O:N atomic ratio as a tool to describe zooplankton metabolism

Use of the atomic 0 : N ratio as a metabolic index requires clarification of the biochemical complexities of zooplankton intermediary metabolism. We review the processes responsible for natural and experimentally-induced changes in the ratio and discuss their relative importance in relation to a variable natural environment. During starvation the 0 : N ratio is clearly linked to the availability of energy reserves and the use of body protein. Using theoretical computations, it can be shown that pure protein catabolism will yield 0 : N ratios in the range 3 to 16, while equal amounts of lipid and protein catabolism will correspond to values between 50 and 60. Under natural feeding conditions, the value of the ratio depends on the use by the animal of each biochemical fraction assimilated. Others factors, such as seasonal events in the life cycle, biochenlical composition of the body and food quality are of importance for correct interpretation of the variations. The concepts behind the rates are discussed, suggesting that such measurements reflect the adaptability of the animals to their total environment. ' ' Correlation coefficient significant at p < 0.01 ' Correlation coefficient significant at p < 0.05