Resposta da comunidade de Odonata ao gradiente ambiental em igarapés da Volta Grande do Xingu

Abstract

The increase in anthropogenic activities in the Amazon has caused significant impacts on terrestrial and aquatic ecosystems. Deforestation, burning, and the construction of hydroelectric dams, among other activities, have contributed to the loss of biodiversity and the degradation of aquatic ecosystems, resulting in the destruction of habitats and the reduction of aquatic species, such as Odonata, which are fundamental for maintaining the balance of these ecosystems. Odonata organisms, popularly known as dragonflies, damselflies, and skimmers, have a close relationship with aquatic and terrestrial environments due to their life cycle, which is aquatic in the larval stage and terrestrial in the adult stage. Odonata respond quickly to changes in the environment and are widely used as bioindicators of environmental alterations due to their high sensitivity to habitat and water quality. In view of this, the objective of this study was to evaluate changes in Odonata communities in response to environmental variables in streams of the Volta Grande do Xingu. Collections were carried out in 19 streams in the region, covering the municipalities of Anapu, Senador José Porfírio, and Vitória do Xingu, in September 2019, during the Amazonian dry season. For insect capture, the fixed zone sweep net method and entomological net (puçá) were used, covering 100 meters in each stream. During the collection process, the following variables were measured: pH, electrical conductivity, water temperature, turbidity, and dissolved oxygen. In all streams, the Habitat Integrity Index (HII) was applied, which assesses the conservation status of the habitat, ranging from 0 to 1 – the closer to 1, the better the conservation status of the stream; the closer to 0, the more degraded the environment. We used TITAN (Threshold Indicator Taxa Analysis) to assess the threshold of the gradient at which the community gains or loses species. In total, we collected 526 individuals, distributed in two suborders (Zygoptera and Anisoptera), 6 families, 26 genera, and 43 species. The results of the present study showed that the Odonata community presented a change in its composition at values from 0.64 for the environmental gradient of HII, with a gain of species in more preserved environments. Regarding the other environmental variables, there were no changes in the composition of the Odonata community. The species A. fumigata Hagen, 1865, of the suborder Zygoptera, stood out as a bioindicator species of preserved environments, thus evidencing that individuals of this suborder are commonly associated with more intact and preserved environments with dense vegetation, due to their ecophysiological requirements. When analyzing the other values in relation to the other variables, no significant results were obtained for the species. Our results demonstrate that environmental changes caused by anthropogenic action directly influence the composition and abundance of Odonata communities. Therefore, this study is fundamental to assess the health of aquatic ecosystems and support conservation policies for the streams of the Volta Grande do Xingu.