TOWARDS THE MEASUREMENT OF SECONDARY PRODUCTION AND RECRUITMENT IN COPEPODS

There is at present no routine method for measuring zooplankton second ary production in the ocean. Such a method is required, however, if we are to be able to estimate the potential productivity of marine ecosy stems and to quantify food transfer from primary producers through mes ozooplankton to higher trophic levels. A practical approach, suitable for measuring both the production of eggs and the recruitment of naupl ii, is presented. It is based on the measurement, in a given species, of only three variables (E = fecundity of females; B-f = biomass of fe males, and V = hatching success) and is expressed by two simple equati ons: P = E X B-f for production and R = E X B-f V for recruitment. Acc uracy of this method relies on the number of replicates of both E and V, estimated in laboratory or shipboard incubations, and on the type o f zooplankton sampler used to monitor biomass (B-f) and distribution o f females in a defined watermass. This approach has been applied to Ca lanus helgolandicus. Although restricted to a fraction of the total po pulation production, the method is accurate, operational, easy to appl y and comparable with parallel measurements of primary production at s imilar scales in time and space. These characteristics have never been met by other methods used for estimating pelagic secondary production and recruitment. (C) 1995 International Council for the Exploration o f the Sea