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The decomposition of Erythrina crista-galli L. (Leguminosa) leaf litter and its colonization by invertebrates were studied in a secondary channel of the Middle Paraná River. This species is native to and very abundant in South America in riverside areas and in Argentina it is known as 'ceibo'. The objectives were to estimate the E. crista-galli leaves' decomposition rate, to determine the proportion of functional feeding groups of invertebrates throughout the process of decomposition, and to evaluate the use of leaf detritus by the benthic invertebrates. The leaves were collected at abscission and 6 g dry weight were placed in 5 mm mesh nylon bags. The samplings were carried out between May and September 2002 and six replicates were collected after 7, 14, 28, 56 and 112 days. The decomposition rate (k) calculated over 112 days of decomposition was 0.0129 d−1. Invertebrate densities increased with the progressive decomposition of the leaves, reaching the maximum at 14 days (306 ind g−1 dw leaf−1) and 112 days (298 ind g−1 dw leaf−1). The highest species richness (18.5) was found at 7 days of leaf decomposition. Colonization of decomposing leaves was dominated by Diptera Chironomidae (Polypedilum spp., Phanopsectra sp.), Crustacea (Cladocera, Ostracoda), Oligochaeta Naididae (Pristina americana, Slavina evelinae, and S. isochaeta), and Mollusca (Limnoperna fortunei). The shredders were dominant at the begining of the decomposition process and the collector-filterers increasing at the end of the period because of the highest density of Limnoperna fortunei which used the leaf litter as substratum. Se estudió la descomposición de hojas de Erythrina crista-galli L. (Leguminosa) y su colonización por invertebrados en un cauce secundario del río Paraná Medio. Esta especie es nativa y muy abundante en América del Sur, principalmente en los bosques riparios en las márgenes de los ríos y en Argentina se conoce como 'ceibo'. Los objetivos fueron estimar la tasa de descomposición de las hojas de E. crista-galli, determinar la proporción de grupos funcionales a lo largo del proceso de descomposición y evaluar el uso que realizan los invertebrados bentónicos del detritus vegetal que colonizan. Las hojas fueron colectadas de los árboles y 6 g de peso seco de hojas fueron colocadas en bolsas de 5 mm de abertura de malla. La experiencia fue llevada a cabo entre Mayo y Setiembre de 2002 y se recolectaron seis réplicas a los 7, 14, 28, 56 y 112 días. La tasa de descomposición (k) a los 112 días fue de 0.0129 d−1. La densidad de los invertebrados aumentó con la progresiva descomposición de las hojas, alcanzando la máxima densidad a los 14 días (306 ind g−1 ps−1) y 112 días (298 ind g−1 ps−1) y la riqueza de especies fue mayor a los 7 días (18.5). Los grupos colonizadores fueron principalmente, Diptera Chironomidae, (Polypedilum spp., Phanopsectra sp.) Crustacea (Cladocera, Ostracoda), Oligochaeta Naididae (Pristina americana, Slavina evelinae and S. isochaeta) and Mollusca (Limnoperna fortunei).Los trituradores fueron dominantes durante las primeras etapas de descomposición y los colectores-filtradores aumentaron hacia el final de la experiencia debido a la gran densidad de Limnoperna fortunei que utilizó a las hojas como sustrato.

Studies on benthic macroinvertebrates of lotic environments usually focus on the occurrence, distribution, and richness of aquatic insects and decapod crustaceans. Only rarely these studies include the Oligochaeta. The aim of the present study was to examine the occurrence and species richness of Oligochaeta in different substrata patches of lotic environments. The studied included seven stream sites at Parque Estadual Intervales (São Paulo, Brazil). Stream sites differed in size and ranged from first to fourth order. In each stream, qualitative collections were made using a D-type net sampler with 0.21 mm mesh. Measures of pH, electrical conductivity, dissolved oxygen, temperature and water turbidity were taken in the studied sites during collections of Oligochaeta. Specimens of the Tubificidae (including Naidinae) and Enchytraeidae families were collected. The Tubificidae Aulodrilus limnobius, Limnodrilus neotropicus and Limnodrilus hoffmeisteri were associated with low-flow habitats containing fine organic material. The most representative species among the Naidinae, Nais communis, was predominantly associated with rocky substrates present in fast current locations. The two other Naidinae species, Pristina osborni and Amphichaeta leydigi, presented low frequency in the studied streams. The Enchytraeidae family was present in only one of the sampled habitats. Estudos sobre macroinvertebrados bentônicos de ambientes lóticos geralmente focam na ocorrência, distribuição e riqueza de insetos aquáticos e de crustáceos decápodos. Tais estudos apenas raramente incluem Oligochaeta. O objetivo do presente estudo foi examinar a ocorrência e riqueza de espécies de Oligochaeta de diferentes substratos em ambientes lóticos. O estudo incluiu sete riachos do Parque Estadual Intervales (São Paulo, Brasil). Os riachos estudados variaram em tamanho desde primeira até quarta ordem. Em cada ambiente, foram realizadas coletas qualitativas utilizando amostrador do tipo rede em D com malha 0,21 mm. Simultaneamente às coletas de Oligochaeta foram tomadas medidas do pH, condutividade elétrica, oxigênio dissolvido, temperatura e turbidez da água dos ambientes. Foram coletados exemplares das famílias Tubificidae (incluindo Naidinae) e Enchytraeidae. Os Tubificidae Aulodrilus limnobius, Limnodrilus neotropicus e Limnodrilus hoffmeisteri estiveram associados à habitats com pouca correnteza e substrato contendo material orgânico fino. Nais communis espécie mais representativa entre os Naidinae, esteve predominantemente associada a substratos rochosos presentes em locais de correntes rápidas. As duas outras espécies de Naidinae, Pristina osborni e Amphichaeta leydigi apresentaram baixa freqüência nos córregos analisados. A família Enchytraeidae esteve presente somente em um dos ambientes amostrados.

A riqueza de espécies de Oligochaeta foi investigada em duas represas construídas no curso do rio Tietê. Em cada represa foram obtidas 360 amostras de sedimento em 90 pontos de amostragem, utilizando-se uma draga Van Veen (378cm²), nos meses de janeiro, abril, julho e outubro de 2001. No total foram examinados 12.826 exemplares de oligoquetos pertencentes a 20 espécies, 10 gêneros e 4 famílias. Naididae e Dero foram a família e o gênero com maiores riquezas de espécies, com 14 e 9 espécies, respectivamente. Do total de espécies identificadas, 6 estiveram presentes em ambas represas, sendo Branchiura sowerbyi (Tubificidae) a espécie mais abundante nestes ambientes. A análise das amostras revelou que a maioria das espécies de oligoquetos é rara e de freqüência de ocorrência acidental, evidenciando que para um melhor conhecimento da riqueza de espécies é realmente necessário um grande esforço amostral, com elevado número de pontos de amostragem. The species richness of Oligochaeta was evaluated in two reservoirs belonging to Tietê River system, Bariri and Ponte Nova Reservoirs. 360 sediment samples were taken in each reservoir at 90 sampling stations using a Van Veen grab (378cm²), in the months January, April, July and October 2001. A total of 12.826 oligochaete specimens were collected, belonging to 20 species, 10 genera and 4 families. The family and genus with the highest species richness were Naididae and Dero, with 14 and 9 species, respectively. Among all species identified 6 occurred in both reservoirs, being Branchiura sowerbyi (Tubificidae) the most abundant species in them. The study also revealed that most Oligochaeta species are rare and have accidental occurrence, thus evidencing that for a better knowledge of species richness is actually necessary a great sampling effort including a large number of sampling points.

Two tubificid oligochaetes, Branchiura sowerbyi and Tubifex tubifex, were evaluated as potential test organisms for sediment bioassays. We attempt to reproduce the sediment bioassay proposed by Reynoldson et al. (1991) using his strain of Tubifex tubifex and his reference sediment and to compare this technique using Branchiura sowerbyi. This species was chosen because it is more common and dominant in tropical and subtropical environments than Tubifex tubifex. Data on survival and reproduction were obtained for both species, and growth estimates were obtained for B. sowerbyi. The sublethal bioassay with T. tubifex confirmed earlier estimates of a test duration of 4 weeks at 22.5 °C. B. sowerbyi cultures can produce usable estimates in 21 days at 30 °C.

The aim of the present study was to determine the life-cycle of Narapa bonettoi in the main channel of the Middle Parana River. The average density varied between 17 and 624 ind. sample-1. The spatial distribution was contagious with a higher degree of aggregation during the first months of the observed cycle, than during the last months. Mature specimens were more abundant in September 1985–86, resulting in greater breeding activity in early summer, when there was a large population increase. Two reproductive strategies were observed: asexual and sexual. After breeding, worms undergo a resorption process of their reproductive organs, returning to a non-sexual condition. Narapa bonettoi probably uses asexual reproduction as an adaptative strategy, because cocoon development will be affected by environmental factors such as the drift in the Parana River which is highly erodable. Population growth was rapid during the first four months and then stabilized.

The benthic invertebrate assemblages and functional feeding groups in different mesohabitats of the Middle Parana River–floodplain system were analyzed. Benthic invertebrates and bottom sediments were sampled in a secondary channel (center and bank mesohabitats), a temporal marginal fluvial wetland adjacent to the river, an isolated lake and a connected lake during low water level. Cluster analysis of average invertebrate densities based on the Bray Curtis dissimilarity index yielded a group composed by the mesohabitats with higher species richness, the floodplain lakes, banks mesohabitats and the wetland. The center mesohabitat of the main channel characterized by sandy sediments with low organic matter content and the lowest invertebrate densities and species richness was classified separately. Alpha diversity increased from the center mesohabitat (6 taxa) to the adjacent wetland (71 taxa), and were similar between the floodplain lakes (24 and 22 taxa) and the river bank mesohabitat (24 taxa). Gamma and beta diversities (Whittaker index) were 92 and 2.19, respectively. The highest turnover of taxa was between the river and the other mesohabitats and the lowest between floodplain lakes. Detrended correspondence analysis (DCA) showed a clear separation of wetland and banks from other mesohabitats (axis 1 and 2 explained 52.25% variance) explained by shredders and collector-filterers. The other mesohabitats were arranged in a gradient from the main channel mostly related to collector-gatherers to the connected lake and the isolated lake that were mostly characterized by predators and scrapers. The invertebrate assemblage complexity and functional feeding groups composition increased in the lateral dimension, from the center of the main channel to the temporal marginal fluvial wetland due to the influences of the spatial heterogeneity caused by different sources of organic matter inputs.

Simple and multiple correlations among physical and chemical parameters and densities of the dominant Oligochaete species were calculated for various channels of the middle Parana valley and its tributaries. Paranadrilus descolei Gavrilov, 1955, was observed in rivers with average depth and current velocity, mud-clay sediments, and low conductivity. Tubifex tubifex f. blanchardi Vejd., 1891, was found in channels of low depth, current velocity and discharge but with high conductivity. Limnodrilus hoffmeisteri Claparede, 1862, and Aulodrilus pigueti Kowalewski, 1914, were ubiquitous species. Narapa bonettoi Righi and Varela, 1983, was typical of rivers highest in depth, current velocity, and discharge with sandy sediments and low conductivity.