A probabilistic model of cell size reduction in Pseudo-nitzschia delicatissima (Bacillariophyta).

The pennate planktonic diatom Pseudo-nitzschia delicatissima is very common in temperate marine waters and often responsible for blooms. Due to its surrounding rigid silicate frustrule the diatom undergoes successive size reduction as its vegetative reproduction cycle proceeds. Since a long time the life cycle of diatoms has raised scientific interest and some years ago extensive samples of Pseudo-nitzschia have been taken from coastal waters. Mating and cell size reduction experiments were carried out and served us as a data basis for a probabilistic model of cell size reduction. We applied a homogenous non-stationary continuous-time Markov chain to model the development of individual diatoms from an initial size of about 80 microm until cell death which occurred when the size reached its low at about 18 microm. In contrast to conventional curve fitting models we are capable of calculating confidence intervals for estimates of the population ages as well as integrate the process of auxospore formation into the model. We thus propose a unique way to describe the stationary size distribution in a diatom population in terms of cell division and auxospore formation probabilities of its individuals.