RNA:DNA ratios of Calanus finmarchicus in the Georges Bank region: relationships with chlorophyll concentration, egg production, and growth rates

M. M. Wagner, R. G. Campbell, and E. G. Durbin

In order to monitor the growth and physiological condition of the copepod Calanus finmarchicus in the Georges Bank region, we measured RNA:DNA ratios of copepods in the area during spring 1995 and 1997. During 1995, RNA:DNA ratios of stages N6 through adult female were between 21% and 117% of ratios for laboratory-reared copepods growing at maximal rates. RNA:DNA ratios of younger juvenile stages (N6, C2, C3) were related to in situ chlorophyll a concentration (chl a) whereas ratios of stages C4 through adult were not. Ratios of C5 and C6 were lowest in January, as these copepods had recently emerged from diapause. RNA:DNA ratios of C1 through C5 were correlated with carbon and nitrogen growth rates, although the association was weak (carbon: r=0.357, nitrogen: r=0.436, P<0.05). There was a strong linear relationship between RNA:DNA and egg production rates of adult females (r2=0.70, P<0.05). Our results demonstrate that RNA:DNA ratios can support current techniques for measuring production of juvenile and adult stages of C. finmarchicus.