SUMMARY. 1. Pelagic environments are inherently and continuously variable. Time scales relevant to phytoplankton behaviour are identified as ranging from the time taken for light to penetrate a cell (10-−15 s) to the creation and disappearance of lakes (1012 s). Each scale invokes characteristic responses in algae, spanning the activation of biochemical pathways to the extinctions of species.
2. With special, though not exclusive, reference to the Freshwater Biological Association's activities through its first 60 years, scientific investigation has touched each point on the scale. The existing knowledge is used to produce simulations of the behaviour of model planktonic species at every level in the series.
3. Emphasis is placed on scale interaction, upon how variability at one level collapses into the steady state of higher levels and, equally, how the ultimate texture or ‘grain’ of biological systems is determined by the structure at finer scales.