Environmental constraints structuring fish assemblages in the river Paraíba do Sul watershed: Land use condition, habitat and physico-chemical water quality. / Condicionantes ambientais estruturadoras das assembléias de peixes da bacia do rio Paraíba do Sul: Condição do uso da terra, do habitat físico e qualidade físico-química da água.

Benjamin Carvalho Teixeira Pinto

Structure and dynamic of the Paraíba do Sul fish assemblages and their relationship with environmental constraints in both regional (e.g. altitude, area of drainage, flow and land use) and local (microhabitat and physico-chemical) scales were studied. A fish sampling programme was carried out in the whole extension of the main channel (1100 km) and in the six main tributaries (>4th. order), in two season: summer/wet versus winter/dry. Additionally, samplings were performed in 42 sites distributed in 26 streams 1st to 3rd order in four ecoregions during the winter/dry season. Fish sampling and environmental variables were carried out between 2001 and 2006. The present study was divided in four Chapters. In the first chapter a general introduction was shown reporting the main problems that the Paraíba do Sul watershed underwent due to anthropogenic activities and their consequences to water and environmental quality, and influences on aquatic biota. In the following three chapters pattern and process of fish assemblages in the main channel and tributaries were described, reporting on themes that complement each other aiming to assess the subsystems (river vs. streams) in separated chapters. In the second chapter spatial and temporal patterns of fish assemblages distribution in the main channel and main tributaries (larger than 4th. order) were assessed along the Paraíba do Sul watershed. It was found that fish assemblages show a continuum distribution, increasing gradually in richness from the upper to the lower reaches, and four assemblages were discriminated along the longitudinal extent, corresponding close to the river dams which obliterate the lotic system. Seasonal difference in fish assemblages were detected for the lower reaches only, possibly related to higher lateral conductivity in this part of the system. Regional environmental constraints determine locals constraints with large area of drainage and flow and lower altitude being associated to larger river width, presence of pools, margins covered by grass and higher temperatures. Species typical of middle-upper reaches were C. natareri, P. caudimaculatus, P. reticulata and T. rendalli, that were associated to muddy substrate, probably associated to environmental degradation. Species typical of the middle-lower reaches were P. fur, A. giton, G. albescens, H. aurogutatus and H. affinis, that were associated to rocky substrate and margin occupied by shrubs. In the lower reaches, species such as P. vivipara and C. gilbert were associated to margins occupied by grass and higher water temperature, while C. lacustris and P. lineatus were associated to pools. The third chapter aimed to evaluate environmental quality by using the Index of Biotic integrity IBI, and their results were compared with the local and regional environmental constraints to validate IBI. Scores of IBI decreased in near to sites of intense anthropogenic influence, and increased in sites near to low land use. Land use by urban area influence local constraints such as conductivity, dissolved oxygen and type of substrate (muddy) with IBI showing sensible to such variation. On the other hand, higher IBI scores higher IBI were associated to riffles and higher dissolved oxygen concentration. Flow impairment by dams also influenced IBI scores. In the fourth Chapter fish assemblages of stream (1st. to 4th. order) were studied, and regional (ecoregion, altitude, climate, geomorphology, distance form the main channel) and local (microhabitats and physico-chemical) constraints were investigated. Stream fish assemblages differed among the 4 ecoregion determined by altitude and, to a lesser extent, distance from the main channel. Plateau assemblages were comprised by species well adapted to high gradient streams, while valley assemblages included species well adapted to low gradient streams. Furthermore, stream assemblages changed according to distance from the main channel, with assemblages from sites located near to 2 km from the main river differing significantly from assemblages in sites located more than 8 km from the main channel. The hypothesis that regional constraints influence local (hábitats and physicochemical parameters), and this later are determinants of fish assemblages was corroborated in the present study. Furthermore, the Index of Biotic Integrity was refined for the Paraíba do Sul whole system, and can be applied for the three main river reaches (middle-upper, middlelower and lower) with minor modifications to the upper reaches. This tool can be used to monitor the whole system and should be preferably applied during low river flow (winter).

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