Comparaison de la biomasse et du contenu énergétique d'un Copépode planctonique: Acanthocyclops vernalis (Fischer 1853)

In Lake Dayet er Roumi, the annual cycle of Acanthocyclops vernalis (Copepoda) is composed of two different cohorts, the first one in autumn, the other, numerically the most important, in spring.Growth rates and size of the individuals are nearly equivalent in the two cohorts, but their chemical composition changes appreciably. Autumn animals have a higher energetic content than spring ones: 2.425 10⁴ Nm · g^–1 and 1.965 10⁴ Nm · g^–1, respectively. The result is a great difference in biomass and production value between the two populations.Because of the difference in population density, the autumn cohort produces much less than the spring one. However, because each autumn specimen has a higher energy content, this difference becomes much smaller, on balance.The difference in numbers between the cohorts could result from the fact that in autumn, but not in spring, A. vernalis, because so rich in energy, is strongly positively selected by predators.