The Dead Sea - alive again

In the thirteen years of quantitative studies on the microbiology of the Dead Sea from 1980 onwards three distinct periods can be discerned. Mass development of the green unicellular alga Dunaliella parva (up to 8,800 cells/ml) and red archaeobacteria (2×10⁷ cells/ml) was observed in 1980, following a dilution of the upper water layers by rain floods. This bloom disappeared at the end of 1982 as a result of a complete mixing of the water column. During the period 1983-1991 the lake was holomictic, and no Dunaliella cells were observed. Viable bacteria were present during this period in very low numbers. Heavy rain floods during the winter of 1991-1992 caused a new stratification as the upper five meters of the water column became diluted to 70% of their normal salinity. In this upper water layer Dunaliella reappeared (up to 3×10⁴ cells/ml at the beginning of May, rapidly declining to less than 40 cells/ml at the end of July), and a bloom of red archaeobacteria (3×10⁷ cells/ml) once more imparted a red coloration to the lake.