Temperature, growth and seasonal succession of phytoplankton in Lake Baikal, Siberia

1. Growth rates of two dominant Lake Baikal phytoplankton, the winter diatom Aulacoseira baicalensis and the summer cyanobacterium Synechocystis limnetica, were measured in the laboratory under varied temperature and light regimes to determine the potential role of these abiotic factors in seasonal species succession in the lake. 2. Aulacoseira baicalensis grew best at low temperature and not at all above 8 °C. Its maximum instantaneous growth rate was 0.15 d -1 recorded at 2-3 °C. Cells grew faster as temperature decreased, apparently in contrast to conventional Q 10 -based temperature-growth relationships. 3. The picoplankter Synechocystis limnetica did not grow at 2-3 or 5-6 °C, but grew at a rate of 0.24 d -1 at the highest incubation temperature of 17 °C. Maximum growth rate was 0.35 d -1 at 8 °C. 4. Saturation irradiances (I k ) for growth of Aulacoseira baicalensis and Synechocystis limnetica were near pre-acclimation values of 40 μmol m -2 s -1 . At temperatures conducive to growth, both phytoplankters grew at all irradiances tested, except for A. baicalensis which would not grow at values above 300 μmol m -2 s -1 at 8 °C. 5. We conclude that temperature is a major driving force for the seasonal succession of species in Lake Baikal. Other factors, including vertical mixing of the water column and grazing by zooplankton, may also play important roles.