Solar salterns, based on a multi-pond system, give a discontinuous gradient of salt concentrations. The heterotrophic bacterial populations of ponds containing from 10% salt to saturation have been studied. Saltern samples were spread on agar plates containing different media for halophilic bacteria and one medium made with water of the pond plus nutrients. Replica plating was done to determine the salt range for growth of the colonies. We studied 150 strains to determine the salt spectra of growth, the morphology, and nutrient requirements. The following conclusions were reached: (a) In salt concentrations above 10% (total salts), most bacteria are halophilic and few are halotolerant; (b) the two types of halophilic bacteria, moderate and extreme, show different distributions; in these ponds a narrow overlap exists between 25% and 32% salts with moderate halophiles predominating below this interval and extreme halophiles above it; (c) the populations of moderate halophiles are highly heterogeneous, and the salt concentration of their habitat affects their taxonomic composition, salt range for growth, and nutrient requirements. The population composition of extreme halophiles is less affected by the salt concentrations at which these bacteria are found.