Biodiversity of testate amoebae (Arcellinida and Euglyphida) in different habitats of a lake in the Upper Paraná River floodplain

This study aimed to investigate the testate amoebae (Arcellinida and Eugliphida) species diversity in plankton, macrophytes and aquatic sediment samples from a shallow lake of the Upper Paraná River floodplain. Samples were carried out from April 2007 to March 2008. We recorded 89 taxa, belonging to 10 families. Eighty-two taxa were found in the aquatic sediment, 71 in the macrophytes and 53 in the plankton. Highest values of alpha diversity were observed in the aquatic sediment. Although the plankton had the highest number of accidental species, accessory and constant species were also observed in this habitat. Most of the species classified as constant for the plankton belonged to the genus Arcella. Most of the constant species in the macrophytes and aquatic sediment belonged to the genus Difflugia. This study supports the idea that the presence of these protists in the plankton should not be attributed only to stochastic processes because (i) the species diversity recorded in this habitat was remarkably high in relation to the total biodiversity of the lake, and (ii) we also recorded frequent and constant species in the plankton.     

Performance trade-off across a natural resource gradient

An important environmental factor determining both phytoplankton and zooplankton community composition is lake depth and thermal stratification. However, there is little information on how the interaction between zooplankton grazers and their phytoplankton food changes along an environmental gradient of lake depth. We contrasted resource availability for daphniid zooplankton populations living in two shallow, unstratified lakes and in two deep, stratified lakes using a novel growth bioassay. Stratified lakes had consistently lower resource richness than shallow unstratified lakes. To test whether resources were important in explaining differences in daphniid composition of shallow and deep lakes, we performed reciprocal transplant experiments. We raised daphniids typical of shallow (Ceriodaphnia reticulata) and deep (Daphnia dentifera) lakes in the resources from replicate shallow and deep lakes and monitored survival and reproduction. The two species exhibited a performance trade-off, measured by life table r and R ₀, across a gradient in natural resource richness. D. dentifera had higher relative fitness than C. reticulata when raised in the poorest resource environment from a deep lake. However, under richer resource conditions typical of shallow lakes, C. reticulata outperformed D. dentifera. We further created a gradient in natural resource quantity (by dilution) to test whether this trade-off in species relative fitness involved aspects of resource quality. No trade-off in species performance was evident across the dilution gradient, indicating that resource quality was important to the trade-off. We conclude that shifts in daphniid species composition along a gradient of lake depth involve an adaptive trade-off in ability to exploit rich versus poor resource quality. Received: 11 May 1998 / Accepted: 15 January 1999     

ARE CYTOPLASMIC POCKETS (MTR/POCKET) PRESENT IN ALL PHOTOSYNTHETIC EUGLENOID GENERA?1

In 1985, the existence of a cytoplasmic pocket formed from the reservoir membrane in the photosynthetic euglenoid Colacium was described. A band of reinforcing microtubules (MTR) derived from the ventral flagellar root lined the pocket, and a dense fibrillar mesh was associated with the membrane. A comparison of bodonid cytostomes, colorless euglenoid cytostomes, and the reservoir pocket found in Colacium suggested that the three structures were homologous and that photosynthetic euglenoids arose from phagotrophic ancestors. MTR/pockets have since been reported in other photosynthetic euglenoids, including Euglena, Eutreptia, Eutreptiella, Cryptoglena, Tetreutreptia, and Phacus. We found MTR/pockets in three additional taxa, Lepocinclis, Trachelomonas, and Strombomonas, thereby demonstrating the presence of this complex in representatives of all the major photosynthetic genera. A comparison of the MTR/pocket complex across genera indicated a reduction in structural complexity that was consistent with recent phylogenetic schemes based on molecular characters. Three alternative hypotheses of the origin of MTR/pockets in phototrophic euglenoids are presented and discussed.     

Long-term variability of the phytoplankton community in an isolated floodplain lake of the Ivinhema River State Park,Brazil

The phytoplankton community of river–floodplain ecosystems shows significant temporal fluctuations in response to hydrosedimentological regime. The aim of our study was analyze the effect of the hydrosedimentological regime of the Paraná and Ivinhema Rivers on the interannual variation in the composition, biovolume and functional groups of phytoplankton in an isolated floodplain lake (Ventura Lagoon) of the Ivinhema River State Park, located in the Upper Paraná River floodplain (Mato Grosso do Sul State, Brazil). Samples of phytoplankton were taken at the sub-surface of the pelagic zone of the lake from February 2000 to December 2005. A total of 132 taxa were recorded, and the species that represented greater contributions to the phytoplankton biovolume were grouped into five functional groups (FG) (H1, H2, M, MP and Y). The distribution of the FGs were linked to the high and low water periods in Ventura lagoon. Functional groups MP and Y were the highest contributors to the phytoplankton biovolume during the high water periods, whereas FGs H1, H2 and M contributed more during the low water periods. The FGs were also useful for the interannual characterization of Ventura Lagoon by taking the changes caused by climatological factors into account. There was a strong dominance of Cyanobacteria (H2 and M) in 2000 and 2001 (La Niña periods) coincident with low precipitation and low hydrometric levels of the Paraná and Ivinhema Rivers and, consequently, lower water depths of Ventura Lagoon. In 2002, 2003, 2004 and 2005 (El Niño periods), when higher precipitation, higher hydrometric levels, higher discharge of the Paraná and Ivinhema Rivers and an increased depth of Ventura Lagoon were observed, Cyanobacteria (H1, H2 and M) were dominant, followed by Bacillariophyceae (MP) and Cryptophyceae (Y). These results reported here corroborate the utility of using FGs as indicators of interannual and seasonal variability in floodplain lakes.     

Gravel dredging alters diversity and structure of riverine fish assemblages

1. Human activities affect fish assemblages in a variety of ways. Large‐scale and long‐term disturbances such as in‐stream dredging and mining alter habitat and hydrodynamic characteristics within rivers which can, in turn, alter fish distribution. Habitat heterogeneity is decreased as the natural riffle–pool–run sequences are lost to continuous pools and, as a consequence, lotic species are displaced by lentic species, while generalist and invasive species displace native habitat specialists. Sediment and organic detritus accumulate in deep, dredged reaches and behind dams, disrupting nutrient flow and destroying critical habitat for habitat specialist species. 2. We used standard ecological metrics such as species richness and diversity, as well as stable isotope analysis of δ¹³C and δ¹⁵N, to quantify the differences in fish assemblages sampled by benthic trawls among dredged and undredged sites in the Allegheny River, Pennsylvania, U.S.A. 3. Using mixed‐effects models, we found that total catch, species richness and diversity were negatively correlated with depth (P < 0.05), while species richness, diversity and proportion of species in lithophilic (‘rock‐loving’) reproductive guilds were lower at dredged than at undredged sites (P < 0.05). 4. Principal components analysis and manova revealed that taxa such as darters in brood hider and substratum chooser reproductive guilds were predominantly associated with undredged sites along principal component axis 1 (PC1 and manova P < 0.05), while nest spawners such as catfish and open substratum spawners including suckers were more associated with dredged sites along PC2 (P < 0.05). 5. Stable isotope analysis of δ¹³C and δ¹⁵N revealed shifts from reliance on shallow water and benthic‐derived nutrients at undredged sites to reliance on phytoplankton and terrestrial detritus at deep‐water dredged sites. Relative trophic positions were also lower at dredged sites for many species; loss of benthic nutrient pathways associated with depth and dredging history is hypothesised. 6. The combination of ecological metrics and stable isotope analysis thus shows how anthropogenic habitat loss caused by gravel dredging can decrease benthic fish abundance and diversity, and that species in substratum‐specific reproductive guilds are at particular risk. The effects of dredging also manifest by altering resource use and nutrient pathways within food webs. Management and conservation decisions should therefore consider the protection of relatively shallow areas with suitable substratum for spawning for the protection of native fishes.     

Sympatry between <Emphasis Type="Italic">Alouatta caraya</Emphasis> and <Emphasis Type="Italic">Alouatta clamitans</Emphasis> and the rediscovery of free-ranging potential hybrids in Southern Brazil

Records of sympatry between Alouatta caraya and A. clamitans are rare despite their extensive range overlap. An example of their current sympatry and the rediscovery of free-ranging potential hybrids of A. caraya and A. clamitans in the forests of the Upper Paraná River, Southern Brazil, are reported in this paper. Eight groups were observed in the study area: five monospecific groups of A. caraya, two of A. clamitans, and a group containing two adult males and two adult females of A. caraya and a sub-adult male and two adult females identified as Alouatta sp. The color of the last three individuals was a mosaic between the two species; this is consistent with previously described variations in museum specimens collected in the Paraná River in the 1940s that had been identified as potential hybrids. The results from this study emphasize the need for scientific studies in the region of the Ilha Grande National Park, one of the few regions in the Paraná River that currently harbors both howler species. Contribution number 1637 of the Departamento de Zoologia, Universidade Federal do Paraná, Caixa Postal 19020, 81531-980, Curitiba, Paraná, Brasil.     

鄂西地区裸藻的初步研究

在鄂西的五峰、宜都、宜昌、当阳及神农架林区一带,采集到裸藻门植物16属140种(包括变种和变型)。属于绿色裸藻类的有116种,无色裸藻类的有24种,其中有5个新种,7个新变种,3个新变型,有20种是我国新记录。在采集区域内的地形大体上可以分成三种不同的类型,即:山岳地区(采得裸藻5种),河谷盆地地区(采得裸藻40种)和沿长江丘陵地区(采得裸藻128种)。静止水体由于地形的差异,体积的大小和水质的肥沃程度不同,都对裸藻门植物的生长有重要的影响。       

The Application of Chironomid Pupal Exuvial Technique (CPET) for Ecological Analysis in a Neotropical Large River System

This field ecological study, based on the chironomid pupal exuvial technique (CPET), is new for the Paraná River and proposes an efficient tool to be used in future ecological approaches and biomonitoring. Drifting of pupal exuviae in a river-floodplain system of the Middle Paraná River floodplain was represented by 34 Chironomidae taxa, being the characteristic association obtained from the CPET: Lopescladius, Onconeura, Paralauterborniella, Polypedilum, and Harnischia complex. Diversity, richness, dominance, total density, and density of dominant taxa were different between the longitudinal and lateral dimensions but not between hydrologic phases, with a greater diversity and richness in the main channel of the river and higher density and dominance in floodplain habitats. The species turnover is the dominant process in structuring studied assemblages in spatial and temporal analysis, increasing in the floodplain habitats and in low-water phase. The results obtained showed that drifting exuviae in the longitudinal axis were coming from different assemblages and environments of a wider area (regional), while exuviae recorded in the connections of the floodplain environments in the lateral dimension could reflect the local assemblages. We demonstrated the ecological value of CPET studies to interpret the attributes of Chironomidae assemblage in river-floodplain systems of large rivers in an integrated way.     

珠三角河网裸藻的多样性特征

珠三角河网是珠江汇入南海的必经之地,2012年对该水域裸藻门及各属的多样性特征及影响因子进行系统阐析。调查期间共发现裸藻12属84种,其中裸藻属是最主要类群,其次为扁裸藻属和囊裸藻属。珠三角河网独特的地理位置和人类活动造成的水体富营养化是该水域裸藻物种多样性丰富的主要原因。季节特征显示,丰水期裸藻的种类丰富度和生物量均明显高于枯水期。除了洪水引发的裸藻物种的外源供给增大外,泄洪所带来的有机质的增加也是有利因素。此外,丰水期对应的高温也是有益条件。空间特征存在明显的季节差异,丰水期河网外侧站位的生物量和种类丰富度高于中部站位,主要原因是受径流影响较大;枯水季节除广州附近站位的值明显偏高外,其它站位间差异不大,营养盐的空间格局是主要决定因素。尽管裸藻主要依赖于沿江静水水体中的外源供给,分析表明,其在随水流下行的过程中存在增长过程。不同藻属相对组成的结果显示,扁裸藻属和囊裸藻属因属于生长缓慢的K-选择策略型,富集营养物质的能力不及裸藻属,仅在枯水期与裸藻属形成互补优势。裸藻门及主要属的生物量与种类丰富度呈线性正相关关系,偏重于多样性单峰模式的上升区。     

Distribution of non‐native suckermouth armoured catfish Pterygoplichthys ambrosettii in the upper Paraná River basin,Brazil

This study describes the invasion of the upper Paraná River basin by Pterygoplichthys ambrosettii based on a literature review and field samples. Pterygoplichthys ambrosettii has been reported in 42 localities throughout the upper Paraná River basin, including the Tietê, Paranapanema, Paraná, Grande and Aguapeí rivers. The ascent of P. ambrosettii after the inundation of the Sete Quedas Falls on the Paraná River and the release of individuals by aquarium hobbyists were the primary drivers of this invasion.     

Habitat heterogeneity drives bird species richness,nestedness and habitat selection by individual species in fluvial wetlands of the Paraná River,Argentina

We assessed the relationship between habitat heterogeneity and bird species richness and composition within wetlands of the floodplain of the Middle Paraná River, Argentina. Given the high habitat heterogeneity in these wetland systems, we sought to determine whether (i) there was a positive relationship between bird species richness and habitat heterogeneity; (ii) whether bird species richness was associated with certain types of individual habitat types; (iii) whether there was a pattern of species nestedness and turnover between sites as a function of habitat heterogeneity and composition, respectively; and (iv) whether individual species exhibited associations with habitat heterogeneity. Point counts were used to survey birds at 60 sites. We estimated the area of eight habitat types found within a 200‐m radius from the centre of each site and calculated number and Pielou's evenness of habitat types. These indices, together with area proportion of each habitat type, were used as explanatory factors of bird species richness in linear regression models. Habitat heterogeneity per se rather than area of individual habitat types was a more important predictor of species richness in these fluvial wetlands. Sites with more habitat types supported more bird species. Results showed that individual bird species were associated with different habitat types and, therefore, sites that contained more habitat types contained more species. Number of habitat types accounted for species nestedness between sites whereas composition of habitat types accounted for species turnover between sites. Results suggest that selection of heterogeneous sites by individual species could help explain the positive heterogeneity–species richness relationship. Our findings highlight the importance of habitat heterogeneity per se resulting from flood disturbances in maintaining bird richness in fluvial systems.     

Patterns of population differentiation in annual killifishes from the Paraná–Uruguay–La Plata Basin: the role of vicariance and dispersal

Aim To elucidate the role of vicariance versus dispersal at the microevolutionary scale in annual killifish populations belonging to the Austrolebias bellottii species complex (Rivulidae). Within this complex, A. bellottii and A. apaii have low vagility and occur widely within the study area, making them excellent models for testing biogeographic hypotheses of differentiation. Location South America, in the Paraná–Uruguay–La Plata river basin. Methods Molecular data and morphometric analyses were used to reconstruct the phylogeographic history and morphological variation of 24 populations of two taxa of the A. bellottii species complex. Phylogenetic analyses using maximum likelihood (ML) and Bayesian inference (BI) model‐based methods, estimates of clade divergence times implemented in beast , non‐metric multidimensional scaling, analysis of molecular variance results, and morphological analyses elucidated the role of vicariance versus dispersal hypotheses in population differentiation in the aforementioned river basin. Results In the A. bellottii species complex from the Paraná–Uruguay–La Plata river basin, past allopatric fragmentation from vicariance events seems to be the most plausible scenario for diversification since the Late Miocene and more recently since the Plio‐Pleistocene. The Plio‐Pleistocene vicariance produced the differentiation of three major clades in A. bellottii populations. One clade from the eastern Uruguay River drainage was separated from another in western Uruguay and the Paraná–La Plata River drainages. A later vicariance event split populations to the south (lower Paraná–La Plata Basin) and north (middle Paraná) of the western Paraná River drainage. However, our results do not exclude the possibility of dispersal events among A. bellottii populations from both the Uruguay and Paraná river drainages, which could occur in these river basins during hypothesized connectivity cycles of the Late Pliocene and Pleistocene. Main conclusions Past allopatric fragmentation caused by different vicariance events seems to be the main driver of diversification in the A. bellottii species complex since the Plio‐Pleistocene. However, the current molecular data suggest that populations from both drainages of the Paraná–Uruguay rivers may have experienced cycles of connectivity during the Pleistocene, perhaps including multiple vicariance or dispersal events from populations located in the western lower Uruguay River drainage, which encompassed climatic and geological changes in the Paraná–Uruguay–La Plata Basin.     

Algal Assemblages Across a Wetland, from a Shallow Lake to Relictual Oxbow Lakes (Lower Paraná River, South America)

This study deals with the variation in the algal assemblages across the transversal dimension of a wetland of the Lower Paraná River from October 1998 to September 1999. The relationship between the algal composition and the physico-chemical variables is analyzed by means of Canonical Correspondence Analysis. The abundant floating macrophytes generated a severe reduction in light penetration in the relictual oxbow lakes (ROLs), almost anoxic conditions and high values of P, N and K. Such characteristics accounted for their very particular algal flora dominated by Cyanobacteria and several diatoms, species probably mixotrophic regarding their capacity to grow in darkness and tolerate very low oxygen contents. In the shallow lake, the phytoplankton comprised many small autotrophic green algae, accompanied by many flagellates of the classes Cryptophyceae, Euglenophyceae and Dinophyceae. Our results indicate that the macrophyte cover was probably the stirring factor in the selection of algal species along the transitional zone comprising a floodplain shallow lake and several ROLs.     

Transcontinental dispersal,ecological opportunity and origins of an adaptive radiation in the Neotropical catfish genus Hypostomus (Siluriformes: Loricariidae)

Ecological opportunity is often proposed as a driver of accelerated diversification, but evidence has been largely derived from either contemporary island radiations or the fossil record. Here, we investigate the potential influence of ecological opportunity on a transcontinental radiation of South American freshwater fishes. We generate a species‐dense, time‐calibrated molecular phylogeny for the suckermouth armored catfish subfamily Hypostominae, with a focus on the species‐rich and geographically widespread genus Hypostomus. We use the resulting chronogram to estimate ancestral geographical ranges, infer historical rates of cladogenesis and diversification in habitat and body size and shape, and test the hypothesis that invasions of previously unoccupied river drainages accelerated evolution and contributed to adaptive radiation. Both the subfamily Hypostominae and the included genus Hypostomus originated in the Amazon/Orinoco ecoregion. Hypostomus subsequently dispersed throughout tropical South America east of the Andes Mountains. Consequent to invasion of the peripheral, low‐diversity Paraná River basin in southeastern Brazil approximately 12.5 Mya, Paraná lineages of Hypostomus, experienced increased rates of cladogenesis and ecological and morphological diversification. Contemporary lineages of Paraná Hypostomus are less species rich but more phenotypically diverse than their congeners elsewhere. Accelerated speciation and morphological diversification rates within Paraná basin Hypostomus are consistent with adaptive radiation. The geographical remoteness of the Paraná River basin, its recent history of marine incursion, and its continuing exclusion of many species that are widespread in other tropical South American rivers suggest that ecological opportunity played an important role in facilitating the observed accelerations in diversification.     

Larvae of the invasive species <Emphasis Type="Italic">Limnoperna fortunei</Emphasis> (Bivalvia) in the diet of fish larvae in the Paraná River,Argentina

To assess the trophic impact of the planktonic larvae of the invasive Asian bivalve Limnoperna fortunei, introduced in South America around 1990, we investigated the gut contents of fish larvae collected at monthly intervals between October 2000 and March 2001 at three locations along a 600 km stretch of the Paraná River, and during November 2004 in two areas of marginal lagoons connected to the river near the city of San Nicolás, Argentina. Zooplankton was also collected in the lagoons in 2004. In total, 11,956 fish larvae were retrieved, of which 1,511 were used for detailed analyses. Of the 15 fish taxa collected, 11 had veligers of L. fortunei in their gut. Fish larvae with empty guts represented 60% (San Nicolás) to 72% (Paraná River) of the total number of fish. Proportions of feeding fish larvae with L. fortunei veligers in their guts varied between 20% (San Nicolás) and 56% (Paraná River); in 15% of the guts analyzed, L. fortunei was the only food item recorded. For those specimens that had consumed L. fortunei larvae and any other food item, L. fortunei was the most important item in 55% (Paraná River) to 71% (San Nicolás) of the animals in terms of biomass. No major temporal or spatial changes in the diet were observed along the Paraná River, but the relative biomass contribution of L. fortunei larvae differed strongly in fishes of different developmental stage. In protolarvae and mesolarvae, veligers accounted for 30–35% of the gut contents. In metalarvae, veligers accounted for only 3%, indicating enhanced food supply for the earliest fish life stages. Comparison of the relative proportions of the three main zooplankton types (L. fortunei veligers, cladocerans, and copepods) in the water and in larval fish guts indicates that L. fortunei is always selected positively over the other two prey types. While our results strongly suggest that the expansion of L. fortunei results in an enhanced food supply for local fish populations, they do not necessarily imply that the overall effect on the ecosystem in general, and on the fish fauna in particular is beneficial.     

Effect of fluctuations in water level on phytoplankton development in three lakes of the Paraná river floodplain (Argentina)

The effect of fluctuations in water level on phytoplankton development (abundance, biomass, size structure, taxonomic composition, species diversity and rate of community compositional change) in three vegetated lakes of the Paraná River floodplain (27° 27′?S; 58° 55′?W) were studied. Between September 1995 and June 1996 there were two inputs of lotic water. Ordering of physical and chemical parameters (Principal Component Analysis) allowed the differentiation of two phases: I) without lotic influence (limnophase) and II) with lotic influence (potamophase). Two-hundred fifty-eight algal taxa were identified, of which Euglenophyceae showed the highest number of taxa (65% of total). Small Chlorophyceae and Cryptophyceae (C-strategists) predominated in density in both periods. During potamophase, the input of nutrients from a flood event produced an increase in algal biomass and a shift in phytoplankton composition from a Chlorophyceae (C-strategists), to a Cyanophyceae and Euglenophyceae (S-strategists), dominated comunity. Bacillariophyceae, Chrysophyceae, Dinophyceae and Xanthophyceae were best represented during limnophase. All phytoplankton attributes showed significant differences between phases (limnophase vs potamophase) but not among lakes. These results support the hypothesis that hydrology (floods) clearly exerts an overall impact on the phytoplankton community composition in lakes of the Paraná River floodplain. Hydrology effects the lake water chemistry, conditioned by the isolation time prior to a flood, the horizontal dragging and exchange of algae during floods, and the water residence time and aquatic vegetation coverage.     

Has the bumblebee <Emphasis Type="Italic">Bombus bellicosus</Emphasis> gone extinct in the northern portion of its distribution range in Brazil?

Evidence for the extinction of the bumblebee Bombus bellicosus in Paraná state, in Brazil, is presented. The species is found in areas covered with open grass fields and shrub vegetation, originally ranging from northwestern Argentina to Paraná, where it reached its northeastern limit. Until the early 1980s, B. bellicosus was relatively abundant in Paraná, when the last known specimens were collected. In recent surveys conducted from 2002 to 2005, no specimens were recovered at sites in which the species was previously known to occur. Possible causes for local extinction of this species are discussed, including habitat conversion, pollution and climate change.     

Productivity gradient affects the temporal dynamics of testate amoebae in a neotropical floodplain

Testate amoeba communities are influenced by temporal variation in the productivity levels in the environment, and may be used as an indicator group for these changing conditions. Here, we analysed the effect of temporal variation in the levels of productivity variables on testate amoeba community of the upper Paraná River floodplain. We evaluated the hypothesis that the frequency and abundance of the testate amoeba community change along an environmental gradient, with different taxa establishing at different points along the gradient in response to changes in the levels of productivity variables. We predicted that the number of species would increase and decrease at points associated with higher and lower levels of productivity variables, respectively. Testate amoeba species were sampled quarterly between 2000 and 2012 from six lakes in the upper Paraná River floodplain, Brazil. We recorded 110 species belonging to 11 families. Threshold Indicator Taxa Analysis identified positive and negative significant shift points in response to the concentration of chlorophyll-a, total nitrogen, and total phosphorus on the frequency and abundance of the testate amoeba community. Our results indicated that change intervals in the levels of productivity variables were associated with the establishment of different taxa. The main bioindicator species of productivity were Difflugia acuminata, D. amphoralis, D. helvetica multilobata, D. kempny, D. lobostoma multilobata, D. parva, D. schurmanni, D. ventricosa, and Lesquereusia ovalis. These species were linked to the increase and decrease in the levels of productivity, confirming the ecological importance of the role of these organisms as bioindicators in aquatic ecosystems.     

Description of Freshwater Bacterial Assemblages from the Upper Paraná River Floodpulse System,Brazil

Bacteria were identified from a large, seasonally flooded river (Paraná River, Brazil) and two floodplain habitats that were part of the same river system yet very different in nature: clearwater Garças Lagoon and the highly humic waters of Patos Lagoon. Bacterioplankton were collected during mid-summer (Jan. 2002) from water samples (2 l) filtered first through a 1.2-μm filter then a 0.2-μm membrane filter representing the particle-attached and free-living sub-communities, respectively. DNA was extracted from filters and purified and a 16S rRNA clone library established for each habitat. Over 300 clones were sequenced and checked for similarity to existing 16S sequences in GenBank using the BLAST algorithm with default parameters. Further classification of clones was done using a species “backbone” attachment followed by parsimony analysis. The majority (85%) of sequences, referred to here as operational taxonomic units (OTUs), were most similar to uncultured bacterium 16S sequences. OTUs from each Proteobacteria sub-phylum (α, β, γ, δ, ?) were present in the Upper Paraná River system, as well as members of the Bacteroidetes. The microbial assemblage from Patos Lagoon was least like other samples in that it had no Firmicutes present and was dominated by Actinobacteria. Verrucomicrobia OTUs were only found in the free-living assemblage. This study documents the presence of globally distributed phyla in Upper Paraná River and taxa unique to habitat and particle attachment.     

First observations on longitudinal succession of Zooplankton in the main course of the Paraná River between Santa Fe and Buenos Aires Harbour

The material was been collected in 1972 during a field trip performed by the research vessel of the National Institute of Limnology, Argentina, along the main course of the Paraná River from the Santa Fe harbor down to the Río de la Plata. Sixty sampling stations were covered. In the lower course of the river sampling was carried out in the Paraná Guazú and the Paraná Bravo branches down to its confluence with the Uruguay River, and the Paraná de las Palmas and the Rio de la Plata down to the Buenos Aires harbor. Water samples for chemical analysis were collected and some physical parameters were measured.

Due to the characteristics of the part of the river under consideration, we have divided it into four sectors.

Sixty six species were seen. The rotifers were always the most important. Trichocerca rattus was the predominant species.

The Zooplankton density and specific diversity showing differences between those from industrialized areas and not industrialized ones.