CONTEMPORARY STATE OF THE ZOOPLANKTON IN LAKE-PEIPSI

L. Peipsi is one of the richest fish lakes in Europe. Planktivorous sm elt dominates in the fish fauna. The abundance of zooplankton fluctuat es between 43 600-2 241 500 ind m(-3), with the average 974 000 ind m( -3) biomass ranges from 0,09-3,69 g m(-3), with the average 1,86 g m(- 3). Since the 1960s the abundance of rotifers has risen considerably w hile the mean zooplankter weight (B/N) has decreased from 0.005 mg to 0.004 mg. Zooplankton production (herbivores 20.6, predators 1.8, whol e zooplankton community 22.4 g C m(-2) per period between May and Octo ber) can be considered high. Predatory zooplankton eats on an average 50% of the production of herbivorous zooplankton; about 50% of the who le zooplankton production (P-Filt+Pred) reaches fishes. The production of herbivorous zooplankton constitutes 10.1% of primary production. T his ratio indicates a direct relationship between zoo- and phytoplankt on in the food chain; the detrital food chain seems of little importan ce. About 6% of phytoplankton energy reaches fishes. The transformatio n of energy in the food web is efficient. On the basis of zooplankton L. Peipsi can be considered a moderately eutrophic or meso-eutrophic l ake.