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A long term record of rotifers in Lake Kinneret (Israel) indicated that Keratella cochlearis is the most common zooplankter in it. Population dynamics parameters (“egg/female ratio” procedure) were combined with limnological data to analyze temporal fluctuations of K. cochlearis in the Kinneret ecosystem. Lake Kinneret is characterized by mesooligotrophic conditions. During the winter-spring period, when the lake is completely mixed and at low temperatures, water and nutrient inputs are maximal. The lake is stratified in the summer, with an oligotrophic epilimnion; at high temperatures, nutrient and water inputs are minimal. Since the early 1990’s, a decline in rainfall and water inputs and a reduction in Peridinium, coinciding with an ascending level of blue greens, were documented. K. cochlearis is affected by the water input regime, temperature, nutrient concentrations and the phytoplankton composition. The densities of individuals and egg bearing females are low in the summer and fall, and high during the late winter-spring, with E/F values being the highest during January-April. Population dynamics parameters were respectively similar. Regressions of densities of individuals and egg bearing females vs time (years) revealed a prominent long term decline.
Moshe Gophen (Sun,) studied this question.