Effects of flood pulses on persistence and variability of pleuston communities in a tropical floodplain lake

Abstract

Large rivers in tropical regions can experience strong variations of abiotic factors owing to the occurrence of flood pulses. Both man-made and natural floods can cause pulses with varying intensity and duration. Here, we test the hypothesis that ostracod communities in the pleuston of floating plants are persistent during regular pulses and more variable during extreme floods. Ostracod communities were monitored in the Manezinho Backwater of the Upper Parana River floodplain (Brazil) for 83 months (seven hydrologic cycles). Flood pulses directly influenced the abiotic variables, which in turn were correlated with the species composition and abundance of ostracods. Variability in the species composition differentiated only between the limnophase of cycle 4 (L4: 2009) and the subsequent extreme flood of cycle 5 (P5: 2009–2010). The longer duration and higher intensity of the extreme flood can increase the exchange of organisms through the aquatic connections between the lake and the river and can potentially trigger the hatching of dry-resistant eggs, increasing variability in ostracod species composition. The absence of significant differences in the species composition variability between the other succeeding periods shows that these communities are persistent and buffered to the effects of natural pulses of short durations.