Dams change the hydrological dynamics, patterns of biological production and distribution of organisms in space and time. In contrast, tributary rivers can function as source areas in reservoirs, since they harbor spawning and early development grounds for native fish species. Here, we analyze a time series of the first 14 years after the impoundment of the Porto Primavera Reservoir, a large reservoir with free tributaries in southeastern Brazil. To evaluate the impact of damming on the fish assemblage, we evaluated the abundance (catch per unit effort, CPUE) and α (species richness and Shannon-Wiener index) and β (Sørensen dissimilarity and turnover) diversity of four sites distributed along the reservoir. Overall, there was no decreasing trend in the α diversity and no increasing trend in the β diversity relative to the initial year or among the sites over time. Despite the expected disturbance in the fish assemblage at the lacustrine site, the sites located near the tributary mouths presented resistant fish assemblages, compensating the results of the overall assessment. We attribute this unusual variation in the ecological attributes to source-sink demographic dynamics, with the undammed tributaries as the source and the reservoir as the sink for native species. We highlight that the presence of these rivers minimized the expected trend towards biotic homogenization, and the preservation of the tributaries is imperative since they contribute to diversity maintenance in areas that are already impacted by damming. The inclusion of this agenda in environmental management programs and new impoundment plans will allow a balance between the demand for electricity production and the conservation of fish diversity.

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This study aimed to evaluate the zooplankton structures and environmental conditions in the interface reservoir‐downstream river and tributaries. Zooplankton structure and environmental variables were analyzed in the lacustrine zone of Itaipu Reservoir and downstream this dam at Paraná River and in two lateral tributaries. A total of nine sites were sampled in July 2009 and January 2010 (winter/dry vs. summer/wet). In the free‐flowing section downstream of the Itaipu Reservoir (Paraná River), the physical–chemical influence of the dammed water can persist for approximately 15 km in the dry period and 30 km in the rainy period. The lateral tributaries (Iguaçu and Monday Rivers) introduce sediments (particulate organic and inorganic matter), nutrients and potamoplankton biota that contribute to fluvial restoration, particularly in the dry period when the main river flow is low. The zooplankton community structure and composition varied over space (longitudinal) and time. Rotifers dominated in the lateral tributaries, whereas microcrustaceans from the reservoir were abundant in the Paraná River. The density of zooplankton downstream of the reservoir decreased, with the highest reduction occurring in the first 5 km downstream of the dam, however, the species composition persisted in the all free‐flowing section downstream studied. Associations were found among zooplankton abundance and environmental variables, mainly the current velocity and water discharge; zooplankton groups had different responses to these variables. Differences in the zooplankton ecological structure along a stretch of the Paraná River clearly indicate the effects of damming and tributaries.

The integration of ecology and historical biogeography is fostering the investigation of diversity patterns. We studied alpha and beta diversity patterns of Brazilian Atlantic Forest harvestman (Arachnida: Opiliones) communities and related them to environmental and historical factors. Our data bank contains 508 species from 63 sites, encompassing almost the entire latitudinal range of Atlantic Forest. Alpha diversity was higher in coastal sites in the south and southeast regions and decreased in sites inland, as well as in sites in the coastal northeast region, especially in northern Bahia state. Alpha diversity was positively influenced by precipitation and altitudinal range, but the low number of species in northeastern coastal sites seems to be more related to the historical distribution of Neotropical harvestman lineages than to recent environmental factors. Geographic distance was the most influential factor for beta diversity. Compositional changes were also remarkably congruent with areas of endemism delimited for Atlantic Forest harvestmen. The percentage of protected areas for each area of endemism was very unbalanced, and Espírito Santo and Pernambuco states were the least protected areas. The turnover process observed in the compositional changes indicates that conservation strategies should include as many reserves as possible because every community presents a unique set of species.

The Cladocera assemblages in two cascade reservoirs located in the Paranapanema River in Brazil were studied during two consecutive years. Upstream Chavantes Reservoir is an accumulation system, with a long water retention time, high depth and oligo-mesotrophic status. The downstream Salto Grande Reservoir is a small, run-of-river reservoir, with a short water retention time, shallow depth and meso-eutrophic status. The goal of this study was to determine the interand intra-reservoir limnological differences with emphasis on the Cladocerans assemblages. The following questions were posed: (i) what are the seasonal dynamics of the reservoir spatial structures; (ii) how dynamics, seasonally, is the reservoirs spatial structure; and (iii) are the reservoir independent systems? A total of 43 Cladoceran species were identified in this study. Ceriodaphnia silvestrii was the most abundant and frequent species found in Chavantes Reservoir, while C. cornuta was most abundant and frequent in Salto Grande Reservoir. The Cladoceran species richness differed significantly among sampling sites for both reservoirs. In terms of abundance, there was a significant variation among sampling sites and periods for both reservoirs. A cluster analysis indicated a higher similarity among the deeper compartments, and the intermediate river-reservoir zones was grouped with the riverine sampling sites. For the smaller Salto Grande Reservoir, the entrance of a middle size tributary causes major changes in the system. A distinct environment was observed in the river mouth zone of another small tributary, representing a shallow environment with aquatic macrophyte stands. A canonical correlation analysis between environmental variables and Cladoceran abundance explained 75% of the data variability, and a complementary factorial analysis explained 65% of the variability. The spatial compartmentalization of the reservoirs, as well as the particular characteristics of the two study reservoirs, directly influenced the structure of the Cladoceran assemblages. The conditions of the lacustrine (dam) zone of the larger Chavantes Reservoir were reflected in the upstream zone of the smaller downstream Salto Grande Reservoir, highlighting the importance of plankton exportation in reservoir cascade systems. The comparative spatial-temporal analysis indicated conspicuous differences between the two reservoirs, reinforcing the necessity of considering tropical ⁄ subtropical reservoirs as complex, multi-compartmental water systems.

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ABSTRACT. Spatial-temporal variation of Rotifera in an eutrophic reservoir in southern Brazil. We analyzed the spatial and temporal variation of rotifers in a small, shallow and eutrophic reservoir, with intense Cyanobacteria blooms, in seven sampling stations during 17 months (March/2002 to July/2003. Fifty-two taxa were identified, comprising 16 families. Brachionidae, Conochilidae, Synchaetidae, Lecanidae, Collothecidae, Trichocercidae, and Gastropodidae were the most commonly found. Collotheca sp. was abundant in the winter (dry period), while numbers of Conochilus coenobasis and Keratella cochlearis were low. The abundance of Brachionus mirus var. reductus, Filinia longiseta and Keratella lenzi peaked in the summer (rainy season), while for Kellicottia bostonensis, Ploesoma truncatum, Polyarthra remata, Polyarthra vulgaris and Ptygura sp., abundance was highest in the winter, mainly associated with atypical rainfall. Significant differences in the number of taxa and abundance of rotifers were observed during the sampling period. The canonical correspondence analysis explained 46% of the relationship between rotifer abundance and environmental variables, positively correlated with rainfall, nitrite, water temperature, organic nitrogen, nitrate and air temperature. Variations in rotifer abundance were observed a month after changes in the phytoplankton community. Taxa, such as Filinia longiseta, Keratella lenzi and Keratella cochlearis, showed a temporal variation similar to that of other eutrophic reservoirs, while the heterogeneous distribution pattern observed in most taxa could be due to the hydrodynamics of the recently built reservoir and the adverse climatic conditions. KEYWORDS.Water supply, eutrophication, Cyanobacteria. RESUMO.A variação espacial e temporal de rotíferos foi analisada em um reservatório pequeno, raso e eutrófico, com intensas florações de algas Cyanobacteria, em sete pontos de amostragem durante 17 meses (março/2002 a julho/2003). Foram identificados 52 táxons em 16 famílias, sendo Brachionidade, Conochilidae, Synchaetidae, Lecanidae, Collothecidae, Trichocercidae e Gastropodidae as mais frequentes. Collotheca sp. foi abundante no inverno (período seco), enquanto Conochilus coenobasis Skorikov, 1914 e Keratella cochlearis Gosse, 1851 apresentaram baixas abundâncias. Brachionus mirus var. reductus (Koste, 1972), Filinia longiseta (Ehrenberg, 1834) e Keratella lenzi (Hauer, 1953) apresentaram picos de abundância no verão (período chuvoso), e Kellicottia bostonensis (Rousselet, 1908), Ploesoma truncatum (Levander, 1894), Polyarthra remata (Skorikov, 1896), Polyarthra vulgaris Carlin, 1943 e Ptygura sp. no inverno, entretanto, relacionados a chuvas atípicas. Diferenças significativas do número de táxons e da abundância total dos rotíferos ocorreram entre os meses amostrados. A análise de correspondência canônica explicou 46% da relação da abundância dos rotíferos e variáveis ambientais, correlacionados com a pluviosidade, nitrito, temperatura da água, nitrogênio orgânico, nitrato e temp...

Copepod assemblages were analysed across La Plata River basin, the second largest in South America. High values of species richness and Shannon–Wiener diversity were found in the lower Paraná River, the main and largest river of the basin, and in eutrophic reservoirs located in the upper basin. The species richness was negatively correlated with turbidity, probably because of the negative impact on filtration rates in calanoids. There was a trend of decreasing richness correlated with high water flow in reservoirs with short water-retention time (<40 days) and simple morphometric shape, and also in deeper oligo-mesotrophic reservoirs with very long water-retention time and dendritic shape (variables that occurred in combination in the present study). The number of copepod species (46) found in our study is only about half of the gamma diversity estimated using Jack1 non-parametric analysis for the basin (86 species). There are groups of copepod species typical of reservoirs and rivers, and others that can occur in both of these habitat types. Reservoir and lentic species are favoured by a deeper water column, higher temperatures and higher transparency, whereas the opposite is the case of typical riverine species. There is also a group of species that occur in both sets of conditions.