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

1. Growth rates of two dominant Lake Baikal phytoplankton, the winter diato m Aulacoseira baicalensis and the summer cyanobacterium Synechocystis limne tica, were measured in the laboratory under varied temperature and light re gimes 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 abov e 8 degrees C. Its maximum instantaneous growth rate was 0.15 d(-1) recorde d at 2-3 degrees 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 degr ees C, but grew at a rate of 0.24 d(-1) at the highest incubation temperatu re of 17 degrees C. Maximum growth rate was 0.35 d(-1) at 8 degrees C. 4. Saturation irradiances (I-k) for growth of Aulacoseira baicalensis and S ynechocystis limnetica were near pre-acclimation values of 40 mu mol m(-2) S-1. At temperatures conducive to growth, both phytoplankters grew at all i rradiances tested, except for A. baicalensis which would not grow at values above 300 mu mol m(-2) s(-1) at 8 degrees C. 5. We conclude that temperature is a major driving force for the seasonal s uccession of species in Lake Baikal. Other factors, including vertical mixi ng of the water column and grazing by zooplankton, may also play important roles.