Despite of several studies done in both peripheral and central areas, and a solid correlation foun generally between seawater, salinity and its zooplankton community (Vuorinen et al. 1998, Möllmann et al. 2000), no model has been applied relating salinity in the Baltic Proper consistently with pelagial biota, such as zooplankton and, furthermore with meteorological or climatic factors controlling salinity. Transfer equations provided us the tool to find a chain of events from a meteorological time series (NAO) to several related meteorological and hydrographical time series (Hänninen et al. 2000). However, the connection between physical governing factors and biological outcome was not made. In this study we related, using transfer function approach, biological time series with hydrographical and meteorological time series collected in the Baltic Proper from the late 1970's to the late 1990's.