a b s t r a c t Viruses and prokaryotes represent the smallest and the most abundant biological entities in marine environments. The interest for viruses and their interactions with marine organisms is continuously rising but the studies are generally limited to short-time investigations. This study conducted in the Gulf of Trieste on monthly resolution investigates for the very first time relationships between viruses and prokaryotes (both heterotrophs-HP and autotrophs-AP) over ten years (2000e2010). From our results emerged that no clear relationship between the abundances of viruses and prokaryotes is observed unless for rather restricted time intervals. Some of the sporadic peaks of viral abundances can be attributable to infections occurred during the autumn phytoplankton blooms, thus probably contributing to the end of the bloom. We infer that the general uncoupling between viruses and prokaryotes in the Gulf of Trieste is due to the variety of factors that regulate viral infection, proliferation and persistence such as the diversity of viral life cycles that are determined by environmental factors, the abundance and the physiological status of their hosts.