The Relationship Between Size, Density and Sinking Velocity Through the Life Cycle of Melosira Granulata (Bacillariophyta)

Measurements have been made of the changes in morphology, density and sinking velocity of the filamentous diatom Melosira granulata through the course of its life cycle. The filament width of the diatom decreased with each cell division in the classic manner, and this was mirrored by an increase in the diatom's density. The cell density was dependent upon cell size, due to variation in the proportion of the cell that consisted of the silica cell wall. Filament length increased during the early part of the life cycle, following regrowth from auxospores, and then decreased. These changes were controlled by the diatom through the production of separation valves. Possible reasons for such changes are discussed. Changes in the sinking velocity of the diatom were correlated with changes in filament morphology rather than cell density. All measured sinking velocities were between one-third and one- seventh of those expected from physical considerations using Stokes' equation. Possible reasons for this discrepancy are discussed.