Zooplankton in the Lake Tana Shore Zone (Ethiopia) at the Beginning of the Dry Season

At the beginning of the dry season, immediately after the end of the rainy season, estimations of zooplankton abundance have been carried out in three types of shore areas of Lake Tana (Ethiopia): (1) open water, (2) borders of thickets, and (3) macrophyte thickets. The minimum quantitative characteristics of plankton animals are reported in macrophyte thickets; the maximum are in areas of open water. Negative correlations are obtained between the level of overgrowth by macrophytes and the quantitative characteristics of zooplankton organisms. The peculiarities of the quantitative development and structure of zooplankton in the zone of thickets and at their border, when compared with open water areas (as well as compared with the second half of the dry season), indicate the leading role of top-control in the formation of invertebrate communities, which is associated with an increase in the number of young fish. Optimal conditions for feeding and shelters for juvenile fish during daylight hours are formed at the boundary of macrophyte thickets, as a result of which the minimum abundance and biomass of zooplankton are found there.