ABSTRACT
Direct microscopic counts of samples stained with nucleic acid fluorochromes such as Acridine Orange (AO) or 4'6-diamidino-2-phenylindole (DAPI) are essential for studying and enumerating populations of bacterioplankton and have become routine over the last 10 to 15 years. In the oceans bacterial concentrations can vary considerably both on the micro- and macroscale so intense sampling frequency in time and space, closely coordinated with measurements of the biology, chemistry, and physics of the water masses is generally attempted in oceanographic investigations of bacterial dynamics. The effect of long-term storage of preserved seawater samples has been shown to dramatically effect the concentration of bacteria such that counts from stored, preserved seawater samples may have grossly underestimated bacterial numbers and their importance in the marine ecosystem. Frozen storage of freshly preserved and prepared seawater samples for up to 70 d results in no cell decrease.
