EFFECT OF FOOD CONCENTRATION ON THE CARBON BALANCE OF BOSMINA-LONGIROSTRIS (CRUSTACEA, CLADOCERA)

1. The carbon balance of the small cladoceran, Bosmina longirostris, was examined at four food concentrations (0.05, 0.10, 0.25, 2.50 mg C l-1) based on long-term growth experiments. 2. At birth, B. longirostris allocated about 60% of assimilation to body growth at all food concentrations. However, allocation to body growth decreased with age and was less than 5% after the fourth instar at the lowest food concentration. The proportion allocated to reproduction increased with increasing food concentration, but was relatively constant among different adult instars. 3. Assimilation rate increased with increasing food concentration and increasing body size: the mean rate from birth to 15 days was 6.6 times higher at the highest food concentration than at the lowest food concentration. However, with decreasing food concentration and increasing body size, a higher proportion of the assimilated carbon was lost as respiration. As a result, the net production rate reached a plateau at intermediate body size and was 9.1 times higher at the highest food concentration than at the lowest food concentration. 4. Comparison with previous studies revealed that B. longirostris is more efficient than Daphnia with regard to carbon production, especially at low food conditions, if the death rate is negligible.