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 colony- forming 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.