The use of aspartate transcarbamylase activity to estimate growth rates in zooplankton

Abstract

Aspartate transcarbamylase activity and growth rates were measured in marine copepods in order to study the feasibility of the use of this enzyme for estimating zooplankton production in the ocean. Growth rates and ATC activities of Acartia clausi (copepodite I) were studied at different food levels. Negative values of growth rates were observed to coincide with higher specific ATC activities during certain periods of the development of organisms. Because of the uncoupling between growth rates and ATC activity, we found no correlation between either parameter. Supplementary measurements of two experiments, one using the artificial cohort method, the other the egg production method, are also presented. The growth/ATC ratios were also studied for comparison with other physiological rate/enzyme activity ratios. The variability observed in this ratio was high and coinciding with a literature value comparing metabolic rates and enzymatic activities. Because of the uncoupling between both parameters, the use of short-term measurements is suggested to calibrate this enzyme and growth rates.