Nucleic acids in Calanus finmarchicus: relationships with food density, temperature, and growth rates

Melissa Wagner, Robert Campbell, and Ted Durbin

RNA content may offer a simple way to measure growth rates of zooplankton. We are currently examining the relationship of RNA with growth rates and physiological condition in Calanus finmarchicus. Our current work is aimed at calibrating the relationship of RNA with growth rate and at using RNA to assess growth rates and relative condition of Calanus in the Georges Bank region throughout 1995. In a recent laboratory experiment, we monitored growth and development of Calanus finmarchicus over the entire life cycle at a range of temperatures and food concentrations (see poster by Campbell et al.) In addition to measuring development rate and carbon and nitrogen growth, we measured RNA, DNA, and protein content. Both food concentration and temperature influenced RNA/DNA ratios of copepods in the experiment, although for some stages the effect of temperature was less important than that of food. Laboratory data were used to develop equations for predicting the temperature-corrected maximum RNA/DNA ratios expected for each stage under conditions of excess food. Comparing these theoretical maximum values with RNA/DNA ratios of copepods collected on three 1995 zooplankton process cruises suggests that Calanus were food-limited for much of the 1995 field season.