THE ROLE OF ZOOBENTHOS IN ENERGY-FLOW IN 2 SHALLOW LAKES

Net production of zoobenthos in two shallow and eutrophic lakes, i.e. the S-basin of Myvatn, Iceland (maximum depth 4.2 m, mean depth 2.3 m) and Hjarbaek Fjord, Denmark (maximum depth 6.5 m, mean depth 1.9 m) were calculated as 878 and 1093 kJ m-2 yr-1, respectively. The zoobenthos in both lakes was dominated by Chironomidae (Diptera) living partly as filtrators feeding on suspended particles (phytoplankton) and partly as surface feeders foraging on benthic algae and/or seston. Respiration and consumption were estimated from the literature. Net production efficiency averaged 0.41 and 0.48 in Hjarbaek Fjord and Myvatn, respectively. Ingestion was dominated by herbivorous chironomids, while detritivorous tubificids were insignificant. Zoobenthic production made up 86% of total secondary production (zooplankton plus zoobenthos) in both lakes. The trophic efficiency between net primary production and benthic net secondary production was 8 % and 11 % in Hjarbaek Fjord and Lake Myvatn S-basin, respectively.