As características geomorfológicas dos canais de maré influenciam na estrutura e composição das assembleias de peixes? Estudo de caso em um estuário tropical

Abstract

The incorporation of a geographic perspective on ecology, has promoted insights were landscape models provide frameworks for understanding the hydrological and geological variability in estuarine regions. In this context, the geomorphological arrangements have explained the Nekton structure at different scales. These models are based on two hypothesis : i) the landscape determines the hydrodynamics and the configuration of the fiscal chemist variables ii) the geomorphology may affect the distribution and habitat use by species since certain geometries can support or attract higher densities. These factors have been observed in drainage systems that composed estuaries, the tidal creeks. In these sites, processes such as energy dissipation tidal stratification, tide and circulation of nutrients, are decisive factors in the structuring of the assemblages. In this context estuarine fish, they tend to have a significant energy expenditure adapting to the conditions of salinity and temperature. In this way, creeks can offer tidal and thermal refuge on the structures that form their landscape, playing a role in the persistence of the species during the tidal cycles. The narrowing of the channels geometry causes the dissipation of the tide, especially due to the braking caused by the friction of the banks. Mediated the channel narrows it had observed physical and chemical gradient associated with geomorphology. Thus assemblies may differ over different portions of the channels. For example, the hydraulic dynamics and hyaline circulation can be decisive in the presence of certain species. Soon varations in geomorphological measures, such as length and width, cause changes in the composition of estuarine fish assemblages. Then channels with different morphometric must differ in their population structure. Therefore, it had assumed therefore that the geomorphology inherent to drainage networks are directly connected to their function in the estuarine environment, so physical and chemical changes associated to landscape can attract fish species seeking for refuge, food and reproduction sites. For this reason the present work aimed to verify the way that the geomorphological features (length, width, split, connection to the main channel and meanders), in two second order creeks, affects the composition, distribution and abundance of fish assemblages over a salt gradient on a seasonal basis. Therefore, we made six excursions (3 in the dry and 3 in the rainy season). In each channel, were set four sample points, two of then represented the lower and other two the upper part. At each point were performed three hauls using a beach seine. Environmental factors were measured using a multiparameter meter. The geomorphometrie was obtained through satellite images A total of 6901 individuals included in 76 species of fish were caught. In this study, we found differentiate between areas next the connection with the main channel that show a greater richness and fish density. We attributed this pattern to the proximity of these zones with the main channel, the creek moth size and the width. The lower portions presented more stable in terms of salinity and dissolved oxygen, thus the upper zone was characterized by dominance of small gobiidae.