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...

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.

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...

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