Estrutura taxonômica e funcional de assembleias de peixes no contínuo rio-estuário do rio São Francisco e impacto das espécies não-nativas

Abstract

The continuous river-estuarine comprises several highly productive environments related to constant fluctuations in environmental conditions due to the mixing of freshwater and saltwater, creating stratified environments that filter the occurrence of species in its extension. The diverse habitats of these ecosystems have been subjected to intense anthropic impacts, such as the damming of rivers and the introduction of exotic species. In the present dissertation, we approach two questions, the first as the taxonomic structure of the community responds to physiographic and seasonal factors and the second as the removal of exotic species modifies the functionality of the native community, having as a model the continuous river-estuarine of the São Francisco River, historically impacted by anthropic activities. For the first question, the response of the taxonomic structure of the fish community to physiographic and seasonal factors was studied. For the second question, the impact of exotic species on the functional diversity of the community based on high resolution trophic traits was verified. The continuous was spatially divided into three regions according to the geomorphology of the lower São Francisco: Depression (upper), Tableland (middle) and Lowland (lower). Bimonthly data on composition and abundance by fish species, as well as quantitative diet data, were collected between 2019 and 2021. Simultaneously, abiotic data (salinity, depth temperature, chlorophyll a, turbidity, conductivity, dissolved oxygen and rainfall) were recorded. The results indicate that seasonality, modelled by rainfall variation, does not influence the taxonomic structure of the fish community in the continuous, but there is spatial differentiation in the composition and use of habitat defined mainly by salinity, in this sense, the impact of the loss of the effect was discussed seasonal in dammed environments. Regarding the impact of exotic species on the native community, simulation scenarios of components of functional diversity were used, evaluating the impact on the trophic structure, by removing exotic species by physiographic region. Based on the concept of trophic niche partition, continuous trophic functional traits were estimated by analysing the diet of native and exotic species. Exotic species were removed from the simulation scenarios, using the trophic level as a criterion. Ten exotic species were identified with trophic levels ranging from detritivores to carnivores, with occurrence and abundance related to region along the continuous. As exotic species were removed from the lowest to the highest trophic level, the functional indices were recalculated. Simulation results indicate an impact on the functional structure of the native community. In the depression region, functional similarity occurs. On the tableland, from the first removal, there is an expansion in the functional space, inferring that the trophic niche of the native species is being compacted by the exotic ones. In the lowland, there is an environmental filtering process, with exotic species being barred by the higher salinity, however, despite all the exotic species found being from freshwater, there was occurrence in low abundance of Bryconops melanurus, Cichla kelberi, Metynnis lippincottianus, Oreochromis niloticus, Pellona castelnaeana e Trachelyopterus galeatus.