Copepod communities in lakes of varying trophic degree

Abstract

Copepod communities in the pelagic of 22 lakes of varying trophic degree were studied during the summer months of the years 1989 to 1991. In total 6 species were monitored, one calanoid copepod (Eudiaptomus gracilis), and 5 species of cyclopoid copepods (Acanthocyclops robustus, Cyclops abyssorum, Cyclops vicinus, Mesocyclops leuckarti, Thermocyclops crassus). The calanoid copepod predominated in the oligo-mesotrophic lakes. Among cyclopoid copepods M. leuckarti and Cyclops abyssorum preferred oligo-mesotrophic conditions while the other species predominated in the eutrophic lakes. C. vicinus, generally regarded as a winter species which should undergo a diapause during summer, formed summer generations in the eutrophic lakes. This particular deviation from the normal life cycle is interpreted as a strategy to optimize the reproductive output. It implies that even during summer when competition with cladocerans is intense eutrophic conditions can provide sufficient food for the development of the nauplii and for the reproduction of the adults. Calculation of the association coefficients revealed that among cyclopoid copepods generally a large species (C. vicinus) and a small species (T. crassus or M. leuckarti) co-exist. However, frequent associations of M. leuckarti and T. crassus suggest that these species use different food sources. The decline of the calanoid copepod in the eutrophic lakes is probably a result of a higher predation pressure on this group; possibly cyclopoid copepods benefit from their distinct mating behaviours.