A new method to estimate respiration rate of biological material based on the reduction of tetrazolium violet.

The traditional method for measuring the activity of the electron-transport system (ETS) gives an estimate of the potential respiration rate, since it measures the rate under saturated substrate conditions (V(max)). Accumulated literature data indicate that this does not relate closely to the actual respiration rate. The new method described here is based on reduction of tetrazolium violet in a homogenate with a natural level of substrates. The analytical protocol ensures that the spectrophotometric reading after 1 h incubation at 40 degrees C reflects the ambient amount of substrates available. This method is superior to the traditional ETS assay in giving a closer correlation with ambient respiration rate. A number of methodological tests have been performed and recommendations are given to optimize the measurements. Macrozooplankton species from the coastal waters of Sweden, representing different taxonomic and trophic groups, showed a range in respiration/ETS ratio from 1.1 to 2.9, and both inter- and intra-specific variability in this ratio were reduced by 50-70% compared with the traditional ETS assay. Results from other environments and for particulate organic matter indicate a similar general improvement. The new analytical assay is simple, cheap and well suited for fieldwork.