Trophic relations in two lakes from the Bulgarian Black Sea coast and possibilities for their restoration.

Based on quantitative data on nutrients, light penetration, phytoplankton, zooplankton and zoobenthos obtained in the period 1992-1994 the relations between trophic levels were studied by means of statistical analysis. The two lakes are distinguished by relatively high transfer efficiency between phytoplankton and zooplankton, which depends on the size distribution among zooplankton and percentage of blue-green algae. The bottom up influence seems to prevail over the top-down influence, water surface area and phosphorus load are large, and mean depth is more than 1 m. All this let us conclude that biomanipulation measures alone are not sufficient for a substantial lake restoration.