LAUSR

Knowledge of the magnitude and variability of plankton respiration is a crucial gap in our understanding of marine carbon cycling. In order to validate the INT reduction method as a proxy for plankton respiration, we have compiled and analysed a dataset (n = 376) of concurrent measurements of dissolved oxygen consumption (CRO2) and in vivo reduction of 2-para (iodophenyl)-3(nitrophenyl)-5(phenyl) tetrazolium chloride tetrazolium salt (INT) spanning a wide range of oceanic regions and physicochemical conditions. Data were randomly divided into two independent subgroups: two thirds of the data were used to derive a regression conversion between dissolved oxygen consumption and INT reduction (“training” dataset) and one third of the data was used to validate the regression (“test” dataset). There was a significant relationship between the log-transformed dissolved oxygen consumption rates and the log-transformed INT reduction rates (INTT) with the “training” dataset (logCRO2 = 0.72logINTT + 0.44, R2 = 0.69, n = 249, p 8 ˚C and chlorophyll-a concentrations >0.2 µg L-1 and reduced at lower temperatures and chlorophyll-a concentrations. The results of this study endorse the adequate performance and reliability of the INT method for natural plankton communities.