Metacomunidade de diatomáceas perifíticas em reservatórios do semiárido brasileiro

Abstract

The aim of this study was to evaluate the taxonomic diversity of periphytic diatoms under the influence of an extreme drought, and to determine the importance of environmental and spatial factors on the functional attributes of periphytic diatoms in semiarid reservoirs. For this purpose, this thesis was divided into two chapters with the following objectives: (i) To analyze the temporal beta diversity of the metacommunity of periphytic diatoms in semiarid reservoirs in an extreme drought event; (ii) To investigate the influence of environmental and spatial factors in determining the structure and distribution of functional attributes of the metacommunity of periphytic algae in semiarid reservoirs. To this end, these objectives were applied using data from periphytic diatoms, collected in 25 sites located in the coastal region in four periods (June, September and December 2014, and March 2015), in the Poções, Sumé and Cordeiro reservoirs located in the Paraíba River basin. We found that extreme drought contributed to the reduction of water volume in the reservoirs and favored the increase in nutrient concentrations in the month with the lowest water volume (March/2015). These environmental changes caused the loss of species in the Sumé and Poções reservoirs, and the gain of species in the Cordeiro reservoir. In our study, we also observed that chlorophyll-a was the variable that contributed most to the loss of species, while electrical conductivity was the variable most representative of the gain of species. These results suggest that environmental variations may act by selecting more resistant species, causing the loss of sensitive species in these ecosystems, while the gain of species may be linked to the presence of species with dispersive capacity, or with adaptive strategies to survive in impacted environments. In line with these findings, we sought to evaluate the effects of space and environment on the functional attributes of periphytic diatoms. We found that the environmental variables were segregated according to the reservoirs, and that the functional attributes with the greatest contribution were from unicellular species, with mucilaginous rods and pads, firmly attached and with larger cell sizes. We also observed through the analysis of variance that the environment was the most important predictor for most of the functional attributes of periphytic diatoms than space. Where the environment was the most important predictor for unicellular algae, with mucilaginous rods, with mucilaginous pads, mobile species, firmly attached, loosely attached, and with the largest cell sizes (MDL-3 and MDL-4). On the other hand, space was the predictor that contributed the most to colonial, prostrate species, and with the smallest cell sizes (MDL-1 and MDL-2). The relationship between space and environment may be linked to the presence of functional attributes that allow greater dispersive capacity, while the relationship between species and the environment may be associated with the fact that environmental variables act as filters selecting resilient species to tolerate environmental impacts.