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This study examines the morphological features, suspended sediment inputs and hydraulic conditions within a large river in association with ecological patterns before and after a tributary confluence. In order to examine these effects, the macroinvertebrate distributions from three reaches of the Paraguay and Bermejo Rivers (Paraguay-Argentina) are investigated. The Bermejo River is a tributary that supplies significant quantities of fine sediment to the Paraguay River, primarily in suspension. Two reaches were examined on the Paraguay River, upstream and downstream of the Bermejo River junction, with the third study reach located on the Bermejo River, upstream of the confluence with the Paraguay River. The results provide clear evidence that a significantly increased loading of fine sediment at a river confluence has effects on the distribution and potential movement of benthic invertebrates in the lotic environment by representing physical barriers at affected sites. These effects may be important at both local and regional scales, and such increases in suspended sediment (especially associated with anthropogenic change) may thus pose a major threat to ecosystem integrity that has been historically underestimated.

Temporal variability in river morphology, sedimentology and flow are a fundamental control on instream habitat structure and riverine ecosystem biodiversity. However, long-term riverine ecological time-series in a wider temporal context are particularly rare. The present research involves long-term data series of riverine physical habitat and benthic macroinvertebrate ecology in the Correntoso River (secondary channel of the Paraná River floodplain).An anthropogenic morphological alteration was identified at the river inlet. As a consequence, a large sedimentation area was originated at the river inlet, preventing the inflow of suspended sand to the Correntoso. However, the natural morphological evolution during the last decades, probably led by three large floodings (1983, 1992 and 1997?8), reconfigured the inlet morphology, allowing the inflow of suspended sand into the channel. These phenomena allowed the sandy sedimentation a few kilometers downstream, redefining its bottom sediment condition over the years. This long-term process prompted great changes on benthic invertebrate ecology, causing a significant fauna depletion. This research demonstrates the value of long-term data series in ecological studies as well as the importance of an interdisciplinary point of view. Linking physical processes to ecology is particularly useful to aid understanding of the ecological legacy of anthropogenic modification and natural evolution on river systems. Fil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Amsler, Mario Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Ezcurra de Drago, Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Bullo, Juan M.. Universidad Nacional del Litoral; Argentina Fil: Paira, Aldo Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Drago, Edmundo Carlos E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Espínola, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Fontana, Livia O.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Eberle Folmer, Eliana Gisel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Instituto de Limnología "dr. Raul A. Ringuelet". Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Limnología ; Argentina

The middle and lower sections of most large rivers have fine-grained bed sediments, which may have a strong influence on the functional and taxonomical structure of benthic invertebrates. Based on results from several studies by the authors on the faunal assemblages and habitat structures of the Paraguay-Paraná River system (Brazil, Paraguay, Argentina), from European (Rhine, Loire) River systems, and data from the literature, this review identifies general patterns which appear to have a global character. At one hand the invertebrate assemblages largely differed between main channel and the corresponding floodplain habitats in different sections, and also the floodplain habitats along the river channel revealed great differences in their biodiversity. At the other hand there was a remarkable homogeneity among the main-channel sections within and even between river systems. We consider physical habitat features as the crucial variable responsible for these patterns. In cross sections from the main channel towards the floodplain habitats, grain size, organic matter content and oxygen supply change dramatically, and different floodplain habitats along the same river system may have different successional stages even at small geographical distances. The sandy structure of potamal habitats (including underwater dunes), however, provides a set of habitat features characterized by continuously changing sediment structures with well-defined grain sizes, low organic matter contents, and good oxygenation, which force a set of adaptations by the invertebrates that limits but stabilizes the diversity of invertebrates in these large river sections. A better understanding of the ecohydrological interactions between habitat dynamics and benthic invertebrates is needed to improve sustainable river ecosystem management. We discuss the nonrecovery of large benthic invertebrate species in the lower section of large rivers after improvement of the water quality in the context of these ecohydrological features. Conclusions are drawn for river restoration. Fil: Wantzen, Karl Matthias. Université François-Rabelais de Tours; Francia Fil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Marchese Garello, Mercedes Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Amsler, Mario Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentina Fil: Bacchi, Michel. Université François-Rabelais de Tours; Francia Fil: Ezcurra, Ines Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Drago, Edmundo Carlos E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina

A detailed hydro-ecological study to identify the effects of bed flow and morphodynamic processes on the distribution (and composition) of benthic invertebrates in a large river is presented herein. A crossing-pool sequence in a meander bend of the Paraguay River (Paraguay–Argentina) was examined. According to the results, there is a link between the benthic fauna, hydraulic and bed sediment size along the bend. The meander pool, with a deep scour hole and the largest bed shear stresses, would be a hostile area for benthic invertebrates, since lower densities were found there. A transversal analysis revealed two different invertebrate assemblages at each of the sampled cross sections: one across the mobile bottom with higher densities but lower diversity, richness and evenness than the other one found close to the banks. On the other hand, a comparison between both Paraguay and Parana rivers revealed that the first one would seem to have optimal hydraulic conditions for the invertebrate's development, because the hydraulic energy of the Parana River was too intense for the favorable settlement of benthic organisms at some specific habitats. The overall conclusion of this paper, that morpho-hydraulic features and biotopes are related, is an important step forward in river ecohydrology. With further development of this concept, river management techniques can improve and river rehabilitation projects can be designed with greater confidence.

Dunes are ubiquitous bed forms in river channels which deeply interact with the mean and turbulent flow dynamic. These interactions involve the intricate mechanisms governing the entrainment, transport, and deposition of bed sediment which are being studied since long time ago. However, the links between dunes and stream ecology, such as the benthic fauna distribution, was not yet investigated to the authors’ knowledge. This study aims to optimize the benthic sampling techniques on bed forms, and links the different hydraulic characteristics prevailing on crests and troughs of dunes and the invertebrate distribution on the Middle Parana River (Argentina). It was also possible to have an insight of the invertebrate distribution living in these bed areas (i.e. crests and troughs) as well as the influence of dunes location on the channel bed. A significant distinction of benthic distribution (densities) on dunes, as a consequence of their location on the bed and hydraulic conditions, was found. The overall results showed a clear preference by invertebrates for the dune with lower bed shear stresses. The study concluded that dunes could be considered as biotopes hydraulically differentiated and, consequently, with a stratified benthic distribution. Consequently, to discriminate bottom areas, by an appropriate selection of the hydraulic variables over the associated geometry of dunes, is an effective way to reduce the variance and to increase the accuracy of benthic samplings in large rivers.

The golden mussel Limnoperna fortunei was introduced into Argentina in 1991 and has since been spreading through the Plata and Guaiba basins at a rate of 240 km.year x1 . To assess their ability to invade the Andean tributaries of the Plata Basin (Pilcomayo, Bermejo and Salado del Norte rivers), their current range was assessed and related to the abiotic parameters of sites where they were present and absent. These data were then compared with their known tolerances to identify possible barriers to invasion. Outputs suggested that three environmental parameters are barriers to invasion: salinity and river flow intermittence in different sectors of the rivers Pilcomayo and Salado del Norte, and concentration of suspended sediments in the Bermejo River and in the upper reaches of the Salado del Norte and Pilcomayo rivers. The importance of these findings is discussed in relation to using environmental data to infer the invasion possibilities and the utility of environmental data to better understand invasion patterns and processes.

Hydraulic and substratum conditions have been identified as two stream features which affect the benthic community composition, abundance and distribution. However, little attention has been given to the influence of hydraulic variables in large river beds. The aim of this study was to analyse the incidence of the near-bottom hydraulic conditions and other environmental variables on the density of Narapa bonettoi (Oligochaeta, Narapidae), a typical and dominant species found in sandy bed rivers of diverse hierarchy of the Parana River basin. A large amount of existing and available benthic data were used. The highest correlations among N. bonettoi densities and environmental variables were obtained with the hydraulic variables of friction Reynolds number (R*) and shear stress (τ0); the substratum type (sand, silt and clay) and organic matter content. The results show that N. bonettoi density would be related with the hydraulic variables following a ‘bell-shaped’ tendency, e.g. with the friction Reynolds number, N. bonettoi would have a preference for transition values of turbulence (∼40 ∼70). Significant but negative correlations were reported in the literature between benthic macroinvertebrates typical of smaller and steeper streams and R* values far beyond the threshold 70 value. N. bonettoi shows a clear preference for a completely sandy substratum and for sand particles sizes around 300 µm. Finally, considering the important role played by the hydraulic variables on the benthic community studied herein, the contagious distribution pattern of N. bonettoi, reported by other authors, would be principally linked with the interactions between current and sediment near the bottom rather than with the mobility of these organisms. Copyright © 2008 John Wiley & Sons, Ltd.

This paper presents the first study of the benthic invertebrate assemblages of the upper section of the Paraguay River, a major tributary to the Pantanal wetland in Brazil. Thirty-eight sites were sampled along a 200 km section below the city of Caceres in November 2000. Sixty-nine species and morphospecies were identified, which were dominated by Oligochaeta and Chironomidae. Mean density of benthic invertebrates varied between 72 and 10 354 m−2 in the meandering sector of the river, 3611–49 629 m−2 in the straight–transitional sectors, 682–5962 m−2 in the floodplain lakes, and 1704–2208 m−2 in floodplain channels. Highest densities were attained in sand-gravel sediments dominated by the psammophilous oligochaete Narapa bonettoi. The Shannon diversity index ranged from 0.75 to 2.08 and was highest in floodplain lakes. Statistical analysis (UPGMA and CCA) revealed that benthic assemblages in the floodplain habitats were clearly distinct from the riverine habitats. In the river channel, the habitats were distinguished by grain size while the floodplain habitats were mostly determined by current and silt-clay concentration (floodplain channels) or by organic matter concentration (floodplain lakes). Conservation efforts in the Upper Paraguay area should aim to maintain the flood pulse as a permanent source of spatial and temporal habitat heterogeneity. Copyright © 2005 John Wiley & Sons, Ltd.

We studied the composition and spatial structure of benthic invertebrate assemblages and their physical and chemical environment on a 331 km long section of the Lower Paraguay River between Asuncion (Paraguay) and the river's confluence with the Parana River near Corrientes (Argentina). Applying the same methods used in former studies in the Upper Paraguay and Parana Rivers, we sampled bottom fauna, bed sediments and water at ten riverine stations, two tributaries, and six floodplain lake sites. Seventy-six taxa, mostly oligochaetes (18 species) and chironomids (17 species), were identified. There was a clear distinction between central sites, river banks, and floodplain habitats. Highly significant regressions between sediment composition and biotic parameters were obtained (clay/diversity, R = 0.60, p < 0.0001; silt/diversity, R = 0.61, p < 0.0001; organic matter/diversity, R = 0.63, p

Limnoperna fortunei (Dunker, 1857) (Bivalvia, Mytilidae) was first reported from Rio de La Plata in 1991; soon thereafter, it spread widely throughout the basin, causing great damage to all sorts of water supply systems. The desiccation period that young and adults can tolerate was analyzed in laboratory and outdoor experiments. L. fortunei is tolerant to desiccation. The tolerance increases with size. About 72 h was required to kill small mussels (up to 6 mm), 192 h to kill medium-sized adults (>6–15 mm) and 276 h to kill maximum-sized mussels adults (>15–27 mm) in laboratory exposures, and 72 h, 96 h and 108 to kill small, medium-sized and maximum sized mussels in outdoor exposures. The results have implications for using desiccation to combat the spread of L. fortunei.

A recent survey of the aquatic fauna in the rio Xingu, Para State, Brazil, revealed a new species of Drulia Gray 1867, an extraordinary genus of freshwater sponge endemic to South America. Drulia cristinae n. sp. is distinguished in part by having gemmoscleres typically with elliptical outline and outer face with small, central crest or irregular bulge (exceptionally nude), oscules set atop conical projections of skeleton, and microscleres minute, wholly nanospined amphioxea. A taxonomic key is presented for the six species now composing the restored and redefined genus Drulia: D. brownii, D. cristata, D. uruguayensis, D. conifera, D. ctenosclera and D. cristinae n. sp. Furthermore, the monotypic South American genus Houssayella is retained as valid in Spongillidae on the basis of sharing gemmoscleres with true birotulate pattern (i.e., symmetrical disks separated by short or long, spiny or smooth shaft).

This scientific communication describes and discusses morphological–behavioral adaptations to flow of two benthic invertebrate species to survive in highly turbulent habitats of the large Paraguay River (Argentina – Paraguay). It is based on field and laboratory observations under microscope made during the performance of usual researches. In this sense, we found that Djalmabatista sp. 1 (Chironomidae, Tanypodinae) ballasts its body by ingestion of fine sediment grains which storage into a dorsal bulge, herein called “dorsal bag”. This specie would have the ability to take or release these grains according to the surrounding hydrodynamic conditions. Otherwise, the juvenile stage of Limnoperna fortunei (Bivalvia, Mytilidae) also ballasts its body but attaching sand grains through the byssal threads. Fil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Eberle Folmer, Eliana Gisel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Bullo Rodrigo, Juan Manuel. Universidad Nacional del Litoral. Facultad de Humanidades y Ciencias; Argentina Fil: Ezcurra, Ines Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Amsler, Mario Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina

[1] This study aims to relate the flow structure over mobile dunes recorded on the channel bed of the Parana River (Argentina) with the spatial distribution of the benthic macroinvertebrates. The following main conclusions have been obtained: (1) the dunes found in the active channel could be considered as hydraulic biotopes at a mesohabitat scale: the bed forms in the thalweg region are subjected to higher shear stresses with low benthic densities; (2) differences in benthic densities were also recorded at within-dunes microhabitat scales: the largest densities were found in the dune troughs where small bed shear stresses occur and minimum densities on the low stoss side of dunes where turbulent agitation near the bottom strongly disturb the bed particles; (3) superimposed dunes on larger dunes may be considered as another microhabitat of still smaller dimensions. Summarizing, multiscale approaches are needed if a comprehensive understanding linking hydrodynamics and morphodynamics processes with benthic ecology is intended.

Heteromeyenia horsti Kilian, was found in the Mascardi lake, Rio Negro Province, Argentina. The taxonomic study was made on the comparative analysis of the microscleres, because the sponges had no gemmules. The present one is the southernmost place for argentinian freshwater sponges. The analysis of the material from different ponds of Corrientes Province (Argentina), allows to extend the geographical distribution of Heteromeyenia baileyi (Bowerbank). Thus, Heteromeyenia Potts is represented by three species in Argentina: H. stepanowi (Dybowsky, 1884), H. baileyi (Bowerbank, 1863), and H. horsti Kilian, 1976.

This paper is the first contribution to the knowledge of the freshwater sponges of Suriname. Four species have been identified up till now: Metania spinata (Carter, 1881), Trochospongilla paulula (Bowerbank, 1863), Radiospongilla crateriformis (Potts, 1882), and Drulia uruguayensis Bonetto & Ezcurra de Drago, 1969. Since in most instances slides were the only available source of data, details on external structure cannot be supplied.

Limnoperna fortunei (Dunker, 1857), during its invasion process in South America, has caused severe impacts both on natural environments altering native biodiversity, ecosystem structure and function-, and on man-made structures causing economic looses. Twenty-one samples were taken from the right bank of the Uruguay River, from tributaries of the Uruguay and Paraná Rivers, the drainage of the Esteros del Ibera Wetland. Based on this fieldwork, the presence of larvae and adults of L. fortunei was determined. Also, through the comparison of environmental characteristic with the known tolerance limits for the species, the possibility of its establishment in environments not yet invaded was determined. Most of the sampling stations have features that allow the development of stable populations L. fortunei, including the rivers that drain the Esteros del Ibera, allowing access of this invasive species to this important wetland., Facultad de Ciencias Naturales y Museo