Influência da precipitação e hidrodinâmica na biodiversidade ictiofaunística e entomológica no baixo curso de rio estuarino pré-amazônico

Abstract

Introduction. Modifications of the hydrological and physical characteristics can alter the biodiversity of a region, since each group of individuals tolerates a certain range of modification of these attributes. Generally the region of the low course of the rivers that flow in the sea are subject to variations of cycles of tides of the ocean, configuring a region of intense hydrodynamics, imposing still more limitation to the aquatic biota. Goal. The objective of this work was to know the hydrological behavior and the influence of the low tide cycles of the Itapecuru river and the spatial and temporal effects on the composition of the aquatic biota (fish communities and aquatic insects). Methodology. To achieve this objective, biological data were collected at three different points located between the municipalities of Santa Rita and Rosario. The fish group was captured from May 2012 to August 2014, and the group of aquatic insects was collected from February to November 2014, every three months. Other on-site campaigns were carried out to obtain current, flow, tidal influence and salinity data. Results. The results suggest that the low course of the Itapecuru river presents great tidal variations in the flow dynamics, which directly influences the increase and decrease of the river quota and the direction and speed of the current. However, the influence of the tide is only dynamic, and there is still the advance of salt tide over the area. For the fish community, multivariate analysis using the non-metric multidimensional scaling technique (MDS) signaled the formation of two seasonal groups, with abundance and richness being the main responsible for similarity. The observed patterns did not indicate changes in the values of diversity, equitability and wealth. The ABC curve characterized the section investigated as an environment under natural conditions. However, based on field assessments, a trend towards degradation scenarios for this group was observed. This trend is associated with impacts on riparian forest, as a result of the occupation of the banks by the riverside communities, and also due to the constant release of sewage, especially in the stretches closer to the municipality of Rosario. In relation to the community of aquatic insects, a greater abundance was verified in the rainy period. Spatially, the point of capture with the highest number of individuals was the intermediate point between the most downstream and the most upstream, where the outflows at the beginning of the rainy season tend to be higher, a determining characteristic for species fixation. Comparisons of the diversity of Shannon-Winner indicated that there is no significant difference between the points, although the highest value was observed in point 3, located in the municipality of Rosario, more downstream subject to the more intense dynamics of the rise and fall of the tide. Seasonally the greatest diversity occurs in the rainy season, with the occurrence of 6 orders and more class collembola. Of the 27 families found in the study, 17 were classified as constants, being the chironomidae family of the dipterous order present in 100% of the samplings.