Cyclical size change and population dynamics of a planktonic diatom,Aulacoseira baicalensis, in Lake Baikal

Most diatoms undergo a cyclical process of size reduction and size restoration, which is used to time their life cycle. However, the effect of this on population dynamics of natural populations is poorly understood. Therefore, their interaction was investigated over several life cycles of a planktonic diatom (Aulacoseira baicalensis) in Lake Baikal as part of a multidisciplinary study lasting 10 years. Changes in abundance and diameter were affected in a complex way by a number of interacting factors that included silica availability, the number of divisions in a growing season, diameter-dependent sedimentation losses, grazing, limited frustule lifetime and faster size decline than predicted in stressed cells. There was also a density-dependent effect on size restoration and the recruitment of large cells into the population, which interacted with the other factors to cause large changes in annual cell abundance observed in the lake over the last 60 years.