VII Congreso de Ecologia do Brasil.

POI NEIFF, ALICIA SUSANA GUADALUPE

Caxambu

Congreso; VII Congreso de Ecologia do Brasil; 2007

Universidad Estadual do Caxambú

In this paper we analyzed the changes in diversity of fish assemblages at different levels of resolution (in space and time). Species turnover from seven vegetated floodplain lakes distributed within an area of 1458 ha were compared among different hydrologic conditions: after a prolonged connection of the floodplain with the main course, during falling water and after a prolonged isolation. We also investigated the size and abundance of large sized migratory species found in these wetlands and the food resources exploited by the dominant fish. For this small area, located in the Site Ramsar Chaco, we found the half of the total species richness reported for the low tract of the Paran¨¢ River. Our results indicated that different dominant populations of fish occur in different hydrological conditions, even though high water and isolation phases occur in the same season of different years. Species turnover decreased from high water (¦Â=40.33) to low water (¦Â=34.33) with the minimum value of beta diversity index obtaining during the isolation of the floodplain wetlands (¦Â=26.83). Since the species composition varied from site to site, the Bray-Curtis analysis indicated low similarity between sites during both the isolation and the prolonged connection. Small size characids fish typically associated with macrophytes dominated the fish assemblages, whereas the young stages of large sized migratory species were found in low abundance. The maximum standard length of the fish captured was 28 cm and the size of large migratory fish varied between 1.6 and 25.0 cm.  The dominant fish used several food resources but littoral macrophytes-associated organisms had a high frequency of occurrence. Few species used predominantly aquatic macrophytes as food and mmolluscs were not found in the gut content of fish from the study area. The studied floodplain has a high heterogeneity, evidenced by the high deviation coefficients of environmental variables, the high turnover of fish species richness and the abundance of generalist species.