ASSESSING THE EQUIVALENCE OF GROWTH AND EGG-PRODUCTION OF COPEPODS

The hypothesis that food-saturated rate of production of egg matter is equivalent to maximal specific growth rate of copepods has not been widely tested, and seems contradicted by some studies. If verified, it would supply, for example, a single P/B ratio for all stages where food is adequate in nature. We test the hypothesis using published data on Calanus species. Logically, rate of production of egg matter at given temperatures should be expressed as a function of structural body mass, with storage lipid and ovary weight discounted. This can be compared with growth rates of younger copepodid stages, based on lab-determined temperature functions for times to reach mid-stages, together with weights from nature or single rearing experiments. Growth of later stages is more relevant, but difficult to assess adequately in the laboratory. We show how body sizes of females, known to be negatively related to temperature, might be used to correct for reduced growth rates in these later stages. Our assumptions and approximations appear to predict quite well the temperature-dependent daily rates of egg production of fully reproductive, well-fed females of four species of Calanus, and we suggest ways of obtaining and presenting data to test the hypothesis more thoroughly. (C) 1995 International Council for the Exploration of the Sea