Quantitative and Qualitative Changes in the Phytoplankton of Lake Kinneret, Israel, 1972-1975

Abstract

During the period 1972-1975, there was a dramatic decline in the algal standing crop in Lake Kinneret [Israel], from an annual average of 80.5 g/m2 to 40 g/m2. This change was evident during the Peridinium bloom period and was caused by a decrease in both cell number and size. Other changes were observed in the composition of the algal assemblage. Throughout the year, the relative proportion of small Chlorophyta and Cyanophyta increased, the latter especially in late summer and fall. Chlorophyll concentrations did not decrease correspondingly because of a general increase in the cellular chlorophyll content of algae. The primary production was maintained, despite the fall-off in algal biomass as freshweight, because of the shift to more rapidly metabolizing species. As a result, assimilation numbers, turnover times and algal growth rates were observed to be higher than previously (1969-1972). These changes suggest a trend away from a detrital food web dominated by Peridinium to a pattern of greater zooplankton grazing.