Institute of Biophysics, Siberian Branch, Russian Academy of Science, Akademgorodok, Krasnoyarsk 660036, Russia

Abstract

The authors investigate seasonal dynamic of number of alive and dead zooplankton individuals, their vertical distribution and the rates of sedimetation using special staining. Seasonal dynamic of natural mortality (ageing, parasites, diseases, toxic substances) was calculated. The mortality was maximum in the middle of a summer (the period of zooplankton depression) and minimum - at the beginning and at the end of summer. The method was compared with traditional method of mortality calculation that includes death from predators. It was shown that zooplankton depression in the middle of summer was caused not by press of predators but other reasons.