In vivo growth fluorometry: accuracy and limits of microalgal growth rate measurements in ecophysiological investigations

In vivo growth fluorometry (Karsten et al. 1996) is based on the sensitive detection of in vivo chlorophyll a (chl a) fluorescence and monitors its increase over time as an indicator for growth. The method offers a simple, rapid, non-invasive, reproducible and calibration-free measurement of growth rates in unialgal cultures and facilitates multifactorial ecophysiological studies on algal cultures. The technical setup is well suited for use on benthic, adhering, filamentous and colonyforming microalgae. Low detection limits avoid self-shading and nutrient limitation during growth rate determination. Acclimated growth rates should be measured after a pre-incubation phase of 1 to 3 d. A broad data set correlating in vivo chl a fluorescence with cell number, organic carbon and chl a concentration in representative members of the Cyanobacteria, Rhodophyta, Chlorophyta and Bacillariophyceae is presented. A calibration of chl a fluorescence is not required for acclimated growth rate measurements of Bacillariophyceae and Chlorophyta but is recommended for high abundances of Cyanobacteria and Rhodophyta.