Some Sources of Variability in Determination of Digestive Enzyme Activity in Zooplankton

Enzyme activity measurements, sometimes used to ascertain the distribution and quantification of physiological activity of marine zooplankton, are sensitive to a number of sources of variability of both methodological and environmental origins. To facilitate multiple enzyme determinations on a single sample, we have developed a method of acetone extraction from neritic zooplankton followed by 50% glycerol homogenization of the resulting powder. An increase in activity was found compared with that of glycerol homogenates of live zooplankton. Because saturation of 50% glycerol was found when extracting increasing amounts of acetone powder, care was taken to prepare homogenates with an identical amount of powder. The problem of protein solubility in the homogenization medium is discussed. The method is repeatable and yields results which are little influenced by short-term storage of animals before extraction but are strongly influenced by species composition of the plankton sample and to a lesser extent by spatial variability of the plankton populations.Key words: variability, determination, digestive enzyme activity, zooplankton