Fontes autotróficas de energia para peixes do canal principal e quelônios ao longo da bacia do médio rio Negro, Amazônia Brasil

Abstract

The main channel of the middle rio Negro basin is characterized by high concentrations of dissolved organic matter, low nutrient levels and low primary production. The principal autotrophs in the river system are phytoplankton, periphyton, and flooded-forest (igapó) trees. Leaves, fruits and seeds fall from igapó forests are responsible for 99% of autotrophic production. The Negro main channel possesses a diverse assemblege of small and medium-sized benthic fish dominated by Gymnotiformes and Siluriformes. Large predatory pimelod catfish also inhabit this system. In contrast, the regional turtles populations are more associated with the aquatic margin of igapó forest. The main objective of this study was to identify the autotrophic energy sources of the channel fish and turtles. Stomach content analyses were used to determine trophic links between the autotrophic energy sources and benthic fish assemblege. Natural variations in the stable carbon isotope ratios (δ13C) of fish and plants were used to identify the energy sources. The hypothesis was that the igapó forest, which is characterized by low δ13C values, is the principal source of energy for these consumers. Average δ13C values (±standart error) were: forest leaves -30.24±0.2; phytoplankton -32.59±0.68;periphyton -38.71±0.6; turtles -31.0±0.4; benthic fish -33.2±0.4 and large catfish - 32.8±0.4 . These results indicate that this fish assemblege derives their energy predominantly from algae, while turtles depend predominantly on energy derived from the igapó forest. Aquatic invertebrates were the main energy transfer link between the plant autotrophs and fish communities which inhabit the main channel of the Rio Negro basin.