Seasonal variation in frequency of dividing cells of freshwater phytoplankters

The frequency of dividing cells (FDC) of a natural phytoplankton community was studied seasonally in a freshwater pond to which water directly from La ke Kasumigaura was supplied. Phytoplankton samples were collected every 3 h at three depths (5, 30 and 75 cm) over 24 h periods in each of the four se asons and examined for FDC, cell size and abundance. Dominant phytoplankton species were Synedra ulna, Cyclotella kutzingiana, Chlamydomonas cingulata and Oscillatoria tenuis with Melosira italica, Cryptomonas ovata, and Syne chococcus sp. being seasonally abundant. All species showed a similar FDC p attern related to the light-dark period that is a moderately phased divisio n with the maximum FDC between 21:00-03:00.