Extreme hydrological periods: effects on phytoplankton variability and persistence in a subtropical floodplain

The variability and persistence of species are appropriate measures of stability for communities that have large fluctuations in composition, such as phytoplankton. Our hypothesis was that phytoplankton species richness and abundance depend on the environmental variability arising from different phases of hydrological cycles, since changes in the limnophase and potamophase promote environmental fluctuations in the floodplain. A sub-basin of the Upper Parana River was assessed between 2000 and 2001, a prolonged limnophase period, and 2010-2011, a period of conspicuous potamophase and limnophase. The phytoplankton community differed between these two periods. The lowest species richness with elevated values of abundance was recorded in 2000-2001, when 18 taxa indicators were verified. Lower variability and greater persistence of phytoplankton were recorded in 2000-2001, when the environmental variability was low. Therefore, the prolonged limnophase had a negative influence on species richness and influenced the pattern of dominant species persistence, thus, corroborating our hypothesis, indicating greater phytoplankton persistence in irregular hydrological cycles. Hydrological cycles with limnophase and potamophase periods present greater variability and less persistence of phytoplankton species richness and abundance.