How periphytic algae respond to short-term emersion in a subtropical floodplain in Brazil

Changes in hydrometric levels caused by dam operations can alter community structure in aquatic environments. We investigated the effects of a short-term emersion on a periphyton community in a lentic environment in a subtropical floodplain in Brazil. Our goals were to identify variations in periphyton community structure and composition during a period of 21 days subsequent to a short-term emersion and to identify taxa associated with periphyton after the emersion event. In situ, we simulated 15 hours of emersion of the periphyton community during the climax stage and investigated the effects of emersion on the structure and composition of this community over 21 days. Periphyton was removed by scrubbing randomly chosen glass slides from the support controls and the treatments. The structure and composition of the periphyton community showed variations soon after emersion, e. g. new taxa were recorded, the diatoms and oedogoniophyceans were lost; furthermore, the community did not return to its initial successional phase after the disturbance. Canonical ordination analysis showed a variation in community composition and structure throughout the successional period, and axis two indicated variation in the community soon after the emersion disturbance occurred in the control and treatment periphyton. Similarities between the control and treatment periphyton communities were lower soon after emersion and higher after the fifth day after emersion. Loosely attached species characterised the treatment periphyton after the disturbance. Recovery of the periphyton community may have been influenced by the reproduction of persistent species and by recruitment from the regional species pool. Short-term emersion affected the structure and composition of the periphyton community in the Upper Parana floodplain; however, its rapid recovery to pre-disturbance conditions suggested that it is already adapted to the intensified variations that occur in this system because of dam operations.