The dynamics of the bacterial population associated with a salt marsh

The distribution and temporal fluctuations in the density of bacteria in the water covering a high-salinity marsh were investigated employing epifluorescence microscopy for quantification as well as by transmission and scanning electron microscopy. The observed densities ranged from about 1 to 19 × 10⁶ bacteria/ml during the course of the study. High-marsh sampling sites had an average population level of 7.8 × 10⁶ bacteria/ml which was more than double the mean density recovered from large creeks near the mouth of the marsh system. Bacteria associated with seston varied tidally and seasonally, whereas the population of free planktonic bacteria varied only seasonally. Very small fluorescing bodies were commonly observed during epifluorescent observation of samples. These small bodies were observed at densities two orders of magnitude higher than easily recognized bacteria. In a salt marsh, the relative density of epibacteria was influenced by short-term tidal effects, and the population of planktobacteria was apparently controlled by long-term seasonal phenomena.