Short communication. The effect of temperature, food concentration and female size on the egg production of the planktonic copepod Acartia bifilosa

Egg production of a brackish water calanoid copepod Acartia bifilosa was measured in the laboratory in different chlorophyll (Chl) a concentrations (0-24 µg l-1) and temperatures (4-24°C), and the cephalothorax length and carbon content of females were determined. Egg production was positively correlated both with Chl a concentration and with temperature; highest egg production was obtained with 14-20 µg Chl a l-1 and at 13-18°C. There was also a significant positive correlation between egg production and female length-specific carbon content (µg C µm-1). However, no correl- ation was observed between egg production and cephalothorax length of females. Female carbon content changed during the 3 day experiments; carbon content was positively related to Chl a concen- tration and negatively related to temperature. We conclude that food availability (Chl a concen- tration), rather than temperature, limits the egg production of A.bifilosa in the present study area in the northern Baltic Sea. Further, both food concentration and temperature affect egg production not only through the direct effect on the numbers of eggs produced per female, but also through their effect on female carbon content.