Seasonal dynamics of Acartia bifilosa and Eurytemora affinis (Copepoda: Calanoida) in relation to abiotic factors in the northern Baltic Sea

Abstract

The seasonal response of the two most abundant calanoid copepods of the northern Baltic Sea , Acartia bifilosa Giesbrecht and Eurytemora ajfinis (Poppe) , to abiotic factors was studied in Tvarminne , the SW coast of Finland , using long - term data from the years 1973 to 1984 . The relationship between copepods and hydrography during the four seasons was evaluated by calculating correlations between deseasonalized and detrended time series of calanoid abundances , temperature and salinity . The dependence of the copepods on temperature and salinity was not the same during the different seasons , nor for copepods of different age . In general , A . bifilosa preferred waters with a salinity of between ca 4 and 7%0 , and E . ajfinis avoided salinities above 6 . 5%0 . 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 seasonally adapted to the prevailing hydrographical conditions and therefore responded to changes in a different way .