This study describes the composition and structure of the benthic community associated with bryophytes in a first-order stream, located in a biological reserve of the Atlantic Forest, during two seasons. During three months of the dry season of 2007 and three months of the rainy season of 2008, samples of bryophytes attached to stones were collected randomly, along a 100 m stream reach. The structure of the community was analyzed through the mean density of individuals, Shannon's diversity index, Pielou's evenness, family richness, dominance index, and the percentage of Ephemeroptera, Plecoptera and Trichoptera (% EPT). Chironomidae larvae were dominant in the two periods of study, followed by Ceratopogonidae in the rainy season, and Naididae in the dry season. The orders EPT contributed 14 families. The results showed that bryophytes constitute suitable habitat which is able to shelter an abundant and diversified benthic fauna in a small extension of the stream. This habitat provides refuge during spates, and thus minimizes downstream transport of the macroinvertebrate fauna.

In order to estimate the water quality of São Pedro stream, through distribution and composition of Chironomidae larvae present in the sediment four sampling sites were selected. In each sampling site, three sediment samples were collected within a period of twelve months using the Petersen (0.0189 m²) and the van Veen (0.0518 m²) dredges. Samples were washed through a sieve with a 0.21 mm mesh and the collected organisms were sorted in transparent trays, with a light shine being reflected into the tray. The sites located in the greatest urban mesh showed high densities of the genus Chironomus and lower values for diversity, uniformity and taxa richness, in relation to sites located in a less urbanized area. A significant difference in density of Chironomidae larvae (p = 0.02; H = 5.89) was observed between the sites without domestic sewage effluents (site I) and those with the input of the effluents (sites II, III and IV). The Chironomidae larvae composition and the physical and chemical parameters were effective as indicators of the environmental alterations in São Pedro stream.

In this note, the occurrence of phoresy between larvae of Rheotanitarsus sp. (Diptera: Chironomidae) and larvae of Heteragrion sp. (Odonata: Megapodagrionidae) and of unidentified genera of Calopterygidae (Odonata) collected in a first-order stream in an area of Atlantic Forest in southeastern Brazil is reported. During the dry season of 2007 and the rainy season of 2008, with the aid of a Surber sampler, 15 samples of each of the following mesohabitats were collected: litter from riffle areas, litter from pool areas and sediment in pool areas. Eighty-five Odonata larvae were obtained, 10 (11.76%) with cases of phoresy by Rheotanytarsus sp.. These chironomids were associated with only one specimen of Megapodagrionidae, whereas the other larvae were recorded in association with Calopterygidae. Most of the Odonata with cases of phoresy by Rheotanytarsus sp. were recorded in the dry season. In the present study, the absence of the phoretic association with other potential hosts for Rheotanytarsus sp. found in the samples indicates a possible preference of these larvae for Odonata, which accounted for only 2.42% of the collected macroinvertebrates in litter and sediment.