Nucleic acids and growth of Calanus finmarchicus in the laboratory under different food and temperature conditions

We examined the effects of food concentration and temperature on nucleic ac ids and protein content of Calanus finmarchicus in order to evaluate the us e of RNA as a growth rate index for this species. We measured RNA, DNA, and protein content of copepods reared from egg to adult stage in 5 combinatio ns of food and temperature conditions (25 to 500 mug C l(-1), 4 to 12 degre esC). At 8 degreesC, DNA, RNA and protein content and RNA:DNA differed amon g food treatments during Stages N6 through to adult female. Protein:DNA rat ios and RNA:protein ratios were significantly different among food levels f or only 3 of the 8 stages examined. At excess food, DNA, RNA, and protein c ontent and RNA:DNA ratios were inversely related to temperature for most st ages from C1 onward, but the effect of temperature was relatively small ove r the range of temperatures investigated. The RNA:DNA and protein:DNA ratio s increased with developmental stage whereas the RNA:protein ratio and grow th rates (measured in terms of protein, nitrogen, DNA, and carbon content) declined with increasing stage. Although the relationship of RNA:DNA to gro wth rates was stage-specific, the two were related when standardized for te mperature and developmental stage. RNA:protein ratios were directly related to growth rates regardless of stage, and the slope of the relationship inc reased with increasing temperature in a nonlinear fashion, Our results emph asize the importance of temperature and developmental stage for the relatio nship of growth rates to RNA concentration and RNA:DNA ratios. We propose 2 ways to estimate in situ growth rates of C, finmarchicus from RNA:DNA or R NA:protein ratios and environmental temperature.