EFFECTS OF FLOOD PULSE ON THE COMMUNITY OF LORICARIIDAE (PISCES, SILURIFORMES) IN OXBOW LAKES OF THE PANTANAL, BRAZIL

Seasonal variations can promote environmental changes, and consecutively, influence the structure of the fish assemblage. The aims of this study were: i) to investigate the effect of flood pulse and lateral connectivity on Loricariidae assemblages in oxbow lakes; and ii) to determine the environmental factors driving the local structure of these species in the northern portion of the Pantanal. For this purpose, the fish community was sampled in two oxbow lakes between September 2005 and August 2007. The assemblages were mainly affected by seasonal fluctuations and were spatially unstructured, demonstrating that the flood pulse has a predominant role in the structuring of Loricariidae. In addition, the homogeneity of the assemblages between the lakes pointed to a frequent movement of the fish among the different subsystems, suggesting a high level of interaction and mixing between the habitats along the floodplain. The flood pulse was also responsible for significant changes in depth, dissolved oxygen and turbidity along the seasons, factors driving the structure of the fish assemblages. It was evident that seasonal environmental changes and connectivity are significant in the structure of Loricariidae assemblages in the Pantanal, sustaining high diversity and abundance.