Distribución de Staurastrum planctonicum var. bullosum (Chlorophyta, Desmidiaceae) en la columna vertical de un embalse eutrófico a diferentes escalas temporales

Abstract

Factors controlling population dynamics of Stuurastrum planctonicum var. bullo.~urn (Chlorophytu, Desmidiuceaei living in El Vellón reservoir (Madrid, Spain) have been considered at three time scales: monthly, daily and hourly. In the year cycle the population appears to be related with water temperature, water density, eeuphotic layer/ mixed layem ratio, inorganic dissolved carbon, thermal stability of the water column and solar radiation (with these two latter factors having time lags of one and two months, respectively), indicating that this taxon thnves during the stagnation period though it can be found al1 year long in the reservoir. At daily time scales, within its exponential growing penod, the population only correlates with dissolved ni- trogen, dissolved phosphorous and with ((dissolved nitrogen/dissolved phosphorous)) ratio, whereas at hourly time scales microcli- matic changes seem to prevail on its dynamics, which is demonstrated by delays in correlation and by fact that factors influencing such dymamics are not the same on two close but weather-contrasting days. These results support the hierarchical hypothesis of phytoplankton responses to environmental changes.