Dispersion patterns of phytoplankton in lakes

The spatial distribution of phytoplankton is considered in relation to factors which may cause deviations from a random distribution. Such deviations may arise over a wide range of scales and attention is focused on small-scale contagion and its possible significance. Evidence is presented that contagion may occur at scales smaller than have previously been considered. Samples covering a range of volumes from 0.1 ml to 10 ml were taken from a small lake and total numbers of several phytoplankton species were counted in each sample to avoid problems arising from sub-sampling. The counts were used to calculate different indices of dispersion. All indices indicated contagion to occur at the scale being considered. Within the range examined the patch size appeared variable between species. The possible derivation and relevance of such micro-patchiness is discussed.