Life cycle of the copepod Eudiaptomus gracilis (Sars, 1863) in lake Onega

In the context of climate changes and seasonal shifts the study of the annual cyclicity in the plankton community and its elements is very important. Eudiaptomus gracilis is the main species in Lake Onega pelagic zooplankton and can be found in the lake all the year round. It takes part in the formation of bioresources, besides it is an important element of planktivorous fish food reserve. On the basis of the long-term observations the life cycle of the crustacean populations from the different areas of the lake was analyzed. Annual trajectories of the seasonal dynamics of age groups were obtained. It was shown that the dicyclic character of the population dynamics in the central part and large bays of Lake Onega is similar, but there are some features connected to the thermal regime and trophic levels. The trophic state determines the maximum summer levels of crustacean population abundance and biomass, which vary 1.5-2 times by areas. The maximum values were recorded in the Kondopozhskaya Bay, they are connected with the anthropogenic eutrophication. The features of the population life cycle in Petrozavodskaya Bay are associated with the hydrodynamic regime of the bay. The state of the population in a subglacial period was studied in detail. It was shown that the beginning of the reproduction depends on the state of ice and snow cover. In comparison with the data of the last century, no noticeable changes in the nature of the annual cyclicity of Eudiaptomus gracilis were observed, despite fluctuations in the anthropogenic load and climatic changes in recent decades.