ENERGY-METABOLISM OF CHIRONOMUS-ANTHRACINUS (DIPTERA, CHIRONOMIDAE) FROM THE PROFUNDAL ZONE OF LAKE ESROM, DENMARK, AS A FUNCTION OF BODY-SIZE, TEMPERATURE AND OXYGEN CONCENTRATION

The profundal zone of Lake Esrom, Denmark has a dense population of Ch ironomus anthracinus, which survives 2-4 months of oxygen depletion ea ch summer during stratification. The metabolism of 3rd and 4th instar larvae was examined in regard to variation in biomass and temperature. Respiration at air saturation was described by a curvilinear multiple regression relating oxygen consumption to individual AFDW and tempera ture. At 10-degrees-C and varying oxygen regimes the O2 consumption an d CO2 production of 4th instar larvae were almost unaltered from satur ation to about 3 mg O2 1(-1), but decreased steeply below this level. The respiratory quotient increased from 0.82 at saturation to about 3. 4 at oxygen concentrations near 0.5 mg O2 1(-1). This implied a shift from aerobic to partially anaerobic metabolism. At 0.5 mg O2 1(-1) the total energy production equalled 20% of the rate at saturation of whi ch more than one third was accounted for by anaerobic degradation of g lycogen. This corresponded to a daily, loss of 12 mug mg AFDW-1 or app roximately 5% of the body reserves. At unchanged metabolic rate the gl ycogen store would last three weeks, but long term oxygen deficiency c auses a further suppression of the energy metabolism in C. anthracinus .