Synchronous cell division and growth rate of a planktonic dinoflagellate, Ceratium hirundinella, in relation to environmental variables

The timing of cell division and the population growth rate of Ceratium hirundinella in Lambert Quarry, a small quarry lake near Oak Ridge, Tennessee, were investigated to relate Ceratium growth to environmental variables. Ceratium growth rates were calculated from counts of binucleated, recently divided and non-divided cells in samples taken in a vertical profile over a 24 hour period on four occasions between July through October, 1982. Maximum frequency of binucleated cells occurred at 0200 and approximately 4% to 10% of the population divided per day. Growth rates calculated from these observations were relatively slow, with a doubling time of 7 to 15 days. Highest growth rates were generally found at depths less than 7 m. Vertical profiles of in vivo chlorophyll fluorescence and cell counts of samples taken throughout the water column suggested that Ceratium hirundinella was vertically migrating. Of the environmental factors governing Ceratium hirundinella growth in the water column, light intensity appeared to be most important, although temperature and nutrient availability may also play important roles. The discovery of a synchronously-dividing Ceratium hirundinella population in Lambert Quarry, a physically protected lake free from watershed perturbations, substantiates previously observed relationships between the presence of synchronously-dividing phytoplankton populations and environmentally stable systems.