Acta Scientiarum: Biological Sciences (Jul 2009)
Produção de folhiço e fauna associada de macroinvertebrados aquáticos em curso d’água de cabeceira em Floresta Ombrófila do Estado do Rio Grande do Sul, Brasil = Litter production and aquatic macroinvertebrates on a headwater subtropical stream in Rio Grande do Sul State, Brazil
Abstract
Os objetivos deste estudo foram verificar a entrada sazonal de material alóctone e a composição de suas estruturas vegetais e da fauna de macroinvertebrados aquáticos associados ao material alóctone em um riacho de cabeceira em clima subtropical. Foram analisadas, trimestralmente, duas transecções longitudinais no curso d’água, onde foram instalados coletores submersos e suspensos (1,5 m acima da calha) de outubro de 2004 a outubro de 2005. Em ambos os coletores, não se verificou diferença para a entrada de material alóctone entre os períodos de coletas, o que sugere ausência definida de sazonalidade. Também não foram verificadas, temporalmente, diferenças para os componentes, flores, frutos e sementes (diásporos), folhas e galhos (vegetativas). O componente foliar foi o item com maior biomassa na formação do material alóctone em ambos os coletores. Larvas de insetos aquáticos, crustáceos, moluscos e vermes oligoquetoscorrespondem aos grupos com maior representatividade. Chironomidae (Insecta, Diptera) e Oligochaeta foram os taxa mais abundantes em ambos os coletores, porém a maior riqueza foi observada nos coletores submersos.The aim of the study was to verify the temporal variation of allochthonous material input into a stream, and which structurescontribute to the organic material pool, as well as to analyze the occurrence of macroinvertebrates associated with the litter. Samples were taken from October, 2004 to October, 2005 in two transects along the riparian zone. At each transect, three sampling stations were chosen. At each one, submersed and suspended collectors (1.5 m above bottom) were installed. Input and retention of coarse benthic organic material were analyzed and classified as flowers and diaspores,(seeds and fruits) and vegetative structures (leaves and branches). There were no statistical differences between input of material in suspended and submersed collectors. Therefore, no statistical differences were verified for exposure time for both the suspended and submersed collectors. Vegetative and seeds and fruits and flowers structures differed in relation to their vegetal composition input for total exposure times for both collectors. Leaves were the mostimportant structure for biomass. Aquatics insects, crustaceans, mussels and worms were the most common macroinvertebrates associated with litter. Insecta-Diptera, mainly Chironomidae – and Oligochaeta were the most abundant taxa associated with the submerged and suspended collectors. The major taxa richness was found in submerged collectors.
