SEASONAL DYNAMICS OF ACARTIA-BIBILOSA AND EURYTEMORA-AFFINIS (COPEPODA, CALANOIDA) IN RELATION TO ABIOTIC FACTORS IN THE NORTHERN BALTIC SEA

The seasonal response of the two most abundant calanoid copepods of th e northern Baltic Sea, Acartia bifilosa Giesbrecht and Eurytemora affi nis (Poppe), to abiotic factors was studied in Tvarminne, the SW coast of Finland, using long-term data from the years 1973 to 1984. The rel ationship between copepods and hydrography during the four seasons was evaluated by calculating correlations between deseasonalized and detr ended time series of calanoid abundances, temperature and salinity. Th e dependence of the copepods on temperature and salinity was not the s ame during the different seasons, nor for copepods of different age. I n general, A. bifilosa preferred waters with a salinity of between ca 4 and 7parts per thousand, and E. affinis avoided salinities above 6.5 parts per thousand. The correlations between copepods and temperature were usually positive, but large season- and stage-specific variation occurred. We suggest that the different copepod generations were seas onally adapted to the prevailing hydrographical conditions and therefo re responded to changes in a different way.