We studied the ecological history of the Gulf of Trieste. Before the 20th century, the only activity here was ore mining, releasing high amounts of mercury into its northern part, Panzano Bay. Mercury did not cause changes to microorganisms, as it is not bioavailable. In the 20th century, agriculture caused nutrient enrichment in the bay and increased diversity of microorganisms. Industrial activities increased the concentrations of pollutants, causing only minor changes to microorganisms.