ANALYSIS OF TIME-SERIES OF PLANKTONIC COMMUNITIES IN THE ADRIATIC SEA- DISTINGUISHING BETWEEN NATURAL AND MAN-INDUCED CHANGES

Time series (> 20 years) of bacterioplankton, phytoplankton and zoopla nkton abundances and of phytoplankton production in the Adriatic Sea w ere analysed. Multivariate methods were used to extract the main patte rns of year-to-year changes in abundances (Principal Component Analysi s), and to discriminate between years and sites (Multidimensional Scal ing). Increasing long-term trends were established for planktonic abun dances and phytoplankton production in both coastal and open sea areas , presumably as a result of eutrophication processes. In the open sea, natural factors (water exchange between the Mediterranean and Adriati c Seas, and temperature) were dominant in controlling year-to-year flu ctuations of plankton. On the other hand, long-term fluctuations of pl ankton in the coastal area were chiefly controlled by man-induced fact ors. Thus, besides natural factors, the dominant pattern of planktonic fluctuation was correlated with the fluctuation of nutrients coming f rom the land as a result of human activities.