Analyses of the in situ growth rates of Cryptophyceae by use of the mitotic index technique

Growth rates of Rhodomonas minuta v. nannoplanctica and Cryptomonas ovata were estimated by determining the fraction of cells undergoing cell division during 24 h. Acetocarmine was very useful for identifying stages of division (especially double nuclei). Division stages of R. minuta were found in Lake Constance during the night over a period of 16 or 17 h, of C. ovata over almost the entire 24‐h cycle. A comparison of potential growth rates with observed changes in population density indicates that the higher temporal variability of loss rates is more influential for changes in population size.