Estrutura e dinâmica da comunidade de protozoários flagelados em riachos tropicais sob influência de atividades humanas.

Abstract

Although the flagellate protozoans are important components of aquatic microbial food chains, there are few studies about them in lotic environments. Nevertheless, this study aimed to investigate the spatial and temporal variations of the attributes (density, biomass and body size) of this community in tropical streams, infer about the effect of agricultural and urban activities on these attributes and verify which factors (abiotic and biotic) may predict the spatial and temporal variations of this community. Samplings were undertaken in 10 streams (5 urban and 5 rural), during the winter (July, 2007) and summer (February, 2008). The values of density, biomass and body size recorded in this study (2.3 x104 cels.mL-1; 281.3 μgC.L-1; 9 μm, respectively) were superior to those commonly found in other lotic environments. The analyses of variance pointed out that the temporal patterns are more evident than the spatial ones. Considering the anthropogenic influence, only the autotrophic fraction was significantly influenced by the agricultural activities. In general, the multiple regression models highlighted that the ciliate density is the main factor regulating the patterns of spatial and temporal distribution of nanoflagellates, although some abiotic variables also had secondary influence on the structure of this community. Meanwhile, negative relationships were not verified, that could indicate the direct effect of predation, probably because the increase in the resources availability may have maintained the growth rate of nanoflagellate higher than the predation rate. Therefore, we suggest that the bottom-up control mechanism is more important than the top-down for the structure of this community in these environments.