Modification of the electron transport system (ETS) method for routine measurements of respiratory rates of zooplankton

Respiratory Electron Transport System activity (ETS) was determined in cell-free homogenates of mesozooplankton samples. Several assays were run to investigate possible improvements to the ETS method and to reduce sample processing time. The results showed that: (i) liquid nitrogen is a suitable method for preserving ETS activity for up to at least two months; (ii) the processed sample can be stored for up to 90 minutes in an ice-water bath without loss of activity; (iii) a glass-fibre filter, normally used in phytoplankton assays, is not necessary to achieve efficient enzyme extraction; (iv) centrifugation can be done prior to the assay without any significant loss in activity; and (v) the partitioned enzyme activities were different from the overall ETS activity, with NADH- dehydrogenase activity playing the major role (71 %) and succinate dehydrogenase the minor (<5%). The overall precision of the methods was about 10%, and automation of the method is suggested as a means of standardizing the precision for routine use at sea.