Influência de alterações da floresta ripária na ocorrência e dieta de loricariídeos (Siluriformes) em igarapés de terra firme da Amazônia central

Abstract

Forest streams represent one of the most important aquatic environment in the Amazon. These streams are heavily shaded by the dense forest canopy but modifications in the riparian vegetation may result in increased light incidence at the water surface. Periphyton is one of the major primary producers in these lotic systems that may vary in species composition in function of differences in daylight radiation, substrate type and location inside the stream. Algae and detritus are common components of the diet of tropical fishes, which include several species of suckermouth armored catfishes of the family Loricariidae. Several different and specialized feeding tactics are known among loricariid catfishes, which may to allow a more precise selection of the food ingested by these fishes. In this study, we tested the hypothesis that canopy openness directly affects the periphyton and indirectly the assemblages of loricariid catfishes in Central Amazonian forest streams. We measured a set of environmental factors, took samples of periphyton and of six loricariid species in 13 forest streams in the vicinity of Manaus, Amazonas State, Brazil. Loricariids were found in only four of the streams sampled. There was a higher abundance of loricariids in the Samaúma stream, possibly related to the chemical characteristics of the water resulting of anthropogenic from disturbances. On the other hand, the higher diversity of loricariid species observed in the Dimona-Capoeira Ponte stream may be related to structural characteristics of that stream (channel width, depth and discharge) and to a higher availability of substrate types as well. There was no significant variation in canopy openness and periphyton density among the studied streams. Differences in the composition of periphyton samples were accompanied by changes in the diet of the loricariid fishes. The six loricariid species showed some degree of feeding preferences related to the major groups of algae ingested, which may have allowed the coexistence of different loricariid species in some streams. Environmental disturbances in Central Amazonian forest streams may result in an increase in the populations of some loricariid species, possibly related to higher primary productivity rates resulting from modifications in water quality, substrate availability, sediment composition, and in the structure of the periphyton communities.