Abstract
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.
Highlights
K. cochlearis is affected by the water input regime, temperature, nutrient concentrations and the phytoplankton composition
The species is common and is a constant constituent of the Lake Kinneret (Israel) zooplankton communities, it only contributes a low biomass to the entire assemblage
The parameters below were employed for the analysis of population dynamics [2,11,12]
Summary
The species is common and is a constant constituent of the Lake Kinneret (Israel) zooplankton communities, it only contributes a low biomass to the entire assemblage. The common spatial and temporal occurrence of K. cochlearis, coinciding with limnological changes, initiated the present study, which deals with the impact of ecological conditions on the distribution of this species. The long term data record, which was established by the Kinneret Limnological Laboratory, was the basis of the study [1,2]. High range fluctuations of natural conditions were recorded, with seasonal ups and downs, as well as a long term decline in the water level, water inputs, plankton biomass and species composition [5]. The subtropical climate conditions of the Kinneret region are characterized by high and low levels of water and nutrient inputs in winter and summer months, respectively. The epilimnetic loads and plankton biomass present similar trends [6,7]
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