Relationships between nucleic acid levels and egg production rates in Acartia bifilosa: implications for growth assessment of copepods in situ

To evaluate the applicability of RNA-based indices in copepod growth assessment, concentrations of nucleic acids in Acartia bifilosa were calibrated against growth rates estimated via egg production experiments, and the relationships between levels of RNA, DNA, and the RNA:DNA ratio and growth rates were examined. Furthermore, to investigate effects of temperature and food availability on the relationships between weight-specific fecundity and nucleic acid levels, incubations were carried out at 9 and 16degreesC, each at 3 food concentrations. There were positive relationships between nucleic acid concentrations and their ratios and weight-specific egg production rates. Overall, RNA concentration was the best predictor of specific growth rate. No correlations between either of the measured variables and female body size were observed. When egg production was elevated by manipulating the feeding regime, RNA concentration and the RNA:DNA ratio increased in concert. Neither growth nor RNA indices were significantly affected by temperature, while a significant increase in DNA concentrations was observed at high food levels and low temperatures. The lack of temperature dependence in RNA-growth relationships allows their direct application for in situ growth estimates in summer populations of A. bifilosa in the northern Baltic Proper.