An elementary theoretical argumentation is advanced in favour of a global approach of some aspects of mesozooplanktonic systems dynamics and specially their production potentialities. For this purpose, measurements of the activity of aspartate transcarbamylase (ATC), an enzyme contributing to biosynthesis of basic components of nucleic acids, are performed on samples of the whole mesozooplankton. The method is applied to the neritic community of the North coast of Brittany (Western English Channel) during the productive period of springtime. The development of ATC activity during the increase of the mesozooplanktonic biomass shows global characteristics similar to those of organisms. The coherence of this result is analysed in connection with prior data.