Population dynamics of Dunaliella parva in the Dead Sea1

Abstract

A bloom of the unicellular green alga Dunaliella parva in the Dead Sea is described, and physicochemical factors triggering its rise and decline are analyzed. The bloom developed in summer 1980, reached population densities of up to 8,800 cells·ml−1, and gradually declined until finally collapsing during the first months of 1981. Algal development was limited to a thin layer of less saline water floating on top of the heavy brines. Laboratory experiments showed that both dilution of Dead Sea water and increase in phosphate concentration are required for algal development in the Dead Sea.The Dunaliella community followed the deepening of the pycnocline to depths of 15–25 m in September–October 1980, with resultant light limitation to part of the population and cell death by starvation in the absence of light. The inflow of new floodwaters generated a new pycnocline which may have prevented the cells below from reaching the euphotic surface layer, resulting in the death of most of the remaining population.