Population dynamics of halobacteria in the Dead Sea water column1

A bloom of halobacteria in the Dead Sea is described, and the factors triggering its rise and decline are analyzed. The bloom developed in summer 1980, reaching population densities of up to 1.9 × 10 7 cells·ml ‒1 and imparting a red color to the water. The bloom was restricted to the upper 10–25 m of the water column. After a sharp decrease in cell numbers during the last months of 1980 the population density stabilized at values of around 5 × 10 6 cells·ml ‒1 surface water for more than a year. Enrichment experiments performed during that period showed that the nutrients limiting bacterial development were phosphate and suitable carbon sources. The turnover of phosphate appeared to be extremely slow (estimated turnover times as long as 240–1,200 days), suggesting that the population, a significant part of which proved viable, existed in a state of very little activity.