Limnoperna fortunei (Bivalvia, Mitylidae) was introduced into South America in 1991 in the La Plata River (Argentina). It arrived in the ballast water of ships coming from Asia, where this species is native. It was first observed in 1998 in the Paraguay River. Limnoperna was introduced into the Pantanal region as hull fouling of vessels using the Paraguay-Parana waterway. This study describes how L. fortunei came to the Pantanal region, and provides details of its occurrence, density, and impacts. From 1999 to 2002, observations and sampling on natural and artificial substrates in the Paraguay River were made. Some aspects of the spread and impacts, based on local community information, were also analyzed. On artificial substrate the density reached 523.8 individuals m )2 and on natural substrate (rocks), up to 10,000 individuals m )2 were found. The densities observed were quite low compared to those found in Southern Brazil, where values up to 100,000 individuals m )2 have been recorded in the last 3 years. In the Paraguay River, the population density of L. fortunei can be negatively impacted by periodic low levels of dissolved oxygen and decreases in pH to between 5 and 6. Such conditions are frequently present during the periodic flooding or inundation of this area. Under these conditions, a high mortality of L. fortunei was recorded in March of 2002, on both natural and artificial substrates. Despite low densities, L. fortunei can colonize water cooling systems of boats, obstructing water circulation and causing motor overheating. Accumulation in water supply equipment, such as pumps and pipes has also been observed.

The aim of this study was to analyze the factors that influence spatial and temporal variations of the Oligochaeta assemblage in the Baía and Ivinhema Rivers, located in the Upper Paraná River floodplain (Mato Grosso do Sul State, Brazil). Samples of Oligochaeta were collected between February 2000 and November 2007. A total of 27 Oligochaeta species were identified. A Principal Component Analysis (PCA) of the physical and chemical variables was used to summarize the total variation in the data and to identify major environmental gradients. Detrended Correspondence Analysis (DCA) was conducted to verify possible spatial and temporal gradients in the Oligochaeta species distribution. The highest Oligochaeta species densities and richness values were recorded during limnophases. The intensity and amplitude of the potamophase influenced the density, richness and composition of Oligochaeta since many species were transported by high water current velocities and/or died due to the low oxygen levels that are characteristic of this phase. L. hoffmeisteri, P. descolei and A. pigueti were recorded in the potamophase and in the limnophase and we concluded that they are adapted to different conditions of rivers (lotic and lentic) due to the presence of these species during the entire study period in both rivers. Nevertheless, these species were dominant in the potamophase periods of these rivers as they have body adaptations to survive in these conditions. Keywords: Oligochaeta species, Baía and Ivinhema Rivers, flood pulse intensity and amplitude. Oito anos de monitoramento de Oligochaeta aquáticas nos Rios Baía e IvinhemaResumo O objetivo do estudo foi analisar os fatores que influenciam as variações espaciais e temporais da assembléia de Oligochaeta nos Rios Baía e Ivinhema, localizados na planície de inundação do Alto Rio Paraná. (Estado do Mato Grosso do Sul, Brasil). As amostras de Oligochaeta foram coletadas de fevereiro de 2000 a novembro de 2007. Um total de 27 espécies foi identificado. Análise de Componentes Principais (PCA) das variáveis físicas e químicas foi usada para sumarizar a variação total nos dados e identificar os principais gradientes ambientais. Para verificar possíveis gradientes espaciais e temporais na distribuição das espécies de Oligochaeta foi realizada uma Análise de Correspondência Dendrítica com remoção do efeito de arco (DCA). As maiores densidades e riqueza de espécies de Oligochaeta foram registradas nos períodos de águas baixas. A intensidade e amplitude da potamofase influenciaram a riqueza, densidade e composição de espécies, uma vez que muitas das espécies foram carreadas pela alta velocidade de corrente de água e/ou mortas devido aos baixos níveis de oxigênio que foram característicos dessa fase. L. hoffmeisteri, P. descolei and A. pigueti foram registradas nos períodos de potamofase e limnofase e nós concluímos que são adaptadas a diferentes condições de rios (lótico e lêntico) devido a preseça dessas espécies durante todo período estudado em ambos os rios. Contudo, essas e...

Chironomid larvae were collected and abiotic variables measured at monthly intervals at 21 sampling stations in two lagoons (Guaraná and Patos) and two tributaries (Baía and Ivinheima) of the Upper Paraná River floodplain. The genera Procladius, Chironomus, Goeldichironomus, and Polypedilum were dominant in the lagoons and in the Baía River, while Cryptochironomus and Lopescladius were more dominant in the Ivinheima River. The similarity in the generic composition of the chironomids of the lagoons and the Baía River is probably due to the fact that this river presents hydrodynamic characteristics similar to those of the lagoons. The results obtained suggest that the hydrodynamics of these environments are the main factor determining spatial variation in the chironomid fauna. This is intuitively clear, as this factor itself determines sediment type, quantity of organic matter and presence or absence of aquatic macrophytes. However, on a seasonal scale, the flood pulse seems to be the main controlling factor of the temporal variation in densities and dominance of chironomid larvae. Given that this factor has a large influence on the temporal dynamics of several limnological variables, this is again a logical correlation. Our results suggest a strong relationship between the variations in the chironomid community and fluctuations in limnological characteristics.Key words: Chironomidae, zoobenthos, floodplain, spatial and temporal variation. RESUMOVariação espacial e temporal da densidade de larvas de quironomídeos (Diptera) em duas lagoas e dois tributários da planície de inundação do alto rio Paraná, Brasil Foram coletadas larvas de quironomídeos e medidas as variáveis abióticas, mensalmente, em 21 pontos distribuídos em duas lagoas (Guaraná e Patos) e dois tributários (Baía e Ivinheima) da planície de inundação do alto rio Paraná. Os gêneros Procladius, Chironomus, Goeldichironomus e Polypedilum foram dominantes nas lagoas e no rio Baía, enquanto Cryptochironomus e Lopescladius dominaram no rio Ivinheima. Essa semelhança na composição genérica de quironomídeos nas lagoas e no rio Baía provavelmente se deve ao fato de esse rio apresentar características hidrodinâmicas mais similares às das lagoas. Os resultados obtidos sugerem que a hidrodinâmica desses ambientes é o principal fator determinante na variação espacial da fauna de quironomídeos. Obviamente, esse fator determina o tipo de sedimento, teor de matéria orgânica e presença ou ausência de macrófitas aquáticas. No entanto, sazonalmente, o pulso de inundação parece ser o principal fator controlador da variação temporal da densidade e da dominância das larvas de quironomídeos. Tendo em vista que esse fator tem grande influência na dinâmica temporal das variáveis limnológicas, isso é novamente uma correlação lógica. Os resultados sugerem forte relação entre as variações na comunidade de quironomídeos e as flutuações nas características limnológicas.Palavras-chave: Chironomidae, zoobentos, planície, variação espacial e temporal.

Summary 1. Community concordance measures the level of association between the compositional patterns shown by two groups of organisms. If strong community concordance occurs, one group could be used as a surrogate for another in conservation planning and biodiversity monitoring. In this study, we evaluated the variability in the strength of community concordance, the likely mechanisms underlying community concordance and the degree to which one community can predict another in a set of Neotropical floodplain lakes (Upper Paraná River floodplain, Brazil). 2. We used a data set including six aquatic communities: fish, macrophytes, benthic macroinvertebrates, zooplankton, phytoplankton and periphyton. We used Mantel and PROTEST approaches to evaluate the levels of community concordance in up to four sampling periods. Also, we used partial Mantel test and information about biotic interactions to investigate reasons for observed patterns of concordance. Finally, we used co‐correspondence analysis to evaluate the performance of one taxonomic group in predicting the structures of other communities. 3. The levels of community concordance varied over time for almost all cross‐taxa comparisons. Concordance between phytoplankton and periphyton probably resulted from similar responses to environmental gradients, whereas other patterns of concordance were likely generated by interactions among groups. However, the levels of predictability were low, and no particular taxonomic group significantly predicted all other groups. 4. The low and temporally variable levels of community concordance cast doubts on the use of surrogate groups for biodiversity management in Neotropical floodplains.

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We designed a field survey (the entire river length; not dammed: First and Second plateaus; dammed: Third Plateau) to test the hypothesis that the cascade of reservoirs promoted a reduction in species richness and changed the composition of Oligochaeta assemblage along the Iguaçu River. Changes in environmental variables and in richness and composition of Oligochaeta were summarized by Canonic Correspondence Analysis. Along the Iguaçu River, conductivity, and altitude decreased, whereas temperature increased. Oligochaeta composition showed a significant spatial variation, with higher abundances of the family Tubificidae and the genus Dero (Naididae) occurring in the First Plateau. In the Second and Third plateaus, few species were dominant, with increases in the presence of species of Naididae below dams. We found a clear decrease in species richness along the Iguaçu River. Moreover, we found that Oligochaeta assemblage was influenced by some environmental variables such as altitude, conductivity, substrate type and temperature, and by anthropogenic activities (human occupation and damming). The results supported the use of Oligochaeta as surrogate taxa to predict environmental changes along impacted (dammed and eutrophic) rivers. The validity of this was indicated by the strong and significant gradient registered, from the headwater to mouth of the Iguaçu River.Keywords: surrogate taxa, reservoir cascade, geomorphologic gradient, human occupation, Iguaçu River. Usando assembléias de Oligochaeta como um indicador de mudanças ambientais ResumoFoi delineada uma pesquisa de campo (toda extensão do rio; não barrado: Primeiro e Segundo planaltos; barrado: Terceiro planalto) para testar a hipótese de que a cascata de reservatórios promove redução na riqueza de espécies e muda a composição da assembléia de Oligochaeta ao longo do Rio Iguaçu. Mudanças nas variáveis ambientais e na riqueza e composição de Oligochaeta foram sumarizadas por Análise de Correspondência Canônica. Ao longo do Rio Iguaçu, a condutividade e a altitude diminuíram, enquanto a temperatura aumentou. A composição de Oligochaeta mostrou variação espacial significativa, com maiores abundâncias da família Tubificidae e do gênero Dero (Naididae) ocorrendo no Primeiro planalto. No Segundo e Terceiro planaltos, poucas espécies foram dominantes, com aumento na presença de espécies de Naididae abaixo de barragens. Foi encontrada uma clara diminuição na riqueza de espécies ao longo do Rio Iguaçu. Além disso, observou-se que a assembléia de Oligochaeta foi influenciada por algumas variáveis ambientais, como altitude, condutividade, tipo de substrato e temperatura, e por atividades antropogênicas (ocupação humana e barramento). Os resultados deste estudo suportam o uso de Oligochaeta como táxon substituto para predizer mudanças ambientais ao longo de rios impactados (barrados e eutróficos). A validade desse estudo foi indicada pelo forte e significativo gradiente, registrado da cabeceira à foz do Rio Iguaçu.Palavras-chave: taxon substituto, cascata de r...

The structural complexity of habitats and the distance from the dispersion source are considered important determinants of species diversity. The fractal dimensions of substrates are a strong alternative measure for quantifying the structural complexity. In this paper, we tested the hypothesis that structural complexity and distance from a dispersion source affect the density and diversity of macro-invertebrates on submersed macrophytes. To test this hypothesis, we used artificial substrates with different fractal dimensions, which were incubated at different distances from a dispersion source (a stand of macrophytes) in a Neotropical floodplain lake. The relationship between the structural complexity of macrophytes and the density and diversity of invertebrates attached to artificial substrates was positive and significant. On the other hand, distance from the dispersion source negatively affected both the density and diversity of the attached invertebrates. For Oligochaeta, however, there was a significant effect of structural complexity for the artificial plants positioned further away, but it was not significant in the plants positioned closer to the dispersion source. Thus, the effects of complexity depended on the distance from the dispersion source, at least for this specific group of macro-invertebrates. These results suggest that both structural complexity and distance from the dispersion source should be considered together to explain the diversity of invertebrates in river-floodplain systems. In addition, our results show that there is great potential for using fractal dimensions as a tool to quantify structural complexity in aquatic habitats, especially at the small spatial scales perceived by macro-invertebrates.Abstract in Portuguese is available at http://www.blackwell-synergy.com/loi/btp.

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