Temporal fluctuations of zooplankton and bacteria in the middle Adriatic Sea

Year-to-year fluctuations in the abundance of zooplankton and bacteria were examined. Three main patterns of year-to-year changes in abundance were extracted by Principal Component Analysis (PCA): (1) Cyclical oscillations with 5.5 yr periodicity. This pattern is well correlated with salinity and southerly weather type (lower atmospheric pressure, southeasterly wind and higher precipitation) and can be accounted for by the water exchange between the Mediterranean and the Adriatic Sea. (2) Long-term trend of increasing abundance presumably due to the open Adriatic eutrophication. (3) Oscillations with 7.3 yr periodicity. This pattern is well correlated with temperature.