Macroinvertebrados associados a folhiço em um córrego de Mata Atlântica no sudeste do Brasil

Abstract

This dissertation was divided in two parts. The first part was related to a study of the Ephemeroptera, Plecoptera and Trichoptera fauna associated with mesohabitat of litter in an Atlantic forest stream in southeastern Brazil. This study had as objective to evaluate the composition as well as the spatial and temporal distribution of the Ephemeroptera, Plecoptera and Trichoptera (EPT) fauna. In order to do it, collections of litter in riffle mesohabitats and pool mesohabitats were carried out in the dry season of 2007 (July, August and September) and the rainy season of 2008 (January, February and March) in a first order stream located in the Municipal Biological Reserve of Poço D’Anta (Juiz de Fora - MG). In each month, two samples (three patches with 10 seconds of collection each one) of each mesohabitat were obtained with the aid of a “D”-net with mesh of 0.21 mm. The immature EPT were identified in genus level. The high diversity found in the two mesohabitats studied, compared to the theoretical maximum, reflect the environmental heterogeneity and its good state of preservation. It was not observed the effect of the mesohabitat (litter in riffles and litter in pools) on the structure of the total fauna of EPT, what may be explained by the transitoriness of the patches in litter, low water speed and low depth of the stream. The increase of the precipitation in the rainy season did not influence the total abundance of EPT either, probably because first order streams, with lower water flows and abundant vegetable material are more stable and have less effect of precipitation on the modification of the environment. Despite the absence of the effect of the mesohabitat and the precipitation upon the total fauna of EPT, some genera were sensitive to these variations, what shows the importance of ecological studies of the EPT fauna in genus level. The second part of this dissertation is an experiment of colonization of leaf debris for aquatic invertebrates in an Atlantic forest stream in southeastern Brazil. For this reason, 21 plastic bags, containing 2.5g weight of two plant species present on riparian vegetation (Alchornea glandulosa (Vell) & Cabralea canjerana End. & Poeppig), were placed in the bed of the stream. Three replicas were taken after 3, 6, 9, 12, 24, 48 and 96 days. A fast weight loss was observed throughout the experiment, remaining only 8% of the initial weight on the 96th day of incubation. The remaining weight was negatively correlated with the taxonomic density of invertebrates. The high density of collectors, as Chironomidae, Oligochaeta and Amphipoda, on the last day of incubation probably occurred due to the increase in fine particulate organic matter in the most advanced

stages of decomposition. The highest values of α diversity were observed on the 3rd and 96th days of the experiment, whereas β diversity showed that those two days presented higher variation in the taxonomic composition, thus demonstrating a different faunistic composition. This study showed that it happened a change in the structure, composition and a relative participation of the functional groups of aquatic invertebrates during the leaf breakdown. The abundance and the faunistic diversity observed in this study show the importance of leaf detritus of terrestrial origin as an energy source for invertebrates in low order streams, and reinforce the need for preservation of the riparian vegetation.