their climatic, hydromorphological and physical and chemical features, and environmental (abiotic) and ecological (community dissimilarities) gradients among regions were clearly identified. Sites from Regions C (wettest) and S (driest) represented non-overlapping clusters of samples, both in terms of their environmental context and ecological (dis)similarity; sites from Region N occupied an intermediate position, and their macroinvertebrate community was highly variable locally. This coincided with overall higher ecological quality and uniformity in Region C, whereas Regions N and S were more heterogeneous and generally presented lower ecological quality. Our data showed that climate (and associated water scarcity) is coupled with other environmental drivers of the macroinvertebrate community structure, highlighting a shared influence of the three environmental components (climatic, hydromorphological, and physical and chemical) in the modulation of macroinvertebrate communities. [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]

Ichthyoplankton drift is threatened by hydropower dams elsewhere. Here we evaluated whether eggs and larvae of fish can perform downstream movements along a large reservoir in a white-water river on the Amazon. Samplings were performed in the reservoir and downstream from Santo Antônio dam. Generalized linear models with negative binomial distribution and logarithmic link function were fitted to model the ichthyoplankton drift throughout the reservoir. Six different models were fitted having the abundances of ichthyoplankton as the response variable. The linear predictor differed as to the inclusion of the predictor variables larval development stage, sampling sites and dam distance (linear and quadratic effect). All ichthyoplankton and the most representative taxonomic orders were analyzed. The results indicate that fish reproductive activity occurred both upstream Jirau Dam and within the Santo Antônio Reservoir. Some part of the ichthyoplankton transposed the Santo Antônio Dam, reaching downstream. However, all of the taxonomic orders presented both reproductive activity and disappearance of at least some of their larval development stages along the reservoir. The most critical section was in the last 10 km of the reservoir, possibly as result of the drifting characteristics or of mortality rates. [ABSTRACT FROM AUTHOR]

Parasitism by isopods is a common phenomenon in marine fishes and may induce negative effects, especially in juvenile stages. The surf-zones of sandy beaches are an important nursery habitat for many fish species, including commercially important ones, and are structured by beach characteristics and human activities, which are suggested to influence the fishes' susceptibility to parasitism. Here, we analyze the early infestation and prevalence of parasitism in surf zones fishes of 27 beaches in southeastern Brazil with different characteristics. Parasites were recorded in only seven of the beaches. A high infestation was found in a single site, the highly urbanized Itaguá beach, where the prevalence of parasitism on juveniles and early adults of the Atlantic anchoveta Cetengraulis edentulus was high (68.11%). Four species of parasitic isopods were found, all belonging to the Cymothoidae family, but Livoneca desterroensis was the most abundant (78.7%). No effects of parasitism were detected on the size, weight and physiological condition of fishes, but presence of parasites and prevalence of infestation were positively affected by urbanization. Overall, our results indicate that the surf-zones have low parasite infestation, yet, they suggest that anthropic effects such as urbanization may enhance the prevalence of isopod parasitism. [ABSTRACT FROM AUTHOR]

Disentangling the role of mechanisms driving metacommunity structure is fundamental for conservation strategies. Several studies have been done in aquatic communities; however, little is known about the factors driving oomycete communities. This research aimed to investigate beta diversity patterns and assess the role of environmental (chemical, physical, and hydrologic), spatial, and temporal (sampling months) factors in driving oomycete beta diversity in a spatial extent of 33 km from two Brazilian rivers. We took water samples in 10 sites quarterly, from August 2017 to May 2018. The partition of beta diversity into its components – species replacement and richness difference – was performed using the Jaccard dissimilarity index. Distance-based redundancy analysis and variation partitioning were used to assess the relationship between explanatory variables and beta diversity. We found that beta diversity was spatially and temporally high, and the replacement component was the main driver of the oomycete metacommunity's beta diversity. Replacement and total beta diversity were explained mainly by spatial location and the month of sampling, while the richness difference was more associated with the environmental variables chlorophyll a and ammonia. Our findings suggest that dispersal limitation (spatial) and temporal factors are the main drivers of the total beta diversity and replacement in the oomycete metacommunity, while species sorting (environmental factor) influences the richness difference. Accordingly, that taking temporal factors into account in metacommunity studies is important to explain beta diversity patterns, especially in rivers with remarkable variability in hydrological regime and under eutrophic conditions. [ABSTRACT FROM AUTHOR]

We assessed how the variation in environmental factors influences mayfly assemblages in conserved streams of different Amazonian interfluves. We hypothesized that environmental variables, mayfly assemblages, and the influence of environmental factors vary among these interfluves, given their distinct evolutionary and ecological histories, and patterns of human interference. We also expected that the effects of environmental variation on species richness and composition would be greater among interfluves than among streams within the same interfluve. Our hypotheses were corroborated, reflecting the considerable heterogeneity of the Amazonian biome, where streams vary naturally among interfluves, determining broad scale divergences in species composition. The environment affected mayfly diversity in different ways among interfluves, reflecting the influence of historical processes that resulted in the formation of centers of endemism delimited by major Amazonian rivers, in which distinct biotic and abiotic factors have prevailed. These regional effects have resulted from the heterogeneity of environmental gradients, which affect mayfly diversity. The results of the present study indicate that, depending on the scale and topography of the interfluve, environmental predictors of the structure of mayfly assemblages vary considerably. This has important implications for the definition of control sites for the assessment and monitoring of environmental quality. [ABSTRACT FROM AUTHOR]

The intermediate disturbance hypothesis (IDH) has been thoroughly investigated, but much controversy has been found for supporting its assumptions, which rely largely on the nature of the disturbance, spatial scale, and biological predictors tested. In this paper, richness of native and non-native species along a suite of Neotropical aquatic ecosystems across a broad latitudinal and geographical range was used to test the IDH predictions. An extensive literature survey was performed to compile native species richness and the occurrence of several taxonomic groups listed as non-native for twenty-four coastal rivers and bays evenly distributed into three climatic zones (tropical, transitional, and subtropical). The climatic gradient was confirmed by NMDS and PERMANOVA, but IDH predictions were only significantly supported for native and total species richness in the coastal bays. The distribution patterns of non-native marine species showed a linear instead unimodal pattern of increase with latitudinal climatic gradient, but the responses are complex and dependent of many non-exclusive factors, such as the sampling effort per ecosystem and the potential interference of other disturbance gradients that should be further addressed to unravel the role of IDH for non-native species distribution. [ABSTRACT FROM AUTHOR]

The effects of invaders on native species are usually tested using species mean trait values over long time scales. However, considering individual variation over short timescales can help us better understand the interaction between invaders and native species. We compared trophic traits of the non-native guppy (Poecilia reticulata) and the native Brazilian poeciliid Phalloceros harpagos using experiments simulating the early stages of an invasive process. We used short-term mesocosms to simulate an early invasion scenario, where the two species were placed together, and a pre-invasion scenario, where species were kept separated, and analyzed interspecific and intraspecific trophic variability. We also compared the foraging efficiency of species in laboratory experiments. We found no differences on the mean diet of both species between pre and early invasion treatments. At the individual level, in the early invasion scenario, individuals of both species reduced their trophic niche as a probable effect of the presence of the heterospecific. Phalloceros harpagos had higher consumption rates than guppies indicating greater efficiency in feeding on invertebrates. Our results suggest that non-native species were not intrinsically better consumers of high-quality resources. Instead, intraspecific variation might be playing an overlooked role in shaping interactions between species during the early stages of invasion. [ABSTRACT FROM AUTHOR]

Agribusiness is one of the main economic activities in Brazil, which caused the removal of much of its natural vegetation for the expansion of monoculture areas. Once aquatic environments have a direct relationship with the surrounding terrestrial environment, it is essential to understand the monocultures' impact on adjacent streams and, especially, how aquatic communities react to these impacts. Our aim was to verify the effects of different monoculture types on stream benthic macroinvertebrate and fish communities' structure. We compared the environmental characteristics and these communities' structure in four streams located in native vegetation areas and four in each of three monoculture types (sugarcane, citrus, and eucalyptus), all belonging to the Paranapanema River basin, Southeastern Brazil. We found lower pH and dissolved oxygen and higher total phosphorus and fine substrate values in monoculture streams and these variables were also related to the lower abundance of macroinvertebrate groups more sensitive to environmental impacts. However, we did not find differences in fish communities or in their relationship with the different environmental characteristics observed. We also did not observe differences between the monoculture types in all comparisons made, which demonstrate that these plantations, although have different cultivation characteristics, cause similar negative impacts in the streams. Our study demonstrates the physical and chemical impacts of monoculture development on stream headwater communities. Regulatory measures such as increased riparian vegetation and contour farming and terracing may be critical to protect and restore headwater streams from monoculture impacts. [ABSTRACT FROM AUTHOR]

Non-native freshwater fish introduced via the aquarium trade can cause major changes at the community level over time and space, resulting in dynamics context dependencies within homogenization process. We investigated fish biodiversity in anthropogenically impacted headwater creeks (i.e., under elevated propagule pressure) located in southeastern Brazil, through a standardized sampling program. We assessed ichthyological community composition with the aim of quantifying spatio-temporal dynamics across creeks. We divided the sampling period according to decades, in which "2000s" represented 2003, 2004, 2005, and 2006, while "2010s" represented 2015. Changes in pairwise community similarity indicated biotic homogenization in the 2000s (i.e., communities became more similar over time). In contrast, changes in pairwise similarity in the 2010s indicated biotic differentiation. We suggest that these changes are caused by the extirpation of both native and non-native species due to environmental degradation and the occurrence of six new non-native species. The beta-diversity increased between sampling seasons and creeks across decades, also indicating biotic differentiation. Our study provides strong evidence for a transition phase from biotic homogenization to differentiation of fish communities over time, caused by interaction between older environmental degradation and more recent impacts from the Brazilian aquarium trade, reinforcing the importance of simple, practical, and inexpensive long-term studies to understand biodiversity-related processes. [ABSTRACT FROM AUTHOR]

The conservation challenges facing freshwater ecosystems necessitate broadening our science from understanding individual species loss to anticipating multi-faceted changes to biodiversity. In recent decades, the process of biotic homogenization by which regional biotas become more similar through time has attracted considerable attention. Here, we (1) quantified spatial and temporal changes in taxonomic and functional similarity of fish assemblages among Neotropical reservoirs, (2) determined nonnative species contributions to changes in taxonomic and functional composition, and (3) evaluated relationships between the changes in taxonomic and functional similarity among reservoirs. We did so by considering different spatial scales: inter- and intra-ecoregions. At inter-ecoregion scale, reservoir fish assemblages have become taxonomically homogenized over time, whereas functional trait composition has tended to differentiate. At intra-ecoregion scale, we detected both taxonomic and functional differentiation over time. Despite these overall trends, different ecoregions exhibited considerable variation in patterns of fish faunal homogenization and differentiation. We found a moderate positive relationship between changes in mean taxonomic and functional similarity among reservoirs at inter-ecoregion scale, which was no longer evident within ecoregions. In conclusion, this study demonstrates the strong scale-dependence of perceived patterns in homogenization, and further highlights the magnitude of threats to freshwater biodiversity in the Neotropical ecosystems. [ABSTRACT FROM AUTHOR]

Anthropogenic impact can alter food web structure through changes in species interactions. In this study, we explored the food web of three Mediterranean stream reaches (two seasonal and one permanent) along an anthropogenic impact gradient to test the hypothesis that increasing impact simplifies food webs. To test this, we applied the isotopic (δ13C and δ15N) niche concept to compare reaches using isotopic metrics (isotopic richness, divergence, dispersion, evenness, and redundancy). The isotopic indices were useful to identify differences in food web architecture among the three reaches. The least impacted site had the highest isotopic richness, dispersion, and isotopic redundancy, suggesting higher ecological resilience at this site. The effect of disturbance in the remaining two sites was masked by the presence of invasive crayfish, which increased isotopic divergence and was responsible for higher food-chain length in the most impacted reach, but not in the moderately impacted reach. Consumers displayed generalistic feeding habits, with Bayesian mixing models indicating that they relied primarily on a mixture of periphyton, other macroinvertebrates, and to a lesser extent, detritus. Some taxa displayed changes in their dietary habitats depending on the site, indicating that the same type of taxa fed on distinct foods at each stream reach. [ABSTRACT FROM AUTHOR]

Despite the socio-environmental importance of ichthyofauna, global fish biodiversity has decreased, and the damming of rivers is one anthropogenic activity that causes this reduction. This scientometric study evaluates the main determinants, directions, and gaps of scientific research on the biodiversity of fishes that are influenced by dams. Between 1991 and 2016, there was an increase in the number of studies about this topic, in proportion to the total number of studies that were evaluated. The distribution of these studies among countries is not random, since some socioeconomic and environmental factors (e.g., gross domestic product, number of researchers, number of large dams) determine the distribution of research. Moreover, these studies mostly address the negative impacts of dams on fish communities on a local scale; several studies have shown the importance of mitigating these impacts. In this particular study, we emphasize the need to research the effects of fishing, cascading dams and the phylogenetic diversity of ichthyofauna. We find that the relationship between dams and fish has become popular among researchers, in particular those who are willing to understand the causes, consequences, and severity of these changes on the ichthyofauna. [ABSTRACT FROM AUTHOR]

The biogeography and conservation of elasmobranch species was increasingly addressed in the recent past, but the southwestern Atlantic Ocean fauna is still one of the least studied. Reliable delimitation of the distribution range of species is fundamental to conservation and development of fisheries management strategies. A recent molecular study of the cryptic Aetobatus narinari species complex restricted that species to western and eastern coasts of the New World. However, the current distribution of A. narinari and phylogenetic relationships within the genus Aetobatus have yet to be clarified, the goal of this phylogeographic analysis. Using mitochondrial and nuclear markers we investigated specimens from the Atlantic coast of Brazil and the Pacific coast of Mexico and related them to previously analyzed specimens from other regions. Our analysis indicates that Aetobatus narinari is present only in the western Atlantic, formed by a single genetic lineage that ranges between Florida and southeastern Brazil, while the Pacific New World lineage is in fact assigned to Aetobatus laticeps. Analysis of divergence times revealed that biogeographic events such as the closure of the Tethys Sea, the formation of the Benguela barrier, and the Isthmus of Panama played major roles in diversification and dispersal of the genus Aetobatus. [ABSTRACT FROM AUTHOR]

The genus Mytilopsis includes some of the most invasive estuarine bivalves in the world, and M. leucophaeata (native to the Gulf of Mexico) and M. sallei (indigenous in the Caribbean Sea) are the most often reported species. Molecular investigations of the COI gene in invasive populations of M. leucophaeata in Europe found only one haplotype, whereas the invasive M. sallei in Asia had high haplotype diversity. The present study investigated COI variability of invasive populations previously identified as M. leucophaeata in Brazil, located at the cities of Recife and Rio de Janeiro. Our genetic analysis revealed that the record of M. leucophaeata from Recife appears erroneous; this population forms a clade adjacent to but genetically separated from the Asian M. cf. sallei. Similarly, samples from Rio de Janeiro clustered close to but not within European/North American sequences of M. leucophaeata. The Automatic Barcode Gap Discovery test suggested the existence of three species: M. leucophaeata, M. cf. sallei (Asia), and M. cf. sallei (Recife), which merit confirmation with nuclear DNA sequences. The discovery of two lineages of Mytilopsis in Brazil augments concerns about their expansion. [ABSTRACT FROM AUTHOR]

Neotropical freshwater ecosystems are experiencing a great expansion in the number of invasive species, which is especially alarming since this region harbours 30% of the world’s fish biodiversity with high levels of endemism. We aimed to evaluate the main predictors of peacock basses (Cichla spp.) abundance outside their native range, which are the Amazon and Tocantins-Araguaia river basins. We used multivariate ordination techniques and multimodel inference to analyse peacock basses abundance in twelve reservoirs of the Paraíba do Sul river basin, southeastern Brazil. Interestingly, reservoirs at higher (southernmost) latitudes, located in more populated areas, had higher water temperature and lower turbidity, due to increased water residence time, and these three variables were also positively correlated with abundance of this warm-water invasive fish. Habitat structure was less important in explaining peacock basses abundance, which was not significantly related to biotic factors (fish species richness and time since peacock basses introduction). We hypothesize that the observed effects of reservoir management on limnological features and peacock bass abundance, particularly water residence time (as a mediator of temperature and turbidity), may apply to other Neotropical basins and could influence the impact of this invader. [ABSTRACT FROM AUTHOR]

Until recently, the distribution of diatom and chironomid assemblages and their attributes (species richness/diversity) in relation to water depth and sedimentary environments have been identified but not quantified. The influence of environmental variables on assemblage distribution and taxa richness in a deep, monomictic lake in São Miguel Island is assessed. Attention is given to community variation along a water-depth gradient. Sediment core samples were analysed for diatom content, chironomids, and grain-size clastic particles along three transects from the shoreline to the central deep basin of the lake at a resolution of 1 m water depth. Linear and unimodal regressions were used to test taxon richness, taxon diversity and taxon evenness versus water depth of each transect. A hump-shaped relationship between species richness and water depth was noted, with a peak occurring at mid-depth, meaning that samples located at that depth better represented the total subfossil assemblage living in lake Azul. Moreover, data indicate that both assemblages in Lake Azul, and taphonomic effects, were influenced by processes of clastic transport depending on the lake morphology. Results from this study allow us to access the spatial distribution of biological assemblages in clastic-dominated lakes with a high topographic gradient, and provide us with principal criteria that will allow us to determine coring locations that capture the true species diversity for studies in lakes. [ABSTRACT FROM AUTHOR]

Recent studies have found that the relative importance of predictors of metacommunity structure is dependent on different factors. Low explanatory power of multivariate models is a frequent result. To increase this power, ecologists have suggested different strategies, including the use of functional approaches. Using a phytoplankton dataset from 17 reservoirs in Southern Brazil, sampled seasonally over eight years, we tested the hypothesis that the explanatory power of multivariate models would be higher when the analyses were based on functional groups than when based on a taxonomic approach. We also modeled the temporal variation in the strength of species sorting (as given by the adjusted coefficient of determination derived from environmental variables). We found high temporal variability in the strength of species sorting, indicating that results from snapshot surveys should be interpreted cautiously. When compared to the taxonomic approach, we did not find an increase in the explanatory power of multivariate models when the analyses were based on a functional approach. The main correlates of the temporal variation in the strength of species sorting were insolation, water temperature, and environmental heterogeneity, suggesting that conditions related to productivity and heterogeneity are important in determining the role of species sorting in phytoplankton communities. [ABSTRACT FROM AUTHOR]

We evaluated the influence of mesohabitats and catchments on the structural and functional composition of invertebrate communities associated with leaf patches in Atlantic Forest streams. We hypothesized that invertebrate communities would be more influenced by inter-habitat than inter-catchment variation, i.e., invertebrate taxonomic and trophic composition would differ more between pools and riffles than among catchments. Invertebrate richness differed among catchments only, while values of total abundance and biomass were higher in pools. The influence of mesohabitats on the structure of invertebrate communities was high, and most taxa had specificities with one mesohabitat. Among insect shredders, Grypopterigidae (Plecoptera) and Blattodea occurred more in riffles; Phylloicus, Nectopsyche, and Triplectides (Trichoptera) occurred more in pools. The biomass of omnivorous macroconsumers ( Trichodactylus fluviatilis and Macrobrachium potiuna) was higher in pools and also differed among catchments. Except gathering-collectors, the taxonomic composition of functional feeding groups differed between pools and riffles. The obtained results corroborated the hypothesis that the structural and functional composition of invertebrate communities is more influenced by inter-habitat than by inter-catchment variation, and reinforced the importance of maintaining the biological and geomorphological characteristics of streams to allow the accumulation of leaves in different mesohabitats and preserve the aquatic biodiversity. [ABSTRACT FROM AUTHOR]

Deforestation of riparian forests can directly influence stream macroinvertebrate communities, through changes in resource availability, habitat quality, and hydrological alterations. Here we evaluated whether mean discharge and discharge coefficient of variation (CV), estimated over a 15-month study, influenced forested and deforested stream macroinvertebrate communities. Higher diversity and mean discharge were recorded in deforested streams, and community composition was strongly related to mean discharge. Streams formed a gradient of both mean discharges and discharge CV, which both influenced patterns of diversity. Discharge CV negatively influenced diversity in a nonlinear model, whereas both mean discharge and discharge CV influenced differentiation of macroinvertebrate communities among five sampling occasions. Similarity among sampling times within each stream estimated by the Morisita-Horn index decreased with increasing mean discharge, whereas response to CV was quadratic, with higher similarity at intermediate values and lower similarity at more extreme values. These results suggest that stability of stream macroinvertebrate communities display different responses to mean discharge and discharge CV, and that hydrological alterations can interact with land use changes to determine community dynamics at local scales. [ABSTRACT FROM AUTHOR]

Little is known about the tolerance of Amazonian fish to ammonia. However, elevated ammonia of anthropogenic origin may now occur. As Amazonian fish evolved in waters which are generally acidic (i.e., low NH), we hypothesized that they would be more sensitive to ammonia than other freshwater fish. The acute (96-h) toxicity of NHCl was tested in native ion-poor soft water (pH 7.0, ~28 °C) using semi-static tests with 11 species. Species sensitivity distributions (SSDs) for LC50 and LC10 and calculations of the hazardous concentrations to the most sensitive 5% (HC5 values) were tabulated. Values of LC50/LC10 (in mM total ammonia) ranged from 2.24/0.78 for Paracheirodon axelrodi (most sensitive) to 19.53/16.07 for Corydoras schwartzi (most tolerant). These results confirm our hypothesis that Amazonian fish are more sensitive to ammonia than other freshwater species. High levels of ammonia may be associated with hypoxia, especially during dry periods. Simultaneous hypoxia (15-20% saturation) exacerbated ammonia toxicity in the most sensitive species ( P. axelrodi), but not in Astronotus ocellatus or Corydoras schwartzi, a facultative air-breather where prevention of air access doubled ammonia toxicity. The present data are useful in generating regulatory guidelines in Amazonian waters and indicate that further studies incorporating hypoxia and air access/denial are needed. [ABSTRACT FROM AUTHOR]

This study relates multiple parameters that are involved in the occurrence and control of malaria in the Amazon. Ebbs and floods, black and white waters, fishponds, and 'repiquete' (Amazonian waters phenomenon) influence the density of Anopheles darlingi Root, 1926. The adaptive processes, genetic background, and resilience of Anopheles vectors change in response to climate and environmental changes. This study covers the diversity of anophelines, which increases due to anthropic activities. Regarding strategies for vector control, the following measures are important: (1) use mechanical barriers inside houses (screens and impregnated mosquito nets), (2) determine the level of anopheline resistance to insecticides, and (3) determine the effect of the physiological state of females on malaria transmission effectiveness. Bioinsecticides were found to be efficient in the control of immatures, and there was no alteration of the associated fauna. Data on genetic variability and vector populations demonstrated greater polymorphism in intradomicile subpopulations. Furthermore, knowledge on the structural genome and transcriptome of A. darlingi, associated with bio-ecology and evolution, may indicate an adaptive strategy of this species to the Amazon biome. There are anthropic activities and environmental and climatic changes that favor increased vector density, requiring specific control strategies to reduce populations of this species. [ABSTRACT FROM AUTHOR]

In the present study, we analyzed eight streams (four located in areas with sugarcane cultivation and four located in preserved areas) and applied a simple method to find Chironomidae indicator species that characterizes groups of sites (preserved or disturbed by sugarcane cultivation). Specimens were collected during March 2002 and November2006, using a D-net (250 µm mesh size) in areas of rapids and backwaters. The organisms collected were identified to morphotypes level. In preserved streams, Parametriocnemus sp., Ablabesmyia ( Karelia) sp., and Endotribelos spp. had high densities. Chironomus spp. and Rheotanytarsus spp. were dominant in streams located in areas of sugarcane cultivation. The analyses of indicator species point to eight taxa in preserved streams and two taxa in the sugarcane streams. Nonmetric Multidimensional Scale analysis points to two groups, one gathered in the streams near the sugarcane plantation and the other in the preserved streams. The similarity test (Analysis of Similarity) pointed to significant differences ( P < 0.05) between these groups. This agricultural activity seems to influence the Chironomidae community structure in low order streams in the Cerrado region. The identification of groups at the morphotypes level was important to establish indicator species. [ABSTRACT FROM AUTHOR]

Ceratium species are not a common component of freshwater phytoplankton in South America. However, these dinoflagellates have often been observed in many water bodies over the past two and a half decades. We investigated Ceratium furcoides' abundance and morphological variation during its initial phase of colonization (2012-2013) in two subtropical reservoirs in southern Brazil in order to explore which environmental factors were related to the occurrence, persistence and bloom formation of this dinoflagellate in those environments. Biomass of C. furcoides showed a strong seasonal pattern, in which warm seasons led to an increase in population density, resulting in cell-size reduction, while in the cold seasons cells increased in volume. Maximum densities over 2,500 cells ml were observed in spring-summer periods in both reservoirs. C. furcoides' abundance in the studied reservoirs was associated, primarily, with a combination of optimal conditions of temperature, organic matter, and pH, and secondarily, with nutrient availability. The possible factors for the successful colonization performed by C. furcoides across distinct Brazilian waterbodies include good swimming performance, low herbivory pressure, and ability to form dense blooms, as strategies that allow maintenance of populations and effective dispersal. [ABSTRACT FROM AUTHOR]

Many arid and semiarid regions are likely to become warmer and drier by the end of this century, due to human-induced climate change. We hypothesize that a reduction in water level caused by droughts will aggravate eutrophication, leading to higher cyanobacteria biomass and dominance in tropical regions. To test this hypothesis, we analyzed physical and chemical variables and plankton communities of 40 man-made lakes in warm semiarid northeastern Brazil at the end of the wet and dry seasons. We also constructed a predictive model of cyanobacteria biovolume in these lakes. The lakes had significantly lower water volume, transparency, and CO concentrations but higher water temperature, water column stability, electrical conductivity, pH, suspended solids, ammonium, total nitrogen concentrations, bacteria biomass, phytoplankton biomass, and cyanobacteria biomass and dominance in the dry than in the wet season. Our regression model suggested that cyanobacteria biovolume was positively related to water column stability, pH, and total nitrogen and negatively related to water transparency and concentrations of inorganic suspended solids. These results suggest that the projected warmer and drier climate in the future will reduce water quantity and quality of man-made lakes in the region, increasing the risks of salinization, anoxia, eutrophication, and cyanobacteria blooms. [ABSTRACT FROM AUTHOR]

Freshwater bivalves provide important ecosystem functions and services, yet many of their ecological traits such as feeding mechanisms and resource use are largely ignored. In this study, we aimed to evaluate the potential overlap in resource use by bivalve species living in sympatry in European freshwater ecosystems. This was accomplished by analyzing the stable isotope ratios of carbon (C) and nitrogen (N) values of six bivalve species (five native species plus the invasive species Corbicula fluminea) in six distinct aquatic ecosystems. Results showed significant inter- and intraspecific differences in both stable isotope ratios. The interspecific variability suggests differences in the food sources consumed, which can be related to differences in feeding behavior. At the intraspecific level, there was a gradient in the stable isotope ratios from the oligotrophic River Paiva (N-depleted and C-enriched) to the eutrophic Mira Lagoon (N-enriched and C-depleted), suggesting a change in the resources used from benthic to pelagic food sources, respectively, and/or differences in the stable isotopic baseline in each ecosystem. Thus, flexible feeding strategies combined with size selectivity may decrease the possible competition for food sources by native and invasive species living in sympatry. [ABSTRACT FROM AUTHOR]

Riparian deforestation in rural areas has led to changes in bankside vegetation communities that may have unexpected effects on stream ecosystems. In particular, plants such as grasses can colonize the streambed from adjacent terrestrial habitats, thus altering the physical structure of the streambed and potential influencing macroinvertebrate communities. Here we evaluated if the presence of patches of grasses ( Urochloa sp.) on the streambed influenced the structure and composition of macroinvertebrate communities in deforested rural streams. We sampled patches with and without grasses in three low-order streams, in the wet and dry seasons. We recorded higher abundances of macroinvertebrates in patches with grasses in the wet season when compared with bare patches. We also found significant differences in taxonomic and functional feeding group composition between patch types, due to higher overall abundances in patches with grasses, probably due to more food and shelter there. These influences were stronger in the wet season, when in-stream grasses may have provided greater refugia from flood disturbance that occur with increased frequency and intensity. Therefore, although deforestation of rural streams can simplify streambed habitats, in-stream grasses such as Urochloa sp. provide resources that contribute for the maintenance of macroinvertebrate communities. [ABSTRACT FROM AUTHOR]

The use of diatoms as bio-indicators of water quality is common in temperate regions worldwide. However, less attention has been accorded to sub-tropical regions, particularly in Australia. This study assessed the value of diatom communities to infer water quality in a sub-tropical riverine system. Epilithic diatom and water samples were collected monthly from an east Australian river. Principal components analysis showed that the Lower Catchment sites were more strongly influenced by the measured environmental variables differentiating them from the Upper Catchment sites. Canonical Correspondence Analysis showed electrical conductivity and total phosphorus strongly influenced the diatom community distribution. The study revealed diatom species that are robust bio-indicators of water quality in this sub-tropical catchment. Cocconeis placentula, C. placentula var lineata, Gomphonema spec 2 and Tabellaria flocculosa were identified as indicators of moderate water quality. Bacillaria paradoxa, Navicula cryptocephala, Navicula mutica var mutica and Achnanthes fogedii were identified as indicators of poor water quality. This study identified that diatoms are effective indicators of water quality. Further research is required to develop a diatom biological index applicable to sub-tropical east Australian river systems to improve the effectiveness of environmental monitoring and sustainable river management. [ABSTRACT FROM AUTHOR]

The identification of higher scale geographical processes (e.g., island location) that shape regional (catchment and landscape patterns) and local factors (e.g., water quality, microhabitat) is crucial to a correct understanding of diatom distribution, especially in isolated oceanic islands'. To assess the contribution of these processes in the composition of diatom assemblages in insular permanent streams, a total of 316 samples were studied from 37 sites along 14 permanent streams in Azores archipelago and related to environmental variables. Ordination techniques were used to identify the forcing factors that best explain the composition of diatom assemblages. The results revealed how individual and collective patterns emerging from local, regional, and geographic factors, and their shared variance, provided us with more detailed insight into what factors determine the structure of insular diatom assemblages in Azorean streams. The variance explained by local factors (24.3%) dominated over the regional (20.9%) and geographic fractions (18.5%). This result supports the notion that insular stream ecosystems and their communities are under strong abiotic control, as well as their continental counterparts. The results of this study provide support for current and future stream ecosystem research and baseline information for developing integrated freshwater management strategies for streams on the Azorean archipelago. [ABSTRACT FROM AUTHOR]

The sampling skills of three common European fish species ( Barbus barbus, Chondrostoma nasus and Squalius cephalus) were tested to assess their potential as biomonitors of past changes in river water quality through the analysis of diatoms in fish guts. The study was performed on three rivers with different chemical and physical conditions. Comparison of similarity indices revealed low diatom assemblage resemblance between epilithic samples and samples collected from fish guts at the same locality. In contrast, a mixed-effect linear model identified significant differences between locations through comparison of diatom-based water quality indices. Among fish species, diatom indices calculated from gut samples of B. barbus and C. nasus were in most cases not significantly different from those from epilithic samples while those from S. cephalus were often significantly different. The results of the study demonstrate that diatom analysis of fish guts provides a clear distinction between eutrophic and hypereutrophic rivers. Finer nutrient variations within hypereutrophic conditions were also found to be significant for some diatom indices. In this context, choice of appropriate diatom water quality index proved to be crucial in maximizing the sensitivity of the method. [ABSTRACT FROM AUTHOR]

In the last decade, dozens of indices based on macroinvertebrates were developed to evaluate lotic ecosystems. In contrast, very few of these indices have been applied in lentic ecosystems. Natural wetlands in southern Brazil are increasingly threatened by the expansion of irrigated rice. The main objective of this study was to develop a multimetric index based on macroinvertebrates to evaluate the water quality of natural wetlands and rice fields in southern Brazil. Three samplings were carried out over the rice growth cycle in four conventional and four biodynamic rice fields, and four natural wetlands. The wetlands were considered as reference sites, and the conventional and biodynamic rice crops were considered as manipulated sites at different levels of degradation. Seven metrics were included in the final index after passing though sensitivity and correlation tests. The results indicated that our index has a power to detect a gradient of variation in water quality. Natural wetlands had the best water quality, biodynamic crops had intermediate water quality, and the conventional crops had the lowest water quality. We believe that development of this macroinvertebrate-based multimetric index of water quality could be an important tool for monitoring natural wetlands and rice crops in southern Brazil. [ABSTRACT FROM AUTHOR]

Óbidos Lagoon is classified as a sensible system according to the eutrophication criteria in the Portuguese Decree-Law 149/2004, which transpose the standards of Urban Waste Water Treatment Directive (Council Directive 91/271/EEC) concerning urban waste water treatment. From September 2005 onwards, the urban loads of five Waste Water Treatment Plant (WWTP) were deviated to a submarine outfall to prevent water degradation and improve the lagoon trophic state (LTS). This paper evaluated the LTS after urban loads diversion, testing the hypothesis behind the management decision. First, the loads reaching the lagoon were determined with the Harp-Nut guidelines and watershed modeling. Then, the water quality in the lagoon was simulated with a hydro-ecological model and compared with measured data. Finally, management scenarios corresponding to nutrient loads reduction were tested to determine hypothesis-driven LTS. Results showed that the loads from pig farms should be diverted instead of the WWTP, to improve the LTS and achieve a 'Good/Bad' status. The proposed method stresses the importance of integrated modeling tools in the Water Framework Directive, given their skill in testing various hypothesis, and ultimately ruling out inadequate management decisions before implementation. [ABSTRACT FROM AUTHOR]

Subfossil biotic assemblages in lakes' surface sediments have been used to infer ecological conditions across environmental gradients. Local variables are usually the major drivers of assemblage composition, but in remote oceanic islands biogeographic filters may play a significant role. To assess the contribution of local and regional filters in the composition of subfossil diatom and chironomid assemblages in surface sediments, 41 lakes in Azores archipelago were studied and related to environmental variables. Ordination techniques were used to identify the forcing factors that best explain the composition of these assemblages. Both assemblages are influenced by multiple limnological variables (conductivity, pH and nutrients). However, diatom assemblages differed mainly in the proportion of planktonic versus benthic species along lakes' depth gradient while chironomids differed significantly among islands but not among lake depths. Thus, biogeographic filters play an important role in shaping islands' freshwater communities, particularly insect ones, more influenced by geographic variables. Results demonstrate the accuracy and potential of biotic remains in sediments for applied studies of lake ecology, trophic status, climatic trends and ecological reconstruction and evolution of lakes. In the Azores, the application of this information for the development of inference models is envisaged as a further step to accomplish these goals. [ABSTRACT FROM AUTHOR]

The majority of studies comparing the response of biotic metrics to environmental stress in rivers are based on relatively small, homogeneous datasets resulting from research projects. Here, we used a large dataset from Austrian and German national river monitoring programmes (2,302 sites) to analyse the response of fish, diatom and macroinvertebrate metrics to four stressors acting at different scales (hydromorphology, physico-chemistry, riparian and catchment land use). Nutrient enrichment and catchment land use were the main discriminating stressors for all organism groups, over-ruling the effects of hydromorphological stress on the site scale. The response of fish metrics to stress was generally low, while macroinvertebrate metrics performed best. The Trophic Diatom Index (TDI) responded most strongly to all stressors in the mountain streams, while different metrics were responsive in the lowlands. Our results suggest that many rivers are still considerably affected by nutrient enrichment (eutrophication), which might directly point at implications of catchment land use. We conclude that monitoring datasets are well-suited to detect major broad-scale trends of degradation and their impact on riverine assemblages, while the more subtle effects of local-scale stressors require stream type-specific approaches. [ABSTRACT FROM AUTHOR]

A correction to the article "Effects of Fish Farming on Plankton Structure in a Brazilian Tropical Reservoir" that was published in a previous issue is presented.

To understand whether seasons influence the ecological quality assessment of streams on the basis of diatoms, a study was undertaken in two lowland water courses located in northwest Portugal, between autumn 2008 and summer 2009. Temporal variation in the chemical pollution of these streams was small as revealed by a number of physical and chemical parameters analyzed. PERMANOVA global test revealed significant variation in water temperature among seasons. The diatom communities also showed a temporal variation although not all the seasons were statistically different. The multidimensional scaling analysis showed that the main differences in the diatom communities were between two groups of seasons: autumn/winter and spring/summer. Species such as Cocconeis pseudolineata, Gomphonema parvulum var. exilissimum, Fragilaria vaucheriae, Encyonema minutum, and Nitzschia recta were more abundant in spring/summer, while species such as Mayamaea atomus and Nitzschia pusilla were more abundant in autumn/winter. The BIOENV routine confirmed that the biological and temperature patterns are highly correlated. Despite the effects observed on diatom communities, these differences were buffered by the EQR (IPS) values which do not reflect seasonal differences. Therefore, the use of the index IPS seems to allow the monitoring of the streams' ecological quality throughout the year without the interference of the natural temporal variability of diatom communities. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate whether biological methods based on epilithic littoral diatoms are a valuable complement to other biological elements for the assessment of the ecological potential of reservoirs in Portugal, in accordance with the requirements of the European Water Framework Directive. The statistical analysis performed (PCA, DCA, ANOSIM and SIMPER) based on the study of diatom communities of 18 reservoirs allowed the following results: (i) the separation of all the a priori defined types (North, Main Courses and South) was proved; (ii) there were no significant differences between reservoirs classified as reference and non-reference and (iii) the classification of the reservoirs as reference or non-reference based on the use of the diatom Specific Pollution sensitivity Index as a complementary variable allowed the definition of Maximum Ecological Potential reservoirs for the North and South types. Methods based on the use of epilithic littoral diatoms can therefore contribute, together with other biological elements, for the assessment of the ecological potential of aquatic lentic systems in Portugal, almost exclusively constituted by reservoirs. [ABSTRACT FROM AUTHOR]

A predictive model for diatoms based on an adaptation of the River Invertebrate Prediction and Classification System/Australian River Assessment System approaches was evaluated as an effective tool for measuring stream ecological quality. This type of model was originally developed in UK and later in Australia and is extensively used to obtain ecological quality assessments with macroinvertebrates. The first step for the model construction was the definition of six consistent reference biological groups (ANOSIM: Global R = 0.77; P < 0.001) after classification (UPGMA) and ordination (nMDS) of 120 reference sites containing 254 different diatom taxa (species and infra-specific rank). A set of five environmental variables (slope, hydrological regime, mean annual temperature, mean annual precipitation and alkalinity) correctly discriminated 67% of reference sites (stepwise forward discriminant analysis, Jackknifed classification). The model was statistically accurate (slope = 1.07, intercept = −0.68, R = 0.65) and was validated by an independent set of reference data (13 reference sites; 70% correct answers). In addition, the model was tested by running data from 113 potentially disturbed sites. The model (DIATMOD) was well correlated with a general abiotic degradation gradient (Spearman correlations, R = 0.53, P < 0.001; and PCA analysis) and also with several specific pressure variables such as nitrates, phosphates, urban area, connectivity and land use ( P < 0.001). Most diatom indices assess chemical contamination and we showed here that through predictive modelling the potential of diatoms as bioindicators increases as they also responded to hydromorphological changes. Further investigation on model potential consists in: testing different probability levels for taxa inclusion (here it was >0.5 as the most common models); comparing with alternative classification systems; assessing the influence of substrate type and seasonal variation in assessments. [ABSTRACT FROM AUTHOR]

Sampling benthic macroinvertebrates in large rivers has several limitations, arising not only from the selectivity of traditional sampling gears but also from difficulty in capturing organisms that inhabit the deeper zones and high current velocities. Considering the importance of benthic macroinvertebrates as a food resource for fishes, the sampling restrictions in sediment collection done by dredges, and the importance of surveying benthos biodiversity, the objective of this study was to evaluate the stomach contents of five commonly-occurring invertivorous fish species as a means of complementing a benthic macroinvertebrate inventory. Three sampling campaigns (fish and benthic macroinvertebrate) were conducted in a reach of the Araguari River (Minas Gerais, Brazil), approximately 9 km long and 90 m wide. Astyanax altiparanae Garutti & Britski 2000, Leporinus friderici (Bloch 1794), Leporinus amblyrhynchus Garavello & Britski 1987, Iheringichthys labrosus (Lütken 1874) and Pimelodus maculatus Lacepède 1803 were the fish species collected and studied. To determine benthic macroinvertebrate taxonomic richness, a total of 54 Van Veen sediment samples were obtained. We compared lists of the benthic taxa found in fish stomachs with those from the sediment samples. The differences in the taxonomic composition of the benthic macroinvertebrate communities between the sediment samples and each fish species stomachs contents were assessed through NMDS and ANOSIM analyses, using a Sorensen similarity index with the presence/absence of taxa data. Independent of sampling period, additional benthic macroinvertebrate families or classes were provided by identifying fish stomach contents. We found a total of 30 taxa in this study, including 5 unique taxa (or 17% of the total) in the sediment samples, 9 unique taxa (30%) in the stomach samples, and 16 taxa (53%) common to both. The NMDS and ANOSIM analyses showed a significant separation between Van Veen sediment samples and two fish species stomach contents- L. amblyrhynchus and P. maculatus. These results indicate that fish can be used as additional samplers and are an efficient method to complement the benthic taxonomic inventory obtained through traditional sediment sampling techniques in large areas, as river segments and catchments. [ABSTRACT FROM AUTHOR]

Diatom-based indices are increasingly becoming important tools for the assessment of ecological conditions in lotic systems. The applicability of regional and foreign diatom-based water quality assessment indices to streams around São Carlos-SP, Brazil, is discussed. The relationship between measured water quality variables and diatom index scores was assessed. The indices, when compared to chemical analyses, proved useful in providing an indication of the quality of the investigated waters. Though all borrowed indices were applicable to the study area because many widely distributed diatom species have similar environmental tolerances to those recorded for these species elsewhere, ecological requirements of some diatom species from Brazil need to be clarified and incorporated in a diatom-based water quality assessment protocol unique to the region. [ABSTRACT FROM AUTHOR]

Tagus estuary is one of the largest estuaries of Western Europe. With the aim of unravelling the drivers of primary production in this shallow and turbid nutrient replete estuary, we tested the hypothesis that light availability is a major factor controlling phytoplankton production. Environmental parameters, phytoplankton biomass, community composition, and photosynthetic parameters were monitored at two sites in the estuary during a complete annual cycle. Despite the fact that nutrient concentrations were always above growth-limiting values, Chl a concentrations were relatively low throughout the study period. High water column turbidity, due to riverine inputs, promoted a rapid attenuation of light and created a compressed profile with optimal photosynthetic conditions. Therefore, the phytoplankton community, dominated by small cells, such as diatoms and cryptophycean flagellates, displayed highly photosynthetic efficiency and low light-saturated photosynthetic rates as a photo-acclimation response to low light conditions year-round. Primary production rate was unimodal, peaking in the summer months. In such estuarine system, gross primary production could thus be predicted by an existing robust empirical model based on pigment standing crop (Chl a), surface irradiance ( E) and optical depth ( Z). Compared to other shallow estuaries, the Tagus can be classified as a low- to moderately productive estuary, being the turbidity-induced low light conditions the principal factor limiting phytoplankton growth. [ABSTRACT FROM AUTHOR]

Hydrilla verticillata (Hydrocharitaceae) is a highly prolific, rooted submerged macrophyte native to Asia that has invaded aquatic systems worldwide, causing many ecological and human-related problems. Hydrilla recently invaded the Paraná River basin in Brazil, making other ecologically and socially important Brazilian watersheds more susceptible to invasion by this plant. Here, I summarize the relevant information about Hydrilla, focusing on its biotic attributes, abiotic tolerance and effects on ecosystems. The aim of this review is to provide background information to assist with planning for the potential impacts of this species in the Neotropical region (particularly in Brazil) and the development of research, monitoring and management strategies. A wide ecological amplitude, resistance organs, and high growth rates and dispersion ability provide Hydrilla with great potential to invade and infest a variety of habitats, often resulting in important physico-chemical and biotic effects on the environment. Hydrilla is similar in its morphological and ecological aspects to Egeria najas and Egeria densa (South American Hydrocharitaceae), but this non-native species is a superior competitor and can be expected to exert significant pressure in habitats colonized by these native Hydrocharitaceae. Socially important rivers (such as the São Francisco River) have a high risk of being infested with Hydrilla, especially in stretches affected by dams, which could prejudice important human activities like hydropower generation. Important wetlands for biodiversity conservation (such as the Pantanal) may also be invaded, but they seem to be more resistant to infestations as long as their natural hydrologies are preserved. Before investing substantial effort to control Hydrilla, managers should weigh the potential costs and benefits of available techniques and consider the potential benefits of Hydrilla in providing ecosystem services. [ABSTRACT FROM AUTHOR]

This study investigated the effects of fish farming on phytoplankton and zooplankton structure in a Brazilian tropical reservoir. Samplings were undertaken among 15 net cages and upstream and downstream of the cages over a 120-day period. Soon after the tilapia feeding, we observed the highest density of phytoplankton, with dominance of Cyanobacteria which probably increased due to the increase in predation pressure by cladocerans and copepods on the Cryptophyceae. However, after 30 days from that, a reduction in zooplankton density was registered due to the dominance of Cyanobacteria. The absence of a clear spatial difference in the phytoplankton and zooplankton densities was observed. The effects of the net cages on the nutrients and planktonic communities were small, probably due to the low number of net cages and fish employed, the seasons (autumn/winter) and the hydrodynamics, as lotic traits, the strong influence of the wind, and the large extension of the mixture zone. [ABSTRACT FROM AUTHOR]

This study investigated the fish fauna of a stream in southeastern Brazil that runs through sugar cane-growing and urban areas that are subject to sewage discharge. It aimed to determine the importance of spatial and environmental factors on fish distributions and to assess the use of fish as indicators of the environmental conditions. A longitudinal pattern of chemical water quality was observed, with more disturbed conditions at the urban sites. Several opportunistic or tolerant and omnivorous species such as Astyanax altiparanae, Poecilia reticulata, and Astyanax fasciatus were numerically abundant at these urban sites, which resulted in a consistent increase in species density and biomass along the stream. Redundancy analysis extracted three axes, identifying a nutrient–productivity gradient associated with different species composition patterns, as also detected by the indicator species analysis. No species could be considered a potential indicator of the agricultural area in the dry season, whereas four different species were judged potential indicators of three urban sites. In order to explain species distribution, variation in species abundance was partitioned into spatial and environmental components. The latter was more important, explaining 25.4% of the variation. We concluded that the fish assemblage of the Guamium stream is undergoing the initial stages of disturbance, with pronounced effects at the urbanized area, but no detectable changes at the sugar cane sites. Therefore, fish assemblages might be used as ecological indicators to detect urban impacts in similar rivers. However, the potential use of fish to diagnose stressors in areas of sugar cane plantations should be complementary to more comprehensive studies aimed at understanding the influence of this crop on freshwater resources. [ABSTRACT FROM AUTHOR]

Phytoplankton communities are structured by factors acting over temporal and spatial scales. Identifying which factors are driving spatial patterns in aquatic communities is the central aim of ecology. In this study, data sets of phytoplankton communities and environmental data of two Portuguese reservoirs types (lowland “riverine reservoirs” and higher altitude “artificial lake reservoirs”) were used to determine the importance of environmental variables at different spatial (geographical, regional and local) and time scales (seasons, years) on the community structure. In all the data sets, the multivariate ordination technique Canonical Correspondence Analysis (CCA) showed that regional and local scales explained the majority (9–18% and 13–19%, respectively) of the taxa variance. However, for “riverine reservoirs”, time variables were more important, explaining 27% of the variability in phytoplankton assemblages. Variance partitioning was used to assess the individual importance of the three spatial scales and time for the community structure of the two reservoir types. The majority of among-site variability (5.9–21.4%) was accounted for by time variables, with local, regional, and geographical scale variables accounting for 3.3–5.6%, 3.7–4.5% and 2.6–2.9%, respectively. The effects of different spatial scales on phytoplankton communities were clearly interrelated; thus, implying that phytoplankton assemblages are capable of detecting stress from catchment to site scales. [ABSTRACT FROM AUTHOR]