Movement and migration of diatoms on sand grains

Abstract

The motile species of diatoms in a largely non-motile association on grains of sand travel to the surface of the sand when buried, although they move more slowly and less often than species living in silt, and ascend each grain in turn. Diatoms on sand grains from a freshwater lake are found to migrate daily to and from the surface grains, whether in a natural daylight régime or in continuous darkness. They do not leave the surface when exposed to 750 lux of constant illumination although they will at 75 lux. Their movements help to keep them in the photic zone during the day.