In recent years, growing concern over increasing UV-R (ultraviolet radiation) has led to several studies of UV-R effects on phytoplankton and primary production. However, the effects of UV-R on bacterioplankton, a vital segment of marine food webs, have largely been overlooked. In this study, a method was developed to monitor rates of DNA repair, which were correlated with bacterial survival and DNA damage. The responses of Vibrio natriegens, a ubiquitous marine microorganism, and the role of recA, a regulatory gene which controls DNA-damage repair in bacteria, were investigated in the laboratory utilizing polychromatic and monochromatic light within the solar ultraviolet spectrum. Utilizing RecA as a molecular tool of in situ gene expression at the translational level, environmental studies of UV-R and DNA repair were done in controlled microcosms as well as natural marine bacterial assemblages. From the laboratory studies, we have learned that recA, which is believed to be universally present among bacteria, is induced at differing proportions to various segments of the solar ultraviolet spectrum. Both UV-A and UV-B were found to induce RecA as well as increase mutagenesis. In microcosm studies RecA was shown to be significantly induced by solar ultraviolet radiation in a control microorganism. Likewise the enzyme was detected in natural populations under UV-R-stress. RecA appears to be a suitable enzyme for monitoring repair in bacterial populations particularly when corroborated with damage assessment and physiological status.